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Notes: Abstract  Root colonization by arbuscular mycorrhizal fungi (AMF) may affect protein and lipid composition of plants by altering P nutrition or by eliciting other metabolic responses in the host plant. This study was conducted to determine the effects of an AMF and soil P on seed protein and lipid contents and yield of two genotypes of durum wheat (Triticum durum L.). Plants were grown in a greenhouse using soil: sand mixes with different levels of P, and with or without the AMF Glomus mosseae [(Nicol. and Gerd.) Gerd. and Trappe]. Percentage AMF root colonization decreased as P added to soil increased. The wheat genotype CR057 had higher AMF root colonization but lower seed P and protein concentrations than CR006. Without added soil P, protein concentration was significantly lower and lipid concentration and seed dry weight higher in arbuscular mycorrhizal (AM) than in nonAM plants. Seed lipid and protein contents were highly correlated with P content of plants. In nonAM plants, seed lipid and protein contents were low with no added soil P and did not differ with added soil P. Seed protein/lipid (Pro/L) concentration ratios of AM plants were higher than those of nonAM plants only when no P was added to the soil. The data indicate different patterns of seed P accumulation and different relationships between seed P and protein and lipid in AM and nonAM plants. Thus, both the presence and degree of AMF root colonization affected seed lipid metabolism in these durum wheat genotypes.

Notes: Abstract  The relationship between nutrient availability and mycorrhizal status has been well studied for terrestrial plant species, but has been examined rarely in aquatic and emergent aquatic species. The purpose of this study was to determine the effect of phosphorus availability on the arbuscular mycorrhizal (AM) status of an emergent aquatic, Lythrum salicaria L. L. salicaria was grown in hydroponic sand culture at five phosphorus concentrations (0, 100, 1000, 10 000, and 47 500 μg PO4/l nutrient solution) for 49 days with or without mycorrhizal inoculum obtained from wetland soil. Inoculated plants at the lowest three phosphorus concentrations were colonized by AM, whereas there was no colonization of plants grown at the highest two phosphorus concentrations. Colonization by AM fungi occurred in conjunction with symptoms of phosphorus deficiency in L. salicaria under experimental conditions: plants at the lowest three phosphorus concentrations had lower biomass and higher root: shoot weight ratios than plants at the highest two concentrations. However, total biomass and internal phosphorus concentration did not differ between inoculated and control plants. Further studies are needed under conditions more closely mimicking natural dynamics.

Notes: Abstract  Our objective was to evaluate the ability of an ectomycorrhizal fungus to alter the competitive interaction of pine seedlings growing with grass, and to determine whether the interaction was modified by soil-phosphorus (P) concentration. Slash pine (Pinus elliottii), inoculated with the ectomycorrhizal fungus Pisolithus arhizus or fortuitously colonized by Thelephora terrestris, and a native grass (Panicum chamaelonche) were grown in a greenhouse at three P levels (0.32, 3.22, 32.26 μM H3PO4). Pine inoculated with P. arhizus took up more P when competing with the nonmycorrhizal grass than when competing with another pine (irrespective of pine mycorrhizal status). Phosphorus uptake kinetics (Cmin, the minimum concentration at which P can be absorbed from a solution; Imax, the maximum uptake rate) for pine and grass were also determined under hydroponic conditions. Pine had a higher Imax than grass but grass had a lower Cmin, suggesting that pine is more competitive at higher nutrient concentrations while grass is more competitive at lower nutrient concentrations. The controlled conditions used in these experiments allowed us to evaluate specific parameters (P uptake and absorbing surface area) affecting plant competition.

Notes: Abstract  Balances between nutrients applied or mineralized and nutrients removed in maize grain and stover were calculated in a hedgerow intercropping experiment in which Leucaena leucocephala and L. pallida prunings and cattle manure were applied. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. In control treatments, nutrient depletion per season was in the order of 7–19 kg N ha–1, 4–12 kg P ha–1, 10–26 kg K ha–1, 0–2 kg Ca ha–1 and 3–6 kg Mg ha–1. N fertilizer reversed the depletion of N, but it accelerated the depletion of the other nutrients. Manure and at least two applications of leucaena prunings resulted in net positive balances of N, K, and Ca between amounts applied or mineralized and amounts removed by maize. The amounts of P and Mg applied with, or mineralized from, prunings or manure were insufficient to offset the negative balances of these nutrients.

Notes: Abstract  A litter bag technique was used to study the decomposition and release of N, P, K, Ca, and Mg from Leucaena leucocephala and L. pallida prunings and cattle manure in a hedgerow intercropping trial conducted in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping or alley farming) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. Manure was the most resistant to decomposition, losing only 15% of its dry matter (DM) in 15 weeks, compared to 41–57% lost by leucaena prunings. Large quantities of K (up to 104 kg ha–1) were mineralized from prunings and manure, but Ca and Mg were mostly immobilized. More N and P were released from prunings than from manure, which resulted in net immobilization of these nutrients in the initial stages of decomposition and net mineralization in later stages. Between the leucaenas more N was mineralized and less Ca and Mg were immobilized when L. leucocephala prunings were applied than when L. pallida prunings were applied. Fertilizer N increased DM decomposition and N mineralization. Mineralization of the nutrients was constrained by lignin and polyphenol contents. It is concluded that leucaena mulch and cattle manure may be significant sources of N and K for crop growth, but external sources of P, Ca and Mg may be required, particularly in acid soils which have low contents of these nutrients. However, this fertility effect has to be evaluated against the competition effect of trees to predict crop response.

Notes: Abstract  The effects of Leucaena leucocephala and L. pallida prunings and cattle manure on maize nutrient uptake and yield were investigated in a hedgerow intercropping trial in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. For each leucaena species, the experiment had 16 treatments resulting from a factorial combination of four levels of leucaena leaf prunings (no prunings applied; first prunings applied; first and second prunings applied; first, second and third prunings applied), two levels of air-dried cattle manure (0 and 3 t dry matter ha–1) and two levels of N fertilizer (0 and 40 kg N ha–1 as urea). Uptake of N, P and K increased significantly with application of the three nutrient sources, but uptake of Ca and Mg either did not respond or decreased with application of prunings and manure. All the three factors increased maize grain and stover yields significantly, usually with no significant interactions between the factors. At least two applications of prunings were required to significantly increase nutrient uptake and maize yield. Maize in the row closest to the hedge did not respond to these nutrient inputs. It is concluded that hedgerow intercropping, with or without manure application, can increase crop yields moderately (to 2–3 t ha–1 maize grain yields) in the highlands, but P, Ca and Mg may have to be supplied from external sources if they are deficient in the soil. Additional N is still required for higher yields (〉4 t ha–1 maize grain yields). However, quantification of the competition effects of the trees is also required to confirm these results.

Notes: Abstract  We investigated whether, under a temperate climate and in a maize crop, earthworm casts could contribute to soil erosion and further favour the exportation of phosphorus by runoff waters. Recording of casts was made in compacted (wheel-tracks) and non-compacted inter-rows, for a 2-month period in spring. To assess the rainfall impact on cast evolution, half of the observation sites were protected against rain splash by a nylon mesh placed above the soil surface. The water runoff was collected and analysed for sediment contents and phosphorus concentration. The mean annual production of surface casts was calculated to be 34 kg (dry weight) year–1 kg–1 earthworm (fresh weight). Synchronization between cast erosion and rainfall events was shown under natural conditions (unprotected sites). The erosion rate was 4 times greater over rainy periods than dry ones, reaching 80% of cast numbers. It appeared that not the runoff effect but the splash effect, due to the kinetics of the drops, disrupted casts. Newly formed casts disappeared first, with the erosion rate decreasing twofold for casts more than 10 days old. Cast erosion and runoff, as well as worm casting activity, were greater under compacted sites than under non-compacted sites, indicating an influence of earthworms on soil erosion from compacted soils. The total phosphorus content was similar in casts and uningested soil (0.80 mg phosphorus g–1). Potential phosphorus losses from cast erosion was calculated to reach 25–49 mg phosphorus m–2 per rainfall event depending on soil compaction. The amounts of particulate phosphorus recovered in water runoff after each rainfall event varied from 1 mg to 11 mg phosphorus. These results are compared and discussed.

Notes: Abstract Nitrate and phosphate solutions were released into two reaches of two central Idaho streams to determine within- and between-stream variability in uptake lengths, uptake rates, and mass transfer coefficients. Physical and biotic stream characteristics and periphyton nitrate-uptake rates in recirculating chambers were measured to determine their influence on nutrient dynamics. Phosphate uptake length did not differ among the four reaches. There were no within-stream differences in nitrate uptake lengths but they did differ between the two streams. Long nitrate uptake lengths likely were due to instream concentrations above saturation but also may have been influenced by differences in active surface area and algal abundance. Nitrate and phosphate uptake lengths were longer, and uptake rates higher, than most other published values. However, mass transfer coefficients were comparable to measurements in other streams. Mass transfer coefficients may be a better parameter for temporal and spatial comparisons of instream nutrient dynamics, and for determining the underlying causes of variability in uptake length.

Notes: Abstract  The natural carbon and nitrogen stable isotope ratios (δ13C, δ15N) of various autotrophs and heterotrophs were measured in a Syringodium isoetifolium-dominated seagrass bed at Dravuni Island, Fiji to define carbon and nitrogen sources for heterotrophic organisms in a system where few animals graze directly on seagrass leaves. The organic carbon, nitrogen, and phosphorus content of organisms was also determined. The δ13C and δ15N data suggest that herbivorous heterotrophs in this seagrass bed depend significantly on epiphytic cyanobacteria rather than seagrass leaves and its detritus. This can be attributed to relative differences in nitrogen content of those organic materials. The cyanobacteria nitrogen content (3.6–4.8% of DW) is nearly half that of heterotrophs (7.0–8.6% N of DW) while that of S. isoetifolium origin (0.6–1.1% N of DW) is less than one third of the cyanobacteria nitrogen content. Phosphorus content was similar among cyanobacteria (0.8–1.1 mg g-1) and S. isoetifolium (0.4–1.4 mg g-1). These results suggest that cyanobacteria are important food sources for heterotrophs at the study site, and that inorganic nitrogen released through breakdown of cyanobacteria by heterotrophs may support the continued production of S. isoetifolium.

Notes: Abstract In many European rivers, including the major streams of the Rhine and Elbe basins, the nutrient load (N and P) still exceeds target levels. In this paper, a model is presented that describes the river nutrient load as a function of nutrient sources, runoff and lithology in the upstream basin. The model was tested with independent data on nutrient sources (input) and nutrient river load (output) for 130 specific combinations of sub-basins and 5 year periods. A wide range of river systems within the Rhine and Elbe basins were included and the analysis covers a period of 25 years from 1970 to 1995. Most of the observed spatial and temporal variation in the average annual river nutrient load was successfully described by the model. It is therefore concluded that the model can be used to predict the effect of changes in nutrient sources (e.g. reduction of livestock numbers, further improvement of waste water treatment plants etc.) on the average annual nutrient loads of the rivers Rhine, Elbe and their main tributaries.

Notes: -1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or -thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4′-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.

Notes: The Staudinger-model reaction H3P (1) + HN3 (2) → H3P=NH (5) + N2 (6) has been investigated at the CCSD(T)/6-31G**//MP2(Full)/6-31G* level. Primary products formed in this reaction are the phosphazides H3P=N-N=NH (3) which exist as trans and cis isomers. In contrast to some previous assumptions, cis -3is 8.2 kcal mol-1 more stable than trans -3 but decomposes rather easily into the expected products H3P=NH and N2. This decomposition can be effectively hampered by intramolecular donor-acceptor interactions as shown by calculations on model compounds as well as by experiments. Thus the reaction of a methylene-σ3,λ3-phosphanyl-σ5,λ5-phosphorane with PhN3 led to a new four-membered heterocycle containing a thermally remarkable stable cis-phosphazide moiety.

Notes: Treatment of calcium bis[bis(trimethylsilyl)amide] with two equivalents of tris(trimethylsilylmethyl)alane yields (Me3SiCH2)2Al-N(SiMe3)2 (1) and the dimer [(Me3Si)2N-Ca(μ-CH2SiMe3)2Al(CH2SiMe3)2]2 (2). The five-coordinate bridging carbon atoms show Ca-C bond lengths of 264 and 268 pm. A similar reaction with calcium bis[bis(trimethylsilyl)phosphanide] gives the dimer [(Me3SiCH2)2Al-P(SiMe3)2]2 (3) with crystallographic C2 symmetry. A calcium-containing species is not isolable, however, in the presence of DME - ether cleavage reactions and the formation of the centrosymmetric dimer [(Me3SiCH2)2Al-OCH2CH2OMe]2 (4) are observed. The central moiety is an Al2O2 cycle with fivefold coordinated aluminium centers.

Notes: The magnesiation of triisopropylsilylphosphane with dibutylmagnesium in toluene yields the octanuclear complex [Mg8(PSiiPr3)6{P(H)SiiPr3}4] (1) which consists of MgPSiiPr3 units forming a hexagonal Mg6P6 prism, with two opposite Mg2P2 moieties capped by additional Mg[P(H)SiiPr3]2 groups. If a small amount of THF is present during the metalation reaction [(THF)4Mg6(PSiiPr3)6] (2) also containing a hexagonal Mg6P6 prism can be isolated. The magnesiation of H2P-SiiPr3 in tetrahydrofuran leads to the formation of the tetrameric complex [(THF)MgPSiiPr3]4(3) with a slightly distorted Mg4P4 cubane-like structure.The structures depend strongly on the steric strain caused by the trialkylsilyl substituents and the neutral coligands at the magnesium center. The highest steric strain, which is induced by coordination to every magnesium atom, leads to the smallest MgnPn polyhedron - the central Mg4P4 heterocubane moiety. In compounds 1 and 2 the hexagonal Mg6P6 prism is formed, however, with reduced steric strain as observed for 2 where the Mg-P bond lengths become more similar.

Notes: Several R3P=N-P(X)R′2 and Fe[C5H4Ph2P=N-P(X)R′2]2 derivatives (X = S, O) are readily obtained from Staudinger reactions between phosphanes and N3-P(X)R′2. The P=N-P=X groups are easily alkylated on the × atom with methyl or isopropyl triflates. The alkylation induces a lengthening of the P-X bond, as shown by X-ray diffraction studies. This corresponds to a weakening of the P-X bond which can be cleaved with P(NMe2)3 to yield [P=N-P:] linkages. The presence of tricoordinated phosphorus atoms opens the way to a versatile reactivity, including the reaction with alkyl iodides and functionalized azides. These molecules are good models for screening which types of reagents and reactions could be used with macromolecules possessing also P=N-P=X linkages, such as dendrimers.

Notes: Metalation of triisopropylsilylphosphane with bis(tetrahydrofuran-O)calcium bis[bis(trimethylsilyl)amide] in tetrahydropyran (thp) in a molar ratio of 3:2 yields (Me3Si)2NCa[μ-P(H)SiiPr3]3Ca(thp)3 (1) containing a trigonal-bipyramidal Ca2P3 core, the metal atoms occupying apical positions. Reaction of two equivalents of triisopropylsilylphosphane or -arsane with bis(tetrahydrofuran-O)barium bis[bis(trimethylsilyl)amide] in tetrahydrofuran gives the corresponding bis(phosphanide) 2 and bis(arsanide) 3, compounds of the type (thf)3Ba[μ-E(H)SiiPr3]Ba(thf)2E(H)SiiPr3 with E = P, As. The equimolar reaction of (tri-tert-butylsilyl)phosphane with (thf)2Ba[N(SiMe3)2]2 in toluene yields heteroleptic dimeric (thf)2Ba[N(SiMe3)2][P(H)SitBu3] (4). Addition of a further equivalent of H2PSitBu3 leads to the formation of homoleptic (thf)nBa[P(H)SitBu3]2 (5). Dissolution of the latter in aromatic hydrocarbons leads to the elimination of H2PSitBu3, yielding dimeric (thf)Ba3(PSitBu3)2[P(H)SitBu3]2 (6). The inner core of 6 consists of the tetramer (BaPSitBu3)4 based on a Ba4P4 heterocubane unit, two opposite faces being capped with (thf)Ba[P(H)SitBu3]2 molecules.

Notes: The coordination behaviour of 2,6-disilyl-substituted phosphinines towards gold(I) has been examined. The reaction of the bis(trimethylsilyl)phosphinine 1 with [AuCl(SMe2)] gives the corresponding AuCl derivative 2. X-ray crystal structure analysis reveals that the aromaticity of the phosphinine ring is slightly reduced as a result of the poor π-back bonding ability of the AuCl fragment. The same phenomenon is observed in the cationic complex [Au(1)2][GaCl4] (3) which was readily prepared by reaction of two equivalents of 1 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. Reaction of 2,6-bis(phenylethynyldimethylsilyl)phosphinine (4) with the same precursor leads similarly to the complex [AuCl(4)] (5). Interestingly, this complex dimerizes upon crystallization to give the bis(phosphabarrelene) complex 6, also structurally characterized. The formation of 6 results from a [4 + 2] cycloaddition between one alkynyl group of each phosphinine with the other phosphinine subunit. The formation of the cationic complex [Au(4)][GaCl4] (8) occurs under classical conditions but it disproportionates to give the cationic complex [Au(4)2][GaCl4] (9) and colloidal gold deposition. The formation of 9 has been ascertained by treating 8 with one equivalent of ligand 4. Additionally, 9 can also be obtained in a straightforward fashion by treating two equivalents of 4 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. The structure of 9 has been elucidated. Despite a particular arrangement of the alkyne groups which encapsulate the gold coordination sphere, no gold-alkyne interactions are visible.

Notes: The dilithium salts of N-methyl-N′,N′′-bis(diisopropyl)- and -(trimethylsilyl)-diethylenetriamine 1a,b react with SnCl2 affording the corresponding stannylenes 2a,b in 60 and 80% yield, respectively. Compound 1b also reacts with BiCl3 to give the bismuth chloride 5 (90% yield). Derivatives 2b and 5 have a symmetrical bicyclic structure and are monomeric both in solution and in the solid state. When 2b is treated with BiCl3 or PCl3, an oxidation reaction leads to the hypercoordinated tin(IV) dichloride 3 (58% yield), or a transmetallation gives rise to the oniophosphane 4 (95% yield), respectively. Transmetalation reactions also occurred when 5 was treated with AlCl3, GaCl3 or SnCl2 affording the corresponding aluminum chloride 6 (81% yield), gallium chloride 7 (38% yield) or tin dichloride 3 (38% yield). The observed reactivity for 2 and 5 is compared to that reported for Veith's stannylene or bismuth chloride.

Notes: New intramolecularly coordinated organotin compounds containing the monoanionic O,C,O-coordinating ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- have been synthesized by substitution reactions starting from organotin halides. In view of the enhanced reactivity of the intramolecularly coordinated compounds {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}SnR2R′ (2, R = Ph, R′ = CH2SiMe3; 3, R = R′ = Ph; 6, R = R′ = Cl), cationic tin species are suggested to occur as intermediates in the formation of the heterocyclic compounds [1(Sn),3(P)-Ph2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (8), [1(Sn), 3(P)-Ph(Me3SiCH2)SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (15), and {[1(Sn),3(P)-Cl2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)]C6H2}2 (16). The latter compounds are formed by intramolecular cyclizations of pentacoordinate cationic tin species under elimination of ethyl halide. Furthermore, the synthesis of [1(Sn),3(P)-Ph2SnOP(O)(OH)-5-tert-Bu-7-P(O)(OH)2]C6H2 (13) is described. Reaction of 8 with an excess of Me3SiBr leads to the unexpected formation of {2-[P(O)(OEt)(OSiMe3)]-4-tert-Bu-6-[P(O)(OEt)2]C6H2}SnPhBr2 (9) as a result of an O-Sn bond cleavage initiated by Me3SiBr and subsequent reaction of the intermediate with further Me3SiBr under Sn-C bond cleavage. The high donor capacity and the rigidity of the new ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- are demonstrated by X-ray diffraction analyses of the tetraorganotin compound 2 and the monoorganotin trichloride 6. Furthermore, the molecular structures of the 2,3,1-oxaphosphastannoles 8 and 16 are discussed.

Notes: Reaction of white phosphorus with [(triphos)Re(CO)2(OTf)] (1) in dichloromethane affords the new tetraphosphorus complex [(triphos)Re(CO)2(η1-P4)](OTf) (2) [triphos = MeC(CH2PPh2)3; OTf = OSO2CF3]. Compound 2 reacts with a second equivalent of 1 to give the binuclear complex [{(triphos)Re(CO)2}2(μ,η1,η1-P4)](OTf)2 (3) in which a tetrahedro-P4 ligand behaves as tethering unit between two [(triphos)Re(CO)2]+ moieties. Complexes 2 and 3 represent the first soluble metal complexes of the tetraphosphorus molecule where the P4 ligand has not undergone any major modification.

Notes: The thermal or photochemical reaction of [Cp′′Co(CO)2] (1) [Cp′′ = C5H3(SiMe3)2-1,3] with white phosphorus (P4) gives [{Cp′′Co}2(P5-P5){CoCp′′}2] (2) and [{Cp′′Co}3P4(μ-CO)] (3) as well as [{Cp′′Co}2(μ-η2:η2-P2)2] (4). Cobalt complexes 2, 3, and 4 have been characterized by an X-ray crystal-structure determination.

Notes: Abstract  The influence of an arbuscular mycorrhizal (AM) fungus on phosphorus (P) and iron (Fe) uptake of peanut (Arachis hypogea L.) and sorghum (Sorghum bicolor L.) plants was studied in a pot experiment under controlled environmental conditions. The plants were grown for 10 weeks in pots containing sterilised calcareous soil with two levels of Fe supply. The soil was inoculated with rhizosphere microorganisms only or with rhizosphere microorganisms together with an AM fungus (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe). An additional small soil compartment accessible to hyphae but not roots was added to each pot after 6 weeks of plant growth. Radiolabelled P and Fe were supplied to the hyphae compartment 2 weeks after addition of this compartment. After a further 2 weeks, plants were harvested and shoots were analysed for radiolabelled elements. In both plant species, P uptake from the labelled soil increased significantly more in shoots of mycorrhizal plants than non-mycorrhizal plants, thus confirming the well-known activity of the fungus in P uptake. Mycorrhizal inoculation had no significant influence on the concentration of labelled Fe in shoots of peanut plants. In contrast, 59Fe increased in shoots of mycorrhizal sorghum plants. The uptake of Fe from labelled soil by sorghum was particularly high under conditions producing a low Fe nutritional status of the plants. These results are preliminary evidence that hyphae of an arbuscular mycorrhizal fungus can mobilise and/or take up Fe from soil and translocate it to the plant.

Notes: Abstract  The effect of root exudates from P-deficient onion on root colonisation by an arbuscular mycorrhizal fungus was examined. Onions (Allium cepa L.) were grown in solution culture at phosphorus concentrations of 0 (P0) and 2 (P2) mg P l–1. Root exudates were collected and fractionated with Amberlite XAD-4 resin to give EtOH and water soluble fractions. Onions inoculated with the arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall were grown with or without (control) root exudates and exudate fractions in a growth chamber. After 24 days, arbuscular mycorrhiza levels and appressoria formation had increased in plants treated with P0-root exudate or the P0-EtOH fraction when compared to corresponding P2 treatments or control plants. P0 and P2 water-soluble fractions did not significantly affect either aspect of fungal development. These results suggest that hydrophobic compounds found in root exudates from P-deficient onion increase appressorium formation and, therefore, enhance mycorrhiza development.

Notes: Abstract  Early-season colonisation of new roots of Hyacinthoides non-scripta (L.) Chouard ex Rothm. was investigated to determine how arbuscular mycorrhizal symbiosis is re-established after the annual root system is shed. During the rootless phase in summer, colonies of bulbs were removed and replanted after the soil around and below the bulb had been mixed (major disturbance) so as to disrupt the external mycelium of arbuscular mycorrhizal (AM) fungi. As a minor disturbance treatment, top soil was removed, bulbs were turned or not in their growth position with as little other disturbance as possible, and the top soil replaced. Control plants were left undisturbed. Half of the plants were harvested 3–4 weeks after the onset of root emergence. Populations of all AM fungi in roots were greatly reduced by major disturbance, whilst those in other treatments and controls were unaffected. At the second harvest, in spring, when shoots had emerged, root colonisation by fine endophytes and Scutellospora morphotypes developed in all treatments, whereas that of Acaulospora morphotypes remained low after major disturbance. Disturbance treatments delayed the appearance, at the second harvest, of mycorrhizas with degenerate arbuscules. Leaf phosphorus concentration was unaffected by soil disturbance, possibly due to partial recovery of AM fungal populations or buffering by resources stored in the bulb.

Notes: Abstract  A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production.

Notes: Abstract  The effects of inorganic phosphate levels and the presence of arbuscular mycorrhiza on disease severity of Aphanomyces euteiches in pea roots were studied. Disease severity on roots and epicotyl as well as the oospore number within infected root tissue were correlated with the phosphorus (P) level in the growth medium. The arbuscular mycorrhizal fungus Glomus intraradices increased P uptake and the P concentration in the plant but reduced disease development in peas. Polyacrylamide gel electrophoresis followed by densitometry of glucose-6-phosphate dehydrogenase specific to A.euteiches was used to measure the activity of the pathogen in roots. The enzyme activity increased with disease severity and disease incidence, except in plants supplemented with P at the highest level, where a peak in activity was seen 12 days after inoculation with the pathogen, followed by a decrease in activity. The epicotyl of mycorrhizal plants showed a reduction in disease severity although this part of the plants was not mycorrhizal. Thus, an induced systemic factor may be responsible for increased resistance in mycorrhizal plants.

Notes: Abstract  A large collection of cowpea rhizobia strains was obtained from soil samples collected from either a semi-arid or a tropical rain forest area located at about the same latitude in the north-eastern region of Brazil and evaluated for their intrinsic antibiotic resistance to eight commercial antibiotics. The aim of this study was to correlate antibiotic resistance of native rhizobia strains to edaphic-climatic factors as a way to establish suitable inoculants for specific areas. A large diversity regarding intrinsic antibiotic resistance was found, and 17 clusters were identified as varying from sensitive to gradually resistant up to 500 μg·ml–1 of the antibiotics tested. Clustering analysis did not show any pattern related to the geographic region where isolates have been obtained. On the other hand, an increase in the antibiotic-resistant rhizobia population was associated with an increase in soil P and Al contents. lsolates which were sensitive to spectinomycin, ampicillin, streptomycin, chloramphenicol and tetracycline were present at higher rates in soils devoid of Al. Rhizobia bacteria producing mucus type I (fluid and capable of spreading over the solid media) were found preferentially in soil with Al concentrations up to 36 mg·kg–1, diminishing quickly at higher levels.

Notes: Abstract We examined soil porewater concentrations of sulfate, alkalinity, phosphorus, nitrogen, and dissolved organic carbon and solid phase concentrations of pyrite in relation to mangrove species distributions along a 3.1-km-long transect that traversed a 47.1-km2 mangrove forest in the Dominican Republic. Iron, phosphorus, and sulfur dynamics are closely coupled to the activity of sulfate-reducing bacteria, the primary decomposers in anoxic soils of mangrove ecosystems. Patterns in the chemistry data suggested that sulfate reduction rates and storage of reduced sulfur were greater in the inland basin forest dominated by Laguncularia racemosa than the Rhizophora mangle dominated forest of the lower tidal region. The distribution of Laguncularia was significantly correlated with concentrations of total phosphorus (r= 0.99) and dissolved organic carbon (r= 0.86), alkalinity (r= 0.60), and the extent of sulfate depletion (r= 0.77) in the soil porewater and soil pyrite concentrations (r= 0.72) across the tidal gradient. Leaf tissue chemistry of Laguncularia was characterized by lower C:N and C:P ratios that could fuel the higher rates of decomposition in the Laguncularia-dominated forest. We suggest that a plant-soil-microbial feedback contributes to the spatial patterning of vegetation and soil variables across the intertidal zone of many mangrove forest communities.

Notes: Abstract Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased by 9% to 22% at elevated CO2 (P 〈 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by elevated CO2 (19.9 ± 1.3 and 21.1 ± 1.3 g N m−2 at ambient and elevated CO2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P and tissue N:P ratios also were not altered by CO2 enrichment (12.5 ± 2 g N g−1 P in both treatments). In contrast to non-legumes (〉98% of community aboveground biomass), legume C/N was not reduced at elevated CO2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO2 to the fact that virtually all legume N originated from symbiotic N2 fixation (%Ndfa ≈ 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO2, microbial N pools increased by +18% under CO2 enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases in the microbial N pool. In order to assess the effects of legumes for ecosystem CO2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using firstly undisturbed grassland monoliths from the field site, and secondly designed `microcosm' communities on natural soil. Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to elevated CO2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities were unaffected by CO2 enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO2. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction between atmospheric CO2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO2 effects on legume growth and their N2 fixation are limited by P.

Notes: Abstract. The electronic mechanism for the gas-phase 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne is studied through a combination of modern valence-bond theory in its spin-coupled (SC) form and intrinsic reaction coordinate calculations utilizing a complete-active-space self-consistent field wavefunction. It is shown that the concerted reaction follows a “heterolytic” route, during which three orbital pairs corresponding to three distinct bonds in the reactants (an in-plane π bond in ethyne, and a C-N and an N-O in-plane bond in HCNO) shift simultaneously to create the two new bonds closing the isoxazole ring and a nitrogen lone pair. The analysis of the SC wavefunction strongly suggests that the reacting system remains nonaromatic throughout the most important part of the cycloaddition process. This investigation provides the first demonstration of an alternative SC description of a bond rearrangement, achieved through the movement of singlet orbital pairs through space, during which at least one of the orbitals within a pair becomes completely detached from the atomic centre with which it is associated initially and ends up localized about another centre.

Notes: Abstract In this work, we show that lattice Monte Carlo simulations can be used to span the time and distance scales between underlying atomistic processes and macroscopic diffusion behavior. We use ab- initio calculations of binding energies versus configuration to calculate hopping rates of vacancies for use in lattice Monte Carlo (LMC) simulations of diffusion and aggregation in silicon. The LMC simulations consider the biased nature of vacancy hop frequencies in the neighborhood of dopants, with interactions up to sixth-nearest- neighbor distances included. We use these simulations to investigate the expected macroscopic diffusion behavior, as well as the process by which dopant/defect aggregation occurs. Specific phenomena investigated include collective behavior leading to greatly enhanced diffusivity at high doping levels, the time dependence of effective diffusivity due to the formation of dopant/vacancy clusters, and dopant fluxes in the presence of a vacancy gradient.

Notes: Abstract  Phosphorus (P) deficiency of soils is a major yield-limiting factor in rice production. Increasing the P-deficiency tolerance of rice cultivars may represent a more cost-effective solution than relying on fertilizer application. The objective of this study was to identify putative QTLs for P-deficiency tolerance in rice, using 98 backcross inbred lines derived from a japonica×indica cross and genotyped at 245 RFLP marker loci. Lines were grown on P-deficient soil and P uptake, internal P-use efficiency, dry weight, and tiller number were determined. Three QTLs were identified for dry weight and four QTLs for P uptake, together explaining 45.4% and 54.5% of the variation for the respective traits. Peaks for both traits were in good agreement which was to be expected considering the tight correlation of r=0.96 between dry weight and P uptake. For both traits the QTL linked to marker C443 on chromosome 12 had a major effect. Two of the three QTLs detected for internal P-use efficiency, including the major one on chromosome 12, coincided with QTLs for P uptake; however, whereas indica alleles increased P uptake they reduced P-use efficiency. We concluded that this was not due to the tight linkage of two genes in repulsion but rather due to an indirect effect of P uptake on P-use efficiency. Most lines with high use efficiency were characterized by very low P uptake and dry weight and apparently experienced extreme P-deficiency stress. Their higher P-use efficiency was thus the result of highly sub-optimal tissue-P concentrations and did not represent a positive adaptation to low P availability. The number of tillers produced under P deficiency is viewed as an indirect indicator of P-deficiency tolerance in rice. In addition to the major QTL on chromosome 12 already identified for all other traits, two QTLs on chromosome 4 and 12 were identified for tiller number. Their position, however, coincided with QTLs for tiller number reported elsewhere under P-sufficient conditions and therefore appear to be not related to P-deficiency tolerance. In this study P-deficiency tolerance was mainly caused by differences in P uptake and not in P-use efficiency. Using a trait indirectly related to P-deficiency tolerance such as tiller number, we detected a major QTL but none of the minor QTLs detected for P uptake or dry weight.

Notes: Abstract  The application of transmission electron microscopy (TEM) and atomic-force microscopy (AFM) aid the acquisition of detailed structural information on the process of hard tissue formation. The sutural mineralization of rat calvaria is taken as a model for a collagen-related mineralization system. After cryofixation or chemical fixation an anhydrous tissue preparation technique with no staining procedures is used. The atomic-force microscope and the transmission electron microscope are used for structural analysis of the mineralizing region of the sutural tissue. With the application of AFM the collagen macroperiod is shown to be well represented in the unmineralized sutural tissue. At the mineralization front the collagen fibrils are found to be thickened and to change to a characteristic stacked platelet structure. Using TEM the macroperiod is faintly visible before mineral crystallites have formed and is more prominent after the apatite crystallization has started in the fibrils. In this step a needle-like structure of the newly formed apatitic crystals is visible.

Notes: Abstract The nutrient losses into the water from rainbow trout (Oncorhynchus mykiss) cage culture using locally caught low-fat Baltic herring, herring-based moist diets and fishmeal-based dry diets were estimated. Feeding with herring led to nitrogen and phosphorus losses into the water twice as high as those feeding with dry pellets (78–162 versus 37–39 g N and 15–39 versus 7–18 g P per kg growth). This was supported by direct measurements of ammonia and phosphate excretion. Increasing feeding frequencies resulted in increased nutrient losses irrespective of diet. Increasing dietary lipid level had a more pronounced effect in reducing the expected nutrient losses in dry pellets than herring. The reduction within the herring was approximately 18% on average for nitrogen and 25% for phosphorus losses. Dietary water content did not affect the nutrient losses. © Rapid Science Ltd. 1998

Notes: To get informations on both the structure and dynamics of hydrogen chelates 1 of heteroaromatic systems, a great variety of quinazoline-2-acetonitrile chelates were synthesized (see 2-4). Similarly to the situation of the corresponding H-chelates in the pyrimidine-2-acetonitrile series, the investigation of these new derivatives 2-4 by NMR spectroscopic methods (DNMR, COSY, NOESY, ROESY, EXSY, HMQC, HMBC) confirms the presence of an equilibrium of the two possible H-chelate structures (two ‘rotamers’ I and II, i.e., (E)/(Z) isomers; see Scheme). The corresponding equilibria I ⇌ II were determined by complete 1H-NMR signal assignment at low temperatures (after freezing the rotational processes). In addition, the tautomer equilibria A ⇌ B (relative energies of the two minima of the nonsymmetrical double-well potential) for both ‘rotamers’ are ascertained by H,H and C,H couplings. The results are an important basis for the interpretation of both the UV/VIS absorptions and the dependence of fluorescence and fluorescence quantum yields on temperature.

Notes: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).

Notes: The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)2]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[1-(naphthalen-1-ylazo-κN2)naphthalen-2-yl-κC2]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[8-(naphthalen-1-ylazo-κN2)naphthalen-1-yl-κC1]-palladium(II) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.

Notes: The photoisomerization behavior of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 1, 2, and 3, and three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 4, 5, and 6, are investigated. The synthetic product (E)-1 could be almost quantitatively (〉 96%) converted into its isomer (Z)-1 under UV light irradiation. In the cases of (E)-2 and (E)-3, a mixture of (E)/(Z) ca. 1:2 was obtained, when the same conditions were applied. The comparison of their UV spectra provides the possible explanation for these different behaviors. Furthermore, it was noticed that the (Z) → (E) isomerization of the C=C bond took place during the purification by reverse-phase high-performance liquid chromatography (RP-HPLC), and the (E)/(Z)-mixture is thus inseparable. The same feature could be observed during the isolation of the (Z,Z)-N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]-spermidines, (Z,Z)-4, (Z,Z)-5, and (Z,Z)-6. Nevertheless, the fractions of (Z,Z)-5 and (Z,Z)-6 were in almost pure state collected, and their 1-NMR spectra are presented.

Notes: The synthesis, absolute configuration, and olfactive evaluation of (-)-(E)-α-trans-bergamotenone (= (-)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (-)-1), as well as its homologue (-)-19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (-)-α-trans-bergamotene (= (-)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (-)-2), together with those of the structurally related aldehydes (-)-3a,b and alcohols (-)-4a,b, have been rigorously assigned.

Notes: (-)-(R)-4,4,4,4′,4′,4′-Hexafluorovaline hydrochloride ((R)-5) of 98% ee is prepared from β,β-bis(trifluoromethyl)acrylic acid (= benzyl 4,4,4-trifluoro-3-(trifluoromethyl)but-2-enoate; 1) in 4 steps with an overall yield of 9.6%. Key step is the separation of the TsOH salts of the diastereoisomers obtained by anti-Michael addition of (+)-(R)-1-phenylethylamine (2) to 1 (→ (R,R)-3). In contrast to the published (S)-chirality, the X-ray structure analysis of (R,S)-6 reveals, that (R)-chirality has to be assigned to the levorotatory (-)-4,4,4,4′,4′,4′-hexafluorovaline hydrochloride.

Notes: The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.

Notes: The reaction of CuO'Bu with CO2, and iPr2NH in the presence of PPh3, gives the dialkylcarbamato complex [Cu(O2CNiPr2)(PPh3)2] (1). The CO2/R2NH system (R = Me, Et) in an appropriate organic medium reacts with Ag2O giving the corresponding N,N-dialkylcarbamato complexes of analytical formula [Ag(C2CNR2)] (R = Me, 2; R = Et, 3). The methyl derivative 2 was characterized by X-ray diffraction methods. Crystal data of 2: for [Ag2(O2CNMe2)2], C6H12Ag2N2O4, mol. wt. 391.9; monoclinic, space group P21/c, a = 12.08(1), b = 3.797(2), c = 11.316(7) Å, β = 113.37(6)°, V = 476.3 Å3, Z = 2, Dc = 2.732 g cm-3; μ(MoKα) = 40.64 cm-1, F(000) = 376.0; R = 0.059, Rw = 0.067; g.o.f. 1.27. The structure consists of dinuclear [(Ag2OCNMe2)2] units with slightly distorted linearly two-coordinated Ag-atoms containing bridging carbamato groups to form a substantially planar eight-membered ring with an intra-annular Ag—Ag distance of 2.837(2) Å; the dinuclear units are further joined by Ag—O bonds to form an infinite array. Compound 3, which is presumably dinuclear, as suggested by cryoscopic measurements in benzene, undergoes a structural fission with PPh3, giving the mononuclear triphenylphosphine derivative [Ag(O2CNEt2)(PPh3)2] (4). The amine-catalyzed conversion of Ag2O into Ag2CO3, in the presence of the iPr2NH/CO2 system, is also reported. Cl-Exchange from [AuCl(PPh3)] with [Ag(O2CNEt2)] (3) gives the first N,N-dialkylcarbamato complex of gold, namely [Au(O2CNEt2)(PPh3)] (5), which crystallizes in the monoclinic system: C23H25AuNO2P · 0.5 C7H16, mol. wt. 625.5, space group P21/c; a = 13.212(5), b = 12.25(1), c = 16.795(6) Å, β = 109.09(2)°, V = 2568(2) Å3, Z = 4, Dc, = 1.618 g cm-3; μ(AgKα) = 31.40 cm-1, F(000) = 1236.0; R = 0.058; Rw = 0.064; g.o.f. 2.121. The compound contains two-coordinated Au-atom, namely to the P-atom and to the O-atom of the monodentate carbamato group, the P—Au—O bond angle being 174.7(3)°. The reaction with MeI showed these compounds to react predominantly at the carbamato O-atom giving the corresponding urethanes R2NCO2Me. Evidence was gathered for the transient coordination of CO to Ag in 3.

Notes: The reactions of α-diazo ketones 1a,b with 9H-fluorene-9-thione (2f) in THF at room temperature yielded the symmetrical 1,3-dithiolanes 7a,b, whereas 1b and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2d) in THF at 60° led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans-9a (Scheme 2). With 2-diazo-1,2-diphenylethanone (1c), thio ketones 2a-d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with 1c were more sluggish than those with 1a,b, they were catalyzed either by the addition of LiClO4 or by Rh2(OAc)4. In the case of 2d in THF/LiClO4 at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans-9b was formed. Monoadduct 4d could be transformed to cis- and trans-9b by treatment with 1c in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and 1c in THF at room temperature reacted only when catalyzed with Rh2(OAc)4, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with α-diazo amides 1d,e (Schemes 5-7). It is worth mentioning that formation of 1,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α-diazo amide. In the case of 1d and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60°, 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide 11b were formed. Thiirane-carboxamides 11d-g were desulfurized with (Me2N)3P in THF at 60°, yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mechanism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a 1,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione (2f) is the thiocarbonyl ylide trapped by a second molecule of 2f to give 1,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.

Notes: The synthesis of a series of chiral enantiomerically pure C2-symmetric binucleating ligands is reported. Ligands of type 1-4, which consist of a phenolic or heterocyclic unit bridging two chiral dihydrooxazole rings. are readily accessible from chiral amino alcohols. Ligands 5a and 5b are composed of a cyclic urea or thiourea unit, respectively, and two 3,4-dihydro-2H-pyrrole rings containing a stereogenic center next to the N-atom. Compounds of this type are readily assembled from ethane-1,2-diamine and an imidothioic ester derived from pyroglutamic acid. These new ligands, which can coordinate two metals in close proximity to each other, are of interest regarding possible applications in asymmetric catalysis.

Notes: Stability constants have been measured for a series of ligands based on a 2,2′-(pyridine-2,6-diyl)bis[1H-benzimidazole] unit which forms dinuclear double-stranded helical complexes with copper(I). Variation of different structural parameters confirms the importance of the coordinate bond, the stacking interactions, and the weakly bridging pyridine units observed by X-ray crystallography. The stabilities of the complexes depend strongly on the solvent, and in MeCN, which is a good solvent for copper(I), the complexes are less stable and assemble in a stepwise manner. The interconversion of the enantiomers may be followed by 1H-NMR and takes place on a millisecond time scale around room temperature. The trends in lability are similar to those found for the stability of the complexes.

Notes: Oligodeoxyribonucleotides containing 7-deaza-2′-deoxy-8-methylguanosine (m8c7Gd; 2b) were prepared. For this purpose, the phosphonate 3a and the phosphoramidite 3b were synthesized and employed in solidphase oligodeoxyribonucleotide synthesis. The structures and the thermodynamic data of duplex formation of oligodeoxyribonucleotides containing 2b were investigated by temperature-dependent CD and UV spectra and compared with those containing 7-deaza-2′-deoxy-7-methylguanosine (m7c7Gd) or 7-deaza-2′-deoxy-guanosine (c7Gd; 2a). In general, compound 2b reduces the duplex stability. In case of the sequence d(m8c7G-C)4 (18), the B → Z transition was facilitated by the incorporation of 2b. Moreover, a single 7-deaza-8-methylguanine residue present in an oligodeoxyribonucleotide tract of guanine residues destabilizes the dG quadruplex significantly. This destabilization is more pronounced than in the case of 7-deazaguanine or 7-deaza-7-methyl-guanine.

Notes: Absolute rate constants and their Arrhenius parameters are obtained for the addition of a cyclic malonyl radical derived from Meldrum's acid to 20 mono- or 1,1-disubstituted alkenes in (±)-propylene oxide and for the addition of the open-chain di(tert-butyl)malonyl radical to six mono- or 1,1-disubstituted alkenes in 1,1,2-trichloro-1,2,2-trifluoroethane by time-resolved electron spin resonance spectroscopy. At room temperature, the radicals add at the unsubstituted C-atoms with rate constants ranging from 1.1. 105 M-1S-1 (acrolein) to 2.4. 106 M-1S-1 (1,1-diphenylethene). The frequency factors are in the narrow ranges of log (A/M-1S-1) = 8.7 ± 0.1 for the cyclic and log (A/M-1S-1) = 8.2 ± 0.2 for the open-chain malonyl species, whereas the activation energies vary from 12.9 kJ/mol (1,1-diphenylethene) to 21.7 kJ/mol (acrylonitrile). They correlate with the alkene ionization potentials and, more weakly, with the reaction enthalpy. No correlation was found between the activation energies and the alkene electron affinities. Hence, the results confirm and quantify the electrophilic nature of malonyl radicals in addition reactions.

Notes: An asymmetric synthesis of (-)-(4R)-dihydroisomyricoidine (28), a 13-membered amino lactam of type A, was performed by a diastereoselective Michael addition between the spermidine derivative 3 and the commercially available optically active ethyl carboxylate 4, and the cyclization of the resulting ω-amino acid 7 using diethyl phosphorocyanidate ((EtO)2POCN), followed by a Wittig reaction to introduce the (Z)-side chain. Some side reactions are also discussed.

Notes: Natural free carboxylic acids from the hadromerid sponge Diacarnus levii (Kelly-Borges and Vacelet) were esterified to yield the new cyclic norditerpene peroxides ent-muqubilin benzyl ester (= (αR,3S,6R)-α,6-dimethyl-6-[(E)-4-methyl-6-(2,6,6-trimethyl-cyclohex-1-en-1-yl)hex-3-enyl]-1,2-dioxan-3-acetic acid benzyl ester; 6, diacarnoate B methyl ester(= (αS,3R,6R)-α,6-dimethyl-6-{2-(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-3-oxo-2,5,5,8a-tetramethylnaphthalen-1-yl)ethyl}-1,2-dioxan-3-acetic acid methyl ester; 9), and deoxydiacarnoate B benzyl ester (= (αS,3R,6R)-α,6-dimethyl-6-{2-[(4aS,8aS)-3,4,4a,5,6,7,8,8a-octahydro-2,5,5,8a-tetramethyl-1-naphthalenyl]ethyl}-1,2-dioxan-3-acetic acid benzyl ester; 10), which were isolated following extensive chromatography. The relative configuration of the peroxide/α-methylacetate moiety of 6, 9, and 10, was directly determined from their NMR spectra. The absolute configurations of the peroxide/α-methylacetate moiety was deduced from comparative 1H-NMR data of the (S)- and (R)-phenylglycine methyl ester derivatives 7 and 8 as well as 11/13 and 12/14, all obtained from a mixture of the precursors of 3, 6, and 10. The absolute configuration at the carbobicyclic moiety of enone 9 and of 10, is identical, as established by chemical interconversion, 9 and 10 belong to the normal labdane series according to empirical CD rules, applied either directly to 9 or to the parent (+)-sclareolide-derived enone 20. In contrast, molar rotation additivity rules suggest the ent-labdane configuration for 9 and 10. The epidioxides 1-3, 6, and 10 proved active in vitro against the malaria parasite Plasmodium falciparum; especially the previously isolated methyl 3-epinuapapuanoate (2) was active against a chloroquine-resistant strain, and this with a good security index.

Notes: 3-Hydroxy-2-cyanoalk-2-enamides, and 2-cyano-2-(tetrahydrofuran-2-ylidene)- and 2-cyano-2-(tetrahydropyran-2-ylidene)acetamides with N-alkyl and N-aryl substituents have been synthesized in three steps from cyanoacetic acid. Their conformations were investigated by X-ray crystallography and 1H-NMR ROESY spectroscopy at room temperature. The enolic compounds 1-3 adopt an extended conformation stabilized by a strong intramolecular O—H … O=C bond both in the solid state and in (D6)DMSO solution. In contrast, the structure of the cyclic derivatives 5a,b-8a,b is solvent-dependent. In the solid state and in CDCl3 solution, the compounds adopt an extended conformation of type I or III, while, in (D6)DMSO solution, their structures undergo time-dependent (Z)/(E)-isomerization structures (of type II or IV). This observation is compatible with a dipolar transition state of rotation. The kinetics of the isomerization are controlled by the N-substituent, the N-(t-Bu) derivatives 7a and 7b having the highest barrier of rotation around the C=C bond. The whole body of experimental evidence together with the results of molecular-mechanics calculations with I-IV, indicate that, in DMSO, two (E)/(Z)-isomers with two conformations are present, and that they undergo interconversion at room temperature with four different constants. The very fast exchange rates kI,II and kIII,IV in the NMR time-scale might be responsible for the detection of only two isomers.

Notes: A new acylated dimeric secoiridoid glycoside, seemannoside A (2), has been isolated from the aerial parts of Lisianthius seemannii (GRISEB) O. KUNTZE (Gentianaceae). The structure was established by spectroscopic analysis (UV, MS, 1H- and 13C-NMR, and 2D-NMR experiments) and chemical reactions as (E-4′-O-p-coumaroyl)lisianthioside. The structure of the (Z)-isomer (seemannoside B, 3), also present in the plant, was confirmed by LC/UV/1H-NMR analysis. The active principle, 6, responsible for the antifungal activity of the apolar extract against Cladosporium cucumerinum, has been isolated. Its structure has been established by NMR spectroscopy and X-ray crystallographic analysis as a rare type of aglycone monoterpene dimer.

Notes: Asymmetric Diels-Alder reaction of the pentadienoic and hexadienoic acids 2a,b with the chiral chloronitroso derivative 3 gave the primary adducts 4a,b with good-to-excellent enantioselectivity. Subsequent as- or trans-dihydroxylation and hydrogenolytic cleavage of the N—O bond led to the 5-amino-5-deoxypentono-δ-lactams 13a, 14, 15a, and 16 in the D-ribose, L-arabinose, D-xylose, and L-lyxose series, respectively, and to the 5-amino-5,6-dideoxyhexono-δ-lactams 13b and 15b in the D-allose and D-glucose series, respectively.

Notes: The synthesis of the monomeric building block 13 and its constitutional isomer 12 of a new type of DNA analog, distamycin-NA, is presented (Schemes 1 and 2). This building block consists of a uracil base attached to a thiophene core unit via a biaryl-like axis. Next to the biaryl-like axis on the thiophene chromophore, a carboxy and an amino substituent are located allowing for oligomerization via peptide coupling. The proof of constitution and the conformational preferences about the biaryl-like axis were established by means of X-ray analyses of the corresponding nitro derivatives 10 and 11. Thus, the uracil bases are propeller-twisted relative to the thiophene core, and bidentate H-bonds occur between two uracil bases in the crystals. The two amino-acid building blocks 12 and 13 were coupled to give the dimers 15 and 16 using dicyclohexylcarbodiimide (DCC) in THF/LiCl and DMF, respectively. While the dimer 15 showed no atropisomerism on the NMR time scale at room temperature, its isomer 16 occurred as distinct diastereoisomers due to the hindered rotation around its biaryl-like axis. Variable-temperature 1H-NMR experiments allowed to determine a rotational barrier of 19 ± 1 kcal/mol in 16. The experimental data were complemented by AM1 calculations.

Notes: Heating of a mixture of N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole]; 1) and 2,5-dihydro-1,3,4-thiadiazole 2a or 2b gave the 1,3-dithiolanes 4a and 4b, respectively, via a regiospecific 1,3-dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a,b onto the C=S group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H-imidazole and during chromatographic workup. The isolated 1,3-dithiole 5 is the product of a base-catalyzed elimination of 1H-imidazole from the initial cycloadduct 4b. The formation of the S,N-acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H-imidazole. With the diazo compounds 8a-e (Scheme 3) 1 underwent a regiospecific 1,3-dipolar cycloaddition to give the corresponding 2,5-dihydro-1,3,4-thiadiazole derivatives 9, which spontaneously eliminated 1H-imidazole to yield (1H-imidazol-1-yl)-1,3,4-thiadiazoles 10. The structures of 10a and 10d were established by X-ray crystallography. In the case of diazodiphenylmethane (8f), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N2 and S to give 1,1′-(2,2-diphenylethenylidene)bis[1H-imidazole] (11; Scheme 3).

Notes: The synthesis of new deoxyribose nucleosides by coupling chloropurines with modified D-ribose derivatives is reported. The methyl 2-deoxy-N-methyl-3-O-(p-toluoyl)-α-D-ribofuranosiduronamide (α-D-8) and the corresponding anomer β-D-8 were synthesized starting from the commercially available 2-deoxy-D-ribose (1) (Scheme 1). Reaction of α-D-8 with the silylated derivative of 2,6-dichloro-9H-purine (9) afforded regioselectively the N9-(2′-deoxyribonucleoside) 10 as anomeric mixture (Scheme 2), whereas β-D-8 did not react. Glycosylation of 9 or of 6-chloro-9H-purine (17) with 1,2-di-O-acetyl-3-deoxy-N-methyl-β-D-ribofuranuronamide (13) yielded only the protected β-D-anomers 14 and 18, respectively (Scheme 3). Subsequent deacetylation and dechlorination afforded the desired nucleosides β-D-11, β-D-12,15, and 16. The 3′-deoxy-2-chloroadenosine derivative 15 showed the highest affinity and selectivity for adenotin binding site vs. A1 and A2A adenosine receptor subtypes.

Notes: (S)-5,5,5,5′,5′,5′-Hexafluoroleucine ((S)-13) of 81 % ee is prepared from hexafluoroacetone (l) and ethyl bromopyruvate (= ethyl 2-oxopropanoate) in 7 steps with an overall yield of 18% (Schemes 1 and 2). Key step in this sequence is the highly enantioselective reduction of the carbonyl group in α-keto ester 4 either by bakers' yeast (91 % ee) or by ‘catecholborane’ 6 utilizing an oxazaborolidine catalyst, yielding hydroxy ester (R)-5 with 99% ee. The absolute configuration was determined by X-ray analysis of the HCl adduct (S,R)-9b of (2S)-N-[(R)- l-phenylethyl]-5,5,5,5′,5′,5′-hexafluoroleucine ethyl ester.

Notes: N-Fmoc-Protected (Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl) β-amino acids are required for an efficient synthesis of β-oligopeptides on solid support. Enantiomerically pure Fmoc-β3-amino acids β3: side chain and NH2 at C(3)(= C(β)) were prepared from Fmoc-protected (S)- and (R)-α-amino acids with aliphatic, aromatic, and functionalized side chains, using the standard or an optimized Arndt-Eistert reaction sequence. Fmoc-β2- Amino acids (β2 side chain at C(2), NH2 at C(3)(= C(β))) configuration bearing the side chain of Ala, Val, Leu, and Phe were synthesized via the Evans' chiral auxiliary methodology. The target β3-heptapeptides 5-8, a β3- pentadecapeptide 9 and a β2-heptapeptide 10 were synthesized on a manual solid-phase synthesis apparatus using conventional solid-phase peptide synthesis procedures (Scheme 3). In the case of β3-peptides, two methods were used to anchor the first β-amino acid: esterification of the ortho-chlorotrityl chloride resin with the first Fmoc-β-amino acid 2 (Method I, Scheme 2) or acylation of the 4-(benzyloxy)benzyl alcohol resin (Wang resin) with the ketene intermediates from the Wolff rearrangement of amino-acid-derived diazo ketone 1 (Method II, Scheme 2). The former technique provided better results, as exemplified by the synthesis of the heptapeptides 5 and 6 (Table 2). The intermediate from the Wolff rearrangement of diazo ketones 1 was also used for sequential peptide-bond formation on solid support (synthesis of the tetrapeptides 11 and 12). The CD spectra of the β2- and β3-peptides 5, 9, and 10 show the typical pattern previously assigned to an (M) 31 helical secondary structure (Fig.). The most intense CD absorption was observed with the pentadecapeptide 9 (strong broad negative Cotton effect at ca. 213 nm); compared to the analogous heptapeptide 5, this corresponds to a 2.5 fold increase in the molar ellipticity per residue!

Notes: On irradiation (350 nm) in the presence of excess 2,3-dimethylbut-2-ene, the newly synthesized title compound 5 affords as main products the unexpected cyclopropylpyrrolidine 10 (50%) and the spiro-oxetane 9 (25%).

Notes: Among seventeen different Lewis acids, TiCl4 was found to be the best catalyst for the [4 + 2] cycloaddition of cyclopentadiene to N,N′-fumaroylbis[(2R)-bornane-10,2-sultam] ((-)-1). Independently of the TiCl4 molar concentration, almost constant and complete (98-89% d.e.) diastereofacial π-selection was achieved in the Diels-Alder addition of (-)-1 to cyclopentadiene, cyclohexadiene, isoprene, and 2,3-dimethylbuta-1,3-diene.

Notes: A new facile synthesis of N,S- and N,Se-acetals starting from aldehydes and primary amines is presented (Schemes 3-5). These acetals are used as precursors for stereoselective radical deuteration and allylation reactions (Schemes 6 and 7, Tables 1 and 2). The stereochemical outcome of the reactions depends on the radical trap and the substituents at the N-atom. Deuterations give always anti products with moderate to high selectivities. The allylation reactions give either syn or anti products with low to moderate selectivities. The observed stereoselectivities can be explained with a model based on minimization of A1,3 strain and are controlled by steric and stereoelectronic effects.

Notes: Based on O-methylasparvenone (1), a N-free 5HT2C antagonist with moderate affinity (pKi = 6.7), derivatives bearing dimethylamino (7), (dimethylamino)methyl (17, 18, 21, and 22), and aminomethyl substituents (26) in place of the benzylic OH group of 1 as well as pyrrolidine- (33) and piperidine-fused derivatives (29, 43, and 45) were synthesized. In contrast to the lead structure 1, these new ligands were active in vivo in the rat. The tricycles 33 and 45 display high affinities for the 5HT2C receptor (pKi = 8).

Notes: Thermal reactions of 1,2,3-trisubstituted aziridines 1 with 1,3-thiazole-5(4H)-thiones 6 in toluene yielded, in general, a mixture of two diastereoisomeric spirocyclic [2+3] cycloadducts. The formation of these products can be explained by a stereoselective electrocyclic ring opening of 1 to give an azomethine ylide 2 as the reactive intermediate, which is trapped immediately by 6 via a stereoselective 1,3-dipolar cycloaddition. Only in the case of trans-dimethyl 1-(4-methoxyphenyl)aziridine-2,3-dicarboxylate (trans-1a), four diastereoisomeric cycloadducts were formed (Scheme 4). This result is rationalized by an isomerization of the intermediate azomethine ylide cis-2a to trans -2a.

Notes: Due to their small mass, adjacent protons (or H-atoms) of molecular systems may exhibit quantum entanglement (or quantum correlations), even at ambient conditions. The considerable thermal disturbance and/or manybody interactions of condensed matter and the associated decoherence effect, however, cause this protonic entanglement to be restricted in space and time. Some aspects of entanglement and decoherence are mentioned. Extending our previous theoretical work, in the present paper the focus is on the possible existence of entangled protons belonging to the H-bonds of adjacent base pairs of B-type DNA. Based on the ‘working hypothesis’ that this effect does really exist, the most probable ‘positions’ for the appearance of protonic entanglement in DNA sequences are qualitatively determined. Furthermore, these ‘positions’ appear to correspond uniquely to dimers of adjacent base pairs of DNA. As a consequence, one can straightforwardly search for an enhanced appearance of such entangled H-bonds in DNA sequences of living organisms, using the existing DNA databases. A quantitative analysis of protein-coding DNA sequences of various organisms has been performed, the results of which provide strong evidence for the existence of the considered effect. The most striking finding may be summarized as follows: Quantum entanglement appears preferably between the third base of a codon and the first base of the following one. Quantitative estimates of this and further obtained results are presented. It is also shown that quantum-chemical considerations of stacking energies cannot account for the results. The new findings provide first evidence for the biological significance of entangled H-bonds.

Notes: The title compounds D-10 and L-10 were prepared from 1 in eight steps and in a combined overall yield of 41-49%.

Notes: The reaction of N,N'-dimethyl-2-nitroethene-1,1-diamine (8) with α,ß-unsaturated acyl isothiocyanates 9 affords 3,3-diamino-2-nitroacrylthioamides 10 (Scheme 2) in moderate-to-good yields. Cyclization of 10 under acidic conditions gives 1,3-thiazin-4-one derivatives of type 11. Oxidative cyclization of 10 with diethyl azodicaboxylate leads to 4-nitro-1,2-thiazol-5(2H)-imine derivatives 12.

Notes: The CH2Cl2 extract of Monotes engleri Gilg. (Dipterocarpaceae) showed antifungal activity against the yeast Candida albicans in our bioautographic TLC assays. After a first fractionation of the crude extract, the bioactivity was located in one of the fractions. To perform an efficient targeted isolation of the active compounds, LC/UV/MS and LC/UV/NMR analyses of the crude extract and the active fraction were performed. LC/UV/, LC/MS, and LC/NMR data (1D and 2D) allowed the identification of 1 as (2S)-2,3-dihydro-5,7-dihydroxy-{3-hydroxy-4-[(3-methylbut-2-enyl) oxy]phenyl}-4H-1-benzopyran-4-one, a new prenylated flavanone, named monoteson A. Subsequent isolation of 1 has permitted the determination of its absolute configuration on the basis of CD measurements. Theree other prenylated flavanoes 2-4 were isolated from the same extract. Compound 3 was identified as 2- (3, 5-dihydroxyphenyl) -2,3-dihydro-5, 7-dihydroxy-6, 8-bis (3-methylbut-2-enyl)-4 H-1-benzopyran-4-one, another new natural product, named monotesone B. The structures of 2 and 4 were established as selinone and lonchocarpol A, respectively. The antifungal activity against Candida albicans was determined for all compounds.

Notes: The disubstituted clusters[Ir4(CO)10(μ2-L—L)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (L—L = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (L—L = (Ph2P)2CHMe, cluste 2; L—L =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1-3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.

Notes: The kinetics of the reaction between pyridoxal 5′-phosphate (PLP) with carbidopa, hydralazine, and isoniazid, in aqueous solution at variable pH and constant ionic strength of 0.1M was studied spectrophotometrically. The rate constants of formation and hydrolysis of the resulting Schiff base, and its stability were determined in a wide range of pH. A comparison is made of the formation rate constants with those of PLP with hydrazine. The reactivity shows the sequence isoniazid 〉 hydrazine 〉 carbidopa 〉 hydralazine in the whole range of pH studied. The Schiff bases studied are more stable than those formed by PLP and hexylamine and as stable as those described for the reactions of PLP with poly(L-lysine) or copolypeptides containing L-lysine.

Notes: The coordination behavior of chiral binucleating ligands of type 1-4 with various transition metals has been investigated. 1H-NMR Titration experiments with zinc(II) salts gave detailed structural information about the structure of the resulting zinc complexes. Ligand 1 forms an unusual C3-symmetric dinuclear zinc complex [Zn2CIL3] (8a) which was characterized by X-ray crystallography. Treatment of complex 8a with various carboxylic acids resulted in ligand-exchange reactions. With ligand 2, a hydroxo-bridged dinuclear copper complex 15 was synthesized and its structure elucidated by X-ray analysis. Solution studies UV and 1H-NMR spectroscopy of the reaction of ligand 3 with ZnII and NII salts revealed the formation of dimeric species of the type [M2X4L2]. Ligand 4 formed well-defined dinuclear complexes with NiII and CuII salts of which the corresponding NiII complex [Ni2(AcO)2(ClO4)2L] (22a) was characterized by crystal-structure analysis.

Notes: Why Pentose- and Not Hexose-Nucleic Acids? Purine-Purine Pairing in homo-DNA: Guanine,Isoguanine, 2,6-Diaminopurine, and XanthineThis paper concludes the series of reports in this journal [1-4] on the chemistry of homo-DNA, the constitutionally simplifie dmodel system of hexopyranosyl-(6′ → 4′)-oligonucleotide systems stidued in our laboratory as potentially natural-nucleic-acid alternatives in the context of a chemical aetiology of nucleic-acid structure. The report describes the synthesis and pairing properties of homo-DNA oligonucleotides which contain as nucleobases exclusively purines, and gives, together with part III of the series [3], a survey of what we know today about purine-purine pairingin homo-DNA. In addition, the paper discusses those aspects of the chemistry of homo-DNA which, we think, influence the way how some of the structural features of DNA (and RNA) are to be interpreted on a qualitative level.Purine-purine pairing occurs in the homo-DNA domain in great variety. Most prominent is a novel tridentate Watson-Crick pair between guanine and isoguanine, as well as one between 2,6-diaminopurine and xanthinone, both giving rise to very stable duplexes containing the all-purine strands in antiparallel orientation. For the guanine-isoguanine pair, constitutional assignment is based on temperature-dependent UV and CD spectroscopy of various guanine- and isoguanine-containg duplexes in comparison with duplexes known to be paired in the reverse guanine is replaced by 7-carbauguanine. Isoguanine and 2,6-diaminopurine also have the capability of self-pariring in the reverse-Hoogsteen mode, as previously observed for adenine and guanine [3]. In this type of pairing, the interchangeably. Fig. 36 provides an overall survey of the relative strength of pairing in all possible purine-purine combinations.Watson-Crick pairing of isoguanine with guanine demands the former to participate in its 3H-tautomeric form; hitherto this specific tautomer had not been considered in the pairing chemistry of isoguanine. Whereas (cumulative) purine-purine pairing in DNA (reverse-Hoogsten or Hoogsteen) seems to occur in triplexes and tetrapalexes only, its occurrence in duplexes in a characteristic feature of homo-DNA chemistry. The occurrence of purine-purine Watson-Crick base pairs is probably a consequence of homo-DNA's quasi-linear ladder structure [1][4]. In a double helix, the distance between the two sugar C-atoms, on which a base pair is anchored, is expected to be constrained by the dimensions of the helix; in a linear duplex, however, there would be no restrictions with regard to base-pair length. Homo-DNA's ladder-like model also allows one to recognize one of the reasons why nucleic-acid duplexes prefer to pair in antiparallel, rather than parallel strand orientation: in homo-DNA duplexes, (averaged) backbone and base pair axes are strongly inclined toward one another [4]; the stronger this inclination, the higher the preference for antiparallel strand orientation is expected to be (Fig. 16).In retrospect, homo-DNA turns out to be one of the first artificial oligonucleotide systems (cf. Footnote 65) to demonstrate in a comprehensive way that informational base pairing involving purines and pyrimidines is not a capability unique to ribofuranosyl systems. Stability and helical shape of pairing complexes are not necessary conditions of one another; it is the potential for extensive conformational cooperativity of hte backbone structure with respect to the constellational demands of base pairing and base stacking that determines whether or nor a given type of base-carrying backbone structure is an informational pairing system. From the viewpoint of the chemical aetiology of nucleic-acid structure, which inspired our investigations on hexopyranosyl-(6′ → 4′)-oligonucleotide systems in the first place, the work on homo-DNA is only an extensive model study, because homo-DNA is not to be considered a potential natural-nucleic-acid altenratie. In retrospect, it seems fortunate that the model study was carried out, because without it we could hardly have comprehended the pairing behavior of the proper nucleic-acid alternatives which we have studied later and which will be discussed in Part VI of this series.The English footnotes to Fig. 1-49 provide an extension of this summary.

Notes: ‘Fully chiral’ dendrimers, containing a stereogenic center at each and every branching point, have been prepared using a chiral core triol with aromatic elongating units (cf. 27) and chiral branch diols (cf. 8, 12, and 24) as building blocks. The biggest dendrimer prepared is of the 4th generation (33: 46 building blocks, 93 stereogenic centers, 1028 possible stereoisomers), and has been obtained by a convergent growth approach in 32 steps starting from the biopolymer poly[(R)-3-hydroxybutanoic acid] (P(3-HB)). All compounds were shown to be monodisperse by MALDI-TOF mass spectrometry. Spin-lattice relaxation-time (T1) measurements and size-exclusion chromatography show typical features of structurally related achiral dendrimers. The influence of the chiral building blocks on the shape of the whole dendrimer has been investigated by chiroptical measurements: the specific rotation can be considered as average of all chiroptical properties of its constituent chiral units, independent of the solvent, the concentration, and the temperature. On the other hand, regularity in the circular dichroism (CD) spectra is completely lost with variation of the solvent (cf. Fig. 13).

Notes: The first steps, believed to be involved in the highly enantioselective copolymerization of styrene and carbon monoxide to poly[1-oxo-2-phenylpropane-1,3-diyl] with phosphinodihydrooxazole-palladium(II) complexes, were investigated. The insertion of carbon monoxide into [Pd(Me)(P^N)(solvent)] TfO (P^N = (S)-2-[2-(5H-benzo[b]phosphindol-5-yl)phenyl]4-benzyl-4,5-dihydrooxazole (1)) and of styrene into [Pd(Me)(P^N)(solvent)] TfO were highly regioselective (alkyl and acyl substituents trans to N); moreover, the olefin insertion took place with essentially complete enantioface discrimination.

Notes: The [4 + 2] cycloadduct 17 of 2,3-dimethylidene-1,2,3,4-tetrahydro-1,4-methanonaphthalene and 4-phenyl-4H-1,2,4-triazole-3,5-dione (PTAD) was subjected to a triplet-sensitized di-π-methane rearrangement. Hydrolysis of the resulting urazol 18 gave the hydrocarbon 7. Hydrolysis of 18 at lower base concentrations led to isomeric stable semicarbazides 24 and 25, which were submitted NiO2 or MnO2 oxidation, to give the target compound 7, and oxidation products 26 and 27.

Notes: The difference between the strong inhibition of retaining β-glucosidases by the tetrazole 1 and the weak inhibition by the triazole 3 has been explained by the protonation by the enzymic catalytic acid of N(3) of 1, replaced by CH in 3. One also expects a contribution to the inhibition from the charge-dipole interaction between the enzymic catalytic nucleophile and the azole ring. The extent of this contribution was estimated from the calculated, distance-dependent heats of formation of the acetate-azole complexes. The calculations were validated by comparison of the charge-dipole interaction between phosphate and the inhibitors 1 and 3 in the glycogen phosphorylase b (GPb)-azole-phosphate complexes, as derived from differences in the Ki values for 1 and 3, while the structural invariance of the complexes was demonstrated by X-ray analysis. The difference between the charge-dipole interactions of (dihydrogen) phosphate and 1 or 3 as derived from Δ Ki is 1.1 kcal mol-1, while the calculated difference is 1.3 kcal mol-1. The calculated difference for the interaction of 1 or 3 with acetate, representing the catalytic nucleophile in β-glycosidases, is 2.0 kcal mol-1, while the differences of the binding energies as derived from the Ki values for the inhibition by 1 or 3 of different β-glycosidases range from 2.4 to 5.3 5 kcal mol-1. The calculated difference for 1 and the imidazole 6 is 2.5 kcal mol-1 in favour of 1, whereas the Ki-derived difference is 3.7 kcal mol-1 in favour of 6, equal to the calculated difference between 1 and the protonated imidazole 6. Thus, protonation by the catalytic acid and the charge-dipole interaction with the catalytic nucleophile contribute cooperatively to the binding of inhibitors possessing a trigonal anomeric centre bonded to a heteroatom.

Notes: Described are the preparation of nanocrystals and the synthesis of molecules that may be covalently or noncovalently assembled in solution to yield heterosupermolecules possessing a well-defined heterosupramolecular function. Also described are preparative and synthetic methods that yield organized assemblies of heterosupermolecules possessing an addressable heterosupramolecular function. Finally, the development of these synthetic strategies to permit the covalent and noncovalent assembly and organization of a wide range of condensed phase and molecular components is outlined.

Notes: For a comparison with the corresponding α- and β-hexapeptides H-(Val-Ala-Leu)2-OH (A) and H-(β-HVal-β-HAla-β-HLeu)2-OH (B), we have now prepared the corresponding γ-hexapeptide 1 built from the homochirally similar (S)-4-aminobutanoic acid, (R)-4-amino-5-methylhexanoic acid, and (R)-4-amino-6-methylheptanoic acid. The precursors were prepared either by double Arndt-Eistert homologation of the protected amino acids Boc-Val-OH, Boc-Ala-OH, and Boc-Leu-OH (Schemes 1 and 2), or by the superior route involving olefination/hydrogenation of the corresponding aldehydes (Boc-valinal, Boc-alaninal, and Boc-leucinal; Scheme 3). Conventional peptide-coupling methodology (EDC/HOBt) furnished the γ-hexapeptide 1 (through the intermediate γ-di- and γ-tripeptide derivatives 9-11). Analysis of NMR measurements in (D5)pyridine and CD3OH solution (COSY, TOCSY, HSQC, HMBC, ROESY) reveals that the γ-hexapeptide 1 adopts a right-handed helical structure ((P)-2.61 helix of ca. 5-Å pitch, containing 14-membered H-bonded rings) which is to be compared with the left-handed helix of the corresponding β-peptide B ((M)-31 helix of 5-Å pitch, 14-membered H-bonded rings) and with the familiar right-handed, so-called α-helix of α-peptides ((P)-3.61 helix of 5.4-Å pitch, 13-membered rings). Like the helix sense, the helix dipole reverses when going from α-, (N + → C) to β-(C + → N) to γ-peptides (N + → C). The surprising difference between the natural α-, and the analogous β- and γ-peptides is that the helix stability increases upon homologation of the residues.

Notes: 7-O-Substituted analogs of deaminodeoxycolchinol thiomethyl ether were synthesized and evaluated for their inhibitory effects on tubulin polymerization in vitro. Ketone 9, a key compound in this study, was derived from thiocolchicone 6 by reaction with aniline. Reaction of compound 6 with MeNH2 or BuNH2 gave tetracyclic lactams 7 and 8, respectively. Optically active alcohols 11a and 11b were obtained from racemic 11 by chemical resolution including a separation of the comphanate diastereoisomers 12a and 12b, followed by basic hydrolysis. The (aR,7R)-configuration of 12b was verified by X-ray crystallographic analysis. Almost all racemic and optically active 7-O-acyl or 7-O-aroyl compounds had strong inhibitory effects on the tubulin polymerization reaction, with IC50 values from 1.7 to 5.1 μM. A few agents, such as the lactams 7 and 8, the camphanates 12a and 12b, the cyclohexanecarboxylates 19a and 19b, and, most notably, the (7S)-benzoate 15a, had negligible effects on polymerization, yielding IC50 values greater than 40μM. Ketone 9 showed strong inhibition of tubulin polymerization comparable to that of thiocolchicone (6). Optically active alcohol 11a and acyl esters 13a and 14a with a (7S)-configuration were more active than the (7R)-esters 13b and 14b. However, the esters 15a-17a with a (7S)-configuration were less active than the (7R)-isomers 15b-17b, in which the (7R)-benzoate 15b was at least 15-fold more inhibitory than the (7S)-isomer 15a. For the most part, the agents causing strongest inhibition of polymerization also caused the greatest inhibition of [3H]colchicine binding. NMR and optical rotatory data indicate that, in polar solvents, the equilibrium in esters with a 7-O-aroyl substituent, i.e., 15a,b, 16a,b, and 17a,b, is reversed from (aS) to (aR) or from (aR) to (aS), as compared to nonpolar solvents.

Notes: As a continuation of our previous studies on the synthesis and antiplatelet activity of quinolin-2(1H)-ones with an α-methylidene-γ-butyrolactone substituted at O(8), the O(6)- and N(1)-substituted isomers were synthesized and evaluated for antiplatelet activity against thrombin (Thr)-, arachidonic acid (AA)-, collagen (Col)-, and platelet-activating-factor (PAF)-induced aggregation in washed rabbit platelets. These compounds were synthesized from 6-hydroxyquinolin-2(1H)-one via alkylation and Reformatsky-type condensation (Schemes 1 and 2). All of them were found to inhibit the platelet aggregation perfectly which was induced by AA and Col. 6-Substituted isomers 5b-g exhibited very strong inhibitory activities against AA- and PAF- induced aggregation and are approximately ten times more potent than their 8-substituted counterparts. However, the 1-substituted (11a and 11b) and the 1,6-disubstituted (6) counterparts were relatively inactive. Their effects on the Ca2+-dependent vasoconstriction induced by high K+, and the phasic and tonic vasoconstrictions induced by norepinephrine (NE) in rat aorta were also evaluated. Except 5g, all of them were found to have significant inhibitory activity on the NE-induced phasic and tonic vasoconstrictions. Compounds 6 and 11b also exhibited strong inhibitory activity on high-K+ medium, Ca2+-induced vasoconstriction.

Notes: The photolysis of N-alkylpyridinium halides 9a-e in alkaline H2O gave 6-azabicyclo[3.1.0]hexenol derivatives 10a-e. N-Substituents bearing ether, acetal, and alcohol functions were found to do not adversely influence the photochemical reaction course. The free OH groups of the N-(3-hydroxypropyl) derivative 10d were protected by benzoylation. The ensuing dibenzoate 14 underwent stereocontrolled opening of the aziridine ring on reaction with MeSH/BF3 to give a thioether 15. With benzoic acid in CHCI3, 10d gave the 4-hydroxy-5-aminocyclopent-2-enyl benzoate 11. The meso-2-aminocyclopent-4-ene-1,3-diol 12 was obtained by hydrolysis of 11. On reaction with Boc2O and NaI, the aziridine ring of 14 was converted to a bicyclic compound 17. Hydrolysis of 17 provided the trans-1,3-diol 18, the epimer of 12. Face-selective dihydroxylation of Boc-protected 12 gave a meso-aminocyclopentanetetrol 23 which was characterized upon peracetylation. Dihydroxylation of 15 provided a racemic analogue of epi-mannostatin A (26).

Notes: An alternative synthesis of enantiomerically pure SDZ 220-881 (1a) and SDZ EAB 515 (1b) starting from L-Z-tyrosine is described.

Notes: Bicyclic thiohydantoins were synthesized in a stereoselective manner by reacting (2R)/(2S)-diastereoisomer mixtures of 1,3-thiazolidine-2,4-dicarboxylic acids or their dimethyl diesters with PhNCS. 5,5-Dimethyl-1,3-thiazolidine-2,4-dicarboxylic acid with PhNCS led to a cyclization involving the C=O group at the C(2) center of the thiazolidine ring, while the acid's dimethyl diester gave cyclization involving the C=O group at C(4). In contrast, reactions involving unsubstituted 1,3-thiazolidine-2,4-dicarboxylic acid or its dimethyl diester led to thiohydantoins in which the ring closure had taken place only with the COO group at C(4). Independently of the direction of the ring closure, all reactions produce exclusively products with the (R)-configuration at C(2). The configurational assignments were based on 1H- and 13C-NMR studies, and confirmed by X-ray crystallographic analyses.

Notes: The new, axially chiral bis(4,5-dihydrooxazoles) 4 have been synthesized in a straightforward manner, starting from the substituted, racemic 1,1′-biphenyl-2,2′-dicarboxylic acids 1 and optically active amino alcohols 2. The adducts were resolved by medium-performance liquid chromatography (MPLC; see Scheme 1). Formation of Cu1 complexes of 4 was followed by 1H-NMR spectroscopy. The catalytic behavior of these complexes has been investigated by asymmetric cyclopropanation of styrene with ethyl diazoacetate. Beside the influence of steric factors, a significant electronic effect on asymmetric induction could also be observed (see Scheme 2 and Table).

Notes: The synthesis of the enantiomerically pure, bridgehead-functionalized bicyclo[3.2.1]octanes 11 and 16, containing a conformationally fixed trihydroxypropyl (aminodihydroxypropyl) unit, as well as the X-ray structure of 11 are described. These compounds are of interest as sugar surrogates in the preparation of DNA analogs. Compounds 11 and 16 became available in 10 and 12 steps, respectively, and in an overall yield of 11 and 4% from D-arabinose via a highly stereoselective pinacol coupling as the key step.

Notes: New derivatives of campholenaldehyde (= 2-(2,2,3-trimethylcyclopent-3-enyl)ethanal bearing two cyclopropane moieties were synthesized, and the structure of the stereoisomer responsible for its exceptionally strong, diffusive, and natural sandalwood-oil scent, ((1S,2S)-1-methyl-2-{[1S,3R,5R)-1,2,2-trimethylbicyclo[3.1.0]hex-3-yl]methyl}cyclopropyl)methanol (13a), was elucidated.

Notes: Titanium-dioxide surfaces have been glycosylated with the benzyl-, 4-fluorobenzyl-, and acetyl-protected diazirines 1-3. The modified TiO2 surfaces were characterized by contact-angle measurement, X-ray photoelectron spectroscopy (XPES), and time-of-flight secondary-ion mass spectrometry (ToF-SIMS). The main by-products of the glucosidation (mostly azines and trehaloses) were identified. Their physisorption slightly reduces the efficiency of the glucosidation by 1 mM solution of 1 or 2 in CH2Cl2, but this influence is neutralized by repeating the glucosidation, or by using a 100 mM solution of the diazirines. The immobilized, acetylated glucosyl moieties were deacetylated in situ. Calculations based on the XPES peaks of Ti 2p and F 1s for the TiO2 surface modified with 2 indicated 1.5 ± 0.9 immobilized glucosyl moieties per nm2.

Notes: A Chemotaxonomic survey for biologically active compounds from Malaysian Calophyllum species led to the findings of the four new benzoylcoumarins 1a, 2, 3, and 4a (including the unusual prenylated 6-benzoylcoumann 1a), two uncommon coumarins 5 and 6a with a pyran-4-one moiety fused at C(6) and C(7), and compounds 7a, 9, and 10, all isolated from the bark of C. teysmannii var. inophylloide. Their structures were determined by spectroscopic analysis and chemical transformations. X-Ray crystal-structure determination of 2 provided information on the conformational preferences of substituents in this class of coumarins. The syntheses of the cytotoxic calanone (7a) and of some related coumarins are described.

Notes: The heme-thiolate protein chloroperoxidase (CPO) catalyzes the chlorination of activated C—H bonds. A reaction mechanism is proposed for this enzymatic transformation (Scheme 1), and a new iron(III) porphyrinate complex 13 is synthesized containing pentafluorophenyl groups at two meso-positions and a thiophenolato ligand coordinating to the Fe-atom (Schemes 2 and 3). Due to the presence of the electron-withdrawing substituents, the catalyst 13 is appreciably resistant to oxidants (HOCl) and chlorinates, e.g., monochlorodimedone (5), with turnover numbers up to 1530. The redox potential of 13, E0 = - 134 mV, and the Soret band (λmax 448 nm) of the CO adduct of the reduced state of 13 are close to the corresponding values of the enzyme CPO.

Notes: The chemical synthesis of 2′-amino-2′-deoxyribonucleosides of uracil, cytosine, adenine, and guanine, and their conversion into suitably protected 3′-phosphoramidite building blocks 35-40 for oligonucleotide synthesis are described. The aglycone and the 2′-amino functions were protected using the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group. The synthesis of the 3′-O-succinyl (3′-O-(3-carboxypropanoyl))-substituted starting nucleoside 41 is described and its behavior examined in solution and on solid phase with regard to an anticipated migration during 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) deprotection. Oligonucleotides were prepared using the new building blocks, and their hybridization properties were studied by UV-melting techniques.

Notes: Chiral supermolecules may be obtained from suitable achiral molecular constituents associated through a dissymmetrizing interaction mode. This is the case for the supermolecules I-IV formed by hydrogen-bonding association between the achiral complementary components 1a,b and 2a,b,c. The crystal structures of the supermolecular pairs I-III and of the homochiral aggregate of two ternary supermolecules IV have been determined. The structural data are discussed.

Notes: Various bifunctional amino-protecting groups such as the phthaloyl, succinyl, and glutaryl group were investigated as potential linker molecules for attachment to solid-support materials. Pentane-1,3,5-tricarboxylic acid 1,3-anhydride (16) offered the best properties and reacted with the amino groups of differently sugar-protected adenosine (see 20 and 22), cytidine (see 29), and guanosine derivatives (see 32) to the corresponding 2-(2-carboxyethyl)glutaryl derivatives 23, 24, 30, and 33. The usefulness of the new linker-type molecules was demonstrated by the solid-support synthesis of the potentially antivirally active 3′-deoxyadenylyl-(2′-5′)-2′-adenylic acid 2′-{2-[(adenin-9-yl)methoxy]ethyl} ester (38) starting from the 2′-end with N6,N6-[2-(2-carboxyethyl)glutaryl]-9-{{2-[(4,4′-dimethoxytrityl)ethoxy]methyl}adenine (12).

Notes: An efficient stereocontrolled synthesis of (S)-N-Cbz-serine (Cbz = benzyloxycarbonyl; 12) and of its (R)-enantiomer is reported. Kinetic resolution of the easily available racemic 3-(hydroxymethyl)-1,4-benzodiazepin-2-ones is performed in the key step via acetylation by the immobilized Mucor miehei lipase (Lipozyme IM) at 60°. This method is characterized by high enantiomer purity (ee's ges; 99%) of the intermediary alcohols (+)-8 and (+)-9 and acetates (-)-10 and (-)-11, as well as of the final products (S)- and (R)-N-Cbz-serine, simple recycling of the biocatalyst, complete recovery of 2-aminobenzophenones (3 and 4) and their recycling into production of 1,4-benzodiazepines, and possibility to selectively racemize ‘wrong’ enantiomers of the alcohols 8 and 9 in the presence of Amberlite CG 400.

Notes: The fate of an insect juvenile hormone analog applied to the insect body of the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively, was studied using three different radiolabeled positions in the parent biologically active compound 1. Several metabolites were found and analyzed. A mechanism of degradation of the applied molecule was designed using a combination of several radioanalytical methods. A unique monitoring of the applied compound and its metabolites was provided, based on the different radiolabeling of the structure (cf. 1a-1c), and established their fate in an insect body during a 10-day experiment. A 14C and 3H radiolabeling, respectively, was employed to synthesize three different radiolabeled forms 1a-1c derived from the parent non-labeled 1. A combination of three different ways of radiolabeling resulted in an advantage in tracing the metabolic pathway of degradation of the employed compound 1 in its radiolabeled forms 1a-1c.