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  • 1
    Electronic Resource
    Electronic Resource
    The reaction cycle of isopenicillin N synthase observed by X-ray diffraction (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 721-724 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Isopenicillin N synthase (IPNS), a non-haem iron-dependent oxidase, catalyses the biosynthesis of isopenicillin N (IPN), the precursor of all penicillins and cephalosporins. The key steps in this reaction are the two iron-dioxygen-mediated ring closures of the tripeptide ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/44400
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  • 2
    Electronic Resource
    Electronic Resource
    Chiral Ruthenium-Sulfene Complexes - Synthesis and C-C Coupling Reactions (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 287-297 
    Details
    ISSN: 1434-1948
    Keywords: Enolates ; Nucleophilic additions ; Ruthenium ; S ligands ; Sulfenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the chiral racemic complex [CpRu(mppe)(SO2)]PF6 (1, mppe = Me2PC2H4PPh2) with diazomethane or -ethane gave the sulfene complexes [CpRu(mppe)(RHC/SO2)]PF6 (R = H, 2a; R = Me, 2b). Treatment of 2a with prochiral enamines or deprotonated β-oxo esters yielded C-C coupling products with 32-60% de. An analog of 2a, [NmcpRu(mppe)(H2C/SO2)]PF6 (8, Nmcp = neomenthylcyclopentadienyl) was prepared in a four-step synthesis starting from LiNmcp and [RuCl2(PPh3)3]. Repeated crystallization of the intermediate [NmcpRu(mppe)Cl] (6) provided diastereomerically pure 6′ which added methylene stereospecifically to give diastereomerically pure 8′. Compound 8 turned out to be much less reactive towards nucleophiles than 2a, but still added deprotonated ethyl 2-methyl-3-oxobutanoate with 44% de. The chiral, enantiomerically pure sulfur dioxide complex [CpRu(chir)(SO2)]PF6 [10, chir = (S,S)-Ph2PCHMeCHMePPh2] was synthesized from [CpRu(chir)Cl] and SO2 and was characterized by X-ray crystallography. Reaction of 10 with diazomethane gave the enantiomerically pure sulfene complex [CpRu(chir)(H2C/SO2)]PF6 (11). Addition reactions of 11 with N-(1-cyclopentenyl)morpholine, as well as with various enolates derived from β-oxo esters or 1,3-diesters proceeded with high yields and 20-90% de. The structure of a diastereomerically pure addition product, [CpRu(chir)(SO2CH2C(Me){C(O)Me}{C(O)OtBu}] (13d′), was determined crystallographically and was shown to have (R) configuration at the quaternary carbon atom. After alkylation of one of the S/O functions, the sulfinate ligand was cleaved from the metal center by ligand substitution with acetonitrile, and the resulting acetonitrile complex 15 was converted back into 10 by treatment with SO2.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chiral Rhenium Complexes of Functionalized Thioaldehydes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1435-1443 
    Details
    ISSN: 1434-1948
    Keywords: Captopril ; Cysteine ; Rhenium ; S ligands ; Thioaldehydes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral racemic rhenium thioaldehyde complexes [CpRe(NO)(PPh3)(η2-S=CHR)]PF6 (2a-g) bearing functionalized aliphatic groups R [R = CH2Ph (a), COOEt (b), CH2COOMe (c), CH2C(O)NHCH2Ph (d), (R)-CH(NC8H4O2)COOMe (e), (S,S)-CH(Me)C(O)NC4H7COOMe (f), C4H3O (g)] have been obtained by hydride abstraction from the corresponding thiolate complexes [CpRe(NO)(PPh3)(SCH2R)] (1a-g). With the exception of 2b, only single stereoisomers with like configurations at rhenium and the thioaldehyde carbon atom were obtained. In some cases, the corresponding sulfinate complexes [CpRe(NO)(PPh3)(SO2CH2R)] (3d-f) were formed as by-products. The analogous toluenesulfinate complex [CpRe(NO)(PPh3){SO2(4-C6H4CH3)}] (3a) has been prepared from [CpRe(NO)(PPh3)(THF)]BF4 (8), and the structure of 3e has been determined by X-ray crystallography. The use of phosphorus ligands other than PPh3 was briefly explored with the synthesis of [CpRe(NO)(PR′3)(η2-S=CHR)]PF6 (5a-d) [R′ = OPh, R = Ph (a), 4-C6H4Cl (b), R′ = iPr, R = Ph (c), H (d)]. Nucleophilic addition of NaSMe to [CpRe(NO)(PPh3){η2-S=CH(4-C6H4OMe)}]PF6 (5e) gave the dithioacetal complex [CpRe(NO)(PPh3){SCH(SMe)(4-C6H4OMe)}] (9) in high yield and with low diastereoselectivity. Diels-Alder additions of 5a, e with 2,3-dimethylbutadiene and 2,3-dimethoxy-butadiene gave complexes of cyclic thioethers (10a-c). From the relative rates of reaction (5a 〉〉 5e) and the low diastereoselectivity, it was concluded that the cycloadditions as well as the nucleophilic addition proceed via the linkage isomers [CpRe(NO)(PR′3)(η1-S=CHR)]PF6.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of Chiral Rhenium Complexes Containing Functionalized Thiolate Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2055-2061 
    Details
    ISSN: 1434-1948
    Keywords: N-Acetylcysteine ; Amino acids ; Captopril ; Rhenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral racemic rhenium thiolate complexes [CpRe(NO)(PPh3)(SR)] were obtained under either acidic or basic conditions. Thus, when [CpRe(NO)(PPh3)(CH3)] (1) was treated with etheral HBF4 and HSR the thiolate complexes [CpRe(NO)(PPh3)(SR)] [SR = SCH2(2-furyl) (2), SCH2C(O)OEt (3)] were obtained after chromatographic workup. Ligand exchange reactions between [CpRe(NO)(PPh3)(OC4H8)]BF4 (4) and sodium thiolates yielded analogous complexes with SR = SH (5), SCH2CH2Ph (6), SCH2CH=CH2 (7). SR groups which tolerate strongly alkaline conditions may be introduced by treatment of 4 with HSR in the presence of sodium ethoxide as demonstrated by the high-yield synthesis of 2 as well as of complexes with SR = SCH2CH2NHAc (8), SCH2CH2C(O)OH (9). A milder synthesis using hydrated sodium carbonate as a base provided 8 and compounds with SR = SCH2CH2C(O)OMe (10), SCH2CH2C(O)NHCH2Ph (11) in high yields. Using similar methods, thiolate complexes of (R)-N-acetylcysteine (13), its methyl ester (14), (R)-N-phthaloylcysteine (16), and N-[(S)-3-mercapto-2-methylpropionyl]-S-proline (Captopril) (17) were obtained as diastereomeric pairs. The formation of 13 was preceded by the O-bonded isomer 12 which slowly rearranges in solution. 13 can be converted under acidic conditions into its methyl (14) or ethyl (15) esters. The diastereomers of 16 were separated by crystallization, and the structure of the (R,R)-isomer 16a determined.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Enantioselective Organic Syntheses Using Chiral Transition Metal Complexes, 9 Atropo-Diastereoselective Ring Opening of Biaryl Thionolactones Using [CpRu{(S,S)-CHIRAPHOS}]+ as a Chiral Auxiliary (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1745-1756 
    Details
    ISSN: 1434-1948
    Keywords: Biaryls ; Lactones ; Nucleophilic additions ; Ruthenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The substitution-labile thiophene complex [CpRu{(S,S)-CHIRAPHOS}(SC4H4)]BF4 (2) [(S,S)-CHIRAPHOS = (2S,3S)bis(diphenylphosphanyl)butane], prepared from [CpRu{(S,S)-CHIRAPHOS}Cl] (1), thiophene, and AgBF4, reacted with the biaryl-thionolactones 3a-f to give the corresponding S-coordinated complexes 4a-f in high yields. The structure of 4c, which crystallized as the pure (S,S,P) diastereoisomer, was determined by X-ray crystallography. Coordination of the ruthenium fragment caused an elongation of the C=S bond, a contraction of the C-O bond within the lactone ring and a flattening of that ring. Single hydride transfer with LiBEt3H converted 4a-f into the thiolactolate complexes 5a-f in good yields and diastereoselectivities. An X-ray structure determination of the major isomer of 5a revealed it to be the (S,S,S,P) diastereoisomer. Protonation with NH4PF6 converted 5a-f into the corresponding ring-opened thioaldehyde complexes 6a-f. Alkylation of 5a with methyl iodide resulted in Ru-S cleavage to give the oxothioacetal 7a and [CpRu{(S,S)-CHIRAPHOS}I] (8). Full reduction of 4a-f with LiAlH4 produced the thiolate complexes 9a-f in high yields and 6-74% de. Methylation at sulfur converted 9a-c into the corresponding thioether complexes 10a-c, which were cleaved to 8 and the free methyl thioethers 11a-c without isomerization of the biaryl axis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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