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  • 11
    Electronic Resource
    Electronic Resource
    Synthesis of Glycosylphosphine Oxides and Related Compounds (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 94-112 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The benzyl-protected glycosyl acetates 1, 6, 11, and 15 react with MeOPPh2 under catalysis by TMSOTf to yield diastereoselectively the glycosylphosphine oxides 2, 3, 8, 12, 13, and 16, with a strong preference for the 1,2-cis-configurated anomers. Hydrogenolysis of the major products gave the crystalline, unprotected phosphine oxides 4, 9, 14, and 17, of which 4 was transformed in to the acetate 5, and 9 into the benzoate 10. The benzylated phosphine oxides 4, 8, 12, and 16 were reduced with Cl3SiH in the presence of a tertiary amine to form the phosphines 18, 21, 24, and 26, which were transformed into the phosphine sulfides 19, 22, 25, and 27. Moreover, 18 and 21, were characterized as the borane adducts 20, and 23. The structure of the (arabinofuranosyl)phosphine oxide 12, the corresponding sulfide 25, and of the borane complex 20 were established by X-ray analysis. According to NMR spectroscopy, the equatorial pyranosylphosphine oxide 8, the sulfide 22, and the borane complex 23 adopt a 4C1 conformation. The axial phosphine oxide 2 is a flattened 4C1, the sulfide 19 exists as a B2,5, and the borane complex 20 is a flattened 4C1 in the solid sate and a B2,5 in solution. Thus, the conformational behavior of these α-D-glucopyranose derivatives reflects the steric requirement of the P-substituents.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760104
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  • 12
    Electronic Resource
    Electronic Resource
    Synthesis of the 6-C-Methyl and 6-C-(Hydroxymethyl) Analogues of N-Acetylneuraminic Acid and of N-Acetyl-2,3-didehydro-2-deoxyneuraminic Acid (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1742-1763 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 6-C-methyl-Neu2en5Ac (4), 6-C-(hydroxymethyl)-Neu2en5Ac (5), and 6-C-methyl-Neu5Ac (6) is described. The 4-methylumbellyferyl glycosides 8 and 9 were also prepared but proved unstable. Protection of the previously reported nitro ether 10 (→11) followed by a Kornblum reaction gave the branched-chain derivative 13 which was transformed into aldehyde 14 and hence via 16 into the-protected 6-C-hydroxymethylated 20 and into the 6-C-methyl-substituted 18 (Scheme 1). Debenzylidenation of 20 and 18 afforded the diols 21 and 19, respectively. Selective oxydation of 19 followed by esterification (→ 22), acetylation (→ 23), and elimination led to the protected 6-C-methyl-Neu2en5Ac derivative 24 (Scheme 2). Bromomethoxylation yielded mainly 25 and some 26, which were reductively debrominated to 27 and 28, respectively. Attempted deprotection of 27 did not lead to the corresponding acid, but to the 2,7- and 2,8-anhydro compounds 29 and 30 which were characterised as their peracetylated esters 31 and 32 (Scheme 3). The structure of 32 was established by X-ray analysis. Oxydation of 19 and 21, followed by deprotection, esterification, and acetylation gave 37 and 38, respectively (Scheme 4). The branched-chain Neu2en5Ac derivatives 4 and 5 were obtained by β-elimination (→ 39 and 40) and deprotection. Omission of the esterification after oxydation of 33 and 34 gave the lactones 35 and 36 which were transformed into 37 and 38, respectively. Bromoacetoxylation of 39 gave 41-43 which were reductively debrominated to 44 (from 41 and 42) and 45 (Scheme 5). Bromoacetoxylation of 40 yielded 46 which was debrominated to 47. Glycosidation of the glycosyl chlorides obtained from 44 and 47 led to the α -D-glycosides 48 and 49 and to the elimination products 39 and 40, respectively (Scheme 6). Transesterification of 48, followed by saponification gave the unstable glycoside 8 and hence 6-C-methyl-Neu5Ac (6). The unstable glycoside 9 was obtained by similar treatment of 49 but yielded 50 under acidic conditions. The branched-chain 4 and 5 were weak inhibitors of Vibrio cholera sialidase, and 8 and 9 were very poor substrates.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730620
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  • 13
    Electronic Resource
    Electronic Resource
    A New Synthesis of Benzylidene AcetalsReported in part at the ‘XVIth International Carbohydrate Symposium’, Paris, July 5-10, 1992. (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 211-221 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aryl-halo-diazirines react under basic conditions with 1,3-cis-, 1,2-cisand 1,2-trans-diols to give acetals. Yields are high. Diastereoselectivities depend upon the diol and upon the reaction conditions. Thus, reaction of the 1,3-cis-diol 1 (Scheme 1) with 2 gave 3 as a single diastereoisomer. The 1,2-cis-diols 4 and 7 led to the endo- and exo-acetals 5/6 (93:7) and 8/9 (ca.10:1), respectively, The 1,2-trans-diols 10, 16, and 19 reacted with 2 to afford 11/12 (90:10), 17/18 (1:1), and 20/21 (6:1), respectively. Reaction of the (4-nitrophenyl)diazirine 13 with 10 at higher temperatures yielded 14/15 (6:4). The uracil moiety, the acetamido group, and the enol-ether moiety are compatible with the reaction conditions. The diastereoselectivity is rationalized on the basis of a reaction sequence involving alkoxy-halogen exchange, which is regioselective or not, thermolysis of the ensuing alkoxydiazirine(s), protonation of the alkoxycarbene to form an (E)-configurated oxycarbenium ion, and attack of the neighboring oxy or hydroxy group, which is only possible for a limited range of conformers.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760115
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  • 14
    Electronic Resource
    Electronic Resource
    Synthese eines 1,2-trans-konfigurierten, äquatorialen Glycosyl-phosphonat-Analogen von D-myo-Inositol-1,4,5-trisphosphat (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1013-1025 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of a 1,2-trans-Configurated, Equatorial Glycosylphosphonate Analogue of D-myo-Inositol 1,4,5-TrisphosphateThe diphosphonate analogue 3 of D-myo-inositol 1,4,5-trisphosphate (1), a 1,2-trans-configurated, equatorial glycosylphosphonate, was synthesized and characterized as its hexasodium salt 3a. In a first approach, the silylated galactal 4 (Scheme 1) was transformed into the oxirane 5 and hence, by treatment with Me3SiP(OMe)2, into a mixture of the glycosylphosphonate 6 and its silyl ether 7. This mixture was desilylated and then treated with acetone and FeCl3 to yield 8 and 9 (64 and 22%, resp., from 4). In a second approach, the acetates 11/12(Scheme 2) were treated with P(OMe)3/Me3SiOTf in MeCN to afford the anomeric glycosylphosphonates 16/17 (1:1, 60%), while the trichloroacetimidate 10 gave mostly the αD-anomer 16. The αD-anomer 20 was obtained from 12 and P(OPh)3. The highest yield of a β-Dphosphonate was realized by treating 12 with the cyclic phosphite 15 (→ 18/19, 40% each). The β-D-phosphonate 17 was debenzylated (→21) and protected to give 8. Transformation of 8 into the bromide 22 (43%) proved difficult due to the facile demethylation of thephosphonate, and was best followed by treatment of the crude product with CH2N2 and 2,2-dimethoxyporpane. Phosphorylation of 22 yielded 41% of the (dimethoxyphosphoryl)phosphate 23. The conditions of the Arbuzov reaction slowly converted the bromide 23 into the bis(phosphoryl)phosphate 24 (69%), which was then deprotected. The resulting 3 was purified via the ammonium salt and transformed into 3a (72%).
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760224
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  • 15
    Electronic Resource
    Electronic Resource
    Preparation and Transmetallation of a Triphenylstannyl β-D-Glucopyranoside: A highly stereoselective route to β-D-C-glycosides via glycosyl dianions (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2060-2069 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The triphenylstannyl β-D-glucopyranoside 4 was synthesized in one step from the 1,2-anhydro-α-D-glucopyranose 3 with (triphenylstannyl)lithium (Scheme 1). Transmetallation of 4 with excess BuLi, followed by quenching the dianion 7 with CD3OD gave (1S)-1,5-anhydro-3,4,6-tri-O-benzyl-[1-2H]-D- glucitol (8) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected β-D-configurated products 11, 12, and 13 in good yields. Preparation of C-acyl glycosides from acid chlorides, such as acetyl or benzoyl chloride was not practicable, but addition of benzonitrile to 7 yielded 84% of the benzoylated product 14. Treatment of 7 with MeI led to 15 (30%) along with 40% of 18, C-alkylation being accompanied by halogen-metal exchange. Prior addition of lithium 2-thienylcyanocuprate increased the yield of 15 to 50% and using dimethyl sulfate instead of MeI led to 77% of 15. No α-D-anomers could be detected, except with allyl bromide as the electrophile, which yielded in a 1:1 mixture of the anomers 16 and 17.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770730
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  • 16
    Electronic Resource
    Electronic Resource
    Synthesis of Pyrrolidine Analogues of N-Acetylneuraminic Acid as Potential Sialidase Inhibitors (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1338-1358 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrrolidine derivatives 3, 4, and 5 were prepared from the methyl ester 7 of Neu2en5Ac via lie pyrrolidine-borane adduct 33. They inhibit Vibrio cholerae sialidase competitively with Ki = 4. 4 10-3 M, 5. 3 10-3 M, and 4. 0 10-2 M, respectively. Benzylation of 7 gave the fully O-benzylated 8 besides 9, 10, and 11. Ozonolysis and reduction with NaBH4 of 8 and 9 gave the 1, 4-diols 12 and 15, the hydroxy acetates 13 and 16, and the furanoses 14 and 17 (Scheme 1), respectively. The diol 12 was selectively protected (→19→20→23) and transformed into the azide 27 by a Mitsunobu reaction. Selective base-catalysed deprotection of the diacetate 22, obtained from 12, was hampered by an easy acetyl-group migration. The mesylate 28 proved unstable. The azide 27 was transformed via 29 into the ketone 30 (Scheme 2). Hydrogenation of 30 gave the dihydropyrrole 31 and, hence, the pyrrole 32. The adduct 33 was obtained from 30 by a Staudinger reaction (→31) and reduction with LiBH4/HBF4. It was transformed into the pyrroudine 34. The structure of 34 was established by X-ray analysis. Reductamination of the pyrrolidine-borane adduct with glyoxylic acid gave 40 and, hence, 3. N-Alkylation afforded 44 and, hence, the phosphonate 4. The acid 5 was obtained from 33 by acylation (→47) and deprotection (Scheme 4).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730522
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  • 17
    Electronic Resource
    Electronic Resource
    Synthesis of 2-Acetamido-2-deoxy-D-gluconhydroximolactone- and Chitobionhydroximolactone-Derived N-Phenylcarbamates, Potential Inhibitors of β-N-Acetylglucosaminidase (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1918-1922 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-phenylcarbamate 7, derived from 2-acetamido-2-deoxy-D-gluconhydroximo-1,5-lactone (3) and the analogous N-phenylcarbamate 14, derived from chitobionhydroximo-1,5-lactone (10) have been prepared as potential inhibitors of β-N-acetylglucosaminidases. The unambiguous synthesis of the hydroximo-1,5-lactone 3 involves oxidation of the oxime 1, followed by deprotection with Na/NH3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730714
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  • 18
    Electronic Resource
    Electronic Resource
    Synthese von Pyrano[3,2-b][1]benzopyranen aus 1-Nitroglycalen (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1923-1930 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Pyranol [3,2-b][1]benzopyrans from 1-NitroglycalsA synthesis of pyrano[3,2-b][l]benzopyrans β-addition of salicylic aldehyde to 1-nitroglycals, followed by a Henry reaction, is described. This sequence gave the cis-annelated pyranobenzopyranes 9 and 11 from 5 in 54 and 9% yield, respectively, demonstrating the pronounced diastereoselectivity of the β-addition. Reductive denitration of the crude product mixture yielded 14(75%), 15(15%), and 16(7%), which were oxidized to the aryl ketones 20 and 21, respectively. Reduction of 20 (NaBH4) gave exclusively 15. The ketone 20 was deprotected to 22 and 23.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730715
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  • 19
    Electronic Resource
    Electronic Resource
    Synthesis of a Phosphonic Acid Analogue of N-Acetyl-2,3-didehydro-2-deoxyneuraminic Acid, an Inhibitor of Vibrio cholerae Sialidase (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 451-463 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the phospha analogue 10 of DANA (2) is described. Bromo-hydroxylation of the known 11 (→ 12 and 13) followed by treatment of the major bromohydrin 13 with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave the oxirane 14 (Scheme 1). Depending on the solvent, TiBr4 transformed 14 into 16 or into a 15/16 mixture. Reductive debromination of 16 (→ 17), followed by benzylation provided 18. Oxidattve decarboxylation (Pb(OAc)4) of the acid, obtained by saponification of 18, yielded the anomeric acetates 19 and 20. While 19 was inert under the conditions of phosphonoylation, the more reactive imidate 22, obtained together with 23 from 19/20 via 21 (Scheme 2), gave a mixture of the phosphonates 24/25 and the bicyclic acetal 26. Debenzylation of 24/25 and acetylation led to the acetoxyphosphonates 27/28. Since β-elimination of AcOH from 27/28 proved difficult, the bromide 34 was prepared from 27/28 by photobromination and subjected to reductive elimination with Zn/Cu (→ 35; Scheme 3). This two-step sequence was first investigated using the model compounds 30 and 31. Transesterification of 35, followed by deacetylation gave 10, which is a strong inhibitor of the Vibrio Cholerae sialidase.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740223
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  • 20
    Electronic Resource
    Electronic Resource
    C-Glykoside der N-Acetylneuraminsäure. Synthese und Untersuchung ihrer Wirkung auf die Vibrio cholerae Sialidase (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1520-1532 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C-Glycosides of N-Acetylneuraminic AcidThe synthesis of the C-glycosides 8, 15, and 9 of N-acetylneuraminic acid is described. Hydroxymethylation of the Li-ester enolate, derived from 5, yielded the protected C-glycosides 7 and 10 (46%; 3:1), which were deprotected to yield 8 (54%) and 15 (51%; Scheme 2). The mesylate 16 was obtained from 7 (73%) and transformed via the azide 17 (75%) into the acid 18 (66%) and the amino acid 9 (Scheme 3). The configuration at C(2) of 17 was proved by transforming 17 into the bicyclic lactam 19. Both 8 and 15 are very weak inhibitors of Vibrio cholerae sialidase; 9 appears to stimulate this enzyme.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740716
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