摘要:

Reaction of diethylaluminum cyanide (DEAC) with methyl 2,3-anhydroribo-furanosides was examined as a potentially useful method for the introduction of the cyano group at C-2 and C-3 of furanosyl sugars. Thus, treatment of methyl 2,3-anhydro-5-O-benzyl-β-D-ribofuranoside with DEAC provided methyl 5-O-benzyl-3-cyano-3-deoxy-β-D-xylyofuranoside (2), while similar treatment of methyl 2,3-anhydro-5-O-benzyl-α-D-ribofuranoside gave a mixture of methyl 5-O-benzyl-3-cyano-3-deoxy-α-D-xylofuranoside (5) and methyl 5-O-benzyl-2-cyano-2-deoxy-α-D-arabinofuranoside (6). Epimerization of2at C-3 was readily effected in the presence of base to give methyl 5-O-benzyl-3-cyano-3-deoxy-β-D-ribofuranoside (9). In contrast,5and6were resistant to base-promoted epimerization. Sequential acetylation and acetolysis converted the cyano sugars2and9into the corresponding tri-O-acetyl derivatives13,14and15.

ISSN:0732-8303    

DOI:10.1080/07328309508005370

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Diels-Alder cycloadditions of 1,3-butadiene and isoprene with D-galacto- and D-manno-(E)-nitroalkenes are described. These reactions showed anunlikestereoselectivity, as a consequence of the configuration of the adjacent chiral centre to the dienophilic double bond. For isoprene adducts, the favored regioisomers were those in which the nitro and the methyl groups on cyclohexene rings are in a 1,4-relationship. Assignment of absolute configurations at the new chiral centres in the adducts were based on NMR data and polarimetric correlations with known compounds.

ISSN:0732-8303    

DOI:10.1080/07328309508005371

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Dimeric methyl (3,4-di-O-acetyl-2-deoxy-2-nitroso-α-d-glucopyranosyl chloride)uronate (1) reacts with nucleophiles such as: ethanol, pyrazole, methylN-tert-butyloxycarbonyl-L-serinate to give corresponding glycosides. The stereospecifity of the glycosidation reaction depends mainly on the employed nucleophile. The configuration and conformation of the obtained glycosides were established on the basis of1H NMR and polarimetric data, and additionally the structure of 1-(methyl 3,4-di-O-acetyl-2-deoxy-2-(Z)-hydroxyimino-α-d-arabino-hexopyranosyluronate)pyrazole (6), was supported by X-ray diffraction data.

ISSN:0732-8303    

DOI:10.1080/07328309508005372

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A multi-step synthesis of a new potential inhibitor (i.e., compound2) of squalene synthase is described, starting from D-galactose. The title compound is a hybrid of presqualene pyrophopshate and the recently discovered zaragozic acids, which are picomolar competitive inhibitors of the enzyme squalene synthase.

ISSN:0732-8303    

DOI:10.1080/07328309508005373

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Analogs of sialyl-α(2→6)-lactotetraosylceramide and sialyl-α(2→6)-neolactotetraosylceramide, in which theN-acetylneuraminic acid residue is replaced by a 3-deoxy-d-glycero-d-glacto-2-nonulopyranosylonic acid (KDN) unit, have been synthesized. MethylO-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio-β-d-galactopyranoside (6) was prepared from the phenyl β-thioglycoside derivative1of KDN and 2-(trimethylsilyl)ethyl 3-O-benzyl-β-d-galactopyranoside (2) in four steps. Each coupling of 2-(trimethylsilyl)ethylO-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-d-glucopyranosyl)-(1→3′)-per-O-benzyl-β-lactoside (7) or 2-(trimethylsilyl)ethylO-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-d-glucopyranosyl)-(1→3′)-per-O-benzyl-β-d-lactoside (8), with6gave the pentasaccharides9and13in good yields. Compounds9and13were converted into the corresponding α-trichloroacetimidates12and16which on glycosylation with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (17), gave the β-glycosides18and21, respectively. Finally,18and21were transformed,viaselective reduction of the azido group, condensation with octadecanoic acid,O-deacylation, and saponification of the methyl ester group, into the target compounds20and23, respectively.

ISSN:0732-8303    

DOI:10.1080/07328309508005374

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

KDN-containing gangliosides GM1, GM2, and GD1ahave been synthesized. Glycosylation of 2-(trimethylsilyl)ethylO-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-d-glycero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-O-(2,6-di-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (3) with methyl 6-O-benzyl-2-deoxy-3,4-O-isopropylidene-2-phthalimido-1-thio-β-d-galactopyranoside (5) gave the tetrasaccharide (6), which was converted,viade-esterification, removal of the phthaloyl group,N-acetylation, andO-deisopropylidenation, into the tetrasaccharide acceptor (9). Reductive removal of the benzyl groups in9,O-acetylation and subsequent removal of the 2-(trimethylsilyl)ethyl group followed by imidate formation, gave the KDN-GM2oligosaccharide glycosyl donor12. Glycosylation of9with methyl 2,4,6-tri-O-benzoyl-3-O-benzyl-1-thio-β-d-galactopyranoside (13) and methyl (methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-d-glcero-α-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (18), using dimethyl(methyl-thio)sulfonium triflate (DMTST), gave the penta- and hexasaccharides14and19, which were convertedviareductive removal of their benzyl groups,O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and reaction with trichloroacetonitrile, into the corresponding α-trichloroacetimidates17and22. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with12,17, and22in the presence of boron trifluoride etherate afforded the expected β-glycosides, which were transformed in good yields,viaselective reduction of the azido group, coupling with octadecanoic acid,O-deacylation, and de-esterification, into the target gangliosides2629, and32.

ISSN:0732-8303    

DOI:10.1080/07328309508005375

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A practical, nine-step protocol is described for the preparation of synthetically usefulN-acetyllactosamine (LacNAc) derivatives as well as LacNAc itself from lactose using the benzoylated oxime of lactos-2-ulosyl bromide2as the key intermediate. All steps are performed with simple reagents, do not require chromatography, are large-scale adaptable and allow overall yields of 30%.

ISSN:0732-8303    

DOI:10.1080/07328309508005376

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A simple route to new surfactants with a sugar-based polar head group coupled to a steroidal hydrophobic group is described. These compounds,N-ursocholyl-d-glucosamine andN-dehydrocholyl-d-glucosamine, were obtained in a three stage process by acylation ofd-glucosamine withN-acylthiazolidine-2-thiones derived from ursocholic and dehydrocholic acids.

ISSN:0732-8303    

DOI:10.1080/07328309508005377

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The primary structure of an elicitor-active oligosaccharide, LN-3, prepared from partially hydrolyzed algal laminaran was determined by means of the analyses of glycosyl-linkage, fragments by acetolysis, and glycosyl-sequence. The elicitor-active oligosaccharide, LN-3, is a pyridylaminated hepta-β-d-glucoside which was shown to have the following linear structure: β-d-Glcp(1→6)-β-d-Glcp(1→3)-β-d-Glcp(1→3)-β-d-Glcp(1→3)-β-d-Glcp(1→6)-β-d-Glcp(1→3)-Glc-PA.

ISSN:0732-8303    

DOI:10.1080/07328309508005378

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Delipidated egg yolk (DEY) was digested with protease. The digest was ultrafiltered using a molecular weight cut-off of 10,000, and the UF permeate was treated with a reverse osmosis membrane. The resulting sialylglycopeptides-rich fraction was purified by the combination of anion exchange and gel filtration chromatography. Two major sialylglycopeptides, A-I and A-II, were characterized as biantennary complex type sialylglycopeptides having one or twoN-acetylneuraminic acid and 1 - 3.5 amino acids including one asparagine residue by composition analyses and1H NMR spectroscopy.

ISSN:0732-8303    

DOI:10.1080/07328309508005379

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor