Glycal

About: Glycal is a research topic. Over the lifetime, 897 publications have been published within this topic receiving 17422 citations.

Lectins and saccharide biology

Abstract: Partial Table of Content CHEMICAL SYNTHESIS OF GLYCOSIDES Trichloroacetimidates (R. Schmidt & K. - H. Jung) Iterative Assembly of Glycals and Glycal Derivatives: The Synthesis of Glycosylated Natural Products and Complex Oligosaccharides (L. Williams, et al.) Thioglycosides (S. Oscarson) Glycosylation Methods: Alkylations of Reducing Sugars (J. Tamura) Other Methods of Glycosylation (L. Panza & L. Lay) Glycolipid Synthesis (H. Ishida) Special Problems in Glycosylation Reactions: 2 - Deoxy Sugars (A. Veyrieres) Orthogonal Strategy in Oligosaccharide Synthesis (O. Kanie) Intramolecular Glycosidation Reactions (J. Madsen & M. Bols) SYNTHESIS OF OLIGOSACCHARIDE MIMICS Saccharide - Peptide Hybrids (H. Wessel) Index.

Preparation and Reactivity of Imino Glycals: Stereocontrolled, Divergent Approach to Imino Sugars.

Abstract: The synthesis of 3,4,6-tri-O-acetyl imino D-glucal 2 from D-glucal is reported. This imino glycal participates in a variety of Lewis acid mediated carbon–carbon bond forming reactions by allylic displacement of the C-3 acetate group by added nucleophiles. Allyl silanes, trimethylsilyl enol ethers, alkenes and dialkyl zinc reagents serve as suitable reaction partners. In all the cases studied, the β-anomer is predominant. Using imino glycal 8, epimeric at C-5, it is established that the configuration at C-5 of the piperidine ring plays a major role in controlling the stereochemical outcome. These results are rationalised by invoking the intermediacy of a conjugated N-acyliminium ion. A short stereocontrolled synthesis of (+)-deoxoprosophylline is achieved using this chemistry. Additionally, imino glucal 2 is transformed into bromo piperidine 16, whose X-ray crystal structure is determined. Bromide 16 participates in palladium catalysed Stille and Suzuki cross-couplings allowing access to C-2 substituted imino sugars 17 and 18. In other studies, imino sugar C-glycosides 21 and 22 are made by combining the Lewis acid mediated carbon–carbon bond forming reactions with stereospecific dihydroxylations.

Additive Pummerer reaction of 3,5-O-(di-t-butylsilylene)-4-thio-furanoid glycal and stereoselective synthesis of _ -anomer of 4’-thioribonucleosides

Abstract: Upon reacting 3,5-O-(di-t-butylsilylene) (DTBS)-4-thiofuranoid glycal S-oxide (7) with Ac2O in the presence of TMSOAc and BF3.OEt2, additive Pummerer reaction proceeded to furnish 1,2-di-O-acetyl-3,5-O-DTBS-4-thioribofuranose (8) in 61% yield. When 8 was reacted with bis-O-TMS-uracil and TMSOTf, 2'-O-acetyl-3',5'-O-DTBS-4'-thiouridine (13a) was obtained along with it's beta-anomer (13b) in 93% yield (13a/13b = 22/1). This highly stereoselective glycosidation reaction was applicable to the synthesis of 14-17. The glycosyl donor 8 was also useful for the synthesis of 4'-thio-C-nucleoside 18 and 19. In contrast to the above results, treatment of 8 with TMSCN gave rise to the formation of the spiro derivative 20. To avoid this intramolecular cyclization, 2-O-TBDMS-protected 21 was prepared from 8. Bromination of 21 with TMSBr and substitution reaction of the resulting bromide 22 with Hg(CN)2 gave 1'-C-cyanide 23.