Pyridine thioglycosides

Nicolaou and coworkers reported a new method for preparing glyco-syl fluorides (38) from phenyl thioglycosides (37) by treatment with di-ethylaminosulfur trifluoride (DAST)-A -bromosuccinimide (NBS), or HF-pyridine-NBS, the phenylthio group of the thioglycosides being initially activated by NBS. Thus prepared were compounds 39, 40, and 42 (see Table I) and 3,4-C)-carbonyl-2,6-dideoxy-3-C-methyl-L-n Z)ohexo-pyranosyl, 2-azido-2,6-dideoxy-3,4-0-isopropylidene-D-altropyranosyl,... 

Treatment of thioglycosides with /V-bromosuccinimide (NBS) in the presence of diethylaminosulfur trifluoride (DAST) or HF-pyridine complex furnishes glycosyl fluorides.23 These can be activated with AgC104/SnCL in the presence of another... 

Scheme 11. The thioglycoside linkage in 50 was activated to yield methyl glycoside 51 (DTBP, 2,6-di-tert-butyl-pyridine).

Irreversible reactions of carbohydrates include the formation of glycosides and 1-deoxy-l-thioglycosides from acylglycosyl halides and thio-acetals, " respectively, esterifications by acyl and sulfonyl halides or anhydrides in pyridine, displacements of sulfonyloxy groups by various reagents, and most examples of formation and scission of anhydro rings, It is more difficult to define the influence of stereo effects on the course of these reactions and some of the results obtained await explanation. 

P. Pomsuriyasak, N. P. Rath, and A. V. Demchenko, 4-(Pyridin-2-yl)thiazol-2-yl thioglycosides as bidentate ligands for oligosaccharide synthesis via temporary deactivation, Chem. Commun., (2008) 5633-5635. 

Lactone substrate 77 was obtained from 57 in one step in 90% yield and its C-4 epimeric analog was prepared by standard inversion procedure. Epoxidation was achieved by action of sodium hypochlorite in pyridine, while conversion to 3-azide required reduction of the epoxide with phenylse-leno(triisopropyloxy)borate, followed by treatment with diphenylphosphory-lazide under Mitsunobu reaction conditions [69]. The acetylated mixture of thioglycosides, obtained from 80, afforded good yield of the desired a-linked antibiotic upon reaction with daimomycinone. All four 2,6-dideoxy-3-azido-L-hexopyranoses were obtained from rhamnal via 4-epimeric lactones. 

Boons and coworkers have used the polystyrylboronic acid as a temporary polymeric support for oligosaccharide synthesis (Scheme 16.3). Polystyrylboronic acid 5, easily prepared from the corresponding bromide by treatment with trimethyl borate and n-BuLi in high loading capacity, was introduced on the 4,6-0 positions of the acceptor 6 by heating in pyridine. The immobilized boronate acceptor 7 was glycosylated with thioglycoside donor... 

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