Glucosyl iodides

The perbenzylated a-glycosyl iodides are thought to react with oxetane via the mechanisms shown in Schemes 21 and 22 (where R=PhCH2).138 The amount of the -product increases as the reaction temperature decreases. In fact, at — 60 °C, the fi a ratio in the product from the perbenzylated derivatives of galactosyl, mannosyl, and glucosyl iodides ranges from 10 1 to 50 1, indicating that the reaction in Scheme 21 is faster than that in Scheme 22. 

Lam, S N, Gervay-Hague, J, Solution-phase hexasaccharide synthesis using glucosyl iodides, Org. 

S. N. Lam and J. Gervay-Hague, Solution- and solid-phase oligosaccharide synthesis using glucosyl iodides A comparative study, Carbohydr. Res., 337 (2002) 1953-1965. 

Perhaps the interplay between sugar amino acids and a-amino acids is more clearly demonstrated in the synthesis of a-D-glucosyl-(i )-alanine reported by Axon and Beckwith [33]. In the reaction, (27 )-methyleneoxazolidinone was treated with 2,3,4,6-tetra-O-acetyl glucosyl iodide in the presence of sodium cyanoborohydride and tributyltin chloride to give the a-C-glycoside in 88% yield (Fig. 15). 

Isolevoglucosenone was the starting material from which the unusual p-D-Glc-(l-CHOH-3)-D-Gal epoxide derivative 153 was made. p-D-Glc-(l-CHOH-6)-a-D-ManOMe was synthesized from the 0-benzylated glucosyl iodide and the 0-benzylated 6-deoxyheptose dialdoside. ° ... 

As illustrated by the preparation of a-D-glucosyl-(7 )-alanine 75, the method is simple and efficient (Scheme 13). Alkene 72a is treated with iodide 73, sodium cya-noborohydride, and tributyltin chloride in r-butanol to give exclusively the dia-stereoisomer 74 (88%) arising from addition of the glucosyl radical on its a-face followed hydrogen-atom transfer to the intermediate oxazolidinonyl radical anti to the bulky t-butyl group [47]. 

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