Site-selective Acylation by Chiral Pyridines

In carbohydrate synthesis, multistep procedures involving protection/ deprotection sequences are usually employed, because of the lack of a direct method for site-selective manipulation of one specific hydroiq l group out of the multiple hydroiqrl groups in carbohydrates. If such site-selective transformation becomes feasible and available as a practical process, it will be a great advance in sustainable and green chemistry because it enables a reduction in the number of synthetic steps. Recently, chiral DMAP- and PPY-derivatives have been developed for site-selective acylation of carbohydrates.  

This protocol for site-selective acylation was applied to diversification of naturally occurring cardiac glycoside, lanatoside C 80, possessing eight free hydro)yl groups. Various acyl groups were introduced at the C(4 )-alcohol 

Site-selective deo ygenation of biologically active polyols is an attractive transformation, which enables expansion of the structural diversity of the polyols and increases the opportunity to find biologically active analogues. Site-selective deojygenation of polyols was investigated by the sequence of site-selective thiocarbonylation and Barton-McCombie reaction. Site-selective thiocarbonylation of a-methyl glucoside 93 was examined with phenyl 

3 A from the primary hydrojy groups of the JV-decanolyglucosamine and mannose moieties, respectively.  

Kawabata, K. Yamamoto, Y. Momose, H. Yoshida, Y. Nagaoka and K. Fuji, Chem. Commun., 2001, 2700. 

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