Synthesis of rare L-altro sugars and C6-Derivatives

Abstract

A divergent synthesis to rare L-altro sugars and C-6 derivatives from easily available d-galactose is described. The important intermediate, L-altro epoxide 28, was provided by regioselective protections, regioselective 6-O-benzoylation/5-O-mesylation, and intramolecular SN2 inversion at C-5 as key steps. The following nucleophilic addition on the epoxide ring with H−, CN−, and N3− afforded the corresponding 6-deoxy-, 6-cyano-, and 6-azido-L-altrofuranosides, respectively. Hydrolysis of the epoxide 28 under acidic conditions furnished the 1,6-anhydro-L-altro sugar 38, which could undergo sequential thioglycosylation and oxidation to yield l-altrose-derived thioglycoside 40.