Identification of variose as 2,6-dideoxy-3-O-methyl-D-ribo-hexose (D-cymarose)

Abstract

Variose, a sugar component of the antibiotic variamycin, has been identified as 2,6-dideoxy-3-O-methyl-D-ribo-hexose (i.e. D-cymarose). This assignment is based on the conversion of D-cymarose into, inter alia, methyl 2,6-dideoxy-3-O-methyl-α-D-ribo-hexofuranoside (6) and then into the 5-benzoate (8), which proved to be identical with methyl varioside benzoate. The α-cymarofuranoside (6) was also prepared by a less direct route that involved reaction of methyl 5-O-benzyl-6-deoxy-α-D-allofuranoside (10) with NN-dimethyl-α-chlorobenzylideneammonium chloride (11) to give methyl 2-O-benzoyl-5-O-benzyl-3-chloro-3,6-dideoxy-α-D-glucofuranoside (19). Reductive cleavage of the α-allo-epoxide (20) derived from (19), followed by methylation and debenzylation, gave the desired product.