Syntheses of methyl 2,3,6-trideoxy-α-L-erythro-hexopyranoside (methyl α-L-amicetoside) and methyl 2,3,4,6-tetradeoxy-4-(dimethylamino)-α-L-threo-hexopyranoside (methyl α-L-ossaminide)

Abstract

Methyl 2,3,6-trideoxy-α-L-erythro-hexopyranoside (12), the free sugar of which is enantiomeric with a constituent of the antibiotic amicetin, has been synthesized in three steps from 3,4-di-O-acetyl-L-rhamnal (7) by its rearrange-ment to, inter alia, methyl 4-O-acetyl-2,3,6-trideoxy-α-L-erythro-hex-2-enopyranoside (8) with boron trifluoride in dichloromethane–methanol. Deacetylation and hydrogenation of the latter compound gave the required product (12). Methyl 2,3,6-trideoxy-4-O-methylsulphonyl-α-L-erythro-hex-2-enopyranoside (15) underwent ready S_N2 displacement of the allylic sulphonate group to give the 4-azide (16), which on hydrogenation and N-dimethyl-ation gave methyl 2,3,4,6-tetradeoxy-4-(dimethylamino)-α-L-threo-hexopyranoside (17). The free sugar liberated from the latter glycoside is enantiomeric with a sugar component of the spiramycin antibiotics.