A facile synthesis of armed and disarmed colitose thioglycosides

Ethyl 2,4-di-O-acetyl-3,6-dideoxy-1-thio-beta-L-xylo-hexopyranoside (10) and ethyl 2,4-di-O-benzyl-3,6-dideoxy-1-thio-beta-L-xylo-hexopyranoside (12) were synthesized in 60% and 55% overall yield, respectively. Starting from alpha-L-fucose, sequential peracetylation, anomeric bromination, nucleophilic substitution of the anomeric bromide with NaSEt and deacetylation gave ethyl 1-thio-beta-L-fucopyranoside (6). Acid catalyzed regioselective cleavage of the orthoester in ethyl 2-O-acetyl-3,4-O-(1-ethoxyethylidene)-1-thio-beta-L-fucopyranoside, prepared from 6, yielded the corresponding 2,4-diacetate, which was deoxygenated at C-3 to provide the disarmed thioglycoside 10. Deacetylation of 10, followed by benzylation, gave armed thioglycoside 12. Several intermediates did not require purification by chromatography.