N-Trichloroethoxycarbonyl-glucosamine derivatives as glycosyl donors

Article abstract of DOI:10.1016/S0008-6215(96)00237-6

D-Glucosamine can be readily transformed into 1,3,4,6-tetra-O-acetyl-2-deoxy-2-(2,2,2-trichlorothoxycarbonylamino)-D -glucopyranose (2). From this intermediate valuable glycosyl donors can be obtained; reaction with ethanethiol in the presence of boron trifluoride etherate afforded ethyl 3,4,6-tri-O-acetyl-2-deoxy-1-thio-2-(2,2,2-trichloroethoxycarbonylamino)β-D -glucopyranoside 4) which gave, upon N-acetylation, the N-acetyl-N-trichloroethoxycarbonyl derivative (5). Selective removal of the 1-O-acetyl group in 2 followed by treatment with trichloroacetonitrile in the presence of base afforded 3,4,6-tri-O-acetyl-2-deoxy-2-(2,2,2-tricchloroethoxycarbonylamino)-α-D -glucopyranosyl trichloroacetimidate (6). Reaction of 5 with five selectively protected glycosides as glycosyl accepters in the presence of N-iodosuccinimide/trifluoromethanesulfonic acid as the promoter system furnished the corresponding β-glycosides in good yields, thus exhibiting the valuable glycosyl donor properties of 5. Reductive removal of the trichloroethoxycarbonyl (Teoc) group afforded the corresponding N-acetyl-protected saccharides in high yields. The imidate 6 reacted with three of the above accepters in the presence of catalytic amounts of trimethylsilyl trifluoromethanesulfonate to give the β-linked disaccharides in even better yields. The direct replacement of the N-Teoc group by the N-acetyl group using zinc/acetic anhydride, via the free amines as transient intermediates, adds to the high efficiency and convenience of this methodology.