SELECTIVELY DEOXYGENATED DERIVATIVES OF BETA-MALTOSYL-(1-]4)-TREHALOSE AS BIOLOGICAL PROBES .2. THE SYNTHESIS OF THE 4-MONODEOXYGENATED AND4'''-MONODEOXYGENATED ANALOGS

Two derivatives of beta-maltosyl-(1-->4)-trehalose monodeoxygenated at positions 4 or 4''' have been synthesized in [2+2] block syntheses, A fter the preparation of precursors with only one free hydroxyl group t he deoxy function was introduced by a Barton-McCombie reaction. Thus, glycosylation of 2,3,6-tri-O-benzyl-alpha-D-glucopyranosyl 2,3,6-tri-O -benzyl-alpha-D-glucopyranoside (4) with octa-O-acetyl-beta-maltose (3 ) gave tetrasaccharide 5 with only one free hydroxyl group at the 4-po sition. The 4'-position of an allyl maltoside was available selectivel y after removal of a 4',6'-cyclic acetal and selective benzoylation of the 6'-position. Reduction of this derivative 11 afforded allyl cetyl -6-O-benzoyl-4-deoxy-alpha-D-glucopyranosyl)- (1-->4)-2,3,6-tri-O-acet yl-beta-D-glucopyranoside (14), which was deallylated, activated as an trichloroacetimidate, and coupled to -O-benzyl-4,6-O-benzylidene-alph a-D-glucopyranosyl 2',3',6'-tri-O-benzyl-alpha-D-glucopyranoside (20). Several compounds were fully characterized by H-1 NMR spectroscopy. D eprotection furnished the monodeoxygenated tetrasaccharides 9 and 23.