SYNTHETIC STUDIES ON SIALOGLYCOCONJUGATES 104 - SYNTHESIS OF KDN-LEWIS X GANGLIOSIDE ANALOGS CONTAINING MODIFIED REDUCING TERMINAL AND L-RHAMNOSE IN-PLACE OF L-FUCOSE

KDN-Le(X) ganglioside analogs (10, 13, 16 and 19) containing the modif ied reducing terminal and L-rhamnose in place of L-fucose have been sy nthesized. Glycosidation of methyl 2,3,4-tri-O-benzyl-1-thio-alpha-L-r hamnopyransoide (1) with 2-(trimethylsilyl)ethyl -(1-->4)-2,3,6-tri-O- benzyl-beta-D-glucopyranoside (2), followed by reductive ring opening of the benzylidene acetal, gave 2-(trimethylsilyl)ethyl -(1-->4)-2,3,6 -tri-O-benzyl-beta-D-glucopyranoside (4). The tetrasaccharide 4 was co upled with methyl O-(methyl glycero-alpha-D-galacto-2-nonulopyranosylo nate)-(2 --> ,4,6-tri-O-benzoyl-1-thio-beta-D-galactopyranoside (5), u sing dimethyl(methylthio)sulfonium triflate (DMTST), to give the hexas accharide 6, which was converted into compound 11 in the usual manner. Compounds 8 and 11 were transformed, via bromination of the reducing terminal, radical reduction, O-deacylation and saponification of the m ethyl ester, into the desired KDN-LeX hexasaccharides (10, 13). On the other hand, glycosylation of 2-(tetradecyl)hexadecanol with alpha-tri chloroacetimidates 14 and 17, afforded the target ganglioside analogs 16 and 19.