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Treatment of 2-(trimethylsilyl)ethyl 2,3-di-O-acetyl-4-O-(3,4,6-tri-O-acetyl-R-D-galactopyranosyl)β-D-galactopyranoside (12) and 2-(trimethylsilyl)ethyl 2,3-di-O-benzyl-β-D-glucopyranoside (15) with the novel reagent combination formaldehyde diphenylmercaptal-N-iodosuccinimide-trifluoromethanesulfonic acid [(PhS) 2 CH 2 /NIS/TfOH], gave the corresponding 6,2′-O-and 4,6-O-methylidene acetals 13 and 16 in 52% and 53% yield, respectively. Deacetylation of 13 gave 2-(trimethylsilyl)ethyl 4-O-R-D-galactopyranosyl-β-D-galactopyranoside (1). The conformation of 1 was similar to that of the non-acetalated parent glycoside. † Dedicated to Professor Hans Paulsen on the occasion of his 75th birthday.

2-(Trimethylsilyl)ethyl 2-O-benzoyl- and 2,3-di-O-acetyl-beta-D-xylopyranosides (12 and 14) were synthesized in high yields and subjected to glycosylation with various glycosyl donors. Galactosylation of 12 gave the xylose analogue of TMSEt lactoside (3), which was transformed into the glycosyl acceptor 19. Sialylation then gave the xylose analogue of G(M3) trisaccharide (5). The TMSEt glycosides 10, 25, and 32 were transformed into the corresponding trichloroacetimidates, which were used for glycosylation of an azidosphingosine derivative. The resulting sphingosyl glycosides were transformed into the title ceramides. Treatment of NeuAcalpha2-3Galbeta1-4XylbetaCer (5) with acetic acid gave the corresponding 1"-->2'-lactone 7. Glycosylation of 12 or 14 with a G(M4)-lactam donor (40) gave the xylose analogue of G(M3)-lactam (42). There was a 3-fold increase in the formation of GAG chains in the presence of 0.5 &mgr;M XylbetaCer (2) in the medium.