Synthesis of di- to hexasaccharide 1,2-linked beta-mannopyranan oligomers,a terminal S-linked tetrasaccharide congener and the corresponding BSA glycoconjugates

Homo oligomers of (1 -->2)-beta -D-mannopyranosyl residues have been synthe sized in order to study the unique immunological properties of the cell wal l mannan of C. albicans. p-Chlorobenzyl-protected ulosyl bromide (2) in com bination with the sterically hindered, participating solvent, pivaloyl nitr ile, facilitated a new approach for the synthesis of these unique homooligo mers ranging from disaccharide up to hexasaccharide. The glycosyl donor 2 d emonstrates high diastereoselectivity over both the glycosylation and subse quent reduction step and minimizes the number of protecting group manipulat ions necessary for the synthesis. Congeners of the (1 -->2)-beta -D-mannote traose were synthesized containing a terminal S-linked (1 -->2)-beta -D-man nopyranosyl residue. Deprotection of these compounds afforded the propyl gl ycosides as well as oligomers with amino terminated aglyconic tethers. The tethers were generated from the oligosaccharide allyl glycosides by photoad dition with 2-aminoethanethiol. The functionalized haptens were coupled to BSA via squarate conjugation, and the degree of incorporation was establish ed by TOF mass spectrometry.