Synthesis of β-D-Ara-(1 → 2)-α-D-Ara-(1 → 5)-α-D-Ara trisaccharides as 2-azidoethyl and 4-(2-trifluoroacetamidoethoxy)phenyl glycosides related to the fragments of mycobacterial polysaccharides.

Two glycosides of β-d-Ara-(1 → 2)-α-d-Ara-(1 → 5)-α-d-Ara trisaccharide related to the fragments of mycobacterial polysaccharides with 4-(2-trifluoroacetamidoethoxy)phenyl and 2-azidoethyl aglycones, required for further conjugation with protein carriers and preparation of neoglycoconjugates, were synthesized using silylated (TIPS or TBDPS) Ara-β-(1 → 2)-Ara disaccharide thioglycosides as glycosyl donors. We found that the protective groups in glycosyl acceptor (benzoyl or 4-tert-butylbenzyl) and aglycone nature do not affect stereoselectivity of glycosylation with silylated Ara-β-(1 → 2)-Ara disaccharide glycosyl donors. Earlier we showed that TIPS-protected Ara-β-(1 → 2)-Ara disaccharide thioglycoside could be prepared by thiolysis of the corresponding 4-(3-chloropropoxy)phenyl glycoside in 50% yield. A study of thiolysis of different mono- and disaccharide substrates containing 4-(2-chloroethoxy)phenyl, 4-(2-azidoethoxy)phenyl and 4-methoxyphenyl aglycones revealed that the highest yield (95%) of the target p-tolyl thioglycoside can be achieved with TBDPS-protected Ara-β-(1 → 2)-Ara dissacharide with 4-methoxyphenyl aglycone.