A Janus Aglycone-Based Divergent Strategy for the Synthesis of the PGL-I Epitopes Ready for Conjugation.

An efficient synthesis of epitopes of PGL-I glycolipids of Mycobacterium leprae was achieved using the 4-methoxyphenyl (MP) group as dual-mode Janus aglycone. Cleavage of the MP aglycone in a disaccharide gave a hemiacetal precursor of the glycosyl donor that was used for the assembly of the trisaccharide PGL-I epitope through α-selective [2+1] rhamnosylation (96:4 α:β). Selective demethylation of the MP aglycone in di- and trisaccharides followed by alkylation of the resulting phenolic hydroxy group gave diverse spacer aglycones suitable for the synthesis of neoglycoconjugates.