Synthesis of an Inositol Phosphoglycan Fragment found in Leishmania Parasites

Synthesis of 1 and 2a is described using a block synthetic strategy. Compound 4 was used as precursor for the two mannose derivatives which, coupled together, forms the dimannoside building block. Thioglycoside 7 was coupled to 8 yielding inositol phosphoglycan 9a, which was selectively deprotected and reacted with 2,3,4,6-tetra-O-benzyl-α-d-glucopyranos-1-yl H-phosphonate to form the protected target molecule 12. Deprotection of 12 by acidic deacetalisation/desilylation and subsequent catalytic hydrogenolysis resulted in cleavage of the anomeric phosphodiester to produce 1. Debenzylation with sodium in liquid ammonia followed by acidic deacetalisation/desilylation gave the target compound 2a.