Capsular polysaccharide of Streptococcus pneumoniae type 19F: synthesis of the repeating unit

A new and more versatile synthesis of β-d-ManpNAc-(1→4)-α-d-Glcp-(1→2)-α-l-Rhap, the trisaccharide repeating unit of the Streptococcus pneumoniae type 19F capsular polysaccharide, is described. The present approach allows a simple access to different fragments containing the trisaccharide and the conjugation of the product(s) to a protein through the selective manipulation of the anomeric position at the reducing end and of the HO-4 function at the nonreducing end. The synthetic scheme shows an efficient application of the sulfoxide method for the stereoselective and high yielding formation of the glycosidic linkages. Copyright (C) 1998 Elsevier Science Ltd.