Convergent synthesis of neoglycopeptides by coupling of 2-bromoethyl glycosides to cysteine and homocysteine residues in T cell stimulating peptides.

The 2-bromoethyl beta-glycosides of the disaccharide galabiose [Gal(alpha1-4)Gal] and the trisaccharides globotriose [Gal(alpha1-4)Gal(beta1-4)Glc] and 3'-sialyllactose [Neu5Ac(alpha2-3)Gal(beta1-4)Glc] have been prepared by improved routes. The 2-bromoethyl glycosides were then used in cesium carbonate promoted alkylations of the sulfhydryl groups of cysteine and homocysteine residues in T cell stimulating peptides. This convergent and general approach was used to prepare 16 neoglycopeptides which were obtained in 52-95% yields after purification by HPLC. 1H NMR spectroscopy revealed that beta-elimination and epimerization of neoglycopeptide stereocentres did not occur during the synthesis.