Synthesis of tumor associated sialyl-T-glycopeptides and their immunogenicity.

Sialyl-T-glycopeptides were synthesized by solid-phase techniques, using a PEGA resin as the solid support. hn appropriately protected building block containing alpha -Neu5Ac-(2 -->3)-beta -Gal-(1 -->3)-alpha -GalN(3)-(1 -->) attached to Fmoc-Thr/Ser-OPfp was employed in a solid-phase glycopeptide assembly of a 10-mer glycopeptide, using a general Fmoc/OPfp-ester strategy. Reduction of the azido group of the GalN(3) residue was effected on solid-phase, using DTT and DBU. After acidolytic cleavage from the resin, the methyl ester of the sialic acid residue and acetyl groups were removed with 30% NaOMe/MeOH in MeOH and Rater pH 14, at -30 degreesC for 2 h. At this low temperature, the highly basic conditions did not result in any detectable beta -elimination. However, one O-acetyl group, located at the 2-position of the Gal was resistant to hydrolysis. To remove this remaining acetyl group, reaction with hydrazine hydrate in CHCl3 and MeOH at room temperature for 2.5 h was successful. The two target sequences of sialyl-T-glycopeptides were obtained in good yield. In contrast to the the analogs carrying the T-antigen, the Sial-T-glycopeptides were nonimmunogenic, supporting the idea that the sialylation is a method of circumventing the recognition by the immune system. Copyright (C) 2000 John Wiley & Sons, Ltd.