DITHIASUCCINOYL (DTS) AMINO-PROTECTING GROUP USED IN SYNTHESES OF 1,2-TRANS-AMINO SUGAR GLYCOSIDES

Suitable protected D-glucosamine derivatives possessing the N-dithiasuccinoyl (N-Dts) protecting group of the amino function have been applied in a new alternative route to 1,2-transglycosylation. The O-(3,4,6-tri-O-acetyl-2-deoxy-2-dithiasuccinoylamino-beta-D-glucopyranosyl) trichloroacetimidate 7 has been used to prepare corresponding beta-glycosides in good yields promoted by Lewis acids. The N-dithiasuccinoyl protecting group was easy to remove by thiolysis using 2-sulfanylethanol or dithiothreitol or reductively using sodium boranuide, thus affording, after N-acetylation, the corresponding N-acetyl-beta-D-glucosamine glycosides. It has been demonstrated that it is possible to reduce the Dts group in the presence of an azido group selectively by sodium boranuide or the Dts- and the azido group simultaneously by dithiothreitol, using diisopropylethylamine as a catalyst. The syntheses of the building blocks, N(a)lpha-Fmoc-Ser(Ac-3-beta-D Dts)-OPfp 10 and N(a)lpha-Fmoc-Thr(Ac-3-beta-D-GlcNDts)-OPfp 11, suitable for the solid-phase glycopeptide synthesis of beta-O linked GlcNAc bearing glycopeptides are described. Furthermore, the preparation of the N(a)lpha-Fmoc-Asn[Ac-3-beta-D-GlcNAc-(1-->4)-Ac-2-beta-D-GlcNAc]-OPfp building block 19, suitable for the solid-phase synthesis of N-glycopeptides, and the synthesis of the beta-D-GlcNAc(1-->6 )-D-GalNAc disaccharide 27, a mucin core structure, demonstrate the use of N-dithiasuccinoyl protection in oligosaccharide synthesis.