Synthesis of S-linked thiooligosaccharide analogues of Nod factors. Part 1: selectively N-protected 4-thiochitobiose precursors
The synthesis of S-linked thio-analogues of chitobiose diversely substituted at both 2-acetamido-2-deoxy-D-glucopyranosyl units has been achieved successfully starting either from a 1,6-anhydro-4-O-triflyl galactosaminide derivative in reaction with a glucosamide 1-thiolate in DMF or a 1,6-anhydro-4-thiolate of a D-glucosaminide derivative with a Troc-protected 2-amino-2-deoxy-D-glucose derivative. Alternatively, reaction of an acylated 4-thiolate of 2-acetamido-2-deoxy glucose with an N-Troc-protected glucosaminyl bromide afforded the expected S-linked 4-thio-analogue of chitobiose. Acid catalysis involving reaction of compound 17 with an N-Troc-protected glucosaminyl imidate in the presence of trimethylsilyl triflate gave only poor yields of the expected 1,6-anhydro 4-thio-S-linked disaccharide.