Synthesis of sulfur-linked analogues of nigerose, laminarabiose, laminaratriose, gentiobiose, gentiotriose, and laminaran trisaccharide Y

Sulfur-linked analogues of 3-O-alpha-D-glucopyranosyl-D-glucose (nigerose), 3-O-beta-D-glucopyranosyl-D-glucose (laminarabiose), 6-O-beta-D-glucopyranosyl-D-glucose (gentiobiose), O-beta-D-glucopyranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 3)-D-glucose (laminaratriose), O-beta-D-glucopyranosyl-(1 --> 6)-O-beta-D-glucopyranosyl-(1 --> 6)-D-glucose (gentiotriose) and 3,6-di-O-beta-D-glucopyranosyl- D-glucose (laminaran trisaccharide Y), namely, respectively, 3-thionigerose (6), 3-thiolaminarabiose (11), 6-thiogentiobiose (21), 3(I),3(II)-dithiolaminaratriose (16), 6(I),6(II)-dithiogentiotriose (29) and 3(I),6(I)-dithiolaminaran trisaccharide Y (37) have been conveniently prepared by S(N)2 reactions of the corresponding anomer of D-glucopyranose 1-thiolate with suitably activated monosaccharide derivatives in N,N-dimethylformamide (for 6 and 21) or in tetrahydrofuran in the presence of a crown ether (for 11). A sequence involving the reaction of non-anomeric thiolates with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide was alternatively used for the preparation of 11 and 21 but proved less satisfactory. The preparation of thiotrisaccharides 16, 29, and 37 involved a mixed approach.