Towards the Modification of the Anomeric Position of Glycosyl Thiols

Modifications of anomeric sulfhydryl groups of glycosyl thiols was studied including symmetrical glycosyl disulfide formation, desulfurisaiton of glycosyl disulfide to access glycosyl thiols, desulfurisaiton of glycosyl thiols for preparation of 1-deoxysugars, epimerisation of β-glycosyl thiols to α-glycosyl thiols, attempts in synthesis of C-glycosides from thioglycoside precursors. Preparation of α-glycosyl thiol by ring opening of 1,6-anhydrosugar was achieved in 59% yield. Synthesis of symmetrical glucosyl α, α-disulfide with iodine was successful with >90% yield. Various glycosyl thiols and disulfides were prepared for study on desulfurisation reactions with tributylphosphines. Cleavage of disulfide produced the glycosyl thiols in high yields of 75-90%. Prepared glycosyl thiols were treated with excess amounts of tributylphosphines and produced 1-deoxysugars in 55-60% yields. Formation of symmetrical disulfide from per-acetylated glucosyl thiol was utilised as a method for anomeric S-protection and subjected to various protecting group manipulations. The disulfide was successfully cleaved with tributylphosphine and a glucosyl thiol with mixed protecting pattern was obtained in 84% yield. New conditions for epimerisation of β-glycosyl thiols to α-glycosyl thiols was achieved using copper triflate as the Lewis metal per-benzoylated glycosyl thiols and produced an α:β ratio of 1:1. Formation of C-glycosides from alkyl and aryl thioglycosides was investigated using tributylphosphines under ambient light conditions. Negative results were obtained, and further studies would be needed to better understand the reaction.