Synthesis and reactions of sugar chlorosulphates

Abstract

Sugar chlorosulphates of furanoid and pyranoid derivatives bearing chlorosulphonyloxy groups at primary and secondary positions, were synthesized and examined mainly with a view to determine their extent of reactivity in terms of nucleophilic substitution reactions, especially with azide. Inversion of configuration occurred at reactive chiral centres, whereas intermediate azidosulphonyloxy derivatives (azidosulphates) were formed via S-Cℓ bond fission of the chlorosulphonyloxy group at less reactive primary or secondary centres, e.g. 1,2:3,4-diO̲isopropyl idene-α-D-galactopyranose 6-azidosulphate, 1,2-O̲isopropylidenea- D-xylofuranose 3-azidosulphate and 1,2:5,6-di-O̲-isopropyl idene-α-Dglucofuranose 3-azidosulphate. 1,2:3,4-Di-O̲-isopropylidene-α-Dgalactopyranose 6-azidosulphate ultimately afforded the 6-azidodeoxy derivative probably by an SN2 mechanism. Some SNi characteristics were,however, evident when substitution occurred at a reactive primary centre (e.g. methyl 2,3,4-tri-O̲-methyla- D-glucopyranoside 6-chlorosulphate), as the 6-azidodeoxy derivative obtained, appeared to be contaminated with a trace amount of the corresponding 6-chlorodeoxy sugar, which had presumably formed via an internal SNi mechanism, while no intermediate azidosulphonyloxy derivative was isolated. In another study, the reaction pathways for the synthesis of benzylated chlorodeoxy sugars having potential biological properties as exemplified by the multivalent drug, tribenoside, were also investigated