Novel observations on thiophosphoryl-group transfer in sugar β-hydroxy phosphorodithioate systems. Synthesis and X-ray molecular structure of 1,6-anhydro-3,4-dideoxy-3,4-epithio-2-O-(p-tolylsulfonyl)-β-D-allopyranose

Abstract

The reaction of 1,6;3,4-dianhydro-2-O-(p-tolylsulfonyl)-β-D-galactopyranose 6 with the triethylammonium salt of 2-mercapto-5,5-dimethyl-1,3,2-dioxaphosphorinane 2-sulfide 7′ gives the hitherto unknown 1,6-anhydro-3,4-dideoxy-3,4-epithio-2-O-(p-tolylsulfonyl)-β-D-allopyranose 8 in high yield. The intermediates in this reaction are: 1,6-anhydro-4-S-(5′, 5′-dimethyl-2′-thioxo-1′,3′,2′-dioxaphosphorinan-2′-yl)-4-thio-2-O-(p-tolylsulfonyl)-β-D-glucopyranose 9 and 1,6-anhydro-3-O-(5′, 5′-dimethyl-2′-thioxo-1′,3′,2′-dioxaphosphorinan-2′-yl)-4-thio-2-O-(p-tolylsulfonyl)-β-D-glucopyranose 10. The former can be obtained by addition of 2-mercapto-5,5-dimethyl-1,3,2-dioxaphosphorinane 2-sulfide 7 to the dianhydro sugar 6. Formation of the latter was confirmed by 31P NMR spectroscopy. Comparative conformational studies of dianhydro compound 6 and of episulfide 8 were undertaken. They revealed that, despite the opposite orientation of the epoxy and epithio groups, the overall conformation of 5- and 6-membered rings remains the same. The absolute configuration of compound 6 has been determined as 1R,2R,3S,4S,5R, and of compound 8 as 1R,2S,3S,4R,5R.