Thiosugars, 2 Preparation of 2,3,4-Tri-O-benzyl-4-thio-L-arabino-furanosides and the Corresponding 4'-Thionucleoside Analogues

摘要

1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabino-furanose (9) has been prepared from D-xylose via the 1,4-dithio-L-arabino-furanoside 8. The crucial step of the reaction, i.e. the intramolecular cyclization of the open-chain dithioacetal 5, has been achieved in a yield of 90% by applying tetrabutylammonium iodide as promoter. Reaction of 9 with bis(trimethylsilyl)uracil or-thymine led to the benzyl derivatives 12 and 13 from which the deprotected 4'-thionucleoside analogues 14 and 15 have been prepared by debenzylation with boron tribromide.