Synthetic approaches to 2-deoxyglycosyl phosphates

By the use of the N-iodosuccinimide (NIS)-procedure, various glycals could be converted into 2-deoxy-2-iodoglycosyl phosphates. Treatment of glycals 1 and 7 with NIS and dibenzyl phosphate gave the corresponding alpha-1,2-trans-diaxial 2-deoxy-2-iodoglycosyl phosphates 2 and 8 as the main products. The beta-1,2-trans-diequatorial compounds 3 and 9 were isolated as by-products. Analogous reaction of glycals 4 and 10 gave the corresponding 2-deoxy-2-iodoglycosyl phosphates 5, 6, 11, and 12 as crude products, which were characterized by 1H NMR spectroscopy. Classical phosphorylation of 2-deoxy-glycosyl chlorides 14 and 16 with silver dibenzyl phosphate gave the corresponding dibenzyl 2-deoxy-alpha-glycosyl phosphates 15 and 17. Alternatively, glycosylation of tri-O-acetyl-D-glucal using dibenzyl phosphate and triphenylphosphine hydrobromide afforded 15 in lower yield. The application of S-(2-deoxyglycosyl) phosphorodithioates as glycosyl donors provided the most convenient way to dibenzyl 2-deoxyglycosyl phosphates. The alpha-glycosyl phosphates 15, 20, and 22 could be synthesized by reaction of the 2-deoxyglycosyl dithiophosphates 18, 19, and 21 with dibenzyl phosphate and activation by iodonium di-sym-collidine perchlorate. Similarly, the 2,6-dideoxyglycosyl dithiophosphates 23 and 25 gave the 2,6-dideoxy phosphates 24 and 26; however, the isolation of these labile compounds could not be effected.