PENTENYL RIBOSIDES - NEW REAGENTS FOR PURINE NUCLEOSIDE SYNTHESIS

Protected pent-4-enyl ribosides and deoxyribosides were synthesized as reagents for the preparation of nucleosides and deoxynucleosides. Rea ction of pent-4-enyl 2',3',5'-tri-O-benzoyl-D-erythro-pentofuranoside with five nucleobases in the presence of N-iodosuccinimide/trifluorome thanesulfonic acid (NIS/TfOH) produced the N-9-beta-nucleosides in 50- 70% yields. ',5'-di-O-p-toluyl-alpha-D-erythro-pentofuranoside coupled with 6-chloropurine in the presence of iodonium dicollidine perchlora te (IDCP) to produce a mixture of deoxynucleoside isomers (N-9, N-7, a lpha,beta) in 91% yield. Under the same conditions, coupling of 6-chlo ropurine with pent-4-enyl opyldisiloxane-1,3-diyl)-D-erythro-pentofura noside produced only N-9alpha and N-9beta products in 40% total yield. The N-9beta nucleoside was the only product of the reaction of 6-chlo ropurine with pent-4-enyl opyldisiloxane-1,3-diyl)-D-erythro-pentofura noside in the presence of NIS/TfOH. Pent-4-enyl ribosides appear to be useful reagents for the synthesis of ribo- and deoxyribonucleosides u nder mild (NIS/TfOH) or neutral (IDCP) conditions.