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Studies on the Total Synthesis of iso-L-Guanosine

An improved route for the total synthesis of iso-L-guanosine was developed. Using L-ribose as the starting material, 3,5-O-dibenzyl-1-deoxy-L-ribose was firstly synthesized. Then, Mitsunobu reaction between N,N-bis(tertbutyloxycarbonyl)-6-chloro-guanine and 3,5-O-dibenzyl-1-deoxy-L-ribose afforded isonucleoside 6. Finally, iso-L-guanosine was synthesized in 9 steps with 37.3% overall yield. Adopting Mitsunobu reaction as the key step, it has the merits of high steroseletivity and regioselectivity, mild reaction condition, and high yield. Currently developed approach could be used as a general synthetic strategy for the synthesis other related guanine isonucleosides.