Synthesis of certain [6:5:6] linear tricyclic nucleosides as potential antitumor agents

Abstract
A new class of tricyclic nucleosides in which the aglycon has a linear [6:5:6] geometry was synthesized using certain pyrrolo[2,3-d]pyrimidine nucleosides as the starting materials. An adenosine-adenosine analog was prepared from 6-aminotoyocamycin using 2 different synthetic routes. An adenosine-guanosine analog and several adenosine-6-mercaptopurine ribonucleoside-type tricyclic nucleoside derivatives were synthesized. Structural assignments were based on 1H NMR spectral studies, as well as an unequivocal chemical proof of structure. An interesting chemical shift for the 2'' hydrogen of certain tricyclic nucleosides was observed and is discussed. The in vitro cytotoxicity of these nucleosides against [mouse] leukemia L-1210 was determined. The in vivo evaluation of these tricyclic nucleosides against mouse leukemia will also be discussed.