Synthetic studies directed towards asmarines; construction of the tetrahydrodiazepinopurine moiety by ring closing metathesis

Asmarines are tetrahydro[1,4]diazepino[1,2,3- g , h ]purine derivatives isolated from marine sponges ( Raspailia sp). They possess profound cytotoxic activity towards cancer cell lines, and are thus attractive synthetic targets. The tetrahydrodiazepinopurine ring skeleton has been prepared employing the RCM reaction on Boc-protected 6-allylamino-7-(propen-1-yl)purine as the key step for the construction of the seven-membered ring. 7-(Propen-1-yl)purines were formed by a novel rearrangement of 7-allylpurines under basic conditions. Boc-protected N 6 ,7-diallylpurine also participated in RCM to give the eight-membered ring analog of the diazepinopurine.