Synthesis of 9-substituted tetrahydrodiazepinopurines—asmarine A analogues

Asmarines are marine alkaloids, with a unique tetrahydro[1,4]diazepino-[1,2,3-g,h]purine (THDAP) structure and interesting biological properties. Three synthetic approaches were employed for the preparation of the THDAP system. Several N-9, of the purine, protecting groups were investigated. 15N-Chemical shifts measured from 15NH HMBC experiments for several compounds, that demonstrate the influence of various structural features on the 15N-resonances are reported.