Aza and deaza analogs of purine nucleosides (review)

Methods for the preparation of aza and deaza analogs of purine nucleosides, viz., nucleosides of imidazo[4,5-d]-v-triazines, imidazo[4,5-b]pyridines, and imidazo[4,5-c]pyridines, and their properties are described. References to the synthesis of nucleosides of imidazo[4,5-d]pyridazines, imidazo[4,5-c]pyridazines, and imidazo[4,5-b]pyrazines are also given.