Photochemical intramolecular cyclisation of purine and pyrimidine nucleosides induced by an electron acceptor

Abstract

Irradiation of appropriately protected purine nucleosides (guanosine and adenosine)(1) and cytidine (2a) in the presence of pyrimido[5,4-g]pteridine N-oxide (5) with u.v.–visible light results in the exclusive formation of the corresponding 5′-O,8-cyclopurine nucleosides (3) and 5′-O,6-cyclocytidine (4a).