Photochemical behavior of 2-azidopurine tri-O-acetylribonucleoside in aqueous solution: unprecedented transformation into 1-(5'-O-acetyl-β-D-ribofuranosyl)-5-[(2-oxo-1,3,5-oxadiazocan-4-ylidene)amino]-1H-imidazole-4-carbaldehyde.

The photochemical behavior of 2-azidopurine 2',3',5'-tri-O-acetylribonucleoside has been investigated in aqueous solution under aerobic and anaerobic conditions. The two major processes under anaerobic irradiation of 2-azidopurine 2',3',5'-tri-O-acetylribonucleoside involve unprecedented transformation into 1-(5'-O-acetyl-β-D-ribofuranosyl)-5-[(2-oxo-1,3,5-oxadiazocan-4-ylidene)amino]-1H-imidazole-4-carbaldehyde and photoreduction to respective 2-aminopurine derivative, whereas under aerobic conditions these two processes occur to a much lesser extent and photooxidation to respective 2-nitropurine derivative dominates. The structures of photoproducts formed were confirmed by NMR and high-resolution electrospray ionization mass spectral data.

Photochemistry of 6-amino-2-azido, 2-amino-6-azido and 2,6-diazido analogues of purine ribonucleosides in aqueous solutions.

The photochemistry of 6-amino-2-azidopurine, 2-amino-6-azidopurine and 2,6-diazidopurine ribonucleosides has been investigated in aqueous solutions under aerobic and anaerobic conditions. Near UV irradiation of 6-amino-2-azido-9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)purine and 2-amino-6-azido-9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)purine in the presence of oxygen leads to efficient formation of 6-amino-2-nitro-9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)purine and 2-amino-6-nitro-9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)purine. Under anaerobic conditions, both azidopurine ribonucleosides preferentially undergo photoreduction to 2,6-diamino-9-(2',3',5'-tri-O-acetyl-β-D-ribofuranosyl)purine.

Photoaddition of 5-bromouracil to uracil in oligonucleotides leading to 5,5'-bipyrimidine-type adducts: mechanism of the photoreaction.

5-Bromouracil ((Br)U) modified di- and hexanucleotides having (Br)U flanked on the 5' or the 3' side by uracil (U) have been synthesized, and their photochemical reactivity was examined under the conditions of irradiation with near UV light. The results indicate that the primary photochemical process in all of these compounds involves the formation of an intermediate cyclobutane phodoadduct composed of (Br)U and U, which undergoes further photochemically and thermally induced transformations to 5,5'-bipyrimidine type adducts.