Studies on the photodynamic reaction of purines and purine analogues with methylene blue

Abstract

1. 1. The susceptibility of purines and purine-like compounds to photodynamic action was studied using methylene blue as the photosensitizing dye. While guanosine, xanthine, theophylline and 2,6-diaminopurine are susceptible to photodynamic action, 8-azaderivatives of purines are resistant; this suggests that a prerequisite for photosusceptibility is a chemical structure that can be oxidized at the 8-position in the purine ring system. Tubercidin and 6-mercaptopurine are also found susceptible. 2. 2. Manometric studies reveal that, while the ratio of molecular oxygen consumed to substrate oxidized for deoxyguanosine and xanthine is approximately unity, it is approximately 1 2 for uric acid. 3. 3. Product analysis of irradiated [ 14C]uric acid suggests that urea may be a primary photoproduct from the C-2 portion of the molecule, while urea from the C-8 portion results from decomposition of a primary photoproduct. The photodegradative pathway of uric acid is probably similar to that of guanine and likely xanthine.