Reaction intermediates of a dihydropyridine derivative of 2',3'-dideoxycytidine related to AIDS dementia studied by laser flash photolysis

A derivative of 2',3'-dideoxycytidine (ddC), carrying one 1,4-dihydro-1-methyl-3-pyridinyl-carbonyl group at the cytidine exocyclic amino group and one at the ribose 5-hydroxyl group, was exposed in water-ethanol solution to high-power pulsed laser emission at a wavelength of 354.7 nm. Measurement of the transient absorption spectra. with nanosecond time resolution shows that the photoejection of an electron occurs due to stepwise two-photon absorption by the dihydropyridine via its fluorescent state. The spectrum of the cation radical formed in this reaction was determined, together with that of the neutral radical appearing following deprotonation of the cation. The electron is apparently abstracted only from the pyridine group attached to the ribose, since a comparative study on ddC carrying a dihydropyridine only at the exocyclic amino group showed no evidence for photoionization in the same experimental conditions.