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 gr oup and one at the ribose 5-hydroxyl group, was exposed in water-ethan ol solution to high-power pulsed laser emission at a wavelength of 354 .7 nm. Measurement of the transient absorption spectra. with nanosecon d time resolution shows that the photoejection of an electron occurs d ue to stepwise two-photon absorption by the dihydropyridine via its fl uorescent state. The spectrum of the cation radical formed in this rea ction was determined, together with that of the neutral radical appear ing 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 exoc yclic amino group showed no evidence for photoionization in the same e xperimental conditions.