Photochemistry of 2-chloropyrimidine.

The photochemistry of 2-chloropyrimidine (ClPy) was investigated by means of nanosecond laser flash photolysis, HPLC, mass spectrometry, polarography and absorption spectroscopy. Two major products were formed on low-intensity UV irradiation (lambda = 254 nm) of ClPy in anaerobic aqueous solution: 2-hydroxypyrimidine (quantum yield approximately 0.01) and a compound identified as 2-chloro-4,2'-bipyrimidine (quantum yield approximately 0.

Reaction mechanism in the photochemistry of the antileukaemic agents 2-chloro- and 2-bromo-2'-deoxyadenosine, studied by nanosecond laser flash photolysis.

The reaction mechanism in the UV photochemistry of 2-chloro-2'-deoxyadenosine (Cladibrine) and 2-bromo-2'-deoxyadenosine in aqueous solution has been studied by laser photolysis at nanosecond time resolution. It is found that excitation at 266 nm wavelength produces heterolytic cleavage of the halogen-carbon bond by one-photon absorption and formation of the unstable 2-hydroxy tautomer of 2'-deoxyisoguanosine as predominant 'primary' product. The 2-hydroxy tautomer then transforms in 10(-6)-10(-5) s into the stable 2-oxo tautomer in an acid-base-catalysed reaction.

Intermediates in the oxidation of a dihydropyridine derivative of AZT related to AIDS dementia, studied by nanosecond laser photolysis.

Radicals of the AZT derivative 5'-(1,4-dihydro-1-methyl-3-pyridinylcarbonyl)-3'-azido-2',3'-dideo xythymidine) were obtained on exposure of this compound in alkaline aqueous solution to pulsed laser emission of lambda = 355 nm and pulsewidth 2 ns FWHM. The radical formation was shown to be due to photoelectron ejection from the pyridine group following two-step excitation of the compound. The radicals were found to deprotonate rapidly.

Electrochemical reduction products of azido nucleosides, including zidovudine (AZT): mechanisms and relevance to their intracellular metabolism.

Previous studies on electrochemical reduction of the HIV reverse transcriptase inhibitor, 3'-azido-3'-deoxythymidine (Zidovudine, AZT) and several of its analogues, have been extended to 2'-AZdT and two of the intracellular metabolites of AZT, the 5'-O-glucuronide (GAZT) and the 5'-phosphate (AZTMP). Also investigated were azido nucleosides with aglycons susceptible to electrochemical reduction, cytosine and adenine. The surface activities of these compounds at the mercury electrode were examined.

Photochemical and enzymatic redox transformations of reduced forms of coenzyme NADP+.

The two reduced forms of NADP+, NADPH and its dimer (NADP)2, on irradiation in aqueous medium at 365 nm, are converted to enzymatically active NADP+, with accompanying formation of H2O2. The rate photooxidation of NADPH is strongly dependent on the presence of oxygen, but that of (NADP)2 is similar under aerobic and anaerobic conditions. In the presence of oxygen, but not in its absence, O2-.

Preparative electrochemical reduction of 2-amino-6-chloropurine and synthesis of 6-deoxyacyclovir, a fluorescent substrate of xanthine oxidase and a prodrug of acyclovir.

D.c. polarography of 2-amino-6-chloropurine in aqueous medium over a broad pH range revealed two diffusion waves, the first of which corresponds to reduction of the C(6)-Cl bond, leading to formation of 2-aminopurine in high yield.

Electrochemical study of the reduction of toyocamycin and sangivamycin in aqueous media.

The redox behaviour of two antibiotics, toyocamycin and sangivamycin, structurally related pyrrolopyrimidine nucleosides, and their reduction products in buffered aqueous media, have been examined by direct current polarography and cyclic voltammetry. Both compounds exhibit one 3-electron polarographic wave in the pH range 1-6. Macroscale electrolysis at the crest of the polarographic wave was followed electrochemically and by UV spectroscopy.