Abstract— Azathioprine is used as an immunosuppressant for renal transplant recipients, but is frequently associated with severe skin cancer as a side effect. 6‐Mercaptopurine, the primary metabolite of azathioprine. absorbs strongly in the UVA region and displays substantial photochemical reactivity. The primary photochemical processes in aqueous solution are triplet state formation and photoionization, as shown by flash photolysis. In oxygenated solution, singlet oxygen and superoxide are produced, and ground state 6MP appears to react with these species. Glutathione inhibits this reaction and is itself oxidized. In deoxygenated solution, reactions implicating the thiyl radical and hydrogen atom and electron transfer occur as shown by reaction with histidine and p‐nitrosodimethylaniline. Nitro Blue Tetrazolium or acrylamide.
Abstract— The antibacterial drugs, nalidixic acid and oxolinic acid, have been tested as photosensitizers in aqueous solution using 365 nm UV light. Absorption and fluorescence spectra indicate that intramolecular hydrogen bonding stabilizes the unionized form of these compounds in the pH region2–4. The ability of the unionized species to sensitize photooxidation by the type II (singlet oxygen) mechanism was found to be lower than when these drugs were ionized. Comparison withquinoline–3‐carboxylic acid and the methyl esters of nalidixic and oxolinic acids emphasised the significance of the hydrogen bonding in relation to the excited state properties. Unionized nalidixic acid undergoes photolysis more readily than the ionized form, apparently by a free radical mechanism, while oxolinic acid is more stable.
Irradiation of oxygenated aqueous solutions of 6-mercaptopurine with near-u.v. light leads to purine-6sulphinate as primary product. The sulphinate is itself unstable to U.V. light and is further oxidized to purine-6-sulphonate. Hypoxanthine is a minor product (
The antimalarial drugs, chloroquine, hydroxychloroquine, quinine, quinacrine, amodiaquine and primaquine and the local anaesthetic, dibucaine, were tested for in uitro photosensitizing capability by irradiation with 365 nm UV light in aqueous solutions. The ability of these compounds to photosensitize the oxidation of 2,5-dimethylfuran, histidine, tryptophan or xanthine, and to initiate the free radical polymerization of acrylamide was examined in the pH range 2-12. Chloroquine and hydroxychloroquine show maximal photooxidative behaviour when in the monocation form at pH 9, in contrast to quinine which is extremely efficient as the dication below pH 4. This pattern appears to relate to the fluorescence yield as a function of pH. Chloroquine in the monocation or neutral form was found to undergo dechlorination upon irradiation, and this correlates directly with its ability to initiate photopolymerization of acrylamide. Quinine also gives rise to small polymerization rates, attributed to photoionization in the quinoline ring, yielding a cation radical. Amodiaquine, primaquine and quinacrine do not have significant photochemical activity in aqueous solution. Dibucaine exhibits a strong photosensitizing capability at low pH, similar to quinine.
Abstract— The photochemical reactivity of the immunosuppressant drug, azathioprine (AZT) and two representative metabolites of the nitroimidazole moiety, 1‐methyl‐4‐nitroimidazole (MNI) and lmethyl‐4‐nitro‐5‐thioimidazole (MNTI) has been examined. No transient species of AZT were observed by laser flash photolysis, inferring a low triplet yield or its rapid deactivation. Consequently AZT, MNI and MNTI displayed little or no photodynamic sensitization via photooxidation reactions. However, AZT and MNI are highly reactive radical scavengers when photoexcited, as determined by reaction with polyacrylamide radicals. The photoreactivity of the metabolites of AZT is greater than that of the parent drug. an observation which may be relevant to the photocarcinogenicity of AZT.
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