Intramolecular Charge Transfer in the Azathioprine Prodrug Quenches Intersystem Crossing to the Reactive Triplet State in 6‐Mercaptopurine

The thiopurine prodrugs 6‐mercaptopurine and azathioprine are among the world’s essential medications for acute lymphoblastic leukemia, immunosuppression and several autoimmune conditions. Thiopurine prodrugs are efficient UVA absorbers and singlet oxygen generators and the long‐term treatment with...

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Bibliographic Details
Published in:Photochemistry and photobiology 2022-05, Vol.98 (3), p.617-632
Main Authors: Ortiz‐Rodríguez, Luis A., Ortiz‐Zayas, Glesmarie, Pollum, Marvin, Hoehn, Sean J., Jockusch, Steffen, Crespo‐Hernández, Carlos E.
Format: Article
Language:English
Subjects:
6-Mercaptopurine
Acute lymphoblastic leukemia
Aqueous solutions
Atomic energy levels
Azathioprine
Charge transfer
Drugs
Humans
Immunosuppression
Leukemia
Mercaptopurine - therapeutic use
Oxygen
Photochemicals
Photoexcitation
Photosensitization
Prodrugs
Side effects
Singlet oxygen
Singlet Oxygen - chemistry
Skin cancer
Triplet state
Ultraviolet Rays
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Summary:The thiopurine prodrugs 6‐mercaptopurine and azathioprine are among the world’s essential medications for acute lymphoblastic leukemia, immunosuppression and several autoimmune conditions. Thiopurine prodrugs are efficient UVA absorbers and singlet oxygen generators and the long‐term treatment with these prodrugs correlates with a high incidence of sunlight‐induced skin cancer in patients. In this contribution, we show that the electronic relaxation mechanisms and photochemical properties of azathioprine are remarkably different from those of 6‐mercaptopurine upon absorption of UVA radiation. UVA excitation of 6‐mercaptopurine results in nearly 100% triplet yield and up to 30% singlet oxygen generation, whereas excitation of azathioprine with UVA leads to triplet yields of 15–3% depending on pH of the aqueous solution and
ISSN:0031-8655
1751-1097
DOI:10.1111/php.13513