Photochemical oxygenation of styrene by pyrimido[5,4,G]pteridine 10- oxide as a chemical mimic of hemin-catalysed oxygenation

✍ Scribed by Magoichi Sako; Seiji Ohara; Kosaku Hirota; Yoshifumi Maki

• Book ID: 104204186
• Publisher: Elsevier Science
• Year: 1990
• Tongue: French
• Weight: 543 KB
• Volume: 46
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)86754-5

✦ Synopsis

Irradiation of styrene (5) in the presence of pyrimido[5,4-g]pteridine IO-oxide (1) with u.v.-visible light resulted in the formation of styrene oxide (6) and phenylacetaldehyde (7) which are proved as primary metabolites of (5). Chemical and physico-chemical facts showed that the photooxygenation of ( 5) by ( 1) involves an initial single-electron transfer followed by oxygen-atom transfer, accommodating the oxygenation mode of cytochrome p-450 and other hemoproteins. Comparative experiments with 3-methylpyridazine 2-oxide (3)and pyridine l-oxide (4)demonstrated the simplicity and the mechanistic characteristic of the photooxygenation by (1).

The complex photochemistry of heterocyclic l-oxides is classified as intramolecular rearrangement of the l-oxide function or oxygen-atom transfer (deoxygenation). 1

Although the latter reaction has been considered to be a simple chemical modelforthe biological oxygenations by hepatic microsomal monooxygenases, e.g., cytochrome p-450, it usually occurs only as a minor process in the photochemical reactions of the x-oxides and its mechanism is not always unequivocal. Some authors favour the oxygen-atom transfer by a collision mechanism between a photoexcited E-oxide (or its oxaziridine isomer) and the substrates. 2b

Currently a majority of authors tend to believe that an atomic oxygen is generated after photoexcitation of theI&oxides andthenintercepted by the substrates.(oxene mechanism)3-5