The allylic hydroxylation of 3,3,6,6-tetradeuteriocyclohexene, methylenecyclohexane, and β-pinene has been examined with phenobarbital-induced liver microsomal cytochrome P-450 (P-450LM2) and with iron porphyrin and chromium porphyrin model systems. Aerobic and peroxide dependent enzymic regimes were investigated with purified P-450LM2 and with microsomal suspensions. Epoixidation and allylic hydroxylation were the primary reactions with all substrates. With 3,3,6,6-tetradeuteriocyclohexene, the major hydroxylation product (60–80%) was the result of hydroxylation at the deuterated allylic site. In all cases, a significant amount (20–40%) of hydroxylation occurred with allylic rearrangement. The iron porphyrin/iodosylbenzene model system also showed preferential hydroxylation of the deuterated allylic site (70%) with significant allylic rearrangement (30%). By contrast, the chromium porphyrin/iodosylbenzene model system showed complete scrambling of the allylic system. Extensive rearrangement accompanied the hydroxylation of methylenecyclohexane and β-pinene by both the enzymic and metalloporphyrin systems whereas the selenium dioxide oxidation of these substrates gave selective allylic hydroxylation without rearrangement. A mechanism is suggested for allylic hydroxylation by cytochrome P-450 and by the metalloporphyrin model systems involving initial hydrogen atom abstraction from the allylic site and geminate, cage recombination of the incipient, allylic free radical.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry