Regioselectivity and Deuterium Isotope Effects in Geraniol Hydroxylation by the Cytochrome P‐450 Monooxygenase from Catharanthus roseus (L.) G. DON

The hydroxylation of geraniol ( 8 ) by cytochrome P‐450 (P‐450 Cath. ) from the subtropical plant Catharanthus roseus (L.) G. D ON was optimised to give 8‐hydroxygeraniol ( 9 ) as the single product in 35% yield. Incubations of different 13 C‐ and 2 H‐labelled geraniols revealed that H‐abstraction is completely regioselective in favour of the CH 3 group trans to the chain at C(6) of 8 . An intramolecular isotope effect k H / k D = 8.0 was determined, suggesting that H‐abstraction is one of the major rate‐contributing steps; however, the intermolecular isotope effect was surprisingly inverse at low conversion k H / k D = 0.50, indicating the existence of rate‐contributing steps preceding the first irreversible, isotope‐sensitive reaction in the sequence.