Acetylation of Racemic cis- and trans-alpha-Irols, Mediated by Porcine Pancreatic Lipase (PPL) - A New Route to (-) and (+)-cis-alpha-Irone.

The mixture of the four racemic stereoisomers of alpha-irol (5-8) was submitted to PPL-mediated acetylation; cis-alpha-irol 8b was converted more quickly than any other diastereoisomer and in enantiopure fashion. By chance, this latter derivative was the precursor of (-)-cis-alpha-irone, the stereoisomer showing the strongest Orris butter character. Suitable manipulation of the material left unchanged by PPL provided (+)-cis-alpha-irone. PPL's mode of transformation of epoxy trans- and cis-alpha-irols was investigated, in order to ascertain the effect of chemical structure on the discriminating properties of this enzyme.