In Vitro Regio- and Stereoselective Oxidation of β-Ionone by Human Liver Microsomes

Abstract

The metabolism of the norisoprenoid -ionone was investigated using human liver microsomes and 11 different recombinant cytochrome P450 enzymes expressed in cells.-Ionone was found to be oxidized via 4-hydroxylation by CYP2B6 in human liver microsomes. CYP1A2 also regioselectively catalyzed the hydroxylation of -ionone to yield 4-hydroxylation; this conversion was not stereoselective. Further kinetic analysis revealed that CYP2B6 exhibited the highest activity for-ionone 4-hydroxylation. Kinetic analysis showed that and for oxidation of -ionone by CYP1A2 and CYP2B6 was 107.9 ± 36.0 µM and 3200.3 ± 323.0 nmol/min/nmol P450 and 5.6 ± 1.2 µM and 572.8 ± 29.8 nmol/min/nmol P450, respectively. The reaction rates observed using human liver microsomes and recombinant CYP2B6 were very high compared with those of other CYP2B6 substrates reported thus far. These results suggest that-ionone, a norisoprenoid present in nature, is one of the effective substrates for CYP2B enzymes in human liver microsomes. To the best of our knowledge, this is the first time that 4-hydroxy -ionone has been described as a human metabolite of-ionone.

Computational-Aided Engineering of a Selective Unspecific Peroxygenase toward Enantiodivergent β-Ionone Hydroxylation

“…29 Enantioselective 4-hydroxy-βionone formation has been achieved both through enzymatic kinetic resolution 32 and by CYP2B6, which was recombinantly expressed inTrichoplusia ni cells. 31 With the maturation of computational modeling methods for the study of biocatalysts, new avenues are opening up for the generation of ever smaller and more intelligent protein library designs. 33 In the present work, we engineered new UPO variants to enantioselectively access C4 hydroxylated stereoisomers of βionone.…”

“…The hydroxylation of α- and β-ionone performed by several UPOs led to a diverse range of hydroxylation and epoxidation products . The hydroxylation of β-ionone has also been pursued using various P450s. − First, P450 engineering efforts showed an up to 280-fold increased product formation rate toward α- and β-ionone hydroxylations, however, enhancing the enantioselectivity proved challenging . Enantioselective 4-hydroxy-β-ionone formation has been achieved both through enzymatic kinetic resolution and by CYP2B6, which was recombinantly expressed in Trichoplusia ni cells …”