DEHYDRATION OF ALKYLALDOXIME AND ARYLALDOXIME AS A NEW CYTOCHROME-P450 CATALYZED REACTION - MECHANISM AND STEREOCHEMICAL CHARACTERISTICS

The Z isomers of benzaldoxime and 4-(hexyloxy)benzaldoxime were dehydr ated into the corresponding nitriles in the presence of rat liver micr osomes and NADPH or dithionite. Their E isomers remained unchanged und er identical conditions. Alkylaldoximes, like phenylacetaldoxime and h eptanaldoxime, are also dehydrated under these conditions, the alkylal doximes being more rapidly transformed than the arylaldoximes. A genet ically well-defined P450 expressed in yeast, P450 3A4, the major P450 isozyme in human liver, was also found to be catalytically active for dehydration of (Z)-benzaldoxime. All these reactions were found to be catalyzed by P450 Fe(II) as they required the use of intact microsomes in the presence of NADPH or dithionite and were strongly inhibited by O-2 and CO as well as by classical P450 inhibitors. A P450 complex ch aracterized by a Soret peak at 442 nm was detected during these reacti ons; its disappearance was found to be concomitant with the consumptio n of the aldoxime and the formation of the corresponding nitrile. (E)- benzaldoximes and all the studied ketoximes failed to give such comple xes with P450 Fe(II). On the basis of these results, a possible mechan ism for this new P450 reaction is proposed. It involves a P450 Fe(II) <-- N(OH)=CHR complex as a key intermediate and a charge transfer from P450 Fe(II) to the aldoxime C=N bond which results in a cleavage of t he aldoxime N-O bond.