Biooxidation of methyl group: Part 2. Evidences for the involvement of cytochromes P450 in microbial multistep oxidation of terfenadine

The actinomycete Streptomyces platensis grown in culture medium containing soybean peptones can transform terfenadine, an antihistamine drug, into its active metabolite fexofenadine. The microbial oxidation of methyl group of terfenadine into carboxylic acid could be an alternative to chemical ways to produce fexofenadine. This bioconversion requires three oxidation steps: a hydroxylation of one methyl group followed by the oxidation of the corresponding alcohol into the aldehyde and finally its oxidation into the carboxylic acid. The oxidation reaction of each step has been studied. Terfenadine and intermediates incubated with whole cells were not oxidized under argon whereas their biotransformation under 18O2-enriched atmosphere gave labeled fexofenadine. P450 inhibitors, such as clotrimazole or fluconazole, inhibited oxidation activity of each step. While the two last steps could be catalyzed by dehydrogenases or oxidases, this study strongly demonstrates the role of at least one, or possibly several cytochromes P450, in the oxidation of terfenadine into fexofenadine by S. platensis cells. To our knowledge, this is one of the few examples of involvement of P450s in such three steps oxidation of a xenobiotic.