Expected and Unexpected Products from the Biochemical Oxidation of Bacterial Alkylquinolones with CYP4F11

Abstract

2-Alkylquinolones are a class of microbial natural products primarily produced in the Pseudomonas and Burkholderia genera that play a key role in modulating quorum sensing. Bacterial alkylquinolones were synthesized and then subjected to oxidative biotransformation using human cytochrome P450 enzyme CYP4F11, heterologously expressed in the fission yeast Schizosaccharomyces pombe. This yielded a range of hydroxylated and carboxylic acid derivatives which had undergone ω-oxidation of the 2-alkyl chain, the structures of which were determined by analysis of NMR and MS data. Oxidation efficiency depended on chain length, with a chain length of eight or nine carbon atoms proving optimal for high yields. Homology modeling suggested that Glu233 was relevant for binding, due to the formation of a hydrogen bond from the quinolone nitrogen to Glu233, and in this position only the longer alkyl chains could come close enough to the heme moiety for effective oxidation. In addition to the direct oxidation products, a number of esters were also isolated, which was attributed to the action of endogenous yeast enzymes on the newly formed ω-hydroxy-alkylquinolones. ω-Oxidation of the alkyl chain significantly reduced the antimicrobial and antibiofilm activity of the quinolones.