The secondary metabolite pseudopyronine B, isolated from Pseudomonas
mosselii P33, was biotransformed
by human P450 enzymes, heterologously expressed in the fission yeast Schizosaccharomyces pombe. Small-scale studies confirmed
that both CYP4F2 and CYP4F3A were capable of oxidizing the substrate,
with the former achieving a higher yield. In larger-scale studies
using CYP4F2, three new oxidation products were obtained, the structures
of which were elucidated by UV–vis, 1D and 2D NMR, and HR-MS
spectroscopy. These corresponded to hydroxylated, carboxylated, and
ester derivatives (1–3) of pseudopyronine
B, all of which had been oxidized exclusively at the ω-position
of the C-6 alkyl chain. In silico homology modeling
experiments highlighted key interactions between oxygen atoms of the
pyrone ring and two serine residues and a histidine residue of CYP4F2,
which hold the substrate in a suitable orientation for oxidation at
the terminus of the C-6 alkyl chain. Additional modeling studies with
all three pseudopyronines revealed that the seven-carbon alkyl chain
of pseudopyronine B was the perfect length for oxidation, with the
terminal carbon lying close to the heme iron. The antibacterial activity
of the substrates and three oxidation products was also assessed,
revealing that oxidation at the ω-position removes all antimicrobial
activity. This study both increases the range of known substrates
for human CYF4F2 and CYP4F3A enzymes and demonstrates their utility
in producing additional natural product derivatives.