Discovery and Biosynthetic Origin of 4,4'-Dihydroxy-3,3',5,5' Tetrachlorobenzophenone Produced by the Clinical Isolate Burkholderia oklahomensis

Burkholderia oklahomensis LMG 23618T is a Burkholderia pseudomallei-like bacterium originally isolated in 1973 from a wound infection caused by a farming accident in Oklahoma. Metabolic profiling of an organic extract from cultures of B. oklahomensis LMG 23618T using UHPLC-ESI-Q-ToF-MS led to identification of three known metabolites, betulinan A, yersiniabactin and ulbactin B, in addition to a novel polycholorinated compound. Mass-directed purification enabled isolation of the novel specialized metabolite, which was shown by X-ray crystallography and NMR spectroscopic analysis to be 4,4'-dihydroxy-3,3',5,5'-tetrachlorobenzophenone. Feeding experiments with stable isotope-labelled precursors established that the carbon skeleton of this unusual metabolite derives from two molecules of tyrosine. This led us to propose a plausible biosynthetic pathway via decarboxylative condensation of 3, 5-dichloro-4-hydroxybenzoic acid with its coenzyme A thioester derivative. The absolute configuration of ulbactin B was also established as 4'R, 3''S, 7''S, 8''R using X-ray crystallography and NMR spectroscopy.