Discovery and Metabolic Origin of 4,4′-Dihydroxy-3,3′,5,5′-Tetrachlorobenzophenone from a Burkholderia oklahomensis Clinical Isolate

Burkholderia oklahomensis LMG 23618 ^T 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 23618 ^T 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.