Microbiological transformation of 1,2-diphenyl-3,5 dioxo-4-n-butyl pyrazolidine (phenylbutazone).

Microbiological conversion of phenylbutazone with Rhizopus arrhizus Fischer gave 4-hydroxy phenylbutazone in excellent yield. Spectral studies, mass spectrometry, in particular, were made of the obtained metabolite; other experiments performed with the intact microorganism or with the cell-free system, as well as studies with the well-known metabolic inhibitor, SKF 525 A, indicated that the obtained 4-hydroxy phenylbutazone was not an artefact. Similar experiments were performed on oxyphenbutazone.