Isolation and characterization of (+)-1,1a-dihydroxy-1-hydrofluoren-9-one formed by angular dioxygenation in the bacterial catabolism of fluorene

Abstract

Transformation of fluorene by washed cells of fluorene-grown Pseudomonas sp. F274 yielded 1,la-dihydroxy-1-hydrofluoren-9-one (up to 100 mg/l) as the stable product of angular dioxygenation of 9-fluorenone. Structural identity of the angular keto-diol was established by 13C- and 1H-NMR, gas chromatography- and direct probe-mass spectrometry. Definitive assignment of 1,1a-dioxygenation, but not 4,4a-, was based on the isolation and rigorous identification of 1-hydroxyfluoren-9-one as the exclusive product of acidic dehydration. Chiral 1H-NMR analysis and optical rotation of isolated 1,1a-dihydroxy-1-hydrofluoren-9-one ([alpha]D = + 132.1 degrees) are indicative of a single enantiomer with an inferred cis-stereochemistry of the hydroxyl groups. This compound is evidently an intermediate of fluorene catabolism by this strain and not a dead-end product because its formation is transient in washed cell incubations and ultimately it is completely consumed with the formation of acidic metabolites.