Flexibility of the endogenous progesterone lactonisation pathway in Aspergillus tamarii KITA: transformation of a series of cortical steroid analogues

A range of cortical steroids have been transformed by the fungusAspergillus tamarii, which has the ability to convert progesterone to testololactone in high yield through a four step enzymatic pathway. 16α,17α-Epoxyprogesterone underwent a rare epoxide opening resulting in a unique inversion of stereochemistry to give 16β-hydroxy-17α-oxa-Image-homo-androst-4-en-3,17-dione. The metabolism of deoxycorticosterone resulted in relatively efficient transformation to testololactone with no other products isolated. Transformation of 17α-hydroxyprogesterone yielded 17α-oxa-Image-homo-androst-1,4-dien-3,17-dione, a lactone not previously isolated from A. tamarii. Cortexolone was transformed to the 20(R)-alcohol with no further transformation observed. Evidence is also presented for the presence of a highly flexible but stereospecific keto-reductase. All metabolites were isolated by column chromatography and were identified by 1H, 13C NMR, DEPT analysis and other spectroscopic data.