Abstract:
The 5a-reductase of Penicillium decumbens ATCC 10436 was
used as a model for the mammalian enzyme to investigate the
mechanism of reduction of testosterone to 5adihydrotestosterone
. The purpose of this study was to search
for specific 5a-reductase inhibitors which antagonize
prostate cancer
.
In a whole-cell biotransformation mode, this organism
reduced testosterone (1) to 5a-dihydrosteroids (8) and 5aandrostane-
3, 17-dione (9) in yields of 28% and 37%
respectively. Control experiments have shown that 5aandrostane-
3, 17-dione (9) can be produced from the
corresponding alcohol (8) in a subsequent reaction separate
from that catalysed by the 5a-reductase enzyme . Androst-4-
ene-3, 17-dione (2) is reduced to give only (9) with a
recovery of 80%
The stereochemistry of the reduction was determined by
500 MHz ^H NMR analysis of the products resulting from the
deuterium labelled substrates. The results were obtained by
an analysis of the NOE difference spectra, double-quantum
filtered phase sensitive COSY 2-D spectra, and ^^c-Ir 2-D
shift correlation spectra of deuterium labelled products.
According to the unambiguous assignment of the signals due to
H-4a and H-4Ii in 5a-dihydro steroids, the NMR data show
clearly that addition of hydrogen to the 4{5)K bond has
occurred in a trans manner at positions 413 and 5a. To Study the reduction mechanism of this enzyme, several
substrates were prepared as following; 3-methyleneandrost-4-en-
17fi-ol(3), androst-4-en-17i5-ol(5) , androst-4-en-3ii, 17fi-diol (6)
and 4, 5ii-epoxyandrostane-3, 17-dione (7) . Results suggest that
this enzyme system requires an oxygen atom at the 3-position of
the steroid in order to bind the substrate. Furthermore, the
mechanism of this 5a-reductase may proceed via direct addition
of hydrogen at the 4,5 position without involvement of a
carbonyl group as an intermediate.
