Clostridium paraputrificum reduction

Much work has been published on the microbiological reduction of a,p-unsaturated ketones. Under anaerobic conditions the reduction of A -3-keto steroids by Clostridium paraputrificum led to the 3-keto 5p-derivatives (Scheme 69) Similar transformations were observed previously with Bacillus putrifi-cus, Penicillium decumbens Rhizopus nigricans or Aspergillus niger. In most cases further reduction led to the corresponding 3a-hydroxy 5P-derivatives. 

A conjugated 3-oxo group is not easily reduced by yeast however. Clostridium paraputrificum selectively reduces these steroids to the 3a-hydroxy compounds. Reduction of the 17-oxo group to 17/ -hydroxysteroids can be achieved with baker s yeast, while reduction of the 20-oxo group can be performed in most cases with S treptomyces strains. 

A more predictable approach to reduction, developed by Schubert, involves the anaerobic application of Clostridium paraputrificum to A -3-ketosteroids (Ap-71, S-823). In linstances (testosterone, progesterone, corticosterone, cortisone) the product is the correspondir 3a-hydroxy-5/3-steroid. From AL -3-ketosteroids the correspondii A -3a-hydroxy-5/3-steroid is formed in good yield, with a lesser amount of fully saturated hexahydrosteroid as a by-product. From AL. -3-keto-steroids or A > -3-ketosteroids the end-product of hydrogenation is the A -3o -hy-droxy-5/3-steroid. 

Sites of Reaction. Reduction of conjugated double bonds was first observed by Mamoli and Schramm (M-548) with a crude culture of putrefactive bacteria. The pure culture, described as Bacillus putrificus, reduced 3-keto-A -androstenes to 3-keto-5 -androstanes and Sa-hydroxy-S S-androstanes (M-545). This culture is no longer available (E-202), but a modern equivalent is Clostridium paraputrificum, described by Schubert (Ap-71, S-823). The properties of the latter are described in greater detail in the section on reduction of carbonyl groups. 

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