Steroids microbial, stereoselectivity

In every case the information provided has been obtained by collating public domain sources of information, but unfortunately very often little data is available, particularly on commercial aspects, even for products that have proved to be big successes. Thus microbial biotransformations for steroid modification, particularly stereoselective hydroxylations, such as the use of Rhizopus arrhizus to convert progesterone into antiinflammatory and other dmgs via 11- -hydroxyprogestrone, have proved to be very successful. However, comparatively little useful information exists from public domain sources, despite (or perhaps because) a market of hundreds of millions /a exists for such microbially transformed steroids (cortisone, aldosterone, prednisolone and prednisone etc.) produced by microbial hydroxylation and dehydrogenation reactions coupled with complimentary chemical steps. 

As an example of a steroid total synthesis, the industrial procedure used to make norgestrel, the gestagen used in many contraceptives, is sketched here. Its basis is the Torgov reaction, a variation of the Robinson annelation, which mns essentially neutral media. The carbanion of 1,3-dioxo compounds adds to allylic alcohols, e.g., 2-ethylcyclopentanol-1,3-dione, under weakly basic conditions. Both the dione and the styrene double bond are stable under these conditions. Regio- and stereoselective microbial reduction of one of the keto groups, acid-... 

Scheme 2.148 Regio- and stereoselective microbial hydroxylation of steroids...

---