Upjohn developed a process for the large scale production of cortisone . The oxygen atom at the 11 position in this steroid is an absolute requirement for biological activity. There are however no known natural sources for starting materials that contain that feature. The only method for preparing this drug prior to 1952 was a lengthy synthesis starting from cholic acid isolated from bile. In 1952 two Upjohn biochemists, Dury Peterson and Herb Murray announced that they were able to introduce this crucial oxygen atom by fermentation of the steroid progesterone with a common mold of the genus Rhizopus . Over the next several years a group of chemists headed by John Hogg developed a process for preparing cortisone from the soybean sterol stigmasterol . The microbiological oxygenation is a key step in this process.