The photochemical decomposition of the progestogenic 19-norsteroid, norethisterone, in aqueous medium.

Norethisterone, a contraceptive 19-norsteroid, was decomposed in aqueous medium (pH 7.4) by UV-B radiation (280-320 nm). This 4-en-3-oxo-19-norsteroid was not prone to the skeletal rearrangement reactions usually observed in steroids possessing a C10-methyl group. Under the reaction conditions applied, products were formed by addition of molecules, such as solvent molecules or a second steroid molecule, and by reduction of the double bond. The prevalence of addition type reactions may have consequences for the application of norethisterone-like steroids in subdermal contraceptive devices.