Altrenogest (17-alpha-allyl-17-beta-hydroxyestra-4,9,11-trien-3-one) is a potent synthetic progestin used in veterinary medicine. Although altrenogest is excreted primarily in an unmetabolized form, there is no literature documenting its environmental fate. In this study, the photochemistry of altrenogest was evaluated under environmentally relevant conditions using a solar simulator. It was determined that direct photolysis is extremely efficient and rapid, and that photolysis rate is not significantly affected by changes in pH or temperature but strongly impacted by the presence of oxygen. An isomer, formed via an internal 2+2 cycloaddition reaction, was identified as a primary photoproduct that undergoes photohydration to form photostable products. Some of these secondary photoproducts are subject to dehydration in dark conditions, which can lead to re-formation of the isomer on a time scale of hours to days. The triplet lifetime and rate constant of the 2+2 cycloaddition reaction were obtained by transient absorption spectroscopy. MDA-Kb2 androgen-responsive cell assays were used to determine that altrenogest and its photoproducts exhibit androgenic activity.

Environmental photochemistry of altrenogest

249th National Meeting (2015)

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