15 (R),19 (R) -hydroxy Prostaglandin F2α

19 (R) -Hydroxylated prostaglandins (PGs) are present at μg/ml concentrations in the semen of some mammalian species, notably primates, with the majority being from the PGE series and featuring a 15 (S),19 (R) hydroxyl stereochemistry. These compounds are also observed in marsupials' seminal plasma, where F-type 1 and 2-series compounds are predominant. The 15 (R) -hydroxy epimer represents the inverse or "unnatural" isomer at C-15 for these 19-hydroxylated PGs. Although the biological function of 19 (R) -hydroxylated PGs remains unclear, 19 (R) -hydroxylation in the F-series leads to a notable reduction in receptor-mediated biological activity in certain assays.