Investigation on the phototransformation of tadalafil in aqueous media. 6-Epimerization vs. solvent trapping reaction

摘要

Irradiation of tadalafil at λ > 290 nm in aqueous solutions leads to 6-epimer and/or water adducts depending on concentration and pH. A rationalization of the results involves the heterolytic cleavage of C6-N5 bond via a well-stabilized zwitterionic intermediate. The drug is stable in the dark except under strongly basic conditions where it undergoes C12a-epimerization.