Degradation products of the promethazine radical cation

The degradation products of the promethazine radical cation, generated from promethazine with horseradish peroxidase/H2O2, have been investigated. Several products have been identified which resulted from fission of the bond between the two ethanamine carbon atoms of the N10 side chain. The main product (approx. 90%) was identified as 10-formyl-5-oxophenothiazine. The likely structure of three minor products was also elucidated. The degradation of the promethazine radical cation is different from that of radical cations derived from the propanamine side chain containing phenothiazine drugs.