Luis Pinero-Santiago - Photophysics and Photochemistry of z-Chlorprothixene in Acetonitrile

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      Chlorprothixene (CPTX, Taractan) is a low potency antipsychotic   mainly used for the treatment of psychotic disorders (e.g.   schizophrenia) and acute mania occurring as part of bipolar   disorders. As in the case of other numerous drugs used in the   treatment of psychiatric disorders, CPTX presents geometric   isomerism. Therefore, in vitro irradiation induces a rapid Z⁄ E   isomerization, which can affect its pharmacokinetic properties.   This photoisomerization is not dependent on the oxygen   concentration. The Z⁄E quantum yields determined for zCPTX in   acetonitrile are 0.22 and 0.21 in anaerobic and aerobic   environments, respectively. In the presence of water, both   isomers decompose to produce 2-chlorothioxanthone (CTX) after   prolonged irradiation. This process strongly depends on the water   concentration and the irradiation time, i.e. it is autocatalyzed   by the CTX through a triplet-energy transfer mechanism. The   protonation state of the terminal amino group, on the other hand,   has no effect on the isomerization process, but inhibits the   formation of CTX. These results indicate that the phototoxicity   of zCPTX is somehow affected by the formation of CTX.

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