THE introduction of neuroleptics of the phenothiazine and thioxanthene classes has revolutionised the treatment of schizophrenia and there is increasing evidence1–3 that links this antipsychotic action to a blockade of dopamine receptors in the brain. The thioxanthene compounds are of particular interest as, because of the presence of an exocyclic double bond and a substituent in the tricyclic nucleus, they exist as cis–trans geometric isomers about the double bond with respect to the ring substituent (Fig. 1). Virtually all the neuroleptic activity is confined to the cis isomer4.
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