Conformational analysis and structural comparisons of (1R,3S)-(+)- and (1S,3R)-(-)-tefludazine, (S)-(+)- and (R)-(-)-octoclothepin, and (+)-dexclamol in relation to dopamine receptor antagonism and amine-uptake inhibition.

Conformational analysis with molecular mechanics (MM2(85] and molecular superimposition studies of (1R,3S)-(+)- and (1S,3R)-(-)-4-[3-(4-fluorophenyl)-6-(trifluoromethyl)indan-1-yl]-1- piperazineethanol (tefludazine) and (S)-(+)- and (R)-(-)-octoclothepin have been employed to identify biologically active conformations of these compounds with respect to dopamine receptor antagonism and amine-uptake inhibition. In contrast to what is commonly assumed, these studies indicate that the conformation of (S)-(+)-octoclothepin responsible for the dopamine receptor antagonism is different from the one observed in the crystal. From least-squares molecular superimpositions with the potent and stereoselective dopamine receptor antagonist (1R,3S)-tefludazine, biologically active conformations for the two compounds on the dopamine receptor have been deduced. This analysis also rationalizes the enantioselectivity of octoclothepin on the dopamine receptor. The X-ray structure of (S)-(+)-octoclothepin is shown to correspond structurally to the 1S,3R enantiomer of tefludazine, which is an amine-uptake inhibitor. This correspondence provides a structural basis for the norepinephrine (NE) uptake blocking properties of octoclothepin. It is predicted that the enantioselectivity of the NE-uptake inhibition of octoclothepin should be low with the S-(+) enantiomer as the more active optical isomer. A comparison of the deduced biologically active conformation of (S)-(+)-octoclothepin with (+)-dexclamol is also discussed on the basis of earlier derived superimposition studies with (+)-dexclamol.