The (R)-enantiomers ((R)-9, -4, -6) are antagonists, whereas the (S)-enantiomers ((S)-9, -4, -6) are partial agonists. Emax is the % of dopamine efficacy. NA, no activity. The efficacies of (S)-enantiomers are significantly different from their corresponding (R)-enantiomers; (S)-9 efficacy is significant different from (S)-4 or (S)-6 efficacy (in each case, P < 0.0001 using one-way ANOVA followed by post hoc Tukey test).