Fig. 8.

Interactions of the drug molecules (1R,2S)-α-methylnoradrenaline and (1R)-noradrenaline with α₂-adrenergic and α₁-adrenergic receptors. (A) α₂-Adrenergic receptors interact with four locations in (1R,2S)-α-methylnoradrenaline in a (2-2) configuration, a (catechol) and b (—OH) on the C1 stereocenter along with c (—NH₂) and d (—CH₃) on the C2 stereocenter. (B) α₁-Adrenergic receptors interact only with three locations in both (1R)-noradrenaline (R = H) and (1R,2S)-α-methylnoradrenaline (R = CH₃), so that both drug molecules are equipotent for this receptor.