High affinity μ-opioid receptor agonist with peripheral selectivity (Ki values are 2, 48 and 1156 nM for μ-, δ- and κ-opioid receptors respectively). Antidiarrhoeal and antihyperalgesic agent. Also a Ca2+ channel blocker; at low micromolar concentrations it blocks broad spectrum neuronal HVA Ca2+ channels and at higher concentrations it reduces Ca2+ flux through NMDA receptor operated channels. Purity 99%. MW (observed): 513.51