Synonym(s): Tyr-D-Pen-Gly-Phe-D-Pen (Disulfide bridge: D-Pen^2-D-Pen^5), [D-Pen^2^,^5] Enkephalin hydrate Formula: C30H39N5O7S2 Formula weight: 645.79 CAS Number: 88373-73-3 Harmonized Tariff Code:  2937.19