Structure-activity study of endomorphin-2 analogs with C-terminal modifications by NMR spectroscopy and molecular modeling

Schematic diagram of EM-2 and its analogs by substitution of the Phe4-NH2 group with -NHNH2, -NHCH3, -N(CH3)2, -OCH3, -OCH2CH3, -OC(CH3)3, and -CH2-OH investigated in this study.