Opioid agonists and uses thereof

A compound selected from the formula:

• wherein:
• R2 is an substituted alkyl;
• (i) R1 and R3 are taken together with their intervening atoms to form a fused, substituted thiazole and R5 is hydrogen, where R1 and R3 are positions 4 and 5 of the thiazole, wherein the thiazole is substituted with —X-POLY at position 2 of the thiazole;
• or
• (ii) R3 and R5 are taken together with their intervening atoms to form a fused, substituted thiazole and R1 is hydrogen, where R1 and R3 are positions 4 and 5 of the thiazole, wherein the thiazole is substituted with —X-POLY at position 2 of the thiazole;
• is a double bond;
• G is ═O;
• X is a spacer moiety selected from a covalent bond, —C(O)—, —NHC(O)—, —NH—, —CH2CHOHCH2NH—, and —O—;
• POLY is a poly(alkylene oxide) oligomer;
• or pharmaceutically acceptable salts thereof.