Crystal structure of naltrexone chloride solvates with ethanol, propan-2-ol, and 2-methyl-propan-2-ol.

Naltrexone [systematic name: 17-(cyclo-propyl-meth-yl)-3,14-di-hydroxy-4,5α-epoxymorphinan-6-one] is an opioid receptor competitive antagonist that has been widely used to prevent relapse in opioid- and alcohol-dependent subjects. Its chloride salt forms non-isomorphic solvates with ethanol (C20H24NO4+·Cl-·C2H5OH) (I), propan-2-ol (C20H24NO4+·Cl-·C3H7OH) (II), and 2-methyl-propan-2-ol (C20H24NO4+·Cl-·C4H9OH) (III). The naltrexone cation can be described as a T-shape made out of two ring systems, a tetra-hydro-2H-naphtho-[1,8-bc]furan system and a deca-hydro-isoquinolinium subunit, that are nearly perpendicular to one another. The flexible cyclo-propyl-methyl group can adopt various different conformations in response to its surroundings: an increase of available space around cyclo-propyl-methyl group may allow it to adopt a more favorable conformation. In all these structures, the alcohol mol-ecules occupy infinite solvent-filled channels. All three compounds described are attractive crystalline forms for unambiguous identification of naltrexone chloride after isolation from a pharmaceutical form. Compound (III) was refined as a two-component twin.