3-{3,3-Di­methyl­spiro­[2,3-di­hydro-1H-indole-2,3′-(3′H-naphtho­[2,1-b][1,4]­oxazin)]-1-yl}propionic acid

The title compound, C24H22N2O3, is dimerized via two intermolecular O—H⋯O hydrogen bonds contributed by two —COOH groups, resulting in the formation of a planar eight-membered ring. The spiro C atom links two planes that are almost perpendicular to each other.