The molecule is a monocarboxylic acid anion that is the conjugate base of pentalenolactone, obtained by deprotonation of the carboxy group; major species at pH 7.3. It is a conjugate base of a pentalenolactone.
(1R,4aR,6aR,7S,9aS)-7,8-dimethyl-2-oxospiro[4,4a,6a,7-tetrahydropentaleno[1,6a-c]pyran-1,2'-oxirane]-5-carboxylate