Absolute configuration of methyl isoeichlerialactone.

The title compound, C(28)H(44)O(4)·0.56H(2)O, is a co-crystal of methyl isoeichlerialactone monohydrate as the major component and methyl isoeichlerialactone as the minor component in a 0.55778 (3):0.44222 (3) ratio. The conformations of both components are identical except for that of the -COOCH(3) group of the methyl propanoate side chain on the cyclo-hexane ring which is positionally disordered over two orientations. The mol-ecule of methyl isoeichlerialactone has three fused rings and all rings are trans-fused. The two cyclo-hexane rings are in standard chair conformations and the cyclo-pentane ring adopts an envelope conformation. In the crystal, weak C-H⋯O inter-actions link methyl isoeichlerialactone mol-ecules into screw chains along [010]. The crystal structure is further stabilized by O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions.