Absolute configuration of methyl isoeichlerialactone Hoong-Kun Fun,a* ‡ Nantiya Joycharat,b

disorder in main residue; R factor = 0.036; wR factor = 0.099; data-to-parameter ratio = 12.1. The title compound, C28H44O40.56H2O, is a co-crystal of methyl isoeichlerialactone monohydrate as the major compo-nent 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 –COOCH3 group of the methyl propanoate side chain on the cyclohexane ring which is positionally disordered over two orientations. The molecule of methyl isoeichlerialactone has three fused rings and all rings are trans-fused. The two cyclohexane rings are in standard chair conformations and the cyclopentane ring adopts an envelope conformation. In the crystal, weak C— H O interactions link methyl isoeichlerialactone molecules into screw chains along [010]. The crystal structure is further stabilized by O—H O hydrogen bonds and weak C—H O interactions. Related literature For details of ring conformations, see: Cremer & Pople (1975). For bond-length data, see: Allen et al. (1987). For previous studies on 3,4-secodammarane triterpenes in Aglaia see: Pointinger et al. (2008); Seger et al. (2008); Joycharat et al. (2010). For related structures, see: Fun et al. (2010); Joycharat et al. (2010). For the stability of the temperature controller used in the data collection, see Cosier & Glazer (1986)