[2-ALPHA(2S,3S,4R,6R),3-BETA,5-ALPHA]-14-HYDROXY-19-OXO-3,2-[(TETRAHYDRO-3,4-DIHYDROXY-6-METHYL-2H-PYRAN-2,3-DIYL)BIS(OXY)]CARD-20(22)-ENOLIDE DIHYDRATE (CALACTIN), C29H39O9.2H2O, A CARDENOLIDE FROM ASCLEPIAS-LINARIA

This X-ray diffraction study establishes the molecular structure of the title compound. The asymmetric unit comprises two independent molecules (A and B). Both molecules are closely similar with regard to bond lengths and angles. In both molecules, the six-membered rings all adopt chair conformations. The D ring of the steroid moiety has an envelope conformation and the lactone ring is almost flat. The A/B, B/C and A/F ring junctions are trans and the C/D and F/G ring junctions are cis. The crystal structure is stabilized by a three-dimensional network of hyrogen bonds and C-H...O interactions.