Absolute structure of (3aS,5S,7aS,7bS,9aR,10-S,5S,7aS,7bS,9aR,10R,12aR,12bS)-7b-hydroxy4,4,7a,9a,12a-pentamethyl-10-[(2′R)-6-methylheptan-2-yl]-2,8,9-trioxooctadecahydrobenzo[d]indeno[4,5-b] azepin-5-yl acetate from 62-year-old crystals

The structure of the title compound, C32H51NO6, was determined from 62-year-old crystals at room temperature and refined with 100 K data in a monoclinic (C2) space group. This compound with a triterpenoid structure, now confirmed by this study, played an important role in the determination of the structure of lanosterol. The molecules pack in linear O-H center dot center dot center dot O hydrogen-bonded chains along the short axis (b), while parallel chains display weak van der Waals interactions that explain the needle-shaped crystal morphology. The structure exhibits disorder of the flexible methylheptane chain at one end of the main molecule with a small void around it. Crystals of the compounds were resistant to data collection for decades with the available cameras and Mo K alpha radiation single-crystal diffractometer in our laboratory until a new instrument with Cu K alpha radiation operating at 100 K allowed the structure to be solved and refined.