Absolute structure of (3a S ,5 S ,7a S ,7b S ,9a R ,10 R ,12a R ,12b S )-7b-hydroxy-4,4,7a,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, C 32 H 51 NO 6 , was determined from 62-year-old crystals at room temperature and refined with 100 K data in a monoclinic ( C 2) 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...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 α radiation single-crystal diffractometer in our laboratory until a new instrument with Cu K α radiation operating at 100 K allowed the structure to be solved and refined.