Structure and conformation of a stoicheiometric adduct of 4-epimatricin with 3β-hydroxydihydrocostunolide and of 4-epimatricin alone

Abstract

The guaianolide 4-epimatricin (2) and the germacrolide 3β-hydroxydihydrocostunolide (3) form in the solid state a stoicheiometric non-covalent adduct through a complex chain of hydrogen bonds involving their hydroxy groups and one water molecule. In this adduct, 3β-hydroxydihydrocostunolide exists as a [¹⁵D_5′1D¹⁴] double-chair rotamer, whereas the cycloheptene ring system of 4-epimatricin adopts a C_s conformation. The crystal structure of 4-epimatricin alone has also been investigated. Comparison of the results for the latter compound alone and in the adduct reveals a somewhat different conformation of the γ-lactone rings and a larger deviation from the ideal C_s symmetry of the cycloheptene ring in the adduct.