Bisabolane Sesquiterpenes with Anti-Chlamydial Activity Isolated from Ligularia narynensis

<i>Chlamydia</i> are obligate intracellular bacterial pathogens affecting humans and animals, causing miscarriage, stillbirth, or weak fetuses in the late stages of pregnancy of goats and sheep. Because there is no commercial vaccine for chlamydia in animals, drug treatment has become the most effective curative method. Natural products, also known as secondary metabolites, are becoming one of the main sources used in new drug development because of their structural diversity and biodiversity. In natural products, plant sources play a major role in the development process of new drugs. In this study, five undescribed highly oxygenated bisabolane sesquiterpenes (Pararubin W, Pararubin X, Pararubin Y., Pararubin Z, and Pararubin AA) were isolated from whole plants of <i>Ligularia narynensis</i>. Their chemical structures were determined via analyses of HRESIMS, IR, 1D, and 2D NMR data, along with the assignment of their relative configurations. These compounds were tested for their anti-chlamydial activity. The results show that compounds <b>1</b> and <b>5</b> inhibited the growth of <i>Chlamydia abortus</i> in host cells in a dose-dependent manner.