Advance in biological activities of natural guaiane-type sesquiterpenes

Belonging to the terpenes family, sesquiterpenes represent a group of natural compounds with diverse skeletal types. Given their unique structural features and various functional groups, these compounds possess numerous biological activities and have received increasing interest in recent years. Guaiane-type sesquiterpenes are a special category of sesquiterpenes with various biological activities, such as antitumor, anti-inflammatory, and antibacterial. Mipsagargin, a prodrug of thapsigargin, could be used in the treatment of glioblastoma multiforme and hepatocellular carcinoma, and has completed the phase II clinical trials. Guaiane-type sesquiterpenes are not only abundant but also diverse, widely distributed, and complex, and have variable structures. To our knowledge, there is no review of guaiane-type sesquiterpenes in extant literature. This review summarizes the distribution of guaiane-type sesquiterpenes in plants, the possible biogenic pathways and chemical structures as well as the research progress on their biological activities from 1990 to 2018. Guaiane-type sesquiterpenes are present in approximately 70 genera of 30 plant families (e.g., Asteraceae, Lamiaceae, Thymelaeaceae, and Zingiberaceae); they can be classified into 12,6-guaianolides, 12,8-guaianolides, pseudoguaianolides, tricycle guaiane-type sesquiterpenes, dimers or trimers containing guaiane-type sesquiterpenes mother nuclei, variant guaiane-type sesquiterpenes, and other guaiane-type sesquiterpenes. Among them, 12,8-guaianolides exerted the broadest biological activity.