Coumarin derivatives from Ainsliaea fragrans and their anticoagulant activity

Coumarin derivatives are an important class of C6–C3 plant metabolites that show a variety of bioactivities. Currently, most clinical anticoagulant agents are coumarins, such as warfarin, dicoumarol and acenocoumarol, and patients taking these drugs must be monitored for adverse reactions. In a search for safe and effective anticoagulant compounds from Chinese herbal medicine, a screening procedure on the whole plant of Ainsliaea fragrans was performed. The phytochemical investigation of this plant afforded five new coumarin derivatives, including a pair of natural 4-hydroxycoumarin enantiomers (1), a pair of coumarin enantiomers with a rare polycyclic pyrano[3-2c] carbon skeleton (2) and a 7-hydroxycoumarin derivative (3), together with 5 known biogenetically related compounds (4–8). Enantioseparation of 1 and 2 produced optically pure compounds 1a, 1b, 2a and 2b. The absolute configurations of the new compounds were confirmed by single-crystal X-ray diffraction analysis. In addition, we evaluated the anticoagulant activity of all isolates via activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT) assays in vitro and in vivo. Of note, compound 3 displayed potent anticoagulant activity and no significant hepatic or renal toxicity, which could make it a promising agent for further preclinical evaluation for preventing abnormal blood clotting.