Uncarialines A-E, new alkaloids from Uncaria rhynchophylla and their anticoagulant activity

Uncarialines A-E ( 1–5 ), five undescribed monoterpene indole alkaloids, together with five known analogues were obtained from the stems of Uncaria rhynchophylla . Alkaloids 1 – 3 were unique 3,4-seco-tricyclic alkaloids with a 6/5/10 ring system, while 4 and 5 possessed a rare rearranged scaffold originated from corynantheine-type alkaloids with C-2/C-7 oxidation. Their structures were characterized by a comprehensive analysis of MS, NMR, and ECD. Their effects on blood clotting times of human plasma were evaluated and alkaloid 5 had a slight prolongation effect on both thrombin time and activated partial thromboplastin time ( p < 0.001). Graphical Abstract