New alkaloids from the seeds of Strychnos nux-vomica

Eight new trace indolomonoterpenic alkaloids (1-8) were isolated from the seeds of Strychnos nux-vomica. Their structures and absolute configurations were determined by extensive analysis of MS, NMR, CD, and ECD. The skeleton of compound 1 is an unprecedented 6/5/6/5/6/6/7 heptacyclic ring system. Compound 2 possesses a 2-pyridone moiety, and has not yet been found in strychnos alkaloids. Compounds 6 and 7 showed neuroprotective activities on PC12 cells with IE 50 values of 0.68-4.81 μM and 0.54-6.50 μM, respectively. The biosynthetic pathway of 1 was also postulated.