Isolation and identification of a tribenzylisoquinoline alkaloid from Nelumbo nucifera Gaertn, a novel potential smooth muscle relaxant.

A new skeleton benzylisoquinoline (BI) named neoliensinine (1) was isolated from embryos of lotus seed (Nelumbo nucifera Gaertn.), a traditional Chinese herb. The tribenzylisoquinoline (TBI) structure of 1 was confirmed by interpreting spectroscopic data of UV, IR, MS, 1D and 2D NMR. The stereo-configurations of the new compound, together with two known bisbenzylisoquinolines (BBI), neferine and isoliensinine were established by analyzing 1H NMR and 13C NMR spectra. The relaxation of 1, neferine, isoliensinine and liensinine in isolated mesenteric vascular smooth muscle (VSM) was evaluated. All the four BIs could efficiently inhibit MVSM contraction induced by 124mM KCl, with IC50 values of 2.407μM (1), 1.169μM (neferine), 3.504μM (isoliensinine) and 3.583μM (liensinine), respectively, suggesting that they were all potential relaxants for abnormal smooth muscle contractions. Interestingly, VSM treated by the three BBIs could re-contract when being stimulated by KCl after the drugs were removed, while VSM dealt with the TBI couldn't. It indicated that 1 has much high affinity with the molecular targets on relaxation of VSM contraction, which may relate to the unique skeleton with three BI groups.