Alkaloids and flavonoid glycosides from the aerial parts of Leonurus japonicus and their opposite effects on uterine smooth muscle.

The crude extract and some Chinese patented medicines of Leonurus japonicus Houtt. have been proven to affect the uterine smooth muscle. L. japonicus injection is widely used in obstetric departments in China for treating postpartum hemorrhage caused by uterine inertia. Bioassay-guided isolation of the 95% EtOH extract of L. japonicus yielded four cyclopeptides, nine alkaloids, and three flavonoid glycosides, including two previously undescribed cyclopeptides, namely, cycloleonuripeptide G and cycloleonuripeptide H. The structures of the cyclopeptides were elucidated to be cyclo-(L-Phe-L-Phe-Gly-L-Pro-Gly-L-Pro) and cyclo-(L-Phe-L-Ala-L-Pro-L-Ile-L-His-Gly-L-Ala-L-Pro), respectively, via spectroscopic and chemical methods. Cyclopeptides (cycloleonuripeptides C and D) and alkaloids (imperialine-3β-D-glucoside and leonurine) promoted contraction of uterine smooth muscle strips isolated from normal rats. However, it was observed that flavonoid glycosides (spinosin, linarin, and apigenin-7-O-β-D-glucopyranoside) significantly inhibited contraction of the uterine smooth muscle strips.