Two new isolated epimers seem to contribute to the bitter principle of Leonurus japonicus Houtt.

Abstract

The aerial parts of Chinese motherwort (Leonurus japonicus Houtt) (Yimucao) are commonly used in traditional Chinese medicine (TCM) to regulate menses and to treat associated conditions. As the herb is more and more used in Europe, it has been started to cultivate the plant in Germany [1]. Since bitterness is an important sensory feature of the plant, the aim of the investigation was to isolate and identify the chemical constituents responsible for the bitter taste of Yimucao. It was found that the bitter principle can be extracted by n-hexane. Therefore, the n-hexane extract of Herba Leonuri has been fractionated using Fast Centrifugal Partition Chromatography (FCPC).This led to a fraction containing a mixture of two compounds which seemed to be responsible for the bitter taste of Yimucao. Structure elucidation by MS and NMR spectroscopy led to two new epimeric diterpenoid compounds 1 and 2 (exact mass 392,2), which are related to furanic labdane type lactones previously found in Leonurus japonicus, Leonurus cardiaca, Leonotis leonurus and Marrubium vulgare [2,3].