Two new labdane diterpenes from fresh leaves of Leonurus japonicus and their degradation during drying.

Degradation of the components of Leonurus Herb was examined during drying. Compounds 1 and 2 were detected on TLC at lower temperature, but not at higher temperature. Their chemical structures were determined by spectral methods. They immediately decomposed even at 40°C in chloroform solution. They are believed to be transformed through a retro-aldol reaction. Compounds 1 and 2 have not been previously reported.