General Alkaloid Extraction Process
7-Hydroxymitragynine

The extraction and crystallization of the parent alkaloid, mitragynine, from dried leaves of Mitragyna speciosa (Kratom), has been described in great detail by A. H. Beckett, E. J. Shellard and A. N. Tackie in Planta Med., 1965, 13, 241-246 (DOI).

(Interestingly, the procedure also furnished speciofoline, a spiroindolo indolizidine alkaloid.)

Leonurine

A first extraction was seeming reported by S. Kubota and S. Nakajima in Nippon Yakubutsuqaku Zasshi, 1930, 153. I don't have a DOI and the source is most likely in Japanese.

I don't have personal experience with the extraction of guanidines from biological material and would probably rather try to synthesize leonurine, following the procedures described in Tetrahedron, 1969, 25, 5155-5161 (DOI).



General guidelines

I have given some hints on extraction in an answer to a question on the use of TLC in alkaloid identification.