Chemotaxonomical alkaloid studies. II. Structures of kuramerine and kumokirine

Chemotaxonomy of the pantropical genus Merremia (Convolvulaceae) based on the distribution of tropane alkaloids

The occurrence and distribution of tropane and biogenetically related pyrrolidine alkaloids in 18 Merremia species of paleo-, neo-, and pantropical occurrence have been studied. The extensive GC-MS study included members of almost all sections of the genus and has been carried out with epigeal vegetative parts as well as with roots. It comprises altogether 74 tropanes and 13 pyrrolidines including nicotine. Along with datumetine known already from a solanaceous species, the study led to the isolation (from M. dissecta and M. guerichii, respectively) and structure elucidation (spectral data) of four novel 3alpha-acyloxytropanes, merresectines A-D: 3alpha-(4-methoxybenzoyloxy)nortropane (A), 3alpha-kurameroyloxytropane (B), 3alpha-nervogenoyloxytropane (C), 3alpha-[4-(beta-D-glucopyranosyloxy)-3-methoxy-5-(3-methyl-2-butenyl)benzoyloxy]tropane (beta-d-glucoside of D). Moreover, the novel 3alpha,6beta-di-(4-methoxybenzoyloxy)tropane (merredissine) has been isolated from M. dissecta and structurally elucidated. In addition the structures of datumetine and merresectine A could be confirmed by synthesis. Spectral data for two known 3alpha-acyloxytropanes (merresectine E beta-D-glucoside, 4'-dihydroconsabatine) and one known 3beta-acyloxytropane (concneorine) are documented for the first time. The structures of three further merresectines (F-H) have been determined by mass spectrometry. Furthermore, the linkage (2',3- and 2',4-, respectively) of two position isomer N-methylpyrrolidinylhygrines was proven by synthesis. The results of the study contribute to the solution of infrageneric taxonomic problems. Whereas all species yield pyrrolidine alkaloids without suitably differentiating results the diverging occurrence of tropane alkaloids leads to three groups of sections: (1) taxa free of tropanes, (2) taxa with simple tropanes, and (3) taxa with merresectines in addition to simple tropanes.

Variation of diastereoisomeric pyrrolizidine alkaloids in Pleurothallis (Orchidaceae)

The alkaloids of leaves and flowers of 18 populations of four Pleurothallis (Orchidaceae) species were characterized. Both leaves and flowers of individuals from all populations have two diasteroisomers of 1-hydroxymethylpyrrolizidine (RI=1290 and 1311). The 1290 isomer was the most abundant in all populations of P. johannensis (74-93%) and P. fabiobarrosii (63-93%), two morphologically closed species. On the other hand, in almost all populations of P. teres the 1311 isomer is the more abundant (61-95%), except in one population occurring disjunct from the core area distribution of the species. These results support the recent taxonomic revision for these three species. Almost all P. ochreata populations also have the 1290 as the most abundant isomer, except in one morphologically differentiated population situated at the southern extreme of the distribution of this species.