Gerhard H. Verdoorn

Esters of quinolizidine alkaloids from the genus Pearsonia

Abstract Alkaloidal extracts of two species from the genus Pearsonia yielded several quinolizidine alkaloids. Amongst these were four new esters of hydroxylated lupanines, cajanifoline (3β-hydroxylupanine-13α- O -angelate), sessilifoline (3β-hydroxylupanine-4α- O -angelate), pearsonine (3β,8α-dihydroxylupanine-13α- O -angelate) and cryptanthine (8α-hydroxylupanine-13α- O -angelate). The correct structure for a hydroxylated lupanine (previously believed to be nuttalline), namely 3β-hydroxylupanine, is reported.

Chemotaxonomic significance of alkaloids in the genus Lebeckia

The alkaloids of six species and subspecies of Pearsonia have been studied to provide data for comparisons with other genera. Four different esters of tetracyclic quinolizidine alkaloids were found to be the major compounds in most of the extracts. These were lupanine-13α-angelate and three hitherto unknown esters, namely cajanifoline (lupanine-3β-hydroxy-13αangelate), sessilifoline (lupanine-3β-hydroxy-4ga-angelate) and pearsonine (lupanine-3β,8α-dihydroxy-13α-angelate). Other major alkaloids were sparteine, α-isolupanine, lupanine, nuttalline and ammodendrine. Our results strongly support the present generic concept of Pearsonia and provide evidence for a close taxonomic affinity with the genus Rothia. In Pearsonia, however, the major cornponents are esters of higher oxidized quinolizidine alkaloids than those of Rothia. The presence of esters of alkaloids in Pearsonia and Rothia is a unique character to distinguish them from all other genera of the tribe Crotalarieae and once again confirms the chemotaxonomic value of alkaloids as a generic character.

Alkaloids as taxonomic characters in the tribe Crotalarieae (Fabaceae)

Abstract Recent studies of alkaloids have led to a better understanding of the intricate taxonomic relationships in the tribe Crotalarieae. Data from alkaloidal metabolites are largely congruent with morphological data, but allow refinement of the understanding of the phylogeny. A well-supported and almost fully resolved cladogram is presented, which shows that the genera can be grouped into four main clades: (1) an unspecialized group without α-pyridone alkaloids and without esters of alkaloids (Aspalathus, Lebeckia, Rafnia, Wiborgia and perhaps Spartidiurn); (2) a group specializing in lupanine-type esters (Pearsonia and Rothia); (3) a group with macrocyclic pyrrolizidine alkaloids (Crotalaria andLotononis); and (4) a specialized group with α-pyridone alkaloids (Argyrolobium, Dichilus, Melolobium and Polhillia).

Chemotaxonomic value of alkaloids in the genus Dichilus

Two bicyclic piperidyl alkaloids (ammodendrine and smipine) and a quinolizidine alkaloid (thermopsine) were identified as major alkaloids of the genus Dichlus. Other piperidyl alkaloids positively identified were bipyridyl, N-methylammodendrineN-acetylhystrine, l-acetyl-l,2,3,4-tetrahydropyridine and piperidinone. The latter two compounds have not been previously reported from the Leguminosae. In the tribe Crotalarieae, the dominance of piperidyl alkaloids appears to be a unique chemotaxonomic character for Dichlus. Our results strongly support the present circumscription and also the isolated position of the genus. An affinity with Melolobium rather than Lebeckia is suggested.

The chemotaxonomic significance of integerrimine in Buchenroedera and Lotononis section Krebsia

Abstract Integerrimine, a pyrrolizidine alkaloid previously known only from species of Cacalia, Senecio and Crotalaria , has been identified as the major alkaloid of several species of Buchenroedera and Lotononis section Krebsia. Chemotaxonomic implications are discussed. Our conclusions are that the genera Buchenroedera and Lotononis are more closely related to Crotalaria than to Lebeckia , despite morphological evidence to the contrary; that Buchenroedera and Lotononis may not be distinct at the generic level and that Lebeckia microphylla should be transferred to Lotononis section Krebsia .

Observations on the occurrence and distribution of alkaloids in some genera and species of the tribe Crotalarieae (Fabaceae)

A general survey of alkaloids in the tribe Crotalarieae showed that useful chemotaxonomic data may be obtained. Although the pyrrolizidine alkaloids of Crotalaria L. have been studied in considerable detail, virtually nothing is known for the other, predominantly southern African genera. The genera Dichilus DC., Lebeckia Thunb., Melolobium Eckl. & Zeyh. and Polhillia Stirton were found to contain several alkaloids in sufficient quantities to warrant further investigation. The major alkaloids (presumably all of the quinolizidine type) seem to be characteristic for each of these genera. Aspalathus L., Buchenroedera Eckl. & Zeyh., Lotononis (DC.) Eckl. & Zeyh., Pearsonia Duemmer, Rafnia Thunb. and Wiborgia Thunb. appear to produce much smaller amounts. The possibility of obtaining useful information from these genera seems limited in view of the large quantities of plant material required to enable proper identification of the compounds. Methods of extraction and detection are described. The R f values of the major alkaloids are given for the different thin-layer chromatographic systems used. Some preliminary identifications were confirmed by mass spectrometry.

Alkaloids of the genera Aspalathus, Rafnia and Wiborgia (Fabaceae – Crotalarieae)

The presence of alkaloids in three southern African genera of the tribe Crotalarieae is reported for the first time. Sparteine, lupanine and nuttalline were detected in several species of Aspalathus L., Rafnia Thunb. and Wiborgia Thunb., but rarely in more than trace quantities. Except for very large quantitative differences, the alkaloids are almost identical to those found in the genus Lebeckia Thunb. Available evidence suggests that the three genera are more closely related to Lebeckia than to any other genus of the tribe. The divergence of these genera seems to be linked to an almost total loss of the ability to produce alkaloids.

A chemotaxonomic survey of major alkaloids in Lotononis and Buchenroedera

Abstract A survey of alkaloids in five species of Buchenroedera and 27 species of Lotononis has shown the presence of several pyrrolizidine, quinolizidine and piperidyl alkaloids. Senecionine, integerrimine, platyphylline, neoplatyphylline, sparteine, lupanine, 11-epi-lupanine, nuttalline and ammodendrine have been positively identified. The co-occurrence of quinolizidine and macrocyclic pyrrolizidine alkaloids in the same genus is a new record for the Leguminosae and also appears to be a unique chemotaxonomic character for Buchenroedera and Lotononis . The distribution of alkaloids in Lotononis does not support the traditional infrageneric classification.

Alkaloidal variation in the genus Pearsonia

Abstract Several quinolizidine alkaloids, including various angelate esters, are known from the genus Pearsonia . In a detailed variation study which included 98 samples from nine of the 11 species, large qualitative and quantitative differences were recorded. The observed variation is ascribed to the following: 1, species (the alkaloids of some species and subspecies are diagnostically different); 2, provenance (various populations of the same species may have unique combinations of alkaloids); 3, developmental stage (in P. cajanifolia there is a marked decreased in esterification towards the end of the growing season); 4, plant parts extracted (seeds, for example, have high concentrations of hydroxylated lupanine-type alkaloids and only small amounts of esters). These results highlight some of the problems associated with the use of alkaloids as taxonomic characters.

Taxonomic significance of major alkaloids in the genus Priestleya

Abstract The genus Priestleya is known to contain the bipiperidyl alkaloid anabasine and an alkaloid tentatively identified as lupanine. In a study of 16 different species, several quinolizidine alkaloids and some bipiperidyl alkaloids were identified. A remarkable difference was found between the two sections of Priestleya : sect. Priestleya contains sparteine, lupanine and other tetracyclic quinolizidine alkaloids, while the sect. Anisothea contains the bipiperidyl alkaloid anabasine and the bicyclic quinolizidine lupinine. The chemical distinction agrees with morphological evidence that the generic concept of Priestleya is artificial and that two distinct genera should be recognized.