STIG AGURELL, JAN G. BRUHN, JAN LUNDSTRÖM AND ULLA SVENSS0N
Department of Pharmacognosy, Faculty of Pharmacy.
Box 6804. 113 86 Stockholm. Sweden
ABSTRACT.- The alkaloids of 14 % species of Trichocereus are reported. Eight different previously known phenethylamines viz. tyramine. N-methyltyramine, hordenine. 3-methoxytyramine. 3.4-dimethoxyphenethylamine. N-methyl-3-methoxytyramine. 3hydroxy-4.5.dimethoxyphenethylamine. and mescaline were identified in these species. Mescaline was found to occur in T. cuzcoensis. T. fulvilanus. T. taquimbalensis and T. validus. Mescaline was also present in small amounts in Stetsonia coryne together with traces of anhalidine and anhalonidine. 3-Hydroxy-4-methoxyphenethylamine is identified in a plant, Pachycereus pecten-aboriginum, apparently for the first time. The commonly occurring isomer 3-methoxytyramine was found to be the major alkaloid of Trichocereus cuzcoensis. A tetrahydroisoquinoline alkaloid, anhalidine, was isolated from Pelecyphora aselliformis.
Results reported in a previous paper, indicated that the occu rence of alkaloids in Cactaceae was common (1). The basic alkaloids in 21 species of cacti mainly belonging to the genera Trichocereus, Helianthocereus and Cereus were reported in part I of this series (1). The structures of those, at that time,
FIG. 1. ldentified alkaloids.
known basic cactus alkaloids were also reviewed (I). Since then salsoline has found to occur in Echinocereus merkeri Hildm. (2) and N-rnethyl-4-hydroxy-3-methoxyphenethylamine in the peyote cactus (8).
The present report is concerned with the identification of alkaloids of cacti belonging mainly to the genus Trichocereus but also alkaloids of Stetsonia coryne, Pachycereus pecten-aboriginum, Pelecyphora aselliformis and Echinopsis rhodotricha.
PLANT MATERIAL.-The cacti used in this investigation were obtained from the following
sources: Stetsonia coryne, Pachycereus pecten-aboriginum, Trichocereus cuzcoensis,
T. santiaguensis, T. strigosus, T. thelegonoides and T. thelegonus from W. Haage, Erfurt, DDR; T. courantii. T. knuthianus. T. rnanguinii, T. pupureopilosus, T. taquimbalensis and T. tunariensis from H. van Donkelaar, Werkendam, The Netherlands; Pachycereus pecten-aboriginum. Stetsonia coryne, T. santiaguensis. Echinopsis rhodotricha and Pelecyphora aselliformis from K. Edelmann, Reeuwijk, The Netherlands; T. fulvilanus, T. santiaguensis and T. skottsbergii from M. Schleipfer, Augsburg, DBR; T. validus, T. thelegonous were gifts from Dr. J. P. M. Brenan, Royal Botanic Gardens, Kew, UK.
The nomenclature of species as proposed by Backeberg (4) is used. Plants were checked to conform with the macromorphological descriptions given by Backeberg. (4). Reference caccti are maintained in our greenhouse.
ISOLATION AND IDENTIFICATION OF ALKALOIDS.- Methods for isolation and separation of alkaloids have been described earlier (1). The basic technique by which the alkaloids were identified has been fully outlined (1). In essence, the naturally occurring compound was considered as identified, if it showed the same chromatographic behaviour as the reference compound (i) on two gas chromatography columns (SE-30, XE-60, or JxR); (ii) by tlc |chloroform- ethanol conc. ammonia (85:15:0.4) or, for phenols, chloroform ethanol diethylamine, (85:5:10)| and (iii) by gas chromatography- mass spectrometry (glc-rns), giving the same mass spectrum as the reference compound. In addition to the previously used 5% SE-30 and 5% XE-60 columns, a column (6 ft X 1/8 in.) of 3% JxR on Gas Chrom Q (100 120 mesh) was found to be in some ways superior (Varian model 204 or 2100 Aerograph). Preparative glc was carried out using columns of 5% SE-30 on Gas Chrom P (Varian model 202 Aerograph).
SPECIAL CHROMATOGRAPHIC SYSTEMS.- 3-Hydroxy-4-methoxyphenethylamine, the isomeric 4-hydroxy-3-methoxyphenethylamine ("3-methoxytyramine"), and the purified phenolic alkaloid fractions of T. cuzcoensis and Pachycereus pecten-aboriginurn were chromatographed on Whatman no. 1 paper with n-butanol-acetic acid -water (4:1:5) as solvent (13). After spraying with Gibbs' reagent, reference 3 hydroxy-4-methoxyphenethylamine (Rt. 0.45) and the major phenolic alkaloid of P. pecten-aboriginum showed a blue color while the isomer 4-hydroxy-3methoxyphenethylamine and the major phenolic compound from T. cuzcoensis (Rt. 0.45) developed a brown cotor, Gibbs' reagent: 0.1% solution of 2,6-dichloroquinone chlorimide in ethanol followed by 10% sodium carbonate in water.
Reference 4-hydroxy-3-rnetboxyphenethylamine (Rf. 0.60) 3-hydroxy-4-methoxyphenethylamine (Rf. 0.45) and the two isomeric compounds isolated from cacti were well separated by tlc on silica gel G plates with chloroform ethanol diethylamide (85:5:10) as solvent (10).
The identity of 3-hydroxy-4-methoxyphenethylamine and the major phenolic alkaloid or P. pecten-aboriginum was further confirmed by glc using trimethylanilinium hydroxide (5) for on-column methylation of the phenolic groups. In both cases a major compound having the retention time of 3,4-dimethoxyphenethylamine was formed.
RESULTS AND DISCUSSION
Our present screening for cactus alkaloids has largely been motivated by the search for biosynthetic intermediates in the formation of mescaline and related tetrahydroisoquinolines. Indeed, three phenolic'alkaloids, 3-rnethoxytyramine (4-hydroxy-3-methoxyphenethylamine), 3-hydroxy-4,5-dimethoxyphenethlamine and 4-hydroxy-3,5-dimethoxyphenethylamine were identified in cacti (3) and were later shown to be true biosynthetic intermediates (9). Still, some plausible progenitors of the tetrahydroisoquinoline skeleton are lacking. Partly, using "mass fragmentography" (7) to simplify the search for likely, presumably phenolic phenethylamine intermediates, a number of the Trichocercus species, and other cacti listed in table 1 were investigated. Some results with biogenetic implications are reported elsewhere (8). The identification of alkaloids has now been verified mainly by glc-ms and the final results reported here (table 1
Earlier, we have investigated (1) twelve species of the genus Trichocereus, which according to Backeberg comprises in all 38 species. We have now (table 1) examined the alkaloids of 14 more Trichocereus species and identified, in all, eight different phenethylamines (table 1). These are previously all known (1) to occur in the genus Trichocereus, except N-methyl-3-methoxytyramine (N-methyl-4-hydroxy-3-methoxyphenethylamine), which is known only from peyote (8). Mescaline, previously isolated from five Trichocereus species (1), is now identified also in T. cuzcoensis, T. fulvilanus, T. taquimbalensis and T. validus. While it occurred as the major alkaloid in T. taquimbalensis and T. validus, mescaline was only a minor constituent in the two other species. It may also be pointed out that the alkaloid-rich T. cuzcoensis contained 3-methoxytyramine as the predominant alkaloid. The macroscopic appearance of the new mescaline-containing species resembled markedly the previously known species and in fact, based on their appearance they were predicted to contain mescaline.
Stetsonia coryne has previously been known (11) to yield the quarternary alkaloid coryneine (N,N,N-trimethyldopamine). The occurrence of tyramine and N-methyltyramine. plausible biochemical progenitors of coryncine, was thus to be expected (fig. 2). Furthermore, plants from three different sources of this species, which is a not too distant relative of the Trichocereus species, were found to contain beside two other simple phenethylamines small amounts of mescaline. Traces of two phenolic tetrahydroisoquinoline alkaloids, viz. anhalonidine and anhalidine were also identified.
Pachycereus pecten-aboriginum was already in 1929 by Späth and Kuffner (14) shown to contain carnegine. This cactus has now been found to contain several alkaloids as will be reported in a later publication. However, the major compound of the phenolic alkaloid fraction turned out to be a hydroxymethoxyphenethylamine, but surprisingly not the commonly occurring 3-methoxytyramine (4-hydroxy-3-methoxyphenethylamine), but rather the isorneric 3-hydroxy-4-methoxyphenethylamine as described in the experimental section. This latter compound might theoretically be a good precursor of some tetrahydroisoquinoline alkaloids, e.g., carnegine and salsolidine, since it may provide an advantageous para-activation for the ring closure. Experiments on the biosynthesis of carnegine and salsolidine in Carnegiea gigantea have, however, not entirely supported such assumptions (6).
Pelecyphora aselliformis has been reported to contain alkaloids, probably tetrahydroisoquinoline alkaloids. This is now found to be correct with the identification of anhalidine in addition to the ubiquitous hordenine. The structure of one major alkaloid of this species still awaits elucidation. In this connection, it is known (12) that cacti of several genera of Cactaccae, among them pelecyphora, in Mexico are popularly, although for unknown reasons, classed as "peyote". Possibly, the alkaloids of P. aselliformis are responsible for its classification as a "peyote".
Echinopsia rhodotricha was earlier reported (1) not to contain detectable amounts of alkaloids. From a large amount of cacti we have now isolated small amounts of hordenine and tyramine.
FIG. 2. Gas chromatogram from glc-ms run of alkaloids of Stetsonia coryne. 5% SE-30 on Gas Chrom P. 150·. l = tyramine and N-methyltyramine, 2 = 3-methoxytyramine, 3 = 3,4-dimethoxyphenthylamine, 4 = mescaline, 5 = anhalidine, 6 = anhalonidine.