Extraction and Isolation of Chemotherapeutic Pyrrolizidine Alkaloids from Plant Substrates

Abstract

Pyrrolizidine alkaloids have long been known to be antitumor active and, more recently, have become of interest as anti-cancer agents. They occur naturally in several plant species, but are often difficult to extract and isolate from the plant material without degradation or the use of toxic solvents. The extraction of a model pyrrolizidine alkaloid, monocrotaline, from the seeds of Crotalaria spectabilis was investigated in this work. The crushed seeds of Crotalaria spectabilis were first contacted with supercritical carbon dioxide and, as expected, the oils comprising the bulk of the seed material were preferentially extracted. The addition of ethanol and water as co-solvents in the fluid phase led to the appearance of monocrotaline in the extract. Monocrotaline contents as high as 24% of the total extract could be obtained with carbon dioxide-ethanol mixtures. In order to increase the extract purity further, two additional processes were developed. The temperature-solubility cross-over point was utilized to obtain extracts containing as much as 50% monocrotaline. A second novel process incorporating ion exchange resins was also studied and yielded extracts containing 94 to 100% monocrotaline. Because this technique depends only on the basic character common to the pyrrolizidine alkaloids, it is expected to be equally effective in the extraction and isolation of the other members of this class and, in fact, could be extended to the other classes of basic alkaloids.