Preparative separation, complex alkaloid

Preparative Separation of Complex Alkaloid Mixture by High-Speed Countercurrent Chromatography... 

L PETROSKI AND POWELL Preparative Separation of Complex Alkaloids 427... 

The combination of preparative high-speed countercurrent chromatography with other separation methods, such as HPLC, and TLC, will enable chemists to isolate minor components of complex alkaloid mixtures more efficiently. This technique is not limited to alkaloid separations and, in theory, other complex mixtures of compounds having only minor differences in their partition coefficients should be efficiently separated by high-speed countercurrent chromatography. 

Frahn, j. L., C. C. j. Culvenor, and J. A. Mills Preparative Separation of the Pyrrolizidine Alkaloids, Intermedine and Lycopsamine, as their Borate Complexes. J. Chromatogr. 195, 379 (1980). 

The methods employed for isolation of the alkaloids depend on the nature of the compounds, and specific conditions have frequently been devised for the selective isolation of particular types of compounds. Usually, fresh or dried plant material is extracted with dilute acid solution or with alcohol, and the extract obtained is further fractionated by extraction into organic solvents with variation of pH. Extraction columns (288), membrane processes (425), and ion-exchange materials (288-290) may be particularly useful for subfractionation or isolation procedures. For further identification and isolation of separate compounds, preparative thin-layer chromatography, (288, 291, 292, 426), liquid chromatography (293, 294), or gas chromatography may be used (202, 296, 297). Because some of the products reviewed in this chapter occur naturally in very small amounts, they have not been isolated in crystalline form. Gas chromatography-mass spectrometry (87, 213, 299), mass fragmentography (192), and mass spectrometry-mass spectrometry (301, 359) have proved to be particularly useful techniques for identification of trace alkaloids in complex mixtures. 

In situations when analysis is required to establish the presence and identity of calystegines in a plant extract it is not necessary to utilize a complex series of chromatographic separations. The plant material can be extracted with methanol or methanol-water and passage over a Dowex 50W-X8 column with dilute ammonium hydroxide as eluant provides substantial purification, yielding the alkaloid fraction, including other polyhydroxy alkaloids, contaminated only by basic amino adds. The extract can thus be rapidly prepared for analysis [29,30]. 

A total synthesis of vinblastine has not as yet been achieved. Methods of preparation involve making initial crude extracts from the periwinkle plant, followed by extraction at selected pH into organic solvents, and final separation of the complex mixture of alkaloids by column chromatography. Several methods have been devised since Noble, Beer, and Cutts1 first reported the isolation of vinblastine as the sulfate salt. A few are briefly described here. 

Demonstrating the abihty of CE to do analysis in complex matrices, Liu and Sheu [38] have reported the separation of 8 quaternary alkaloids from Coptidis rhizoma which are commonly found in Chinese herbal remedies (Figxire 6). These investigators also determined ephedrine and pseudophedrine in Chinese herbal preparations [39]. Stuppner, et al. demonstrated the separation of 6 oxindole alkaloids from the root bark of Unicaria tomentosa [40]. 

Once the imprinting system has been devised to yield favorable monomer-template complexation and the necessary porosity, the preparation of monolithic polymer rods for HPLC is relatively simple. The general protocol detailed below uses an in situ polymerization method developed by Frechet and Svec [4]. This technique was used by Matsui in the preparation of MIP monolith rods for HPLC separation of antimalarial cinchona alkaloids, ( ) cinchonidine and (+) cinchonine, as well as the structural analogues quinidine and quinine [45]. 

For the muscle relaxing properties of tubocurarine (D 22.1.2), for instance, only part of the complex structure of this alkaloid is necessary the presence of two quarternary iV-atoms at a certain distance from each other. This structure is mimicked in the pharmacologically similar synthetically prepared compounds of the decamethonium and suxamethonium type, in which both the quarternary A -atoms are separated either by a simple saturated carbon chain or a succinic acid-bischoline-ester residue. 

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