Plant extracts alkaloids

Trichloroethanoic acid, CCI3COOH. A crystalline solid which rapidly absorbs water vapour m.p. 58°C, b.p. 196-5" C. Manufactured by the action of chlorine on ethanoic acid at 160°C in the presence of red phosphorus, sulphur or iodine. It is decomposed into chloroform and carbon dioxide by boiling water. It is a much stronger acid than either the mono- or the dichloro-acids and has been used to extract alkaloids and ascorbic acid from plant and animal tissues. It is a precipitant for proteins and may be used to test for the presence of albumin in urine. The sodium salt is used as a selective weedkiller. 

Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material. 

Both of the alkaloids anhalamine (62) from l ophophora williamsii and lophocerine (63) from l ophocereus schotti were isolated (after the properties of purified mescaline had been noted) in the search for materials of similar behavior. Interestingly, lophocerine, isolated as its methyl ether, after dia2omethane treatment of the alkaU-soluble fraction of total plant extract, is racemic. It is not known if the alkaloid in the plant is also racemic or if the isolation procedure causes racemization. 

For thousands of years, humans have used plants to make medicines and dmgs. Many of the biologically active ingredients in plant extracts contain at least one nitrogen atom with a lone pair of electrons, making them weak bases. Such naturally occurring weak bases are classified as alkaloids. Modem pharmaceutical chemists have built upon nature s chemistry by synthesizing new compounds that are important medicines. 

Plant extracts (e.g. alkaloids) Various, including pain relief... 

Most alkaloids are isolated from plant extracts by conversion into the difficultly soluble salts which they form with complex acids such as hexachloroplatinic acid, chlorauric add, phosphotungstic add, hydroferro-cyanic add, Rdnecke s add, etc. Perchloric add, picric add, flavianic add, mercuric chloride, iodine in potassium iodide are also used. 

Mateus, L., Cherkaoui, S., Christen, R, and Veuthey, J. L. (1999). Capillary electrophoresis-diode array detection-electrospray mass spectrometry for the analysis of selected tropane alkaloids in plant extracts. Electrophoresis 20, 3402—3409. 

The classic cholinesterase inhibitor is the alkaloid physostigmine (6)/ eserine (7). It was first isolated from the calabar bean, the seeds of Physostigma venenosum. Many novel natural products with AchE-inhibifing properties have shown promise as therapeutics for AD. Some examples of such products (pure compounds/plant extracts or formulations) are briefly reviewed here. 

The chemical properties of water determine what compounds will leach out of soil and vegetation, and hence what chemicals other plants and animals will be exposed to. For instance, acidic water will extract alkaloids from plant materials. 

Alkaloids are found mainly in plants, and are nitrogenous bases, typically primary, secondary, or tertiary amines. The basic properties facilitate their isolation and purification. Water-soluble salts are formed in the presence of mineral acids (see Section 4.11.1), and this allows separation of the alkaloids from any other compounds that are neutral or acidic. It is a simple matter to take a plant extract in a water-immiscible organic solvent, and to extract this solution with aqueous acid. Salts of the alkaloids are formed, and, being water soluble, these transfer to the aqueous acid phase. On basifying the acid phase, the alkaloids revert back to an uncharged form, and may be extracted into fresh organic solvent. 

One approach to the discovery of new insecticides which fulfill the criteria of efficacy, safety, selectivity, etc., is through the study of the natural chemical defenses of plants. Extracts of plants have been used as Insecticides by humans since before the time of the ancient Romans, a practice that continues today with many of the 2000 species of plants known to have insecticidal properties (4-5). The use of insecticidal" plants is especially prevalent among subsistence farmers since plants grown locally are cheaper, and sometimes more accessible, than synthetic chemical pesticides. Commercially, however, only a few of these plants. Including those containing pyrethrins, rotenoids, and alkaloids, have been used to any extent in the United States as sources of insecticides (6-8). 

Quinolizidine alkaloids, pure or in mixtures of plant extract, can be used to protect plants against noxious insects. Scientific data has shown that quinolizidine alkaloids play a role in the resistance of some lupine varieties to the pea... 

Morphine is the most abundant of the opium alkaloids. It constitutes as much as 15 percent of the plant extract. Morphine has been used as a medicine and narcotic for thousands of years. Therapeutically, morphine has three principal uses as an analgesic for the relief of acute and chronic pain, as a respiratory depressant, and as an antidiarrheal agent. The analgesic properties are morphine s most important clinical use. 

In another processing procedure, Platis and Fabrou (2006) purihed anti-HIV MAb from plants using a PEG/Pi aqueous two-phase system. This techihque purihes the plant extract from any additional alkaloids and phe-nolics. The sample can then be applied to a protein A or G affinity column without the need for any further treatment. The authors were able to use this techihque to achieve over 95% recovery. 

Alkaloids are weak bases, capable of forming salts, which are commonly extracted form tissues with an acidic, aqueous solvent. Alternatively, free bases can be extracted with organic solvents (see Chapter 11). Plants containing alkaloids with anticancer properties include the following ... 

Currently pest control by natural plant extracts is practiced primarily by subsistence farmers in those less developed part of the world where it is still an economic necessity.(ref. 3). Of the approximately 2000 plant species with known insecticidal properties (ref. 4), few have been developed commercially. These include the pyrethrins, rotenones and some of the alkaloids. Pyrethrins were the most important natural plant extracts in the early commercial insecticide formulations and were already in use in Persia and Yugoslavia during the early 1800s. By 1939 pyrethrum imports to the United States were 13-5 million lbs, declining from this peak as the synthetic analogs (e.g., the allethrins) appeared on the market. The addition of stabilizers (antioxidants) and synergists to the original pyrethrum formulations saved the natural product from commercial extinction. Currently the demand for pyrethrum flowers is still over 25,000 tons per annum—met by hand-harvested crops from Ecuador, Kenya and Tanzania (ref. 5) ... 

The tubulin-binding properties of (-)-rhazinilam were discovered through screening of a number of Malaysian plant extracts [60]. Natural (-)-rhazinilam induces tubulin spiralization, inhibiting tubulin assembly in the same way as vinblastine-like alkaloids, and protects microtubules from cold disassembly such as with paclitaxel [67]. This effect has never been observed with other microtubule poisons. For this reason, and despite the in vivo inactivity of (-)-rhazinilam [67], a number of analogues have been prepared by semi-synthesis and total synthesis (see Sections 3.1.3. and 3.2.3.) in order to improve the pharmacological properties of this molecule. 

Studies of the biological activity of Nuphar alkaloids have been carried out in two ways, either by concentrating on biological activity of plant extracts or, as in the case of research carried out by LaLonde, by focusing attention on a particular chemical compound of determined structure and stereochemistry. Investigations were carried out on the antibiotic activity of a mixture of alkaloids, isolated from Nuphar lutea, but of unknown structure (75-77). Studies were also performed on hot water extracts from N. japonicum for their inhibitory effect on beef heart phosphodiesterase (78). A positive result for the extract from N. japonicum... 

Alkaloids of Delphinium tricorne Tricomine.—Examination of the alkaloid fraction of the whole-plant extract from D. tricorne Michaux revealed lycoctonine (39), Alkaloid A (36), Alkaloid B ( delsemine ), and a new base, tricomine (46), C27H43N08, m.pt. 187—189 °C.34 35... 

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