252 



ALKALOIDS 



line with this suggestion is the observation of Dawson (3) that feeding nicotine 

 to tobacco root cultures increased their uptake of nitrate. Laroze and Alves 

 da Silva (4) favor the view that alkaloids function by exchanging with soil ca- 

 tions, and they have found alkaloids to be excreted by the roots of several 

 alkaloid plants. 



Further discussion of the function of alkaloids may be found in the reviews of 

 James (5) Mothes (6, 7) and Bezanger-Beauquesne (8). 



Alkaloids are widely distributed throughout the plant kingdom. Although some 

 groups of plants are rich in alkaloids and other groups have none, there does not appear 

 to be any facile generalization to be made about alkaloid distribution. There is some 

 tendency for higher plants to have more than lower plants, but alkaloids are well known 

 in the club mosses and horsetails, not to mention certain fungi (ergot). Alkaloids are 

 not known in the Bryophytes, but probably no thorough search has been made for them 

 there. It has been suggested (9) that the formation of volatile terpenes somehow com- 

 petes with the formation of alkaloids so that plants having one lack the other. A special 

 illustration of this principle is shown by the work of Tallent and Horning (10) who found 

 that species of pine which have alkaloids also have straight-chain, aliphatic hydrocarbons 

 rather than terpenes in their turpentines. 



ISOLATION 



The single, most important chemical property of the alkaloids is their basicity. 

 Purification and characterization methods generally rely on this property, and special 

 approaches must be developed for those few alkaloids (e. g. rutaecarpine, colchicine, 

 ricinine) which are not basic. 



Alkaloids are normally obtained by extracting the plant material with an acidic, 

 aqueous solvent which dissolves the alkaloids as their salts, or the plant material may 

 be made alkaline with sodium carbonate, etc. and the free bases extracted into organic 

 solvents such as chloroform, ether, etc. Some volatile alkaloids such as nicotine may 

 be purified by steam distillation from an alkaline solution. An acidic aqueous solution 

 containing alkaloids may be made basic and the alkaloids extracted with an organic sol- 

 vent so that neutral and acidic water-soluble compounds are left behind. Another useful 

 way of removing alkaloids from acidic solution is by adsorption on Lloyd's reagent (11). 

 They can then be eluted with dilute base. Many alkaloids can be separated by precipitating 

 them as reineckates. A mixture of reineckates can then be resolved into its components 

 by ion exchange chromatography (12). For detailed applications of these methods consult 

 the articles by Cromwell (13) and Manske (14). Sangster (15) has also presented a gen- 

 eral discussion on methods for isolating and characterizing alkaloids. 



Additional purification of alkaloids can sometimes be carried out by extraction with 

 selective solvents. The most general and convenient method of separation now available 

 for separation of mixtures is column chromatography either using ion exchange resins or 

 adsorbents such as aluminum oxide. Paper chromatography (see below) is useful for pre- 

 liminary determination of the number of components to be separated and something of 

 their nature. A procedure for isolation and identification of alkaloids fi»om milligram 

 quantities of plant material uses a combination of column chromatography on alumina and 

 paper chromatography (16). 



CHARA CTERIZA TION 



Qualitative evidence for the presence of alkaloids in a solution and a rough charac- 

 terization may be obtained by application of the various "alkaloidal reagents". 



