Properties of alkaloids

Alkaloids are generally white or colonrless crystalline solids containing oxygen. A minority of alkaloids are oxygen free, existing 

With few exceptions (colchicine, berberine) alkaloids are bases, tnrning red litmns paper bine. Many are precipitated by varions reagents, for example Meyers (mercuric chloride and potassinm iodide). Some give more or less characteristic colonr reactions with certain reagents. Most are snsceptible to destruction by heat, some by exposure to air and light. 

Most alkaloids are solnble in organic solvents such as chloroform, ether and alcohol, bnt are practically water insoluble. Water-soluble alkaloids include ephedrine and colchicine. Alkaloidal salts are generally solnble in water and alcohol. 

All alkaloid names end in ine . Otherwise their names have a number of origins  

From discoverer s name—lobeline (after L Obel) 

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Houghton PJ, Agbedahunsi JM, Adegbulugbe A, Choline esterase inhibitory properties of alkaloids from two Nigerian Crinum species. Phytochemistry 65 2893-2896, 2004. 

Wink, M. and Latz-Bruning, B. 1995. Allelopathic properties of alkaloids and other natural products Possible modes of action. In Inderjit, K.M.M. Dakshini and F.A. Einhellig, (Eds), Allelopathy. Organisms, Processes and Applications. ACS Symposium Series 582, American Chemical Society, Washington, DC, 117-126... 

Wink, M. and Twardowski, T. 1992. Allelochemical properties of alkaloids. Effects on plants, bacteria and protein biosynthesis. In Rizvi, S. J. H. and Rizvi, V. (Eds), Allelopathy Basic and Applied Asspects. Chapman Hall, London, 129-150. 

Wippich, C. and Wink, M. 1985. Biological properties of alkaloids. Influence of quinolizidine alkaloids and gramine on the germination and development of powdery mildew, Erysiphe graminis f. sp. hordei. Experientia 41,1477-1478... 

Wink, M. and Latz-Brunning, B. 1995. Allelopathic properties of alkaloids and other natural products. ACS Symposium Series 582,117-126... 

Only the defensive properties of alkaloids vfill be discussed in more detail in this chapter. 

In this chapter the focus is on the biological activity of alkaloids (the information available on the pharmacological properties of alkaloids is mostly excluded), and we try to discuss these data from an ecological perspective. In the following, the possible functions of alkaloids in plant-animal, plant-plant, and plant-microbe interactions are discussed in more detail. 

It is nearly impossible to cover the literature exhaustively. Therefore, an overview of the allelochemical properties of alkaloids is presented. Because of the large amount of data (literature up to 1990 is included), the selection of examples must remain subjective to some degree. Nevertheless, the author would be grateful to receive information or publications about relevant omissions. 

Because Homo sapiens and domestic animals are to some degree herbivores, a large body of empirical knowledge has accumulated on the toxic properties of alkaloids (Tables I through V) and alkaloid-containing plants. Previously, the toxic properties of alkaloids in vertebrates was part of the definition (as a common denominator) for this group of natural products 38,39). In the following, the toxic or adverse effects of alkaloids are separately discussed for invertebrates (mainly insects) and vertebrates. 

Although the ionic properties of alkaloids would make them suitable objects for ion-exchange chromatography, this technique has only found limited applications in the analysis of alkaloids. 

The ionic properties of alkaloids under acidic conditions make them suitable for ion-pair chromatography. In ion-pair chromatography the alkaloidal cation is basically combined with an anion to yield an ion-pair, which can act as a neutral molecule. The ion-pair is partitioned between a mobile phase and a stationary phase during the chromatographic process. Ion-pair chromatography can be practised in the normal or in the reversed-phase mode. 

The ergot alkaloids having the properties of producing mixed crystals between the levo- and dextro-rotary form, often false conclusions have been made, so that mixtures of different products have often been considered as pure individuals. It will be seen in the following that the property of alkaloids consisting in giving isomorph crystallizations has also led to the fact that preparations from ergot have been considered as uniform compounds, whereas in truth they were mixtures of different alkaloids. 

Japanese workers are at the forefront in the search for physiologically active microbial metabolies. Their detection methods are worthy of note for lack of satisfactory testing methods has long hampered this search. Umezawa and his co-workers used in vitro enzyme inhibition tests to detect fusaric acid, pepstatin, chymostatin, and the leupeptins. Nigrifactin was discovered by Terashima and co-workers by seeking in experimental fermentations, materials having the chemical properties of alkaloids. 

Are the agonistic or antagonistic properties of alkaloids at neuroreceptors, ion channels or other elements of the signal pathway (Tables 3-15) relevant for plant-herbivore interactions or toxicological assessments ... 

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