Alkaloids bitterness

C8H10N4O2. An alkaloid occurring in tea, coffee and guarana, from which it may be prepared by extraction, It is also manufactured by the methylation of theobromine and by the condensation of cyanoacetic acid with urea. Crystallizes with H2O or anhydrous from organic solvents. M.p. (anhydrous) 235"C, sublimes at 176 C. Odourless, and with a very bitter taste. Caffeine acts as a stimulant and diuretic, and is a constituent of cola drinks, tea and coffee. 

Organic aromatic molecules are usually sweet, bitter, a combination of these, or tasteless, probably owing to lack of water solubiUty. Most characteristic taste substances, especially salty and sweet, are nonvolatile compounds. Many different types of molecules produce the bitter taste, eg, divalent cations, alkaloids, some amino acids, and denatoirium (14,15). 

These methods are employed for the detection and determination of antibiotics and substances with similar effects, like alkaloids, insecticides, fungicides, mycotoxins, vitamins, bitter principles and saponins [14]. 

Manual transfer of the chromatographically separated substance to the detector . These include, for example, the detection of antibiotically active substances, plant and animal hormones, mycotoxins, insecticides, spice and bitter principles and alkaloids. The frequency distribution of their employment is shown in Figure 54 [295]. 

The Aristolochias are used in medicine as tonics due to the presence of bitter principles, though Hesse suggested that A. reticulata Nutt, then the serpentary root of commerce, might contain aristolochine, and the view that the bitter constituents are of alkaloidal character has been confirmed by Krishnaswamy, Manjunath and Rao, for A. indica L. 

Melia azadirachta L. (neem or margosa). The bark, according to Cornish, yields a minute amount of a bitter alkaloid, margosine. The fruit is reported to be toxic and to contain an alkaloid, azaridine. The leaves are stated to be insect-repellent and from them an alkaloid paraisine has been prepared. The flowers are alkaloid-free. ((1) Ind. Ann. Med. Sci., 1857, 4, 104 (2) Carratala, Rev. Asoc. med. Arg., 1939, 53, 338 (3) Volkonsky, Arch. Inst. Pasteur Alg rie, 1937, 427 (4) Subramanian and Rangaswamy, Curr. Sci., 1947, 16, 182.)... 

Tramadol is an alkaloid, with an amine group (where the nitrogen atom is), which puts it in a group of bitter plant chemicals that often have potent biological activity. 

Bitter taste, like sweet taste, is exhibited by a very diverse group of chemical compounds. Because the bitter taste is generally regarded as unpleasant, and because it is often associated with such compounds as those alkaloids and glycosides that are harmful to man, detailed studies have been minimal. There is thus very little information available from which to deduce the chemical grouping common to those compounds eliciting the bitter response. 

Alkaloids are compounds that contain nitrogen in a heterocyclic ring and are commonly found in about 15-20% of all vascular plants. Alkaloids are subclassified on the basis of the chemical type of their nitrogen-containing ring. They are formed as secondary metabolites from amino acids and usually present a bitter taste accompanied by toxicity that should help to repel insects and herbivores. Alkaloids are found in seeds, leaves, and roots of plants such as coffee beans, guarana seeds, cocoa beans, mate tea leaves, peppermint leaves, coca leaves, and many other plant sources. The most common alkaloids are caffeine, theophylline, nicotine, codeine, and indole... 

We knew Utetheisa to feed on poisonous plants as a larva (Figure 1B). The plants, of the genus Crotalaria (family Leguminosae), were known to contain pyrrolizidine alkaloids (henceforth abbreviated as PAs), intensely bitter compounds potently hepatotoxic to mammals (7). Other species of Utetheisa were known to sequester PAs (8). We found this to be true for U. ornatrix as well. Adult Utetheisa raised on Crotalaria spectabilis, one of the principal foodplants available to the moth in the United States, contain on average about 700 p,g of monocrotaline (1), the principal PA in that plant (9, 10). 

When disturbed or molested, these insects release small droplets of hemo-lymph from the tibio-femoral joints of their legs, and it is now well established that the deterrency exhibited by many species of coccinellids towards potential predators results from the presence of repellent and bitter alkaloids in that fluid [ 12,13]. In ladybirds, this unpalatability is associated with a bright aposematic coloration and a characteristic smell due to 3-alkyl-2-methoxypyrazines [14, 15]. The beetles use these molecules not only to reinforce the visual alerting signal on an olfactory level, but also as aggregation pheromones [16]. 

In the Andes, nearly all of the about 160 varieties of wild potatoes, and two of the eight cultivated species are toxic. Some frost-resistant species that grow above 3600 m have high levels of alkaloids, which are bitter and potentially toxic. These are hybrids between Solanum stenotonum and wild potatoes such as Solanum megistacrolohum and Solanum acaulc. Other secondary plant compounds in potatoes are saponins, phytohemagglutinin, proteinase inhibitors, sesquiterpene phytoalexins, and phenols. 

All these data support the idea that QA may function as chemical defense compounds. We also tested whether this chemical defense is relevant for the survival of a lupin plant. Lupins offer a unique chance to explore this question experimentally plant breeders have selected "sweet" varieties, which have a very low alkaloid content. These varieties can be compared to semi-bitter or bitter ones. We have grown Lupinus albus strains that differ in their alkaloid content in our experimental garden and greenhouse and have monitored their susceptibility to attack by plant pests. As can be seen from Figure 2, "sweet" lupins are preferentially eaten by rabbits (Cuniculus europaeus) or are infested by aphids (Aphidae) or leaf miners (Agromyzidae). Literature data also support the assumption that alkaloid-rich lupins are much more resistant to plant pests than "sweet" varieties (30-32). We conclude therefore, that QA are indeed important for the fitness of a lupin plant and that they constitute a major part of its chemical defense system, in which... 

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