Alkaloids

True alkaloids derive from amino acid and they share a heterocyclic ring with nitrogen. These alkaloids are highly reactive substances with biological activity even in low doses. All true alkaloids have a bitter taste and appear as a white solid, with the exception of nicotine which has a brown liquid. True alkaloids form water-soluble salts. Moreover, most of them are well-defined crystalline substances which unite with acids to form salts. True alkaloids may occur in plants (1) in the free state, (2) as salts and (3) as N-oxides. These alkaloids occur in a limited number of species and families, and are those compounds in which decarboxylated amino acids are condensed with a nonnitrogenous structural moiety. The primary precursors of true alkaloids are such amino acids as l-ornithine, l-lysine, l-phenylalanine/l-tyrosine, l-tryptophan and l-histidine2332. Examples of true alkaloids include such biologically active alkaloids as cocaine, quinine, dopamine, morphine and usambarensine

Protoalkaloids are compounds, in which the N atom derived from an amino acid
is not a part of the heterocyclic31. Such kinds of alkaloid include compounds
derived from l-tyrosine and l-tryptophan. Protoalkaloids are those with a closed ring, being perfect but structurally simple alkaloids. They form
a minority of all alkaloids. Hordenine, mescaline (Figure 5) and yohimbine are
good examples of these kinds of alkaloid. Chini et al.33 have found new alkaloids,
stachydrine and 4-hydroxystachydrine, derived from Boscia angustifolia, a plant
belonging to the Capparidacea family. These alkaloids have a pyrroline nucleus
and are basic alkaloids in the genus Boscia. The species from this genus have
been used in folk medicine in East and South Africa. Boscia angustifolia is
used for the treatment of mental illness, and occasionally to combat pain and
neuralgia.

Pseudoalkaloids are compounds, the basic carbon skeletons of which are not derived from amino acids31. In reality, pseudoalkaloids are connected with amino acid pathways. They are derived from the precursors or postcursors (derivatives the indegradation process) of amino acids. They can also result from the amination and transamination reactions32 of the different pathways connected with precursors or postcursors of amino acids. These alkaloids can also be derived from non-aminoacid precursors. The N atom is inserted into the molecule at a relatively late stage, for example, in the case of steroidal or terpenoid skeletons. Certainly, the N atom can also be donated by an amino acid source across a transamination reaction, if there is a
suitable aldehyde or ketone. Pseudoalkaloids can be acetate and phenylalaninederived or terpenoid, as well as steroidal alkaloids. Examples of pseudoalkaloids include such compounds as coniine, capsaicin, ephedrine, solanidine, caffeine, theobromine and pinidine.

Occurance of alkaloids
Alkaloids are substances very well known for their biological activity at the beginning of world civilization. They were used in shamanism, in traditional herbal medicine for the cure of diseases and in weapons as toxins during tribal wars and during hunting. They also had, and still have, socio-cultural and personal significance in ethnobotany34. Moreover, they have been and continue to be the object of human interest concerning new possibilities for their safe utilization
and ensuing health benefits. Of all secondary compounds, historically and contemporaneously, only alkaloids are molecules of natural origin with highly important benefits and diagnostic uses. They can be characterized as the most useful and also the most dangerous products of nature. They can be extracted and purified Alkaloids are most abundant in higher plants. At least 25% of higher plants contain these molecules. In effect this means that on average, at least one in fourth
plants contains some alkaloids. In reality, it is not impossible that alkaloids occur more commonly. Using the latest equipment and technology, such slight traces of alkaloids may be detected (e.g., less than 10 gigagrams per kg of plant mass) that these have no real influence on biological receptors and activity. Generally these species are not considered as alkaloid species. Hegnauer1213 has defined alkaloid plants as those species which contain more than 0.01% of alkaloids. This is right from the point of view of the classification. From the genetic point of view, and the genetic mechanism of alkaloid synthesis, it is a real limitation. Paying attention to slight traces of alkaloids in plants, we see the members of the plant family which are relatives. They have a genetically determined alkaloid mechanism with a species expression. Moreover, this expression is also on the hybrid level.