Alkaloids are generally classified by their common molec-ular precursors, based on the biological pathway used to construct the molecule. From a structural point of view, alkaloids are divided according to their shapes and origins.....
Drugs Containing Alkaloids
CLASSIFICATION
Alkaloids are generally classified by their common
molec-ular precursors, based on the biological pathway used to construct the
molecule. From a structural point of view, alkaloids are divided according to
their shapes and origins. There are three main types of alkaloids: (1) true
alkaloids, (2) protoalkaloids, and (3) pseudoalkaloids. True alkaloids and
protoalkaloids are derived from amino acids, whereas pseudoalkaloids are not
derived from these compounds.
True 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-histidine. Examples of true alkaloids include such biologically active
alkaloids as cocaine, quinine, dopamine and morphine.
Protoalkaloids
Protoalkaloids are compounds, in which the N atom derived
from an amino acid is not a part of the heterocyclic. Such kinds of alkaloid
include compounds derived from L-ty-rosine and L-tryptophan. Protoalkaloids are
those with a closed ring, being perfect but structurally simple alkaloids. They
form a minority of all alkaloids. Hordenine, mesca-line and yohimbine are good
examples of these kinds of alkaloid. Chini et al. have found new alkaloids,
stachydrine and 4-hydroxystachydrine, derived from Boscia angustifolia, a plant belonging to the Capparidacea family.
These alka-loids 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
Pseudoalkaloids are compounds, the basic carbon skeletons of
which are not derived from amino acids. In reality, pseudoalkaloids are
connected with amino acid pathways. They are derived from the precursors or
post-cursors (derivatives the indegradation process) of amino acids. They can
also result from the amination and transamination reactions of the different
pathways connected with precursors or post-cursors of amino acids.
These alkaloids can also be derived from nonaminoacid
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 trans-amination
reaction, if there is a suitable aldehyde or ketone. Pseudoalkaloids can be
acetate and phenylala-nine derived or terpenoid, as well as steroidal
alkaloids. Examples of pseudoalkaloids include such compounds as coniine, capsaicin,
ephedrine, solanidine, caffeine and theobromine.
Alkaloids are mainly divided into two categories on the
basis of their chemical structure, that is, heterocyclic rings (Table 15.1).
Atypical
alkaloids
These are also known as nonheterocyclic alkaloids and
contain nitrogen in aliphatic chain.
Typical
alkaloids
These are also known as heterocyclic alkaloids and contain
nitrogen in heterocyclic ring system.
Table : Classification of alkaloids
The interrelationship between different ways of
classifications can be summarized by the Table below.
TH 2019 - 2025 pharmacy180.com; Developed by Therithal info.