10.1 Introduction
A plant may be regarded as a large biosynthetic laboratory not only for the
preparation of primary metabolites but also for a huge number of secondary
metabolites having pharmaceutical importance. Primary metabolite synthesized by
green plant includes glucose prepared by photosynthesis process, citric acid,
phosphoenolpyruvate from glycolysis, acetyl CoA, citric acid, a- keto glutaric acid
as Kreb’s cycle intermediates, erythrose-4-phosphate from pentose phosphate
pathway, amino acids by transaminase enzyme, protein, nucleic acid by de novo
synthesis process, and polysaccharides. The basic roles of primary metabolites are
general growth and physiological development, involvement in respiratory, storage,
and reproductive system. Practically, primary metabolites are identical from lower
to higher plant systems (Seigler 1995; Kokate et al. 2005).
Secondary metabolites biosynthetically produced from primary metabolites are
considered as chemical adaptation due to environmental stresses such as light,
temperature, and different metals but their distribution is mostly limited, generally
restricted to a taxonomical group (Fig. 10.1). A particular family generates a similar
group of phytoconstituents due to the presence of the definite enzymatic system in
those plants. The different biosynthetic processes occurring in plant cells are
dependent on enzymes that act as catalysts for such reactions. As it occurs by the
control of enzyme activity, it is always directed into a specific pathway resulting
formation of a definite phytoconstituent. For example, tropane alkaloids are
obtained from the Solanaceae family, volatile oils from the Umbelliferae family.
The idea of the secondary metabolite was primarily given by Albrecht Kossel, who
got Nobel Prize for physiology or medicine in 1910, for his contribution (Jones
et al. 1953). Later, Czapek described the secondary metabolites as ultimate products
and also regarded as waste products or secretory substances of plant metabolism but
very much essential for all the animals in the World (Bourgaud et al. 2001). These
products are synthesized by nitrogen metabolism, i.e., secondary modification like
deamination as per the opinion of the scientist. The development of analytical
chemistry in the mid of the previous century become easier to recover of more and
more of these phytoconstituents, and ultimately, this was the pillar for the development of the well-known discipline of phytochemistry. Secondary metabolites are
very much expensive to produce, as well as accumulate in the different plant parts
and that is why they are available in much smaller quantities than primary
metabolites. Nowadays, the extraction of a few secondary metabolites has become
costly due to their less availability (Kokate et al. 2005; Bourgaud et al. 2001).
The isotopically labeled markers are used to elucidate the biosynthetic pathways
in plant cells for the manufacturing of numerous plant metabolites. With the help of
radioactive carbon (C
14 ), hydrogen (H
3 ), and in few cases phosphorus (P
32 ), sulphur (S
36 ), the biosynthetic pathways are established and become easy to understand the different chemical steps. The specific information regarding biosynthetic
pathways of alkaloid, proteins, and amino acids was achieved by using labeled
nitrogen atom (N
14 ) (Kokate et al. 2005).
330
C. C. Kandar
A plant may be regarded as a large biosynthetic laboratory not only for the
preparation of primary metabolites but also for a huge number of secondary
metabolites having pharmaceutical importance. Primary metabolite synthesized by
green plant includes glucose prepared by photosynthesis process, citric acid,
phosphoenolpyruvate from glycolysis, acetyl CoA, citric acid, a- keto glutaric acid
as Kreb’s cycle intermediates, erythrose-4-phosphate from pentose phosphate
pathway, amino acids by transaminase enzyme, protein, nucleic acid by de novo
synthesis process, and polysaccharides. The basic roles of primary metabolites are
general growth and physiological development, involvement in respiratory, storage,
and reproductive system. Practically, primary metabolites are identical from lower
to higher plant systems (Seigler 1995; Kokate et al. 2005).
Secondary metabolites biosynthetically produced from primary metabolites are
considered as chemical adaptation due to environmental stresses such as light,
temperature, and different metals but their distribution is mostly limited, generally
restricted to a taxonomical group (Fig. 10.1). A particular family generates a similar
group of phytoconstituents due to the presence of the definite enzymatic system in
those plants. The different biosynthetic processes occurring in plant cells are
dependent on enzymes that act as catalysts for such reactions. As it occurs by the
control of enzyme activity, it is always directed into a specific pathway resulting
formation of a definite phytoconstituent. For example, tropane alkaloids are
obtained from the Solanaceae family, volatile oils from the Umbelliferae family.
The idea of the secondary metabolite was primarily given by Albrecht Kossel, who
got Nobel Prize for physiology or medicine in 1910, for his contribution (Jones
et al. 1953). Later, Czapek described the secondary metabolites as ultimate products
and also regarded as waste products or secretory substances of plant metabolism but
very much essential for all the animals in the World (Bourgaud et al. 2001). These
products are synthesized by nitrogen metabolism, i.e., secondary modification like
deamination as per the opinion of the scientist. The development of analytical
chemistry in the mid of the previous century become easier to recover of more and
more of these phytoconstituents, and ultimately, this was the pillar for the development of the well-known discipline of phytochemistry. Secondary metabolites are
very much expensive to produce, as well as accumulate in the different plant parts
and that is why they are available in much smaller quantities than primary
metabolites. Nowadays, the extraction of a few secondary metabolites has become
costly due to their less availability (Kokate et al. 2005; Bourgaud et al. 2001).
The isotopically labeled markers are used to elucidate the biosynthetic pathways
in plant cells for the manufacturing of numerous plant metabolites. With the help of
radioactive carbon (C
14 ), hydrogen (H
3 ), and in few cases phosphorus (P
32 ), sulphur (S
36 ), the biosynthetic pathways are established and become easy to understand the different chemical steps. The specific information regarding biosynthetic
pathways of alkaloid, proteins, and amino acids was achieved by using labeled
nitrogen atom (N
14 ) (Kokate et al. 2005).
330
C. C. Kandar