2. Biosynthesis
The biosynthetic pathway is greener and more efficient for producing
structurally diverse natural products. This pathway acts as an
alternative to chemical synthesis and microbial transformation, which
suffer from complex routes, difficult isomer separation, and high cost.
Biosynthesis, also known as anabolism, is a simple compound that is
joined together and forms a macromolecule using enzymes. Extreme
reaction conditions and many toxic chemicals are required for the
chemical synthesis of flavonoids [23]. One of the advantages of
biosynthesis is the production of rare and expensive natural products
because of the development of molecular biological tools and
availability of genome information from a variety of organisms.
Biosynthesis can be used in simple and complex transformations without
disturbing the blocking and deblocking steps, which are common in
organic synthesis [24]. The mechanism of the flavonoid biosynthesis
pathway in mulberry leaves is not yet clear, and currently, this is a
much-needed topic for scientists to explore. Flavonoids are synthesized
through the shikimate pathway followed by the phenylpropanoid metabolic
pathway and possess approximately 15 carbon atoms arranged in three
aromatic rings linked as C6-C3-C6 [25]. Several enzymes are involved
in the shikimate pathway, which is a six-step reaction in the
biosynthesis of shikimic acid. The reaction as shown in figure 5 begins
with a simple aldol condensation reaction of phosphoenolpyruvic acid and
D-erythrose 4-phosphate [Dias MC, Pinto DCGA, Silva AMS. (2021) Plant
flavnoids: Chemical Characteristics and Biological Activity. Molecules,
26:5377.]. The end product of chorismic acid is converted into the
amino acid phenylalanine by the action of prephenate-aminotransferase
(PhAT) and aromate-dehydrate (ADT) enzymes [Tariq H, Asif S, Andleeb
A, Hano C, Abbasi BH. (2023) Flavonoid Production: Current trends in
plant metabolic engineering and de novo microbial production.
Metabolites, 13:124.].