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Page 2 of 50 Siddiqui et al. Chem Synth 2023;3:25 https://dx.doi.org/10.20517/cs.2023.02

BIOTRANSFORMATION- AN EFFICIENT GREEN CHEMISTRY APPROACH
Biotransformation techniques are among the most efficient approaches for structural transformation of
various classes of organic compounds. These techniques involve the use of low-cost, eco-friendly, and non-
toxic biocatalysts. They are normally conducted under ambient reaction conditions and involve oxidation,
dehydrogenation, chlorination, reduction, aromatization, methylation, demethylation, rearrangements, etc.
Biotransformation procedures can also reduce the total number of reaction steps towards the desired
products. They do not require the use of toxic chemicals and harsh conditions that may otherwise be
necessary for the functional group activation, protection, and deprotection steps, resulting in less
production of wastes as compared to the desired products. These techniques have effectively been employed
in drug discovery and development, affording libraries of compounds around core structures. These
libraries are then evaluated for various biological activities in the drug discovery phase. The most significant
aspect of biocatalytic transformations is the conservation of the original carbon skeleton of the starting
material after transformation [1-10] .

Biotransformation techniques are catalyzed by various biological systems, such as actinomycetes, algae,
fungi, bacteria, yeasts, and plants and animals cell cultures, as well as by pure enzymes, affording
compounds with high stereo-, regio-, and chemo-selectivity. They may be applied on potentially important
scaffolds for the design, discovery, and development of new bioactive multi-functional compounds,
including pharmaceuticals. Fungi have been widely used in whole-cell biocatalysis of organic compounds
due to the presence of cytochrome P450 systems. In addition, fungi have higher metabolic and
multiplication rates, thus serving as an excellent source for whole-cell biocatalysis. Pure enzyme-catalyzed
biotransformation reactions often produce single and specific metabolites. Biotransformation reactions with
whole colonies of microorganisms or plant/animal cell cultures may, however, produce more than one
metabolite due to the involvement of a range of enzymes. Whole-cell biocatalysts are cost-effective, easy to
handle, and usually stable in the long term. Moreover, biotransformation reactions by whole-cell colonies
do not require co-factors [11-20] .

BIOTRANSFORMATION STUDIES ON BIOACTIVE COMPOUNDS
Bioactive compounds are extra-nutritional constituents that usually occur in small quantities in plants/
foods. They have been extensively evaluated for their effects on human health. These bioactive compounds
have diverse structures and distributions in nature. At present, several bioactive compounds have been
derivatized through bio-catalysis with applications in the field of medicine. Bio-catalytic transformation of
bioactive compounds has emerged as a frontier field of chemical sciences that is being extensively employed
in numerous other fields. Several natural products, e.g., monoterpenes, sesquiterpenes, diterpenes,
sesterterpenes, triterpenes, anabolic, contraceptive, and anti-cancer steroids, steroidal alkaloids, and
flavonoids, as well as other bioactive compounds of synthetic origin, have been structurally transformed
using biocatalytic approaches in our laboratories since 1997. In the present review, we have compiled the
results of these biotransformation studies.

For the biotransformation studies, media was prepared by mixing specific media ingredients, transferred
into flasks, cotton plugged, autoclaved, inoculated with microbial/plant cell cultures under sterilized
conditions, and placed on a rotary shaker (2-4 days). After the maximum growth of microbial/plant cell
cultures, substrates/drugs were dissolved in water-miscible solvents, such as methanol, DMSO, and acetone,
and fed in flasks containing microbial/plant cell cultures. The material was placed again on a rotary shaker
for 2 to 15 days. Oxidation, reduction, dehydrogenation, chlorination, aromatization, methylation,
demethylation, and rearrangements were the main reactions observed during the biotransformation studies.
The reaction was terminated by adding water-immiscible solvents, such as dichloromethane (DCM) or ethyl