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64 Herbal Pharmacopeia
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Principles of Drug Discovery
4
from Plants
Sayyeda Sabahat Babar, Zarghoona Jawad,
Fatima Ayub, and Muhammad Imran Khan
Department of Biomedical Sciences, Pak Austria Fachhochschule:
Institute of Applied Sciences and Technology, Haripur, Pakistan
4.1 INTRODUCTION
Plants have played a role in providing substances for many years, contributing greatly to the
advancement of modern medicine [1]. The standing connection between humans and plants has
resulted in the identication of healing compounds that continue to be essential in today’s medical
eld [2]. This section aims to investigate the principals involved in discovering, extracting, and utilizing plant- based compounds for purposes. By combining knowledge of plants with cutting- edge
techniques in photochemistry and biotechnology, we can better tap into the healing properties of
plants [3]. Additionally, this section will explore methods for isolating compounds through testing the impact of metabolomics and genomics on drug development and how nanotechnology can
improve the effectiveness and delivery of plant- derived substances. It will also showcase examples
of medications derived from plants to illustrate both the promise and the obstacles associated with
plant- based drug discovery within today’s pharmaceutical industry.
4.2 HISTORICAL CONTEXT OF PLANT- BASED MEDICINES
4.2.1 E
Throughout history civilizations have relied on plants for medicinal purposes, with local healers harnessing the power of ora to treat a variety of health issues. Ancient records from Egypt, China,
India, and Greece highlight the practice of utilizing plant- based remedies [4]. For example, the Ebers
Papyrus, a manuscript dating back to around 1550 BCE, documents more than 700 plant- derived medicines [5]. Similarly, traditional healing systems like Ayurveda in India and traditional Chinese medicine (TCM) have traditions of employing plants for such purposes. Texts such as the Charaka Samhita
and the Compendium of Materia Medica offer insights into plants and their therapeutic properties [6].
4.2.2 dEvElopmEnt of pharmaCognosy
The scientic study of medicinal plants, known as pharmacognosy, emerged as a formal discipline
in the 19th century. Pioneering work by scientists such as Friedrich Sertürner, who extracted morphine from opium in 1805, marked the beginning of the isolation and characterization of active
compounds from plants [7]. This period saw signicant advancements in extracting and isolating
compounds, laying the groundwork for modern pharmacology.
4.2.3 impaCt of plant- BasEd mEdiCinEs on modErn pharmaCology
Many of the medicines we use today have their origins in plants, showing how plant- based remedies
have greatly inuenced medicine. For example, the active ingredient of aspirin was sourced from
arly UsE and CUltUral signifiCanCE
65
66 Herbal Pharmacopeia
the bark of willow trees, and that of quinine, which was used to treat malaria, comes from the bark
of cinchona trees. These discoveries led to the exploration of plant- derived molecules, which led
in turn to the development of drugs and treatments for various conditions. According to the World
Health Organization (WHO), more than a quarter of medications stem from plants, with many others
being versions of natural compounds [2].
4.3 DIVERSITY AND SIGNIFICANCE OF BIOACTIVE COMPOUNDS
INMODERN PHARMACOLOGY
Plants produce metabolites, such as terpenoids, alkaloids, avonoids, and phenolics. These compounds have a range of effects and can be used for different purposes in nature, such as defending
against infections and herbivores. For example, the alkaloid vincristine, which is taken from the
Madagascar periwinkle, is used to treat cancers while a range of fruits and vegetables contain quercetin known for its anti- inammatory and antioxidant properties [3].
4.3.1 intEgration of EthnoBotaniCal KnowlEdgE
Traditional knowledge about plants, known as ethnobotanical knowledge, is crucial in helping
researchers nd medicinal compounds. By studying how indigenous peoples use plants for healing
purposes scientists can pinpoint plants that show potential for use and give them priority for study
[8]. This approach has led to the discovery of medications such, as paclitaxel, an anti- cancer drug
originally derived from the bark of the Pacic yew tree (Taxus brevifolia) and used in traditional
medicine by Native American tribes [9].
4.3.2 advanCEd phytoChEmiCal tEChniqUEs
Advancements in phytochemistry technology have signicantly enhanced the ability to isolate and
detect compounds from plants. Modern analytical methods such as nuclear magnetic resonance
(NMR) spectroscopy, mass spectrometry (MS), and high- performance liquid chromatography
(HPLC) can accurately analyze complex plant extracts. These techniques simplify the process of
discovering compounds and comprehending their compositions, paving the way for developing new
medications [10].
4.3.3 Bioassay- gUidEd fraCtionation
Bioassay- guided fractionation plays a role in uncovering substances derived from plants. This process entails methodically dividing a plant extract into its parts, examining each part for its biological
effects. Once active components are identied, they undergo purication and examination to isolate
the compounds responsible for the desired results [11]. This ongoing process integrates assessments,
with scrutiny to pinpoint and understand the most effective compounds.
4.3.4 rolE of mEtaBolomiCs and gEnomiCs
The study of metabolomics and genomics presents perspectives on how plants produce metabolites
through metabolic pathways and genetic factors. Metabolomics involves identifying compounds and
studying their creation and regulation within a system while genomics focuses on understanding
the genetic components responsible, in order to generate secondary metabolites. Integrating these
approaches allows researchers to improve the production of substances and gain insights into the
molecular mechanisms that drive plant metabolism [9].
Principles of Drug Discovery from Plants 67
4.3.5 intEgration of nanotEChnology
Nanotechnology presents solutions to enhance the effectiveness and strength of plant- based compounds. By designing nanoparticles to encase these compounds derived from plants, their solubility, stability, and ability to be absorbed by the body can be enhanced. This method can boost the
effectiveness of these compounds. It can facilitate drug delivery, thereby reducing side effects and
improving treatment outcomes [12]. For instance curcumin, a substance found in turmeric (Curcuma
longa), usually has bioavailability; however, when enclosed in nanoparticles its therapeutic benets
are greatly enhanced [13].
4.4 ETHNOBOTANICAL APPROACHES
For generations, the practice of ethnobotany has played a role in uncovering the benets of plantbased substances. Drawing on wisdom and customs, these methods help pinpoint plants that may
offer value. Through documentation and the study of plant usage across societies ethnobotanical
studies lay a solid groundwork, for today’s pharmaceutical research endeavors [14].
4.4.1 traditional KnowlEdgE and indigEnoUs appliCations
Ethnobotany delves into how individuals within a culture utilize plants, forming crucial groundwork for uncovering medicinal compounds. The wealth of wisdom amassed over generations provides insights into the healing properties of plants. Passed down through lines, indigenous practices
involve leveraging plants to address a range of health issues [15]. This accumulated knowledge isn't
just anecdotal; it often stems from observations and real experiences.
One notable illustration of the signicance of knowledge lies, as mentioned in passing above, in
the utilization of the Cinchona tree (Cinchona spp.) by indigenous communities to combat malaria
[16]. This accumulated knowledge isn't just anecdotal; it often stems from observations and real
experiences.
A notable illustration of the signicance of knowledge lies in the utilization of the Cinchona tree
(Cinchona spp.) by indigenous communities to combat malaria. The extraction of quinine its component, proved pivotal in the development of an antimalarial medication. Likewise the rosy periwinkle (Catharanthus roseus), traditionally used in Madagascar’s folk medicine, contributed to the
discovery of vincristine and vinblastine drugs in cancer treatment [17].
The wealth of information possessed by groups regarding plant- based medicine serves as an asset
for contemporary drug exploration. These communities often hold knowledge about biodiversity
and the therapeutic applications of diverse plant species. This expertise is frequently embedded
within traditions, rituals, and traditional healthcare systems—underscoring a bond between community members and their natural surroundings [14].
Studies show that indigenous healers utilize plants not only for their immediate benets but
also taking into account the broader context, such as spiritual and cultural elements of healing.
For example, the use by Native American tribes of Echinacea for treating infections and wounds
integrates both the spiritual aspects and the healing traditions. This comprehensive perspective
can assist researchers in exploring the roles of plant compounds beyond their direct medicinal
impacts [18].
4.4.2 EthnopharmaCologiCal sUrvEys and thEir rElEvanCE
Ethnopharmacological surveys are organized studies that record the wisdom and utilization of healing plants, among cultural communities. These surveys entail thorough on- site research, including
discussions with healers and community members well as the gathering of plant samples for further
examination. They play a role in identifying plants that may have properties and in grasping the
68 Herbal Pharmacopeia
cultural signicance of their usage. One illustrative case demonstrating the impact of surveys is the
unearthing of the inammatory attributes of turmeric (Curcuma longa) in traditional Indian medicine [19]. Research into ethnopharmacology revealed that turmeric was widely used in Ayurveda
due to its inammatory and antioxidant qualities [20]. Subsequent scientic investigations validated
these properties resulting in the application of curcumin, the active component of turmeric, in various therapeutic contexts [13].
Ethnopharmacological surveys act as a link between knowledge and contemporary scientic
exploration. By documenting the application of plants, these surveys aid in conserving wisdom and
serve as a foundation for validating scientically and developing medications. They frequently lead
to the discovery of compounds and therapeutic substances that might otherwise remain undiscovered. For instance, studying the herb Artemisia annua through ethnopharmacology. A herb long
used in medicine to combat fevers led to the discovery of artemisinin. This particular substance has
become an element in combating malaria, thereby showcasing the promise of studying traditional
medicinal practices [21].
4.5 PHYTOCHEMICAL TECHNIQUES
4.5.1 mEthods of plant ExtraCtion and isolation
The extraction and retrieval of bioactive compounds from plants are fundamental steps in phytochemical research, providing the initial materials for further analysis and development. Various
methods have evolved to efciently isolate these compounds, each with its own advantages and
limitations (Figure 4.1).
4.5.1.1 Solvent Extraction
One of the methods employed for creating plant extracts is through solvent extraction. This process
involves dissolving the phytochemicals using solvents such as ethanol, methanol, hexane, or chloroform [23]. The choice of solvent is inuenced by the polarity of the target molecules. For instance
polar solvents such as ethanol and methanol are typically used to extract chemicals like avonoids
and phenolics while non- polar solvents such as hexane are preferable for extracting compounds
such as terpenoids and essential oils. Percolation, maceration and soxhlet extraction are among the
techniques employed in this type of extraction process [24].
4.5.1.2 Supercritical Fluid Extraction (SFE)
Supercritical uid extraction (SFE) is a technique that utilizes uids, with carbon dioxide (CO2)
being a prominent choice as the extracting agent. When subjected to pressures and temperatures
beyond its critical point (31.1°C and 73.8 bar), CO2 transforms into a state displaying unique properties of both liquid and gas that set it apart from traditional liquids and gases.
This approach is known for its efciency, eco friendliness and effectiveness in extracting compounds without causing degradation. The safe nature of CO2 and its ability to target compounds
through temperature and pressure adjustments have established SFE as a preferred method for
extracting phytochemicals [25].
4.5.1.3 Microwave- Assisted Extraction (MAE)
By using microwave energy to heat up the solvent and plant material, microwave- assisted extraction
(MAE) enhances the efciency of extracting bioactive components. This method offers advantages,
including extraction times, reduced solvent usage, and increased yields and quality of extracts [26].
The heating and uniform energy distribution from microwaves facilitates the breakdown of plant cell
walls allowing for the penetration of solvents and the release of intracellular chemicals. The application of MAE has shown success in extracting stable compounds such as polyphenols, alkaloids, and
essential oils [27].
Principles of Drug Discovery from Plants 69
FIGURE 4.1 Methods of plant extraction and isolation.
4.5.1.4 Ultrasound- Assisted Extraction (UAE)
Ultrasound- assisted extraction (UAE) involves using waves to create cavitation in the solvent, which
helps break down plant cell walls and facilitates the transfer of phytochemicals into the solvent. This
method is recognized for its simplicity, cost- effectiveness, and ability to function at room temperature, making it ideal for extracting heat compounds [28]. UAE has proven effective in extracting
phytochemicals such as avonoids, terpenoids, and glycosides, resulting in extraction efciency and
higher yields compared to traditional methods [28].
4.5.1.5 Enzyme- Assisted Extraction (EAE)
Enzyme- assisted extraction (EAE) uses specic enzymes to hydrolyze plant cell walls, thereby
facilitating the delivery of bioactive compounds. Enzymes such as cellulase, pectinase, and hemicellulase break down the structural polysaccharides in plant cell walls, increasing the permeability and
solubility of the target compounds [29]. EAE is considered to be a ‘green’ extraction method due to
its mild operating conditions and the reduced use of harsh solvents. This technique is particularly
effective for extracting polysaccharides, saponins, and other complex macromolecules [30].
70 Herbal Pharmacopeia
4.6 BIOASSAY- GUIDED FRACTIONATION
One systematic approach to isolating and characterizing compounds from plant extracts involves the
use of bioassay- guided fractionation. This method entails dividing the extract into fractions, evaluating
each fraction for its effects and further rening the fractions to obtain pure bioactive substances [31].
4.6.1 fraCtionation tEChniqUEs
Plant extracts are initially separated using techniques such as liquid–liquid extraction, solid phase
extraction, or column chromatography. These methods divide the extract into parts based on variations
in polarity, solubility, or molecular size [32]. Liquid–liquid extraction involves dividing the extract
between two solvents; by contrast, solid phase extraction uses an adsorbent to selectively retain specic compounds. Column chromatography, which includes methods like silica gel chromatography
and Sephadex LH 20, sorts compounds according to their interactions with the mobile phases [33].
4.6.2 BiologiCal assays
The effectiveness of each portion is evaluated through a variety of tests, which can range from lab
tests, animal studies to the use of tissues or organs. Lab tests, like cell cultures or enzyme inhibition,
are commonly preferred for their simplicity and cost- effectiveness. Animal studies are conducted to
assess the effects and toxicity of the fractions [34]. Ex vivo tests involve the use of tissues or organs
to study the compounds’ biological activity in a natural setting. The choice of test depends on the
intended purpose and the specic type of effect being studied, such as antimicrobial, anticancer, or
anti- inammatory properties [35].
4.6.3 itErativE pUrifiCation
After determining fractions through bioassay testing they are puried using chromatographic methods, such as high- performance liquid chromatography (HPLC) or preparative thin layer chromatography (TLC). HPLC stands out for its clarity, sensitivity, and capacity to manage mixtures. The goal
of each fractionation and bioassay stage is to extract the substances in their most rened state while
considering their bioactivity retention [36].
4.7 CHROMATOGRAPHIC AND SPECTROSCOPIC METHODS FOR
COMPOUND IDENTIFICATION
Once bioactive compounds are isolated, their identication and structural elucidation are critical
steps in phytochemical research. Chromatographic and spectroscopic methods are essential tools
for this purpose [32].
4.7.1 high- pErformanCE liqUid Chromatography (hplC)
High- performance liquid chromatography (HPLC) is a method used for analyzing and distinguishing molecules in a mixture [37]. In this process, a column lled with a phase lters the plant extract
while a liquid mobile phase carries the sample through the column. The separation of compounds
occurs due to factors such as size and polarity inuenced by how the stationary phase interacts with
the chemicals in the sample [38].
4.7.2 gas Chromatography- mass spECtromEtry (gC- ms)
The method of gas chromatography- mass spectrometry (GC- MS) combines the detection and identication capabilities of mass spectrometry, with the separation abilities of gas chromatography.
Principles of Drug Discovery from Plants 71
This technique is particularly effective for analyzing semi- volatile substances [39]. By utilizing a
column and an inert gas to transport the vaporized sample, GC- MS separates components based
on their volatility and interactions with the columns phase. After the compounds are separated, the
mass spectrometer breaks them down to generate a mass spectrum containing structural and molecular weight information. GC- MS is commonly used for analyzing phytochemicals, such as terpenoids
and essential oils [40].
4.7.3 nUClEar magnEtiC rEsonanCE (nmr) spECtrosCopy
Nuclear magnetic resonance (NMR) spectroscopy, an invasive analytical technique, offers detailed
insights into the dynamics, environment, and structure of molecules [41]. By utilizing radiofrequency radiation and a powerful magnetic eld to interact with nuclei, NMR spectroscopy generates resonance signals for deciphering molecule structures. The used ^1H NMR and ^13C NMR
techniques reveal information about hydrogen and carbon atoms. This method plays a role in determining the structure of complex phytochemicals, including stereochemistry and functional group
identication.
4.7.4 foUriEr transform infrarEd (ftir) spECtrosCopy
Fourier transform infrared (FTIR) spectroscopy is utilized to detect groups and describe structures by analyzing their vibrational changes. When a molecule absorbs infrared light it experiences
excitement, leading to an IR spectrum that showcases its molecular characteristics [42]. FTIR spectroscopy is commonly employed for recognizing groups, like hydroxyl, carbonyl, and amine groups,
in plant compounds. This method is frequently combined with techniques to verify particular functional groups and offer additional structural insights.
4.7.5 mEtaBolomiCs and gEnomiCs in plant drUg disCovEry
The emergence of metabolomics and genomics has brought about a transformation in the realm of
plant- based drug exploration. These innovative techniques offer in- depth understandings into the
metabolic and genetic structures of plants, facilitating the detection and improvement of substances.
In the next section we delve into the functions of metabolomics and genomics in pinpointing compounds the genetic strategies employed to uncover and amplify phytochemicals as well as realworld examples showcasing the utilization of genetic technologies, in drug discovery [43].
4.8 ROLE OF METABOLOMICS IN IDENTIFYING BIOACTIVE COMPOUNDS
Metabolomics involves examining the metabolites in a biological system, thereby providing an overview of the organism’s metabolic condition. In the realm of plant- based drug exploration, metabolomics plays a role in pinpointing substances uncovering how they are produced and grasping their
signicance in plant function and environmental interactions (Figure 4.2).
4.8.1 idEntifiCation of BioaCtivE CompoUnds
At rst, we extract substances from plants, and separate and analyze them using methods like gas
chromatography mass spectrometry (GC- MS), liquid chromatography mass spectrometry (LCMS), and nuclear magnetic resonance (NMR) spectroscopy. These techniques help us recognize
and quantify substances, both additional ones that could potentially offer medicinal benets [44].
When scientists analyze the compositions of plants grown in environments or with different
genetic makeups they can pinpoint certain substances linked to their health benets. For example,
research has revealed that studying the metabolites of healing plants such as Catharanthus roseus
72 Herbal Pharmacopeia
FIGURE 4.2 Role of metabolomics and genomics in plant drug discovery.
has uncovered vinca alkaloids, which play a role in their ability to combat cancer. Furthermore,
delving into metabolomics can shed light on how these substances work, thereby offering information on their medical uses [45].
4.8.2 Explanation of BiosynthEtiC pathways
Studying how bioactive compounds are produced and improved requires an understanding of their
pathways. Metabolomics, conjugating with omics techniques, helps in mapping out these pathways.
For instance the process of creating taxol, a substance with anticancer properties found in the Pacic
yew tree (Taxus brevifolia) has been extensively researched using metabolomics. This method has
unveiled the web of enzymes and substances that play a role in taxol production, making it easier
to develop approaches to boost its output [46]. The identication and explanation of plant genomes
through advancements in technologies have uncovered the genes responsible for producing bioactive substances [47].
4.8.3 disCovEry of BiosynthEtiC gEnEs
Detecting the biosynthetic gene clusters (BGCs) plays a role in the creation of metabolites through
genome- based approaches. These clusters contain genes that produce enzymes for guiding the stages
of biosynthesis. Through methods like association studies (GWAS) and Mapping Quantitative Trait
Loci (QTL) Mapping scientists can associate particular genes with the generation of bioactive substances [48]. For example, determining the gene cluster in Artemisia annua has been crucial for
genetically modifying the plant to produce the chemical [49].
Principles of Drug Discovery from Plants 73
4.8.4 EnhanCEmEnt of phytoChEmiCal prodUCtion
Genetic tools also play a role in boosting the production of plant chemicals through methods such as
metabolic engineering and biology. Researchers can enhance the output of compounds by amplifying biosynthetic genes or introducing new pathways [50]. For example, boosting the activity of the
gene for diphosphate synthase in tomato plants has resulted in higher levels of carotenoids, which
are known for their antioxidant properties [51]. Furthermore, scientists have utilized synthetic biology techniques to recreate pathways in microbial hosts, allowing for the efcient production of
plant- based compounds, on a larger scale [2].
4.9 CASE STUDIES OF GENOMIC APPLICATIONS IN DRUG DISCOVERY
4.9.1 CasE stUdy 1: artEmisinin prodUCtion in ArtemisiA AnnuA
Artemisinin, a compound used to combat malaria which is extracted from the Artemisia annua plant,
showcases how genomics has played a role in discovering drugs. By studying the composition of
Artemisia annua, scientists have been able to modify the plants genes to increase production. This
was achieved by boosting the activity of enzymes like amorpha 4,11 diene synthase in the pathway.
4.9.2 CasE stUdy 2: taxol BiosynthEsis in tAxus spp.
Taxol, a cancer medication, is naturally found in the Pacic yew tree (Taxus brevifolia). Through
research, scientists have identied the gene clusters responsible for Taxol production and the intricate enzymatic processes involved. Through genetic manipulation techniques, these genes have been
transferred into plants and microorganisms to enhance Taxol production. For instance, by introducing taxadiene synthase into Escherichia coli bacteria researchers have successfully generated precursors of Taxol without relying on its extraction from yew trees [52].
4.9.3 CasE stUdy 3: rEsvEratrol prodUCtion in vitis vinifEra
Resveratrol, a compound found in grapes, has been linked to health benets such as protecting the
heart and reducing inammation. Scientists can now boost resveratrol production in grapevine cell
cultures through modications following the discovery of the genes, thereby achieving resveratrol
synthesis. By enhancing the expression of the gene that produces synthase researchers have successfully raised the resveratrol levels in grapevine tissues, showcasing how genomics can enhance the
yield of plant compounds [54].
4.10 BIOTECHNOLOGICAL ADVANCES
The use of methods has completely transformed the realm of discovering plant- based medicines
allowing for the production and increased effectiveness of natural compounds. This section delves
into the progress in biotechnology that has shaped this eld, highlighting advancements in tissue
culture, the modication of sustainable production practices through biotechnology, and the impact
of synthetic biology on developing plant- based medications.
4.10.1 tissUE CUltUrE and thE gEnEtiC modifiCation of mEdiCinal plants
Tissue culture and genetic modication also play a role as tools in the arsenal of biotechnology for
improving the cultivation of plants. Tissue culture, also known as in vitro culture, involves growing
plant cells, tissues, or organs on a medium under sterile conditions. This technique eliminates the
need for farming methods by facilitating plant growth and phytochemical production [55].