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a mixture is manipulated to carry out their purication. This involves heating the
mixture of liquid. The vapors formed move upward in a glass tube known as the
fractionation column. Fractional distillation is preferred over simple distillation
because glass beads present in the fractionation column provide a site for vapors
to condense, re-evaporate and re-condense, allowing the distillation of compounds
multiple times. The vapors will eventually reach the condenser where they liquefy
and are gathered in a collection vessel (Velmurugan et al, 2018).
NeuroPhytomedicine
3.4.3 frActionAl crystAllizAtion
Fractional crystallization brings about the purication of compounds based on differences in solubility. Fractionation is done via differences in their crystallization
properties. If a mixture is allowed to crystallize by decreasing the temperature of the
solution, the major portion of resulting precipitates will contain substances with low
solubility. The value of solubility products will govern the proportion of components.
For compounds with very similar solubility products, a cascade operation will be
required to achieve complete separation. A large number of compounds exist in the
form of crystals in plants. Their separation is actualized by the formation of crystals
that occur during the process of concentration of a given extract via refrigeration or
heating (Beulah et al, 2022).
3.4.4 frActionAl liBerAtion
This method is used for the isolation of compounds that can form precipitates in the
mixture. Precipitate formation usually occurs upon a change of compound in salt.
For instance, when a mixture of alkaloid salts in an aqueous solution is allowed to
react with an alkali, it will progressively release bases in ascending order of alkalinity. The same principle is applied to the separation of organic acids that could dissolve in water-immiscible solvents. Separation of acids from the mixture is done via
the addition of mineral acids. This technique is usually employed for the separation
of cinnamon alkaloids (Gil-Martín et al, 2022).
3.4.5 suBlimAtion
The change of a substance directly from a solid to a gaseous state without passing
through the central liquid phase is known as sublimation. Material such as volatile
oils and camphor can convert directly into gas upon heating. A deposition is the
reverse process of sublimation that involves a transition directly from the gas phase to
the solid phase (Kovačević et al, 2018).
3.4.6 chromAtogrAPhic techniques
Chromatography involves the isolation of compounds from a mixture based on their
shape, size, and charge. It involves the use of two phases. One employs the use of
solvent of extraction also known as the mobile phase and the other one is the stationary phase that contains substances like Sephadex blended with calcium sulfate as
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a binder and silica gel. Sephadex is used for the purication of proteins and amino
acids. Silica gel is utilized for the purication of sugars, fatty acids, lipids, alkaloids, amino acids, and proteins. Aluminum is applied for the separation of phenols,
steroids, alkaloids, lipids, and fatty acids. Celite for the separation of steroids and
organic cations and cellulose powder for phenols, alkaloids, steroids, amino acids,
and food dyes. Numerous mechanisms are utilized for the separation of compounds
using chromatographic techniques such as ion exchange, adsorption, partition, afnity, and size exclusion. Given below is a detailed description of each of these mechanisms (Yasmeen et al, 2018).
3.4.6.1 Adsorption Chromatography
In this technique interaction between the compounds targeted for separation is
manipulated. The stationary phase pulls compounds via non-covalent Van der Waal
forces and hydrophobic interactions. The weakly bonded compounds will be eluted
by the mobile phase at rst and so on (Lavenburg et al, 2021).
3.4.6.2 Partition Chromatography
Partition chromatography involves the separation of compounds by adding two or
more immiscible solvents into the mixture. Each of the constituents of the mixture
will separate by dissolving in the solvent of relatable polarity. Afterward, individual
compounds are obtained by separating the immiscible solvent via a separating funnel (Guntur et al, 2018).
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3.4.6.3 Afnity Chromatography (AC)
Separation of biomolecules from a mixture using AC is done based on macromolecular binding between compounds. The stationary phase comprises a ligand and
is placed in a separating column. Compounds with no afnity toward the stationary
phase will be washed down by the mobile phase. Likewise, compounds with high
afnity for the stationary phase will be attracted toward it and thus separated (Alara
et al, 2018).
3.4.6.4 Ion Exchange Chromatography
Ion exchange chromatography is preferred for the separation of polar compounds
based on the kind of charge they possess. As the principle goes; “Like attracts like.”
Similar to other types of column-based liquid chromatography techniques, ionexchange chromatography, which is specically intended for the separation of differently charged or ionizable chemicals, consists of mobile and stationary phases.
The combination to be resolved is placed into an aqueous buffer system in the
mobile phase. The stationary phase is typically a chemically derivate of an inert
organic matrix with ionizable functional groups (xed ions) that can displace an
opposing charged ion. Counter ions are ions that are in equilibrium between the
stationary and mobile phases, giving birth to the two alternative formats of anion
and cation exchange. Protons (H+), hydroxide groups (OH−), single-charged monoatomic ions (Na+, K+, Cl−), double-charged monoatomic ions (Ca2+, Mg2+), polyatomicinorganic ions (SO42−, PO43−), as well as organic bases (NR2H+) and acids,
are examples of exchangeable matrix counter ions (COO−). On a column made of
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cation-exchange resin, cations are separated from the anion. According to variations
in their net surface charge, separation is based on the binding of analytes to positively or negatively charged groups that are immobilized on a stationary phase and
that are in equilibrium with free counter ions in the mobile phase.
3.4.6.5 Size Exclusion Cchromatography
The chromatographic technique known as size-exclusion chromatography (SEC),
also referred to as molecular sieve chromatography (MSC), separates molecules
in solution based on their size and, in some situations, molecular weight. Proteins
and commercial polymers are typical examples of big molecules or macromolecular
complexes to which it is typically applied. The method is typically referred to as
gel-ltration chromatography when an aqueous solution is used to move the sample through the column, as opposed to the name gel permeation chromatography,
which is used when an organic solvent is employed as a mobile phase. Fine, porous
beads that are frequently made of dextran, agarose, or polyacrylamide polymers are
crammed into the chromatography column. The separation of compounds on the
base of their size is actualized by using a mesh of different diameters. Separation is
done in ascending order, that is, smaller size molecules are separated at rst followed
by the separation of medium and larger ones (Altemimi et al, 2017). The advantages of this procedure include maintaining the biological activity of the particles
to separate while providing effective separation of large molecules from small molecules with a small volume of eluate and the ability to use different solutions without
interfering with the ltration process. The method is typically used in conjunction
with others that further categorize molecules according to traits like charge, acidity,
basicity, and afnity for particular chemicals. Since solutes don’t interact with the
stationary phase, there is also no sample loss.
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3.4.7 tyPes of chromAtogrAPhy
3.4.7.1 Paper Chromatography (PC)
PC operates based on the mechanism of adsorption chromatography. The apparatus
constitutes a stationary phase that comprises a lter paper synthesized from cellulose and a glass chamber. The lter paper is hooked to the top and suspended in
the glass chamber. The mixture is spotted at the bottom of the lter paper. This is
followed by the addition of solvent in the container which will act as a mobile phase.
The solvent will begin to travel upward; separation will occur during the upward
movement of the solvent via capillary action. Soluble compounds will dissolve in
the solvent and attach to lter paper according to their solubility. The speed of separation is governed by the type of lter paper used. Traveling of mobile phase and
separation is faster with thick lter paper while it becomes quite slow with porous
lter paper. Identication of the isolated compound is done by determining the
retardation factor, which is calculated by taking the ratio of the distance traversed
by the compound to the distance traversed by the solvent. The main benet of this
technique lies in its cost-effectiveness, simplicity, and sensitivity to a quite small
quantity of substances. Because of the fragility of lter paper which makes it prone
to destruction by chemicals, long operation time, and difculty in identication
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and quantication, this technique is not used as frequently as before (Kumar and
Khanum, 2012).
3.4.7.2 Thin-Layer Chromatography (TLC)
This purication technique also operates based on an adsorption mechanism.
Separation is done on the base of the interaction between the stationary phase and
compounds in the mixture. It is employed for the isolation of low-molecular-weight
compounds. The stationary phase comprises a slurry made by mixing 100 g of silica
gel with distilled water. However, Sephadex is also used in certain cases. The slurry
is transferred to a glass plate with a dimension of 20 cm × 20 cm. It is then allowed
to solidify at 105°C for 1 hour. This is followed by an injection of 10 ml of extract at
the bottom of the plate. The plate is then transferred to a solvent separation chamber
and kept for 30 minutes. The compounds in the mixture will travel upward at different rates depending on their solubility. Identication of each segregated compound
will be done by calculation of the retardation factor. The isolated compounds are
scrapped using a spatula and re-extracted using numerous solvents. The benets of
using TLC include less operation time, stability to acids as solvents, and production
of clear spots (Ghotekar et al, 2020).
3.4.7.3 Column Chromatography (CC)
CC is based upon several mechanisms such as molecular sieve, ion exchange, and
adsorption chromatography. The column is composed of a long glass tube with an
average length of 5 cm–1 m and a diameter of 5–50 mm. The bottom is lined witha
lter made of tap and glass wool. Furthermore, Sephadex, cellulose, alumina, and
silica gel act as stationary phases, and the mobile phase constitutes a solvent. A total
of 30 g of silica gel is packed into a translucent glass column such that no air bubbles
are formed. Afterward, the extract is poured into the column from the top. Solvents
were added to increase polarity, starting from n-hexane to chloroform, ethyl acetate,
n-butanol, and methanol. Fractions of each of these solvents were gathered at different periods and then characterized (Tsao and Deng, 2004).
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3.4.7.4 Gas Chromatography (GC)
As the name suggests, the mobile phase in GC is a carrier gas that is used to carry
out the separation. Ideally, the carrier gas does not interact with the sample or harm
the instrument’s parts while it moves the sample molecules through the GC system.
A syringe or transfer from an auto-sampler that can also extract the chemical components from solid or liquid sample matrices is used to rst deliver the sample into the
GC. A septum that allows for the injection of the sample mixture without losing the
mobile phase is used to introduce the sample into the GC inlet. GC involves the use of
two immiscible solvents: The mobile phase in gaseous form and the stationary phase
comprising a liquid absorbed on the surface of an inert solvent. Compounds will dissolve in their respective phases according to their solubilities. The analytical column,
a long (10–150 m), thin (0.1–0.53 mm internal diameter), fused silica or metal tube
connected to the intake, holds the stationary phase coated on the interior walls. It is
also connected to the inlet. The column oven in which the analytical column is kept
is heated throughout the analysis to elute the less volatile components. The detector,
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which responds to the chemical components eluting from the column by producing a
signal, is put into the column outlet. To create a chromatogram, the acquisition software on a computer records the signal. This procedure is often used for the purication of plant material contaminated with volatile pesticides and is often employed in
quality control testing. Regardless of sensitivity and high resolution, the use of GC is
limited because the majority of plant compounds have low volatility. Moreover, it is
difcult to apply for large-scale purication (Guntur et al, 2018).
3.4.7.5 HPLC
High-pressure pumps are used in HPLC, a type of column chromatography, to
move a sample mixture or analyte through a column with chromatographic packing
material (stationary phase). A helium or nitrogen-moving carrier gas stream carries
the sample. Compounds that are present in any sample that may dissolve in a liquid
at trace amounts as low as parts per trillion can be separated and identied using
HPLC. Because of its adaptability, HPLC is utilized in a wide range of scientic,
industrial, and medicinal elds, including forensics, the environment, and pharmaceuticals. This technique operates on the principle of adsorption and is appropriate
for the separation of organic as well as inorganic compounds. The mobile phase
employs the use of a solvent whereas the stationary phase is solid. Separation is
actualized via interaction between particles of solid phase and mixture. The process
commences with the application of a mixture at the bottom of HPLC, followed by the
addition of solvent. The tap is then opened, allowing downward movement of solvent
which is pushed via a pressure pump, thus mixing it with the mixture. Finally, the
mixture travels to the diode detector, waste is removed, compounds are separated,
and the rened content is transferred to further processing units (Jakovljević et al,
2020). The interaction between the stationary phase, the molecules being examined,
and the solvent or solvents utilized will affect sample retention time. Due to the
different polarity of the analytes, the sample interacts between the two phases as it
moves through the column at a different rate. Analytes that interact with the stationary phase less frequently or more frequently with the mobile phase will leave the
column more quickly.
3.5 IDENTIFICATION OF PHYTOCHEMICALS
Techniques used for the identication of phytochemicals are based upon the detection of carbon and hydrogen conguration, identication of functional groups, and
multiple bonds and rings present. These spectroscopic techniques provide sufcient
information for quantitative as well as qualitative analysis of phytochemicals. These
techniques are founded upon the principle that an organic molecule upon interaction
with electromagnetic radiation absorbs waves of precise frequency according to its
structure as a result of which a spectrum is formed. These spectrums are peculiar for
functional groups, based on which the complete structure is laid out. Usually, spectra
are formed in three or four regions, UV, infrared (IR), visible, radio frequency, and
the electron beam employed. Nuclear magnetic resonance spectroscopy (NMR), IR,
UV, and mass spectroscopy (MS) are some of the most commonly used spectroscopic techniques (Eswaraiah et al, 2020) (Figure 3.3).
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FIGURE 3.3 List of techniques used for the identication of phytochemicals.
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3.5.1 uv–visiBle sPectroscoPy
In the UV and the adjacent, adjoining visible region of the electromagnetic spectrum, absorption spectroscopy or reectance spectroscopy is referred to as UV spectroscopy or UV-visible spectrophotometry (UV–Vis or UV/Vis). This methodology
is frequently employed in a variety of practical and theoretical applications since it
is reasonably affordable and simple to execute. The sample must only be a chromophore and absorb in the UV-visible range. Fluorescence spectroscopy is enhanced
by absorption spectroscopy. Aside from the measurement wavelength, variables of
importance include absorbance (A), transmittance (%T), and reectance (%R), as
well as how they change over time. Identication of compounds both in the mixture
and pure form can be done via UV-visible spectroscopy. It is preferably used for
quantitative analysis as aromatic molecules are powerful chromophores in the UV
range. Identication of numerous phytochemicals is carried out using this method
via maximum absorption (λ
phenolic acids (360 nm), anthocyanins (520 nm), avones (320 nm), and phenolic
extract (280 nm). However, this technique is less discriminatory and gives information about overall phenolic content. Observation by the mean of UV-visible spectroscopy takes very little time and is very cost-effective as well (Guntur et al, 2018).
An HPLC detector is a UV/Vis spectrophotometer. When an analyte is present, a
response that is thought to be proportional to concentration occurs. Similar to the use
of calibration curves, the instrument’s reaction to the analyte in the unknown should
be compared with the response to a standard for correct results. The term “response
factor” refers to the response (for example, peak height) for a specic concentration.
To identify the functional groups contained within a specic molecule, it is useful to
link the wavelengths of absorption peaks with the different types of bonds present
in that molecule. The Woodward–Fieser rules, for instance, are a set of empirical
) values of their respective features, for instance,
max
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observations used to predict λ
, the wavelength of the most intense UV/Vis absorp-
max
tion, for conjugated organic compounds such as dienes and ketones. However, the
spectrum by itself does not serve as a precise diagnostic for any particular sample.
The absorption spectrum can be affected by the kind of solvent, the pH of the solution, temperature, high electrolyte concentrations, and the presence of interfering
compounds. The spectrum will also be affected by experimental changes like the
spectrophotometer’s effective bandwidth (slit width). To identify the compounds
present, these variables must be regulated or taken into account when using UV/Vis
spectroscopy for examination (Guntur et al, 2018).
3.5.2 infrAreD (ir) sPectroscoPy
IR spectroscopy, also known as vibrational spectroscopy, aims to identify a number
of bonds and the functional group present in a given compound. This helps in the
elucidation of the physical and chemical properties of the compounds. The organic
compound is allowed to pass through IR radiations where it is absorbed at a particular frequency. It detects the changes in vibration produced upon elongation and bending of the molecules upon interaction with the IR range of electromagnetic radiation.
Various chemical bonds and functional groups have a characteristic vibrational
frequency governed by the values of force constant (bond strength) and decreased
mass. Therefore, analysis of the frequency absorption band on the IR spectrum of the
respective functional group can be manipulated to determine the structure of a bioactive compound. Identication of solid samples is done by milling with potassium
bromide and compressing it into a thin pellet whereas that of liquid samples is done
using sodium chloride plates. An even high-resolution of constituent chemicals and
elucidation of molecular structure can be performed using Fourier transform infrared spectroscopy (FTIR) (Guntur et al, 2018).
3.5.3 nucleAr mAgnetic resonAnce sPectroscoPy (nmr)
Identication using NMR is done by elucidating physical properties such as the
arrangement of atoms and molecules in a compound, the total count and array of
carbon atoms, and the identication of isotopes of hydrogen, carbon, and protons.
Magnetic properties of certain nuclei, for instance, 19F, 1H, 13C, and 31P can be
determined using NMR. Interaction of magnetically active nuclei with the radio
frequency range of electromagnetic radiations generates a signal with a frequency
similar to the one that will be produced upon application of an external magnetic
eld resonance will be produced upon equivalence of oscillation frequency with
intrinsic frequency. Its measurement is commonly done in terms of chemical shift,
governed by the chemical environment, magnetic properties of nuclei, and power of
the applied magnetic eld (Tsao and Deng, 2004). NMR is a tool used by biochemists to identify complicated compounds such as proteins. NMR spectroscopy offers
comprehensive details about the structure, dynamics, reaction state, and chemical
environment of molecules in addition to molecular identication. Proton and carbon-13 NMR spectroscopy are the two most popular types of NMR, but they can
be used with any sample that has nuclei with spin. For minuscule compounds, NMR
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spectra are distinctive, sharp, analytically manageable, and frequently very predictable. Different functional groups can be easily distinguished from one another and
signals can still be distinguished between identical functional groups with different adjacent substituents. NMR has essentially taken the place of conventional wet
chemistry tests for identication like color reagents or usual chromatography. The
requirement of a relatively signicant dose of a puried drug, ranging from 2 to
50 mg, notwithstanding the possibility of recovery through a workup, is a drawback. The sample should ideally be dissolved in a solvent because solids cannot be
analyzed by NMR without spinning equipment, which may result in less accurately
resolved spectra. NMR produces only an averaged spectrum because its timeframe
is relatively long, making it unsuitable for viewing rapid processes. Although signicant levels of contaminants do appear on an NMR spectrum, better methods for
identifying impurities already exist because NMR is intrinsically not very sensitive,
though sensitivity increases at higher frequencies (Tsao and Deng, 2004).
3.5.4 mAss sPectroscoPy (ms)
MS is used for the detection of compounds based on their molecular weight and
chemical structure. Substances like oligonucleotides and peptides are usually identied. It involves the conversion of organic molecules into highly energized charged
species by bombarding them either with lasers or electrons. The electron ionization
energy of 70 eV was rst used to detect the signal. Moreover, the percentage peak
of sample spectra is detected and recorded. A mass spectrum is a graph of the mass/
charge ratio of ions against the relative abundance of fragmented ions. The relative
molecular mass of detached ions along with the site of detachment can be determined which can be further utilized for the prediction of the molecular formula of
bioactive compound. Henceforth, MS provides sufcient information required for
structure determination. MS coupled with electrospray ionization (for producing
charged species from macromolecules) has been proven to be a very efcient tool for
the structural elucidation of phenolic compounds. MS provides plenty of information
about organic molecules and is a preferred procedure for the identication of medicinal plant constituents, especially when coupled with HPLC (Beulah et al, 2022).
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4
Effect of Alkaloids and
Synthetic Derivatives
Likhit Akotkar, Aditya Ganeshpurkar,
and Ankit Ganeshpurkar
4.1 INTRODUCTION
Natural products are an essential element in the development of human civilisation. Mankind uses a variety of plant parts, extracts and phytoconstituents for
the treatment of numerous diseases and ailments. Various traditional medicinal
systems, treaties and folklores have emphasised the importance of phytomedicines.
Phytomedicines are plants and their originated products with some healing and
therapeutic properties (Petrovska, 2012). The plants are a rich source of a variety of
secondary metabolites produced for signalling, defence and other functions.
Alkaloids, glycosides, avonoids, tannins and saponins are abundantly found in ora
across the globe, especially in owering plants. Alkaloids are one of the signicant
classes which have numerous uses along with medicinal benets. These are small
molecular nitrogenous natural products with basic nature. The compounds bear heterocyclic rings along with a carbon skeleton with at least one nitrogen. These are
classied as true, pseudo and proto alkaloids and other classications based on their
phytochemical and therapeutic use (Kurek, 2019). The various nitrogenous rings, viz.
pyrrolidine, tropane, pyrrolizidine, piperidine, quinolizidine, indolizidine, pyridine,
isoquinoline, thiazole, quinoline, indole,imidazole, purines and others, constitute
various alkaloidal skeleton. An estimate suggests that about 25% of higher plants
contain alkaloids and several thousand types have been identied to date (Dewick
Paul, 2009). Alkaloids are present in almost every plant part, including bark, leaf,
root, stem and owers. Various plant families, viz. Ranunculaceae, Solanaceae,
Papaveraceae and Amaryllidaceae, are predominantly rich in alkaloids (Cushnie
et al, 2014). The alkaloids show a broad spectrum of biological activities, including
hypoglycaemic, anti-inammatory, antimalarial, cardioprotective, anti-cancer, antibacterial, antiasthma, vasodilatory, antibrosis, anti-tussive actions, etc. (Adamski
et al, 2020). The alkaloids, such as codeine caffeine (central nervous system [CNS]
stimulant), (anti-tussive), morphine (painkillers), quinine (antimalarial), sanguinarine (antibacterial), galantamine and physostigmine (anti-Alzheimer agents), vinblastine and vincristine (anti-cancer) are used in modern medicine.
Alkaloids are one of the critical components of treatments for various CNS
diseases and disorders, viz. Alzheimer’s disease (AD), schizophrenia, depression
55DOI: 10.1201/9781003389781-4
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