Download Phytochemistry 2 * lecture 9

[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
Alkaloids
The Alkaloids are derived from amino acids pathway, during glycolysis process
all the essential amino acids are produced and during shikimate pathway the
three aromatic amino acid was produced, all these amino acids are considered as
starting material for the production of Alkaloids -which are the most important
source of the drugs- , the Alkaloids have nitrogenous compound came from the
amino acid. The nitrogen has two free electrons which give the Alkaloids its
characteristics. Mainly the compounds which have Nitrogen are considered as a
base (Alkaloids word came from Alkali which are bases).
Usually in Alkaloids the nitrogen is found in the heterocycle (not as free form),
as they are considered one of the most important secondary metabolites, so we
distinguish most of them by the suffix “-ine” at the end, e.g.: Caffeine,
Morphine, Cocaine, Atropine, and Vincristine.
Notice that the Oleandrin, Kampherol, Quercetin… doesn’t end with “-ine” so
it’s not an Alkaloids.
Be careful, even though the starting material of the Alkaloids biosynthesis is
amino acids, but they are not proteins nor nucleic acid nor polypeptides.
The naming of the Alkaloids is derived mainly from:
1- The genus part like: Atropa belladonna- Atropine.
2- The species like: Erythroxylum coca- Cocaine.
3- According to their mechanism of action like: Emetine which induces emesis.
4- Or according to the inventor name like: Pelletierine.
Why does the plant produce the Alkaloids or any secondary metabolite?
 Due to defence mechanism, or as a waste, or as a reserve for them (the
plant’s nitrogen before pollination is higher than during pollination, which
means that the plant reutilize the nitrogen in the Alkaloids to obtain the
necessary amount for the growth of the nitrogenous compounds).
 Another reason that these Alkaloids have been created by “Allah” as
DRUGS and we have to search for them and isolate them, we know nothing
about the sympathomimetic drugs without the discovery of them.
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
Methods of identification and extraction of Alkaloids:
1- Precipitate when treated with heavy iodide metals by many agents such as
Dragendorff’s reagent (its bisthmus iodide salt) when it’s reacted with the
Alkaloids it will give an orange colour or with TLC technique to give orange
colour too.
2- Mayer’s reaction which will give white ppt.
How do the cocaine abusers take the cocaine- the method of administration?
Snorting, smoking, I.V .
To be administered by IV, it must be water soluble-in a salt form, and to be
snorted or smoked it must be free base (able to burn)-not a salt.
So I used both the salt and the non salt forms of cocaine, which is something
very easy!
Focus here please,
My Alkaloids which have the Nitrogen, when we add to it HCl, and make
distribution for this (in a separatory funnel), once in aqueous(water) and other in
organic(chloroform), the Alkaloids will distribute and separate depending on the
media we add;
When we add an acid HCl to the Alkaloids (base); a salt will be formed, so
I’ll find my Alkaloids in the aqueous phase.
If we added a base NaOH to the aqueous phase, the salt will be expelled from
it’s salt form and will become a free base dissolved mainly in the organic
phase(Again, if we added an acid HCl to the organic phase (which is basic), a
salt will be formed, so I’ll find my Alkaloids in the aqueous phase…) and so on.
All these process are controlled by the pair of electrons in the Nitrogen.
The method of extraction of any plant which contains Alkaloids is dependent on
pH manipulation; in which we can move easily from salt to free base by
changing the pH, low pH will go to salt, and high pH will go to base.
Note that when we add the HCl to the Alkaloids, not only the Alkaloids will
go to the aqueous phase but either any water soluble materials will also be
moved and stay there.
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
Then, with the addition of NaOH, the Alkaloids will go to the organic phase,
and the dissolved water soluble materials are still in the aqueous.
So this process is not only an Extraction method, rather than it’s for
Purification of the compound. [Only in Alkaloids]
Also when we add NaOH to the Alkaloids, not only the Alkaloids will go to
the organic phase but either any organic soluble materials(wax, fats…) will also
be moved and stay there.
Then, with the addition of HCl, the Alkaloids will go alone to the aqueous
phase, and the dissolved organic soluble materials are still in the organic.
When we do extraction, first we start with a De fatting step: in order to get rid
of any fatty material, it’s done by washing the powdered plant material with
petroleum ether; which extracts non-polar fats and waxes, so the residue is polar
material.
Then we add to the residue an acid solution and it will go to the aqueous
solution, if we then added a base (Ammonia) it will become free base.
******************************************************
Example of typical Alkaloids is the morphine; it has heterocycle which have
Nitrogen.
There are three main types of Alkaloids:
1-Mainly, True Alkaloids: it’s originally derived from Amino Acid and the
nitrogen is in the heterocycle.
2- Proto Alkaloids: are derived from Amino Acid ,but don't have any
heterocycle, like: colchicines.
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
3-Psedo Alkaloids: have heterocycle but is not derived from Amino Acid, like
the Terpenoids and Purines.
We have many ways for the Classification of Alkaloids:
 Depending on the heterocycle (indole, pyrolidine,pyridine…).
 Or according to the Amino Acid(ornithine ,tyrosine, tryptophan) each
type of this Amino Acid will give me different type of heterocycle .
E.g.: tryptophan gives me indole (no way to get the indole heterocycle from any
other Amino Acid rather than the tryptophan) .
HETEROCYCLIC RING SYSTEMS: (Please memorize all of their structures)
H
N
N
H
H
H
pyrrole
piperidine
pyrrolidine
N
N
N
N
N
tropane
pyrrolizidine
quinolizidine
pyridine
N
N
N
C C N
N
N
N
N
H
quinoline
isoquinoline
indole
N
H
dihydroindole
N
H
benzylisoquinoline
purine
-phenylethylamine
Another table showing the Amino Acid precursors which is found in all of
these plants:
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
We will study the Alkaloids according to the Amino Acid; these structures
are for other types of Alkaloids:
1-Nicotine; the C5 comes usually from the ornithine Amino Acid.
2-Phenelethyl amine comes from tyrosine.
3-Indole comes from tryptophan (C6).
4-Lycopodine; the C5-N comes from Lysine.
[We will study each of them in details one by one later on]
In some cases, the Alkaloids start from Amino Acid as aliphatic but in most
cases they cyclise, e.g.:
****The steps and the structures of the “biosynthesis” are not for
memorizing, it’s just a demonstration for you to understand
1- Cocaine biosynthesis:
Started from Ornithine Amino Acid, then cyclisation, then methylation by SAM
(s-adenosylmethionine),… until reaching to the cocaine.
Note that whenever you see SAM; so methylation happens [note the structure in
the slides became CH3-NH].
2- Morphine biosynthesis; came from tyrosine.
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
Decarboxylation of tyrosine  gives tyramine , hydroxylation of tyramine
gives Dopamine.
Then the tyrosine gives an intermediate, which work with dopamine to give us a
compound named as “Norcoclaurine” with two SAM molecules , a methyl
group displaces two of the H atoms of the OH group… with multi steps we
reach Codeine compound, then finally the Morphine.
*Notes:
-All of these steps came from only one Amino Acid !!
-the tyrosine resembles the phenylalanine structure but with an extra OH.
3- Physostigmine; it’s structure have iodole, so definitely it came from
tryptophan.
Tryptophan decarboxylatongives Tryptamine, then with multi steps it gives
Physostigmine [which is a cholinergic drug used for glaucoma].
We have many Classification of Alkaloids Based on Amino Acid from which
they were derived: (Biosynthetic Origin)
1. Ornithine Derived Alkaloids
2. Lysine Derived Alkaloids
3. Nicotinic Acid Derived Alkaloids
4. Tyrosine Derived Alkaloids
5. Tryptophan Derived Alkaloids
6. Anthranilic Acid Derived Alkaloids
7. Histidine Derived Alkaloids
8. Amination Reaction Derived Alkaloids
9. Purine Alkaloids
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
Let’s start with the first group, and we will talk about part of it in this lecture:
*** Ornithine Derived Alkaloids :
4 carbons: C4-N, by its decarboxylation it gives two major KEY Alkaloids:1- Solanaceae ‫الفصيلة الباذنجية‬, e.g.; Hyoscyamine, Hyoscine, Atropine.
2- Coca: e.g.; Cocaine .
* In other words, Atropine and Cocaine came from the same precursor, but from
pharmacological point of view they are totally different; Atropine is an
anticholinergic drug, while Cocaine is a CNS stimulant.
* Both Solanaceae and Coca have Tropane nucleus;
The Solanaceae Alkaloids:
They are the key drugs for us, before them we weren’t able to know any of the
sympathomimetic drugs ,parasympathomimetic drugs…. and so on.
1- Atropine/ Hyoscyamine
Be careful that the plant itself doesn’t have Atropine, but the Atropine (which is
optically inactive) is extracted from Hyoscyamine, so it’s the racemic mixture
of hyoscyamine (both have the same exact structure).
Tropic Acid
Me
NCH3
N
H
O
Me
O
*
Tropine base
CH 2OH
O
N
CH 2OH
O
O
O
OH
(-)-Hyoscyamine
Atropine
The atropine is the ester of tropine base and tropic acid.
Tropic Acid
[Tropane+OH tropine]
O
NCH3
O
2- Hyoscin ; 6,7-Epoxy Atropine.
Scopoline base
O
OH
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
Separation of the Alkaloid mixtures:
Alkaloids in the form of HCl salts
1- Alkalinize by NaHCO3 pH 7.5
2- Extract with Ether
Ether
Hyoscine free base
(pKa = 6.2)
Aqueous layer
Atropine & Hyoscyamine HCl
(pKa = 9.3)
Convert to oxalate salts,
Fractional Crystallization
(Acetone/ Ether)
Atropine Oxalate
Crystals
Hyoscyamine Oxalate
Solution
In order to separate the hyoscine from atropine, we use weak base NaHCO3
pH=7.5 , so in the aqueous layer we will find the strong hyoscyamine because
its pKa is 9.3 , but hyoscine went out as a free base because its weaker than the
hyoscyamine  This is the meaning of pH Manipulation .
*** Chemical tests: specific tests which give specific colours with the
Solanaceae Alkaloids, to distinguish Atropine from hyoscine
•
Vitali-Morin’s test: Solid Alkaloids + fuming HNO3 → Evaporate to dryness,
dissolve residue in acetone, add methanolic solution of KOH → Violet colour.
•
P-dimethylaminobenzaldehyde: Alkaloids + reagent in porcelain dish and heat on
boiling water path → Intense Red Colour → Cherry Red after cooling.
•
Gerrard’s test: Alkaloids + 2% HgCl2 in 50% Ethanol → Red colour - Atropine
Red after warming - Hyoscyamine
White ppt - Hyoscine
Structure Activity Relationship
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
 Cationic Head: Positively charged Quaternary ammonium compounds
(the Alkaloids will not work with any modification of the nitrogen).
 Cyclic substitution: at least one cyclic substituent, aromatic is the most
used, came from tropic acid.
 Esteratic Group: Necessary for effective binding.
Pharmacological Activity:
Anticholinergics: Inhibit the neurological signals transmitted by the endogenous
neurotransmitter, acetylcholine.
All the activity of Atropine depends on its mechanism of action and its
similarity of Ach.
Symptoms of poisoning includes: mouth dryness (first sign), dilated pupils,
ataxia, urinary retention, hallucinations, convulsions, coma, and death.
*Solanaceae Alkaloids compete with acetylcholine for the muscarinic site of
the parasympathetic nervous systemthus preventing the passage of nerve
impulses, and are classified as anticholinergics.
*Acetylcholine binds to two types of receptor site, described as muscarinic or
nicotinic, from the specific triggering of a response by the Amanita muscaria
Alkaloids muscarine or the tobacco Alkaloids nicotine respectively.
*From this picture:
Look at the muscarine’s quaternary ammonium (which have N+) and the Ach’s
quaternary ammonium,,, they are similar, so this is why the Muscarine is an
agonist for Ach.
The Atropine structure have quaternary ammonium (this charged structure is the
one we find in our body), but because of the similarity and distance between the
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
nitrogen , oxygen and bulky phenolic group, it will compete with Ach at the
muscaranic receptors. [Not any quaternary ammonium can compete!]
• The structural similarity between acetylcholine and muscarine can readily
be appreciated, and hyoscyamine is able to occupy the same receptor at
the active site.
• As you know, the side-chain also plays a role in the strength between
head and drugs, also in the binding, explaining the difference in activities
between the two enantiomeric forms.
• The agonist properties of hyoscyamine and hyoscine give rise to a
number of useful effects, Including:
1. Anti spasmodic action on the gastrointestinal tract (Spasmopan)- mainly
we use scopolamine (hyoscine) .
2. Anti secretory effect controlling salivary secretions during surgical
operations.
3. Mydriasis to dilate the pupil of the eye for examination.
The mydriatic use also has a very long history. Indeed, the specific name
belladonna for deadly nightshade means ‘beautiful lady’ and refers to the
practice of ladies at court who applied the juice of the fruit to the eyes,
giving widely dilated pupils and a striking appearance, though at the expense
of blurred vision through an inability to focus.
• Agonist effect of Ach: Hyoscine has a depressant action on the central
nervous system and finds particular use as a sedative to control motion
sickness.
• One of the side-effects from oral administration of tropane Alkaloids is
dry mouth (the antisecretory effect) but this can be much reduced by
transdermal administration.
• In motion sickness treatment, hyoscine can be supplied via an
impregnated patch worn behind the ear.
• Hyoscine under its synonym scopolamine is also well known, especially
in fiction, as a ‘truth drug’ used with criminals.
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[PHYTOCHEMISTRY 2 – LECTURE 9]
Prof. Talal AbuRjai
November 24, 2016
• This combination of sedation, lack of will, and amnesia was first
employed in child-birth, giving what was termed ‘twilight sleep’, and
may be compared with the mediaeval use of stramonium.
• Atropine also has useful antidote action in cases of poisoning caused by
cholinesterase inhibitors, e.g. physostigmine and neostigmine and
organophosphate insecticides.
*We have two types of poisoning:
1- Systemic method
2- Antidote method
If I know that the person swallowed a specific known material, so I will give
him an antidote for the known material.
But unfortunately, mainly we don’t know what did the patient swallow, so we:
a. Delay the absorption; by induce vomiting, by Charcoal, or by gastric
lavage.
b. Then we should give a systemic Atropine. (it’s the DOC)
*In any war threats we give Atropine; because any chemical weapon will
collapse the heart, so giving anticholinergic drug will prevent this collapsing.
But excess giving of Atropine can kill the patient!
*Last Note: Atropine intoxication causes hypertension and increased heart rate.
< The End of the sheet >
Be kind.. for everyone you meet is fighting a battle, you
Know nothing about…
Best of success… :)
Written by: Qamar AbuHassan
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