Download L04 Cannabinoids Part 1 Medicinal Plants

Lecture (4)
18-Feb-2013
In the last lecture we discussed the formation of usnic acid as a secondary
metabolite of lichen. We also mentioned depsides and depsidone as important
constituents of the lichens, and we talked about Cetraria islandica which is a lichen.
In Cetraria islandica we have depsides and depsidone which are bitter substances.
The most important biological activity of the lichens is due to the antimicrobial
compounds such as usnic acid, and regarding the formation of usnic acid for which
we said there are different isomers possible, the essential fact that is the occurrence
of enol and the keto form together, and the C-methylation.
There are two types of methylation; 1- when the hydroxyl group is methylated,
and the conversion of hydroxyl group into OCH3 group: O-methylation, any
hydroxyl group can be methylated
2- When we have one of the carbons of the link is methylated, then we are
talking about C-methylation
C-methylation
So we have an O-glycosidation and C-glycosidation; sugar can be linked to a
hydroxyl group then we are talking about O-glycoside, sugar can be linked to a
carbon then we are talking about C-glycosidaton
Sugar
C-glycosidation
O-glycosidation
Sugar
In the same way we have methylation process, there’s O and C methylation,
and in the formation of usnic acid we have two characteristics; one of them is the
occurrence of C-methylation, the second one is the occurrence of keto-enol
tautomerism; because we mentioned that when we have hydroxyl group then this is
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the enol form which can occur in equilibrium with its keto form; the hydroxyl group
will change into a carbonyl group; which is called Keto-Enol tautomerism.
Tautomerisation
In the formation of usnic acid for which we have several isomers, we have these
two facts; 1- C-methylation
2- Two benzene rings linked via a furan ring, so called di-benzo furan
and one of the monomeric aromatic parts occur in enol form and the other one occur
in the keto form:
This is what we were discussing in the last lecture 
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We will continue today with the nicest topic in medicinal chemistry,
phytochemistry or even in pharmacology, which is discussed in the different
disciplines of PHARMACY♥, the Cannabinoids, we headline it as the chemistry of the
metabolism of cannabinoids because it’s such a big topic not a lecture of one hour
can cover this topic. You might find several books about the important plant
Cannabis sativa, because we consider Cannabis sativa as the most widely used
euphoric drug worldwide beside alcohol, and the most misused chemical agent.
Cannabis sativa has many interesting aspects; generally when we are talking
about the natural product chemistry as well as medicinal chemistry and when you
read chapters talking about agents that cause euphoria, you will always find nitrogen
in their structures, but we have one exception: a drug that doesn’t possess nitrogen
in its structure and have euphoric activity are the substances of Cannabis sativa.
Cannabis sativa is a drug that is very famous because it has been used by
more than 500 million people worldwide, it was spread in Vietnam War in 1970s and
before, it was widely used because of its euphoric characteristics. It’s not legitimate
to use Cannabis sativa in the majority of countries with the exception of some
European countries where it’s not illegal to have Cannabis sativa for personal use
like Marijuana or Hashish ( :P ‫) حشيش‬.
The word Cannabis comes from the an old Greek word that means Hemp,
throughout the years different genotypes or chemotypes of the same plant has been
produced, one of them is the drug type which is rich in biological active constituents,
the other one only possessing minute amounts or concentrations of this active
principle which is the Fiber type and it’s used for the production of fibers, and
there’s another type which is called intermediate type containing small percentage
of the active principles.
There are still some questions about the origin of this plant and one might
think that the term Hashish is an Arabic word and it’s a plant primarily growing in
the Arabic countries but in fact NO!
Throughout the years it has been transported from the origin of the Cannabis
sativa plant in South East Asia or most probably around Pakistan, and throughout
the wars has been transported to West world and South world, and it became famous
in Egypt, when Napoleon was in Egypt he took it to Europe.
You also read in the news from time to time that people are growing Cannabis
sativa for their self utilization, in pots or balconies; this is was possible because this
plant needs warm climate.
The plant grows in all temperatures, but in order to produce active secondary
metabolites, this is primarily dictated by environmental conditions.
- The warmer the climate  the higher the concentration of the active
constituents. It’s like 2% up to 7%.
There has been different studies carried out by exchanging the seeds of the
plant collected in warmer climate with the seeds collected in cold climate, and it has
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been proved that the seeds produced high percentage of active principles when were
grown in Egypt (warm climate), and when the same seeds were grown in Scandinavia
(cold climate) the plant stopped producing the active principles.
- The seeds of the plants that are growing in Scandinavian countries producing
the fiber type, when they were grown in Egypt, and after 2-3 years it started to
produce the active principles.
The capability of Cannabis sativa to produce the active principle is primarily
determined by climate and environmental conditions. - And again; the warmer the
climate  the higher the concentration of the active constituents. - The active
constituents aren’t occurring in the green plants, active principles are produced
during drying or during Pyrolysis, (Pyrolysis means burning).
Therefore this plant is primarily used by smoking instead of administering it by
parenteral route, it’s produced during drying; the inactive precursor of the fresh plant
are converted to the active principles during drying; because in all plants we have
different enzymes and the active principles exist in different types of cells, during
drying process the enzymes and secondary metabolites are coming next to each other
and causing the necessary changes.
To sum up: during drying process some of the inactive precursors are
converted to the active principles or this can be done more quickly by pyrolysis.
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During pyrolysis the plant material is smoked (during burning process) the
inactive precursors are converted to the active compounds, and by inhalation
they will reach very quickly within few minutes to the brain, and they will exert
their euphoric activity (euphoria) or the condition of wellbeing, exaltation,
escaping the reality … etc.
But when the dose is very high it will not give a pleasant condition, it will
change into fear of death, anxiety, panic and so on, so the state of wellbeing is going
to be changed and will be interrupted by conditions like disturbing the personality.
Smoking Marijuana is also associated with hallucination.
- What parts of the plant contain active principles?
When it’s a drug type plant the active principles are found to a certain degree
in male and female plants, but the highest percentage is found in the flowering tops
of the female plants; because in the flowering tops of the female plants we have the
glandular hairs, and within these glandular hairs there are resinous substances
which contain the active principles.
We have to mention and emphasize that no resinous substances have been
removed by a chemical extraction process. So you have to collect the plant and dry it,
then by powdering a special female flowering head you will obtain the active
principles, the so called Cannabinoids.
There are many constituents of six different cannabinoids have been isolated,
most of them are inactive precursors of the Tetrahydrocannabinol (THC)
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There are different terminologies depending on the country, users are using
different names but scientifically there are two terms should be known to the
students; one of the common names is Marijuana. Marijuana is the plant Cannabis
sativa - the binominal Latin name-. The local name Marijuana refers to the plant
material.
When we are talking about Hashish we are talking about the extracted
resinous material, therefore even in countries like Holland it’s not permitted to smoke
Hashish; because Hashish is the extracted pure resinous material and more potent
than Marijuana. In the case of Marijuana it’s the dried plant material but Hashish is
an extracted material that is composed of resinous material which occurs only in the
glandular hairs. Therefore Hashish is a very potent and strong compound.
To sum up: scientifically the terms Marijuana and Hashish shouldn’t be mixed,
Marijuana refers to the plant material which is much milder in its euphoric activity,
very toxic hallucinations are not observed with Marijuana smoking; this is observed
when the person is using Hashish because it’s a concentrated extract of this
hallucinogenic substance.
These psychotomimetic agents major activity is on the CNS, but it might cause
certain conditions like head and neck cancers. In general head and neck cancers are
observed in people over the age 60, it’s a very rare case to observe head and neck
cancer in young persons, but when it’s observed in young persons in ages between
20-40, most commonly these people are users of Marijuana or Hashish.
So the prevalence of head and neck cancer is affected in addition to CNS
activity also by using Marijuana.
Pregnant females definitely have a big problem for the effect of these agents on
the fetus or on the newborn babies (causing low circumference of the head of
newborns).
At the early stages of using these agents, they will improve the sexual activity,
but on the long term they will cause impotence and female like breast in male
population.
They also interfere with the turnover of neurotransmitters such as serotonin or
acetylcholine, and when the turnover and production of these neurotransmitters is
interfered then we will expect different effects on the users.
Any compound which is produced by nature and misused will also possess
pharmacological benefits, and in the case of Marijuana or Cannabis sativa, different
benefits have been proved when it’s used in therapeutic doses, such as:
1- The antimicrobial activity especially against Gram positive bacteria, it’s
considered as a very potent antibacterial agent.
2- It acts on the CNS causing analgesia and hypnosis; and these effects are
dose-dependent.
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3- It has an effect on the ocular system decreasing lacrimation, and it is used
in the treatment of glaucoma, decreasing the intra-ocular pressure.
4- It has an activity on the bronchi, when it’s used in therapeutic doses it can
be considered as an anti-asthmatic agent because it possesses a bronchodilating
effect.
5- Anti-hypertensive activity, decreasing blood pressure.
6- Anticonvulsant and antiepileptic activity.
7- Antiemetic activity. It is used for its antemetic activity by two types of
patients: Cancer and AIDS patients, and were permitted by the FDA and several
European authorities.
We said that head and neck cancer is observed by young population when they
use Marijuana for long term, and such population when submitted to chemotherapy,
the emetic effect accompanied by majority of the chemotherapeutic agents wasn’t
observed by these patients. (Explanation: one of chemotherapeutic agents’ side effects
is inducing emesis, but these cancer patients who are using Marijuana will not suffer
from this side effect of the chemotherapeutic agents)
So Cannabis sativa and its products are available in the markets of United
States and several European countries, marketed as Marinol and Nabilone which
are synthetic cannabinoid analogues used as an antiemetic by cancer and AIDS
patients. This is one of the permissions to be utilized for therapeutic purposes.
But why this is limited to these patients only? Because euphoria which is one
of the major disadvantages of using Cannabis sativa as a therapeutic agent. And
another disadvantage of the most effective form which is inhalation, because by
inhalation the dose is 200-250 mg/kg, which is the double of oral administration.
In some countries like in China, the misuse isn’t only limited to inhalation but
also they make a cup of tea of Marijuana! It’s utilized in the far eastern countries as a
hot tea prepared from Marijuana, and it’s also used in the form of infusion.
When it’s used by inhalation the activity is quick (only few minutes) but it will
not last long, and when it’s taken orally it will take about half an hour until the effect
is observed, but it will last longer, it will keep the feeling of wellbeing or euphoria for
longer time.
The major limitation beside euphoria is the development of tolerance, there
will be always higher doses needed in order to observe the same effect.
Let’s now talk about the chemistry and metabolism of cannabinoids.
Cannabinoids are hybrid substances having 21 Carbons. When we talk about a
hybrid compound then there’s more than one pathway involved in its biogenesis.
We are discussing the chapter of secondary metabolites originating from
Acetate-malonate pathway, it must be an acetate originating compound, but when we
say it’s a hybrid compound, there must be a second pathway involved in its
biogenesis. The second pathway is the Mevalonic acid pathway.
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So we can make a diagonal cut and we will observe one part of the molecule is
an aromatic part originating from Acetate-malonate pathway, the second part
originates from Mevalonic acid pathway, and when you count the carbons you will
find ten carbons in the Mevalonate originating part (monoterpenoid).
Originating
from Acetate
pathway
(aromatic part)
Originating from
Mevalonic acid
pathway
(non-aromatic part)
Pyran ring
THC
So it’s acetate originating aromatic part plus Mevalonic acid pathway
originating monoterpene which is a 10 Carbons compound.
This compound is interesting from different points of view, and the scientist
didn’t unify to use a single numbering system for the carbons.
In chemistry they insisted to use numbering based on the monoterpenoid, and
in pharmacology they are using the pyran ring system. So we have a terpenoid and
pyran because the aromatic part and the non aromatic six-membered cyclohexane
ring are linked via a six member oxygen containing pyran ring. So there is a pyran
type of numbering, structurally it’s a dibenzopyran, so there is a pyran type or
terpenoid type of numbering.
We have to know that there are different carbons which are important
especially with regard to the active compound, this is the main point with terpenoid
and pyran ring systems.
The molecule has an aromatic part and terpenoid part, so we have to number
them separately. The aromatic part is numbered as 1‛, 2‛, up to 6‛, and the terpenoid
part is numbered 1, 2, 3, etc.
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Pharmacological
Chemical
So in order to designate these two parts of the molecule, we will use different
pathways.
The pharmacologists use a continuous numbering even using a 6a or 6b or
10a, while for the chemists the position 3 and 4 are very important because it’s trans,
the hydrogens are not on the same side – it’s 3,4 trans – which is very important for
the chemists, but for pharmacologist it’s not important, so they will name the
carbons at the junctions as 6a and 10a .
So in the case of pyran nomenclature it’s continuously numbered, but we have
certain positions, and when we talk about the most important compound which is
responsible for the main biological activity it’s the Δ1 THC “ THC stands for
Tetrahydrocannabinol”, which is the same compound as Δ9 THC.
When we are talking about chemistry then we will say the most active
compound is Δ1,3,4 trans-THC, while the one who is interested in pharmacology he
will say simple Δ9 THC, without referring to the positions 3 and 4 that they are trans
oriented, he doesn’t care! For him the important issue is Δ9 THC.
When they say Δ9 or Δ1 they are referring to the solo double bond in the
cyclohexane ring which is indicated for in terpenoid nomenclature. Logically when we
say Δ1 we assume automatically that the double bond is between carbons 1 and 2,
and when it’s Δ9 then it’s between carbons 9 and 10.
So Δ1 THC or Δ9 THC they are the same compound using different types of
nomenclature.
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There are 6 different and closely related substances that are isolated, when we
are talking about one single double bond, then this double bond can be between
positions 9 and 10 or between 1 and 2, but it can be the opposite direction (anticlock wise numbering), it can be between Carbons 6 and 1 or between 8 and 9.
So when we say Δ6 , you might think that the double bond is between 6 and 7
which is NOT true!, and in order to overcome this problem, it is written as Δ1(6) THC,
when (6) is written between brackets; it indicates that it’s not following the common
way of numbering and the double bond occur between 1 and 6.
So when we write Δ9 it’s not the same active compound but it’s an isomer,
will have an isomer when we have a double bond and we change the direction of
numbering of it), in this case we should write it as Δ9(8) to indicate that it’s not
active principle where the double bond occur between carbons 9 and 10, but it’s
anti clock-wise numbering.
(we
the
the
the
THC is the most active compound, there are many constituents, and we have to
go through biochemistry because all compounds even the active ones are
accompanied with their acidic analogous, when we say Δ1 , Δ9 , Δ8 , whatever it is, we
are referring to the neutral part, it’s accompanied within the plant by an acidic
analogue.
When we say acid, simply we are referring to a structure containing a Carboxyl
group, and all these isolated constituents have an acidic companion, so we say THC,
then we can add THC-Carboxylic acid, so we will have an acid moiety attached to the
structure.
So all these compounds if we are talking about THC, Cannabigerol ( CBG ) or
Cannabidiol ( CBD ), they all have an acidic partner by adding CBG-Carboxylic acid
and attaching it to the aromatic part. So we will have from each compound an acidic
partner and a neutral one. The neutral is de-carboxylated, while the acidic partner
has a carboxyl group in its structure.
In the biosynthesis of these substances, when we talk about THC, we said that
we have an aromatic and a six membered cyclohexane ring linked via a pyran ring,
and then we are talking about a tricyclic nucleus, but we are discussing this topic in
the chapter of monocyclic aromatic compounds because all the aromatic parts
originate from Acetate-malonate pathway and the biosynthesis starts according to
what we mentioned: 1 Acyl CoA + 3 Malonyl CoA
When we discuss the biosynthesis in the chapter of terpenoids we will start
first by: Acetyl + Acetyl  Acetoacetyl, and then we will form Mevalonic acid then will
be converted to isoprene…etc.
But when we discuss the biosynthesis in Acetate-malonate pathway, the
biosynthesis will start with Acyl CoA + 3 Malonyl CoA to form our polyketomethylene
chain.
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The difference is in the starter compound, Acyl CoA, the active Δ9 THC or Δ1
THC, or the basic big important intermediate compounds, which all have a side chain
of C5H11.
We always have a side chain in the active compound. Your sheet showing only
nomenclature without it, but actually we have C5H11.
When you look to this structure what do you think the type of cyclization?
Orsellenic acid type or Phloroglucinol type?
All the compounds we have in the sheet (Slide no. 19) they have an acidic
partner and the acidic partner have a carboxyl group, and when you have a carboxyl
group then you will fix this carboxyl group because you have also two hydroxyl
groups, when we have phloroglucinol type, we will have 1-acyl-2,4,6-tri-hydroxy. But
we have only two hydroxyl groups, and the two hydroxyl groups are observed in the
orsellenic acid, because we said that orsellenic acid is 2,4-di-hydroxy-6-alkylbenzoic
acid.
We said that all these neutral compounds have a carboxyl group; here you will
fix the carboxyl group at position 6 which also possesses an alkyl C5H11 group (long
chain corresponding to the simple CH3 of orsellenic acid).
To sum up: in the biosynthesis the starter is Acyl CoA (not Acetyl CoA), which
is an n-hexanoic acid (it’s an acid with 5 carbon chain bearing a carboxyl group)
which means it’s an n-hexanoic or n-caproic acid. Our starter Acyl CoA is the ncaproic acid to which we are adding 3 Malonyl CoA step wise with carboxylation to
obtain our polyketomethylene chain, and by cyclization we will obtain olivetolic
acid. In olivetolic acid we will have a carboxyl group – it’s a benzoic acid derivative –
similar to orsellenic acid, the difference that we have a 5 carbon chain instead of the
simple CH3 group of orsellenic acid, and this olivetolic acid is used for addition of
mevalonic acid originating 10 carbon unit.
olivetolic acid
10
- OH
Remember that this type of structures is very similar to Menthol. Menthol is
the most important monoterpenoid compound, when we break the linkage and
remove the hydroxyl group we will have the basic nucleus of monoterpenoid C10, and
you will observe the same case in the formation of the non-aromatic part of the
cannabis.
The Dr said that you have to go over the biosynthesis scheme in the sheet.

Good Luck
Done By: Alshaima’ Qunies
Don’t forget:
Beautiful sunsets need cloudy sky …
- Paulo Coelho
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