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Cannabidiol: an overview of some chemical and
pharmacological aspects. Part I: chemical aspects
Raphael Mechoulam , Lumı´r Hanusˇ
Department of Medicinal Chemistry and Natural Products, Medical Faculty, Hebrew University of Jerusalem, Ein Kerem Campus, 91120
Received 15 June 2002; accepted 20 August 2002
Over the last few years considerable attention has focused on cannabidiol (CBD), a major non-psychotropic
constituent of Cannabis. In Part I of this review we present a condensed survey of the chemistry of CBD; in Part II, to
be published later, we shall discuss the anti-convulsive, anti-anxiety, anti-psychotic, anti-nausea and anti-rheumatoid
arthritic properties of CBD. CBD does not bind to the known cannabinoid receptors and its mechanism of action is yet
unknown. In Part II we shall also present evidence that it is conceivable that, in part at least, its effects are due to its
recently discovered inhibition of anandamide uptake and hydrolysis and to its anti-oxidative effect.
#2002 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Cannabidiol; Chemical and pharmacological aspects; Cannabis
Since the isolation and elucidation of the
structure of the main active constituent of mar-
-tetrahydrocannabinol (THC; Gaoni
and Mechoulam, 1964) an enormous number of
published articles have dealt with its chemistry,
biochemistry, pharmacology and clinical effects.
However, considerable anecdotal evidence has
emerged that the effects of marijuana are not due
to THC alone (Grinspoon and Bakalar, 1997). At
least one constituent, cannabidiol (CBD) was
found to cause a plethora of pharmacological
effects, some of which may modify the metabolism
and effects of THC (see for example Jaeger et al.,
1996; Karniol et al., 1974).
In the present overview we shall try to cover
some aspects of CBD chemistry and its pharma-
cological and clinical effects. It is by no means
exhaustive. The effects of CBD in numerous
systems have been investigated and this short
review is not intended to be of encyclopedic
nature, but mostly expresses the areas of interest
of the authors. The known interactions between
THC and CBD are not presented. They require a
thorough, separate critical evaluation of the lit-
erature, mostly of the 1970’s and 1980’s, based on
Corresponding author. Tel.: /972-2-675-8634; fax: /972-
E-mail address: firstname.lastname@example.org (R. Mechoulam).
Chemistry and Physics of Lipids 121 (2002) 35 /43
0009-3084/02/$ - see front matter #2002 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 0 0 9 - 3 0 8 4 ( 0 2 ) 0 0 1 4 4 - 5
the new knowledge of cannabinoid receptors and
of CBD effects.
In Part I of this review we present a condensed
survey of the chemistry of CBD; in Part II, to be
published later, we shall discuss the anti-convul-
sive, anti-anxiety, anti-psychotic, anti-nausea and
anti-rheumatoid arthritic properties of CBD.
2. Isolation, structure and absolute stereochemistry
CBD was first isolated from Mexican marijuana
by Roger Adams and from Indian charas by
Alexander Todd, both in 1940. For reviews of
the early work see Adams (1941), Todd (1946).On
the basis of chemical degradation and correlation
with cannabinol, a general structure was proposed.
However, quite surprisingly, for almost 25 years
no further work was reported. In 1963 our group
isolated CBD from Lebanese hashish and estab-
lished its structure and relative stereochemistry, at
positions 3 and 4, mostly on the basis of NMR
measurements (Fig. 1;Mechoulam and Shvo,
1963). A few years later its absolute stereochem-
istry was determined by conversion of CBD into
menthane carboxylic acid of well established
absolute stereochemistry (Mechoulam and Gaoni,
1967;Fig. 1). These early results were of consider-
able importance for the later elucidation of the
structure and stereochemisty of D
psychoactive component of Cannabis (Gaoni and
The crystal structure of CBD was determined by
Jones et al. (1977). Two independent forms of this
molecule were noted, which differ mainly in the
conformation of the pentyl side chain. The aro-
matic ring and the terpene ring are almost
perpendicular to each other. The two conformers
are linked by hydrogen bonding of the hydroxyl
The chemical nomenclature of CBD differs from
that of THC. While the latter has a pyran ring,
which determines its numbering (see Fig. 1), CBD
has no heterocyclic ring and its numbering stems
from that of the terpene ring. This, somewhat
unfortunate, technicality leads to the same carbon
atom being numbered differently in CBD and
Fig. 1. Conversion of cannabidiol into D
-cannabidiol and degradation to menthane carboxylic acid.
R. Mechoulam, L. Hanusˇ / Chemistry and Physics of Lipids 121 (2002) 35/4336
3. Acid cyclizations of CBD
Acid catalyzed cyclizations within the CBD
molecule take place leading to D
-THC and to
iso-THC (Fig. 2) formed from the respective
carbocations on C-8 and C-1 of the CBD skeleton,
respectively (Gaoni and Mechoulam, 1966a, 1968).
The double bond of THC may further isomerize,
leading to D
-THC (Gaoni and Mechoulam,
While the THC’s, in particular D
been thoroughly explored, with thousands of
publications appearing since its establishment as
the major, or essentially the sole psychoactive
Cannabis constituent, the iso-THC’s and its deri-
vatives have received almost no attention.
4. Reactions of CBD under basic conditions
The double bond in CBD on heating with t-
pentyl potassium in toluene-hexamethyl-phospho-
ric triamide undergoes isomerization to the D
position, leading to D
-CBD (Srebnik et al., 1984;
Fig. 1). Contrary to natural CBD, the D
showed THC-like activity in rhesus monkeys
Fig. 2. Cyclizations of CBD and related compounds under acidic conditions.
R. Mechoulam, L. Hanusˇ / Chemistry and Physics of Lipids 121 (2002) 35/43 37
(unpublished observations). It should be of con-
siderable interest to compare the conformations of
the two CBD isomers, in order to establish
whether the unexpected difference in activity is
due to a steric change. Recently, Wiley et al. (2002)
prepared and evaluated the binding and some in
vivo effects of a series of bicyclic resorcinols that
resemble CBD. Unlike CBD, most of these
resorcinol derivatives had good activity in binding
. The lack of activity of CBD
remains an enigma.
5. Oxidation of CBD and CBD acid
CBD in base in the presence of oxygen is
oxidized to monomeric and dimeric hydroxy-
quinones (Fig. 3). The anions of the oxidized
compounds have a deep violet color (Mechoulam
et al., 1968). This is the basis of the Beam reaction
used for identification of Cannabis.
Oxidation of CBD diacetate with selenium
dioxide leads mainly to the aldehyde on the C-10
position (Fig. 4), with no oxidation of the C-7
position as seen with THC (Lander et al., 1976).
However, oxidation with sodium chromate takes
place on the C-6 position (Lander et al., 1976).
An alternative entry to substitution at C-10 of
CBD was reported (Jorapur et al., 1985), using the
10-bromo-CBD acetate obtained by treatment of
CBD diacetate with N-bromosuccinimide (Jora-
pur et al., 1984).
Cannabidiolic acid methyl ester on oxidation
with manganese dioxide gave mainly the epimers
of the methyl esters of the naturally occurring
cannabielsoic acid (Shani and Mechoulam, 1970).
This reaction could be significantly improved on
bubbling of oxygen, which presumably reactivated
the manganese dioxide (Fig. 5).
The same reaction took place without manga-
nese dioxide by oxidative cyclization in the pre-
sence of air under irradiation (Fig. 5,Shani and
Mechoulam, 1970, 1974).
Most of these CBD derivatives were prepared
before the biological properties of CBD were
discovered and their evaluation may lead to novel
6. Photochemical reactions of CBD
In a review of the pharmacological work of his
group Loewe mentions that ‘‘... unwirksamen
Cannabidiol wurde nach Ultraviolet-bestrahlung
ein wirkstoffgehalt nachgewiesen ...’’, but this
work was never reported in detail (Loewe, 1950).
We have found that irradiation of CBD in
methanol with a 450 W lamp in a Corex vessel
gave a mixture from which mainly isomeric 1-
methoxy dihydro CBD’s were obtained (Shani and
Mechoulam, 1971). However, irradiation in cyclo-
hexane led to the formation of some THC, in
addition to iso-THC, reduced CBD and the
addition product of cyclohexane to CBD, giving
cyclohexyl CBD (Fig. 6). These reactions indicate
that CBD is photoreactive and should be guarded
from light when stored.
7. Synthesis of CBD
Several syntheses of CBD have been reported.
The most efficient one apparently is the acid
condensation of p-mentha-2,8-dien-1-ol with oli-
Fig. 3. Quinone formation from CBD.
R. Mechoulam, L. Hanusˇ / Chemistry and Physics of Lipids 121 (2002) 35/4338
vetol, as originally proposed by Petrzilka et al.
(1967) and later improved by Baek et al., (1985)
(Fig. 7). The yield reported (41% of crystalline
material) in this one step reaction makes CBD
8. Metabolism of CBD
The metabolism of CBD is well established. In
numerous species, including man, the first step is
hydroxylation, mostly on C-7, leading to 7-hy-
droxy-CBD, followed by further oxidations, lead-
ing to CBD-7-oic acid, and numerous
hydroxylated derivatives of this acid (Fig. 8,
Harvey and Mechoulam, 1990; Harvey et al.,
1991). Glucuronides of these oxidized metabolites
are also formed (for a review see Agurell et al.,
The syntheses of both 7-hydroxy-CBD (Tchili-
bon and Mechoulam, 2000) and of CBD-7-oic acid
(unpublished) have recently been achieved (Fig. 9).
Fig. 4. Oxidations of CBD diacetate.
Fig. 5. Formation of cannabelsoic acid-type compounds from CBD.
R. Mechoulam, L. Hanusˇ / Chemistry and Physics of Lipids 121 (2002) 35/43 39
Fig. 6. Photochemical reactions of CBD.
Fig. 7. Synthesis of CBD.
R. Mechoulam, L. Hanusˇ / Chemistry and Physics of Lipids 121 (2002) 35/4340
9. CBD chemistry: a summary
The chemistry of CBD has been well explored
over the last 35 years. In view of the various,
potentially therapeutic, effects caused by CBD, it
seems plausible that novel synthetic approaches
will be developed in the future to lead to new types
Fig. 8. Metabolites of CBD.
R. Mechoulam, L. Hanusˇ / Chemistry and Physics of Lipids 121 (2002) 35/43 41
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