Synthesis of o-substituted derivatives of tetrahydrocannabinol with potential butyrylcholinesterase activity

Article abstract of DOI:10.14233/ajchem.2013.14829

Tetrahydrocannabinol is the major active constituent of cannabis sativa and has many medicinal properties. In present work, a pure compound, tetrahydrocannabinol (1) was isolated from the dark viscous oil of cannabis sativa by column chromatography using different solvent systems. The purified tetrahydrocannabinol compound (1) on further treatment with different electrophiles (2a-f) in the presence of sodium hydride and N,N-dimethyl formamide furnished O-substituted derivatives of tetrahydrocannabinol (3a-f). The structures of all the synthesized compounds have been deduced from their spectral (¹H NMR, IR and EI-MS) data. Further, all these compounds were screened against butyrylcholinesterase enzyme and found that these compounds displayed activity to varying degree.

Full text of DOI:10.14233/ajchem.2013.14829

Asian Journal of Chemistry; Vol. 25, No. 15 (2013), 8522-8526
http://dx.doi.org/10.14233/ajchem.2013.14829
Synthesis of O-Substituted Derivatives of Tetrahydrocannabinol
with Potential Butyrylcholinesterase Activity
1,*
1
1
1
1
AZIZ-UR-REHMAN , SAAD ALI JAVED , MUHAMMAD ATHAR ABBASI , MISBAH IRSHAD , SAMREEN GUL ,
1
1
1
2
GHULAM HUSSAIN , KHADIJA NAFEESA , KANIZ RUBAB and IRSHAD AHMAD
1Department of Chemistry, Government College University, Lahore-54000, Pakistan
2Department of Pharmacy, The Islamia University of Bahawalpur, Bahawalpur, Pakistan
*Corresponding author: E-mail: azizryk@yahoo.com
(Received: 17 November 2012;
Accepted: 26 August 2013)
AJC-13987
Tetrahydrocannabinol is the major active constituent of cannabis sativa and has many medicinal properties. In present work, a pure
compound, tetrahydrocannabinol (1) was isolated from the dark viscous oil of cannabis sativa by column chromatography using different
solvent systems. The purified tetrahydrocannabinol compound (1) on further treatment with different electrophiles (2a-f) in the presence
of sodium hydride and N,N-dimethyl formamide furnished O-substituted derivatives of tetrahydrocannabinol (3a-f). The structures of all
the synthesized compounds have been deduced from their spectral (1H NMR, IR and EI-MS) data. Further, all these compounds were
screened against butyrylcholinesterase enzyme and found that these compounds displayed activity to varying degree.
Key Words: Tetrahydrocannabinol, Column chromatography, Butyrylcholinesterase, IR, EI-MS, 1H NMR.
affects the brain by altering the function of CNS system pro-
ducing excitement followed by hallucinations and subsequent
sleep. Chronic users may develop tolerance and withdrawal
symptoms including sleeplessness, depression, anxiety, increased
INTRODUCTION
Cannabis sativa L., (marijuana) belongs to the family of
Moraceae. This plant is indigenous to South East Asia,
Africa and NorthAmerica. The female plants are more preferred
and used as they are rich in glandular trichomes containing
resins. The possession, commercial sale, distribution and
purchase of cannabis are prohibited under the drug act 1971.
It is scheduled under the “Class B” of drugs that are abused.
The prepared cannabis is deteriorated by oxidation if stored
for more than 1 year and loses its grandness in the drug market.
So it is dried and stored in well closed containers. Cannabis
contains over 60 compounds that are collectively known as,
cannabinoids. The major resin components include: tetrahydro-
cannabinol, cannabinol, cannabidiol, cannabidinolic acid,
cannabichromene and cannabigerol1-3 (Fig. 1)
tension, agitation, anorexia and muscular tremors4-15
.
Butyryl cholinesterase (BChE, EC 3.1.1.8) constitutes a
group of enzymes including serine hydrolazes. The different
particularities for substrates and inhibitors for this enzyme are
because of the differences in amino acid residues of the active
sites of BChE. This enzyme system is credit worthy for the
termination of acetylcholine at cholinergic synapses which are
the basic components of cholinergic brain synapses and
neuromuscular junctions. The main function of BChE is to
catalyze hydrolysis of the neurotransmitter acetylcholine and
termination of the nerve impulse in cholinergic synapses. It’s
now known that BChE is present in Alzheimer’s plaques in
non-negligibly greater quantities than in the normal age asso-
ciated with non-dementia of brains. Cholinesterase inhibitors
enhance the quantity of acetylcholine useable for neuronal
and neuromuscular transmission due to their ability, reversibly
or irreversibly.Thus the seeking new cholinesterase inhibitors
is believed an essential and continuing Scheme-I to inaugurate
new drug candidates for the treatment ofAlzheimer’s syndrome
Tetrahydrocannabinol (the main active constituent of
cannabis) has been in use in many ailments and medical
conditions for a long period. It is used in the field of medicine
as hypnotic, anti-consulvant and an analgesic and also in
anxiety and cough. It is used to relief vomiting and nausea in
chemotherapy patients and as an appetite stimulant in AIDS
patients. With long term usage of tetrahydrocannabinol, it has
many adverse effects and is addictive in nature. It can cause
complex disorders in patients like attention defects, loss of
concentration and unable to perform high ranked tasks. It also
and other related diseases16-19
.
In protraction of our previous synthetic work20, the present
research work was an effective effort to synthesize O-substituted

Vol. 25, No. 15 (2013)
Synthesis of O-Substituted Derivatives of Tetrahydrocannabinol 8523
CH3
CH3
CH3
OH
H
OH
OH
H
H3C
O
C5H11
H3C
C5H11
HO
CH2
O
C5H11
H3C
H3C
CH3
Cannabidiol
Tetrahydrocannabinol
Cannabinol
OH
OH
HO
C5H11
C5H11
Cannabichromene
Cannabigerol
Fig. 1
CH3
CH3
9
R
9
8
7
10
OH
8
7
10
O
H
H
1
1
10a
2
10a
2
LiH, DMF
6a
6a
H
H
2'
4'
6
2'
4'
R-X
6
3
1'
3'
5
H3C
H3C
3
1'
3'
5
H3C
H3C
O
CH
5'
3
2a-f
O
CH
4
5'
3
4
3a-f
1
Compound No.
-R
Compound No.
-R
2''
CH3
1''
2''
1''
2a
2d
H2C CH3
CH
3''
CH3
Cl
1''
2''
H2C
7''
2b
2c
2e
2f
1''
H2C CH2 Br
3''
5''
H2C
Ha
H
1''
3''
5''
7''
C
2''
C
1''
CH2
3'' Hb
Cl
Scheme-I: Synthesis of O-substituted derivatives of tetrahydrocannabinol (THC)
derivatives of tetrahydrocannabinol by alkyl/aralkyl halides
with an objective to produce new drug candidates that would
have enhanced substantial biological and medicinal activities
and can help to control various ailments.
TLC plates was carried out under UV at 254 and 366 nm and
also by spraying with ceric sulfate solution (with heating).
The IR spectra were recorded in KBr pellet method on a Jasco-
1
320-A spectrophotometer (wave number in cm-1). H NMR
spectra were recorded in CD3OD on a Bruker spectrometers
operating at 400 MHz. The chemical shift values are reported
in ppm (δ) units taking TMS as reference standard and the
coupling constants (J) are in Hz. Mass spectra (EIMS) were
recorded on a JMS-HX-110 spectrometer. Alkyl/aralkyl
halides were purchased from Merck and Alfa Aeser through
EXPERIMENTAL
Purity of the compounds was checked by thin layer
chromatography (TLC) with solvent systems using EtOAc and
n-hexane on aluminum sheets precoated with silica gel 60 F254
(20 cm × 20 cm, 0.2 mm thick; E-Merck). Visualization of the

8524 Aziz-ur-Rehman et al.
Asian J. Chem.
local suppliers. All the other used solvents were of analytical
grade.
(KBr, νmax, cm-1): 3350 (O-H, stretching), 3035 (C-H, stretching
of aromatic ring), 2919 (-CH2-, stretching), 1543 (C=C, stretching
of aromatic ring), 1225 (C-O-C, stretching of ring); 1H NMR
(400 MHz, CD3OD, ppm): δ 6.20 (s, 1H, H-2), 6.11 (s, 1H, H-
4), 5.54 (br.s, 1H, H-10), 4.54 (m, 1H, H-10a), 2.44 (t, J = 8.0
Hz, 2H, CH2-1'), 1.77 (s, 3H, CH3-9), 1.65-1.76 (m, J =6.4
Hz, 1H, H-6a), 1.58-1.64 (m, 2H, CH2-8), 1.53-1.55 (m, 2H,
H-2'), 1.38 (s, 6H, 2CH3-6), 1.23-1.41 (m, 4H, CH2-3', CH2-
4'), 0.84 (t, J = 14.0 Hz, 3H, CH3-5'), 0.78-1.07 (m, 2H, CH2-
7); EIMS: m/z 314 [M]+, 299 [M-CH3]+, 272 [M-C3H6]+, 232
[M-C6H10]+, 54 [C4H6]+.
Isolation of tetrahydrocannabinol by column chroma-
tography: The dark viscous oil of cannabis sativa was obtained
(50 g) from Punjab ForensicAgency, Lahore, Pakistan for this
study. The dark viscous oil (10 g) was dissolved in methanol
and then filtered it by using the filter paper in order to remove
all the suspended impurities. The filtrate then used to form
slurry by using small amount of flash silica. The slurry was
then subjected to column chromatography over flash silica
using n-hexane, n-hexane-EtOAc and EtOAc as eluents in
increasing order of polarity. The fraction obtained from n-
hexane-EtOAc (8:2) was rechromatographed over flash silica
using n-hexane-CHCl3 (8.5:1.5) to afford the title compound,
tetrahydrocannabinol (2 g).
(6aR,10aR)-1-Ethoxy-6,6,9-trimethyl-3-pentyl-
6a,7,8,10a-tetrahydro-6H-benzo[c]chromene (3a):Yield: 67
%; m.f. C23H34O2; m.w. 342 g/mol; IR (KBr, νmax, cm-1): 3030
(C-H, stretching of aromatic ring), 2923 (-CH2-, stretching),
1548 (C=C, stretching of aromatic ring), 1229 (C-O-C, stretch-
General procedure for the synthesis of O-alky substi-
tuted derivatives (3a-f): Tetrahydrocannabinol (0.064 mol,
1) was taken in round bottom flask and N,N-dimethyl
formamide (around 5 mL) and sodium hydride (0.01g, 0.42
mmol) were added in it at room temperature. The reaction
mixture was stirred for 0.5 h and then the corresponding
electrophiles (0.064 mol, 2a-f) were added into the mixture.
The reaction mass was further stirred and monitored through
thin layer chromatographic (TLC) plate using ethyl acetate
and n-hexane (80:20) as mobile phase. After completion of
the reaction, the reaction mixture was quenched with cold water
(100 mL). The received solid was filtered, washed with distilled
water and dried to yield the corresponding O-substituted
1
ing of ring); H NMR (400 MHz, CD3OD, ppm): δ 6.25 (s,
1H, H-2), 6.18 (s, 1H, H-4), 5.53 (br.s, 1H, H-10), 4.51 (s, 1H,
H-10a), 4.36 (q, J = 7.2 Hz, 2H, CH2-1'’), 2.41 (t, J = 8.0 Hz,
2H, CH2-1'), 1.75 (s, 3H, CH3-9), 1.63-1.74 (m, J = 6.4 Hz,
1H, H-6a), 1.56-1.66 (m, 2H, CH2-8), 1.51-1.54 (m, 2H, H-
2'), 1.38 (s, 6H, 2CH3-6), 1.27 (t, J = 7.2 Hz, 3H, CH3-2'’),
1.23-1.41 (m, 4H, CH2-3', CH2-4'), 0.85 (t, J = 14.0 Hz, 3H,
CH3-5'), 0.78-1.07 (m, 2H, CH2-7); EIMS: m/z 342 [M]+, 327
[M-CH3]+, 300 [M-C3H6]+, 297 [M-OC2H5]+, 260 [M-C6H10]+,
54 [C4H6]+.
(6aR,10aR)-1-(2-Bromoethoxy)-6,6,9-trimethyl-3-
pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c] chromene (3b):
derivatives of tetrahydrocannabinol (3a-f)20-21
.
Yield: 59 %; m.f. C23H33BrO2;m.w. 421 g/mol; IR (KBr, νmax,
Butyrylcholinesterse assay: The BChE inhibition was
accomplished according to the reported method22 with some
differences. Volume of the reaction contents was 100 µL with
60 µL buffer (Na2HPO4, 50 mM with pH 7.7), 10 µL test
compound (0.5 mM well-1) and 10 µL BChE (0.5 unit well-1).
The reaction contents were fused and pre-read at 405 nm; also
pre-incubated for 10 min at 37ºC. The reaction was originated
by the addition of 10 µLsubstrate (butyrylthiocholine bromide,
0.5 mM well-1) followed by 10 µL DTNB (0.5 mM well-1).
After 15 min of incubation at 37 ºC, absorbance was measured
at 405 nm. Synergy HT (Bio Tek, USA) 96-well plate reader
was used in all experiments. All experiments were carried out
with their respective controls in triplicate. Eserine (0.5 mM
well-1) was used as a positive control. Inhibition (%) = (Abs of
control – Abs of test comp/Abs of control) × 100. IC50 values
were designed using EZ-Fit Enzyme kinetics software (Perrella
Scientific Inc. Amherst, USA).
cm-1): 3033 (C-H, stretching of aromatic ring), 2917 (-CH2-,
stretching), 1541 (C=C, stretching of aromatic ring), 1223 (C-
O-C, stretching of ring), 510 (C-Br, stretching); 1H NMR (400
MHz, CD3OD, ppm): δ 6.23 (s, 1H, H-2), 6.17 (s, 1H, H-4),
5.51 (br.s, 1H, H-10), 4.49 (s, 1H, H-10a), 4.33 (q, J = 7.2 Hz,
2H, CH2-1'’), 3.84 (t, J = 7.2 Hz, 2H, CH2-1'’), 3.53 (t, J = 7.2
Hz, 2H, CH2-2'’), 1.76 (s, 3H, CH3-9), 1.63-1.75 (m, 1H,
H-6a), 1.53-1.62 (m, 2H, CH2-8), 1.52-1.55 (m, 2H, H-2'),
1.39 (s, 6H, 2CH3-6), 1.25-1.38 (m, 4H, CH2-3', CH2-4'), 0.81
(t, J = 14.0 Hz, 3H, CH3-5'), 0.79-1.10 (m, 2H, CH2-7); EIMS:
m/z 423 [M + 2]+, 421 [M]+, 406 [M-CH3]+, 379 [M-C3H6]+,
339 [M-C6H10]+, 298 [M-OC2H4Br]+, 54 [C4H6]+.
(6aR,10aR)-1-(Allyloxy)-6,6,9-trimethyl-3-pentyl-
6a,7,8,10a-tetrahydro-6H-benzo[c] chromene (3c): Yield:
63 %; m.f. C24H34O2; m.w. 354 g/mol; IR (KBr, νmax, cm-1):
3036 (C-H, stretching of aromatic ring), 2920 (-CH2-, stretch-
ing), 1544 (C=C, stretching of aromatic ring), 1226 (C-O-C,
stretching of ring); 1H NMR (400 MHz, CD3OD, ppm): δ 6.24
(s, 1H, H-2), 6.18 (s, 1H, H-4), 5.99 (m, 1H, CH-allylic-2'’),
5.52 (br.s, 1H, H-10), 5.33 (dd, J = 15.9, 1.2 Hz, 1H, Ha-3'’),
5.17 (dd, J = 15.9, 1.2 Hz, 1H, Hb-3'’), 4.47 (s, 1H, H-10a),
3.80 (d, J = 7.2 Hz, 2H, H-1'’), 1.74 (s, 3H, CH3-9), 1.61-1.76
(m, J = 6.4 Hz, 1H, H-6a), 1.53-1.57 (m, 2H, H-2'), 1.51-1.60
(m, 2H, CH2-8), 1.40 (s, 6H, 2CH3-6), 1.24-1.36 (m, 4H, CH2-
3', CH2-4'), 0.82 (t, J = 14.0 Hz, 3H, CH3-5'), 0.80-1.11 (m,
2H, CH2-7); EIMS: m/z 354 [M]+, 339 [M-CH3]+, 312 [M-
C3H6]+, 297 [M-OC3H5]+, 272 [M-C6H10]+, 54 [C4H6]+.
IC50 values were determined by serial dilution of the
compounds from 0.5 mM to 0.25, 0.125, 0.0625, 0.03125,
0.015625 mM. IC50 value was calculated from the graph, the
concentration at which the enzyme inhibition was 50 %.
Values are mean of 3 independent experiments.
Statistical analysis: All the measurements were done in
triplicate and statistical analysis was performed by Microsoft
Excel 2010. Results are presented as mean sem.
Characterization of the synthesized compounds
(6aR,10aR)-6,6,9-Trimethyl-3-pentyl-6a,7,8,10a-
tetrahydro-6H-benzo[c]chromen-1-ol (1): Sticky brownish
black solid; Yield: 63 %; m.f. C21H30O2; m.w. 314 g/mol; IR
(6aR,10aR)-1-Isopropoxy-6,6,9-trimethyl-3-pentyl-
6a,7,8,10a-tetrahydro-6H-benzo[c] chromene (3d): Yield:
72 %; m.f. C24H36O2; m.w. 356 g/mol; IR (KBr, νmax, cm-1):

Vol. 25, No. 15 (2013)
Synthesis of O-Substituted Derivatives of Tetrahydrocannabinol 8525
C21H30O2 was established by EI-MS showing molecular ion
3037 (C-H, stretching of aromatic ring), 2921 (-CH2-, stretch-
ing), 1546 (C=C, stretching of aromatic ring), 1228 (C-O-C,
stretching of ring); 1H NMR (400 MHz, CD3OD, ppm): δ 6.20
(s, 1H, H-2), 6.15 (s, 1H, H-4), 5.54 (br.s, 1H, H-10), 4.45 (s,
1H, H-10a), 2.88 (m, 1H, H-1'’), 1.75 (s, 3H, CH3-9), 1.60-
1.74 (m, J = 6.4 Hz, 1H, H-6a), 1.54-1.56 (m, 2H, H-2'), 1.52-
1.62 (m, 2H, CH2-8), 1.42 (s, 6H, 2CH3-6), 1.25-1.37 (m, 4H,
CH2-3', CH2-4'), 1.13 (d, J = 6.0 Hz 6H, CH3-2'’, CH3-3'’),
0.83-1.12 (m, 2H, CH2-7), 0.81 (t, J = 14.0 Hz, 3H, CH3-5');
EIMS: m/z 356 [M]+, 341 [M-CH3]+, 314 [M-C3H6]+, 297
[M-OC3H7]+, 274 [M-C6H10]+, 54 [C4H6]+.
1
peak 314 and by counting the number of protons in its H
NMR spectrum. The IR spectra showed absorption bands at
3350, 3035, 2919, 1543 and 1225 cm-1 which were assigned to
O-H (stretching of hydroxyl group), C-H (aromatic stretching),
-CH2- (stretching of aliphatic), C=C (stretching of aromatic
ring) and –C-O-C- (stretching of ring), respectively. The EI-
MS gave peaks at m/z 299 and 271 which were attributed to
the loss of methyl and propyl groups, respectively. A distinct
peak at m/z 54 was due to butadiene cation. In the aromatic
1
region of the H NMR spectrum, the signals emerging at δ
(6aR,10aR)-1-(2-Chlorobenzyloxy)-6,6,9-trimethyl-3-
pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromene (3e):
Yield: 57 %; m.f. C28H35O2Cl; m.w. 438.5 g/mol; IR (KBr,
νmax, cm-1): 3031 (C-H, stretching of aromatic ring), 2916
(-CH2-, stretching), 1541 (C=C, stretching of aromatic ring),
1221 (C-O-C, stretching of ring), 720 (C-Cl, stretching); 1H
NMR (400 MHz, CD3OD, ppm): δ 7.38 (dd, J = 6.0, 1.5 Hz,
1H, H-3'’), 7.25 (m, 3H, H-4'’ to H-6'’), 6.24 (s, 1H, H-2),
6.18 (s, 1H, H-4), 5.52 (br.s, 1H, H-10), 4.51 (s, 2H, CH2-7'’),
4.47 (s, 1H, H-10a), 1.74 (s, 3H, CH3-9), 1.61-1.76 (m, J =
6.4 Hz, 1H, H-6a), 1.53-1.57 (m, 2H, H-2'), 1.51-1.60 (m,
2H, CH2-8), 1.40 (s, 6H, 2CH3-6), 1.24-1.36 (m, 4H, CH2-3',
CH2-4'), 0.82 (t, J = 14.0 Hz, 3H, CH3-5'), 0.80-1.11 (m, 2H,
CH2-7); EIMS: m/z 440 [M+2]+, 438 [M]+, 347 [M-C7H7]+,
423 [M-CH3]+, 396 [M-C3H6]+, 356 [M-C6H10]+, 91 [C7H7]+,
54 [C4H6]+.
6.20 (s, 1H, H-2) and 6.11 (s, 1H, H-4) showed the presence
of benzene ring. In the aliphatic region, the signals appearing
at δ 5.54 (s, 1H, H-10), 4.54 (s, 1H, H-10a), 1.77 (s, 3H, CH3-
9), 1.65-1.76 (m, 1H, H-6a), 1.58-1.64 (m, 2H, CH2-8) and
0.78-1.07 (m, 2H, CH2-7) demonstrated the presence of
cyclohexene ring having a methyl group linked to it; the signals
present at δ 1.38 (s, 6H, 2CH3-6) revealed the bearing of two
methyl groups at the same carbon linked with oxygen; the
signals appeared at δ 2.44 (t, J = 8.0 Hz, 2H, CH2-1'), 1.53-
1.55 (m, 2H, H-2'), 1.23-1.41 (m, 4H, CH2-3', CH2-4), 0.84 (t,
J = 14.0 Hz, 3H, CH3-5) revealed the presence of a pentyl
group attached to aromatic ring. On the basis of above men-
tioned cumulative evidences, the structure of (1) was assigned
(6aR,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-
6H-benzo[c]chromen-1-ol. Similarly, the structures of other
compounds (3a-f) were characterized by 1H NMR, IR and mass
spectral data as described in experimental section.
(6aR,10aR)-1-(4-Chlorobenzyloxy)-6,6,9-trimethyl-3-
pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromene (3f):
Yield: 57 %; m.f. C28H35O2Cl; m.w. 438.5 g/mol; IR (KBr,
νmax, cm-1): 3038 (C-H, stretching of aromatic ring), 2923
(-CH2-, stretching), 1547 (C=C, stretching of aromatic ring),
1229 (C-O-C, stretching of ring), 718 (C-Cl, stretching); 1H-
NMR (400 MHz, CD3OD, ppm): δ 7.34 (s, 1H, H-2), 7.21 (s,
1H, H-4), 6.27 (d, J = 8.4 Hz, 2H, H-3'’, H-5'’), 6.16 (d, J =
8.8 Hz 2H, H-2'’, H-6'’), 5.52 (br.s, 1H, H-10), 4.48 (s, 1H, H-
10a), 1.72 (s, 3H, CH3-9), 1.64-1.78 (m, J = 6.4 Hz, 1H, H-
6a), 1.54-1.58 (m, 2H, H-2'), 1.53-1.63 (m, 2H, CH2-8), 1.42
(s, 6H, 2CH3-6), 1.25-1.37 (m, 4H, CH2-3', CH2-4'), 0.84-1.13
(m, 2H, CH2-7), 0.83 (t, J = 14.0 Hz, 3H, CH3-5'); EIMS: m/z
440 [M+2]+, 438 [M]+, 347 [M-C7H7]+, 423 [M-CH3]+, 396
[M-C3H6]+, 356 [M-C6H10]+, 91 [C7H7]+, 54 [C4H6]+.
Enzyme inhibition activity: The screening of all these
synthesized compounds against butyrylcholinesterase (BChE)
enzymes revealed that these molecules exhibited good inhibi-
tory potential against butyrylcholinesterase, as evident from
their IC50 values (Table-1). The parent compound (1) and
(6aR,10aR)-1-(4-chlorobenzyloxy)-6,6,9-trimethyl-3-pentyl-
6a,7,8,10a-tetrahydro-6H-benzo[c]chromene (3f) showed
promising activity against butyrylcholinesterase enzyme
having IC50 values 48.71 0.25 and 59.31 0.11 µmol/L,
respectively, relative to Eserine, a reference standard with IC50
value of 0.85 0.0001 µmol/L. These two compounds were
the most active; the most probably because of the presence of
alkyl/alkoxy/aralkyl groups in their structures. The compounds
(6aR,10aR)-1-ethoxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-
tetrahydro-6H-benzo[c] chromene (3a), (6aR,10aR)-1-(2-
bromo ethoxy)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-
tetrahydro-6H-benzo[c]chromeneand (3b) and (6aR,10aR)-1-
isopropoxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-
6H-benzo[c]chromene (3d) exhibited good inhibitory poten-
tial having IC50 values of 71.61 0.08, 61.21 0.31 and 73.31
0.04 µmol/L, respectively. The only two compounds,
(6aR,10aR)-1-(allyloxy)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-
tetrahydro-6H-benzo[c]chromene (3c) and (6aR,10aR)-1-(2-
chlorobenzyloxy)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-
tetrahydro-6H-benzo[c]chromene (3e) showed weak inhibitory
potential against butyrylcholinesterase enzyme. These com-
pounds can further be exploited and their derivatives could be
synthesized to get closer to IC50 value of the standard, eserine.
In this way, the compounds could be potential target in the
drug discovery and drug development program.
RESULTS AND DISCUSSION
In the undertaken research, a series of O-substituted
derivatives of tetrahydrocannabinol (3a-f) were synthesized
and screened against butyrylcholinesterase enzyme. These were
developed by the coupling of tetrahydrocannabinol (1) with
different electrophiles (2a-f) in the presence of sodium hydride
and N,N-dimethyl formamide. Complete conversion was achieved
within 30-60 min by stirring. The products were isolated by
adding cold distilled water in the reaction mixture and filtering
off the precipitated solid. In some cases, compound was taken
out through solvent extraction method using chloroform or
ethyl acetate. Structures of the parent compound and its
O-substituted derivatives were confirmed by spectral data as
described in experimental section. Parent compound (1) was
separated as brown sticky solid. The molecular formula

8526 Aziz-ur-Rehman et al.
Asian J. Chem.
3. C.H. Ashton, Br. J. Psychiatry, 178, 101 (2001).
TABLE-1
BUTYRYLCHOLINESTERASE ENZYME INHIBITION
ACTIVITY OF THC AND ITS DERIVATIVES
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BChE
Sample code
Conc. (mM)
0.50
Inhibition (%)
88.08 0.26
85.29 0.18
86.85 0.27
76.96 0.11
79.21 0.55
78.65 0.39
84.95 0.14
82.82 1.09
IC50 (µmol)
48.71 0.25
71.61 0.08
61.21 0.31
95.21 0.56
73.31 0.04
112.31 0.52
59.31 0.11
0.85 0.0001
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1
0.50
3a
0.50
3b
0.50
3c
0.50
3d
0.50
3e
3f
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0.50
Control (eserine)
0.25
Note: IC50 values (concentration at which there is 50 % enzyme
inhibition) of compounds were calculated using EZ-fit enzyme kinetics
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36, 2035 (1987).
software (Perella Scientific Inc. Amherst, USA). BChE
Butyrylcholinesterase.
=
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ACKNOWLEDGEMENTS
The authors are thankful to Punjab Forensic Agency,
Lahore, Pakistan to provide the dark viscous oily material of
Cannabis sativa plant.
20. Aziz-ur-Rehman, S. Rasool, M.A. Abbasi, H. Khalid, K.M. Khan, M.
Ashraf, I.Ahmad and I.Afzal, Asian J. Pharm. Biol. Res., 2, 100 (2012).
21. Aziz-ur-Rehman, W. Tanveer, M.A. Abbasi, S. Afroz, K.M. Khan, M.
Ashraf and I. Afzal, Int. J. Chem. Res., 3, 99 (2011).
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