Pharmacophoric requirements for cannabinoid side chains: Multiple bond and C1'-substituted Δ8-tetrahydrocannabinols

Article abstract of DOI:10.1021/jm970277i

Accumulated evidence indicates that within the cannabinoid structure the aliphatic side chain plays a pivotal role in determining cannabimimetic activity. We describe the synthesis and affinities for the CB1 and CB2 receptors of a series of novel Δ^8<

Full text of DOI:10.1021/jm970277i

1195
J . Med. Chem. 1998, 41, 1195-1200
Notes
P h a r m a cop h or ic Requ ir em en ts for Ca n n a bin oid Sid e Ch a in s: Mu ltip le Bon d
a n d C1′-Su bstitu ted ∆8-Tetr a h yd r oca n n a bin ols
Demetris P. Papahatjis,*,† Therapia Kourouli,† Vasiliki Abadji,‡ Andreas Goutopoulos,‡ and
Alexandros Makriyannis*,‡
Institute of Organic and Pharmaceutical Chemistry, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue,
Athens 116-35, Greece, and Departments of Pharmaceutical Sciences and Molecular and Cell Biology,
University of Connecticut, Storrs, Connecticut 06269
Received April 28, 1997
Accumulated evidence indicates that within the cannabinoid structure the aliphatic side chain
plays a pivotal role in determining cannabimimetic activity. We describe the synthesis and
affinities for the CB1 and CB2 receptors of a series of novel ∆8-THC analogues in which the
side-chain pharmacophores are conformationally more defined than in the parent molecule.
No analogue has the side-chain pharmacophore in a fully restricted conformation. However,
our design serves to narrow down the scope of options for conformational requirements at the
receptor active sites. All the analogues tested showed nanomolar or subnanomolar affinities
for the receptors; 2-(6a,7,10,10a-tetrahydro-6,6,9-trimethyl-1-hydroxy-6H-dibenzo[b,d]pyranyl)-
2-hexyl-1,3-dithiolane was found to possess very high affinity for both cannabinoid receptors
(CB1, Ki ) 0.32 nM; CB2, Ki ) 0.52 nM).
In tr od u ction
(-)-∆8-Tetrahydrocannabinol (∆8-THC) has a very simi-
lar pharmacologic profile as (-)-∆9-tetrahydrocannab-
inol (∆9-THC), the most active constituent of cannabis,
and was chosen as the prototype in this series because
of its greater chemical stability. On the basis of earlier
literature reports,7 the length of the side chain was
optimized to seven carbon atoms.
In this paper we seek to extend work we recently
published in which the cannabinoid side chain was
partially immobilized through the introduction of mul-
tiple carbon-carbon bonds between its first two C1′ and
C2′ carbons.9 We now describe the synthesis and
affinities for the CB1 and CB2 receptors of a series of
novel ∆8-THC analogues in which the side-chain phar-
macophores are conformationally more defined than in
the parent molecule. No analogue has the side-chain
pharmacophore in a fully restricted conformation. How-
ever, our design serves to narrow down the scope of
options for conformational requirements at the receptor
active sites. One of the analogues synthesized, namely,
2-(6a,7,10,10a-tetrahydro-6,6,9-trimethyl-1-hydroxy-6H-
dibenzo[b,d]pyranyl)-2-hexyl]-1,3-dithiolane (5), was
found to possess very high affinity for the cannabinoid
receptor.
The identification of a cannabinoid receptor1 (CB1)
in mammalian brains and its further characterization
as being G-protein-coupled2 have been the topic of
intense investigation leading to its cloning from rat3 and
human4 cDNA libraries. In addition, efforts aimed at
elucidating the physiological role of the cannabinoid
receptor resulted in the isolation and identification of
arachidonylethanolamide (anandamide) as a putative
endogenous ligand.5 More recently, a new peripheral
cannabinoid receptor was cloned and expressed in
macrophages in the marginal zone of the spleen (CB2).6
In an effort to obtain more detailed information on
the regiochemical and stereochemical requirements for
productive binding at the active site within a specific
class of cannabimimetic (CBMM) agents, we have
sought to develop novel ligands possessing high affinity
and selectivity for the cannabinoid receptors. Ac-
cumulated evidence indicated that within the cannab-
inoid structure the aliphatic side chain plays a pivotal
role in determining CBMM activity. Structural varia-
tions within this pharmacophore can result in analogues
varying by up to 3 orders of magnitude in affinity for
the receptor and in pharmacological potency.7 The
present paper aims at exploring, in part, the side chain’s
stereoelectronic requirements for activity within the
classical tetrahydrocannabinol (THC) structure. More
specifically and following earlier leads,8 we have focused
on the C1′ position of the side chain and explored the
role of different substituents on the affinities of these
analogues for the CB1 and CB2 cannabinoid receptors.
Ch em istr y
Generally, the synthesis of side-chain congeners of ∆8-
THC was accomplished by the condensation of a mono-
terpene with an appropriately substituted resorcinol.
For the synthesis of (-)-(1-heptynyl)-∆8-THC (1) (Chart
1), we followed a modification of the method described
in the literature10 and condensed 5-(1-heptynyl)resor-
cinol (9) with (+)-cis/ trans-p-mentha-2,8-dien-1-ol11 in
the presence of p-toluenesulfonic acid. On the other
* To whom correspondence should be addressed.
† National Hellenic Research Foundation.
‡ University of Connecticut.
S0022-2623(97)00277-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/14/1998

1196 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7
Notes
Sch em e 1
Sch em e 2
hand, condensation of 2-(3,5-dihydroxyphenyl)-2-hexyl-
1,3-dithiolane (13) with (+)-cis/ trans-p-menta-2,8-dien-
1-ol was accomplished by sequential treatment with
p-toluenesulfonic acid and boron trifluoride etherate12
to give 2-(6a,7,10,10a-tetrahydro-6,6,9-trimethyl-1-hy-
droxy-6H-dibenzo[b,d]pyranyl)-2-hexyl-1,3-dithiolane (5)
(Chart 1), in a 63% overall yield.
Ch a r t 1
The two resorcinols, 5-(1-heptynyl)resorcinol (9)
(Scheme 1) and 2-(3,5-dihydroxyphenyl)-2-hexyl-1,3-
dithiolane (13) (Scheme 2), were synthesized from a
common, commercially available starting material, 3,5-
dimethoxybenzaldehyde (6). Thus, the Wittig reaction
of 3,5-dimethoxybenzaldehyde (6) with R,R-dibromo-
methylenetriphenylphosphorane13 gave the vinylic di-
bromide 7 in a 99% yield. Sequential treatment of 7
with n-butyllithium and 1-bromopentane in the pres-
ence of hexamethylphosphoric triamide14 (HMPA) af-
forded 1,3-dimethoxy-5-(1-heptynyl)benzene (8) in 60%
yield. Subsequently, deprotection of the methoxy groups
to provide 5-(1-heptynyl)resorcinol (9) was achieved
using boron tribromide in methylene chloride at -10
°C for 16 h, resulting in a 66% yield after purification.
Reaction of 3,5-dimethoxybenzaldehyde with hexyl-
magnesium bromide occurred under the usual condi-

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7 1197
Ta ble 1. Affinities (Ki) of Cannabinoid Analogues for the CB1
and CB2 Receptors (95% Confidence Limits)
affinity 11-hydroxyhexahydrocannabinol prototype, we
had observed that the 1′-alkyne analogue showed a
considerable (10-fold) selectivity for CB1. The corre-
sponding ∆8-THC analogue 1 included in this study also
showed selectivity for CB1 (5-fold). On the basis of
earlier work in which 11-hydroxyhexahydrocannabinol
(11-OH-HHC) analogues had optimal pharmacophoric
requirements for CB1,12,18 we had anticipated that 1
would show a lower affinity for CB1 than its corre-
sponding 11-OH-HHC analogue. To our surprise 1 had
a higher affinity with a subnanomolar Ki value. This
perhaps indicates that the presence of the C1′-triple
bond in the 11-OH-HHC prototype does not allow the
simultaneous optimal alignment of both the 11-hydroxy
and side-chain pharmacophores in the CB1 active site
thus reducing this analogue’s affinity for the receptor.
The introduction of a 1′-methylene group (4) results
in a high-affinity ∆8-THC ligand with only limited
selectivity for CB1. However, this high affinity is
severely reduced when the sp2 carbon atom in 4 is
substituted with an oxygen in the more polar keto
analogue 3. This analogue now has a 10-fold lower
affinity for CB1 and an even lower affinity for CB2. The
affinity for CB1 is further reduced with a hydroxyl group
substitution at C1′. This equally populated diastereo-
meric mixture (2) shows relatively low affinity for CB1
and virtually no selectivity with respect to CB2. The
results indicate a requirement for hydrophobic groups
at C1′ for optimal selectivity for both CB receptors and
reduced tolerance for more polar substituents. The
above conclusion is strongly reinforced by our results
with the 1′,1′-dithiolane analogue 5. This compound
with Ki values of 0.32 and 0.52 nM for CB1 and CB2,
respectively is a cannabimimetic molecular probe with
one of the highest affinities reported to date. This
increase in affinity can clearly be attributed to the
hydrophobic subsite for both CB1 and CB2 at the level
of the benzylic side-chain carbon. Currently, we are
investigating the structural requirements for interaction
of this subsite through the design and synthesis of a
series of new analogues. We are hopeful that the
identification of the above-mentioned subsite will pro-
vide us with new opportunities for the design of very
high-affinity novel analogues with selectivities for the
two cannabinoid receptor subtypes.
Ki (nM)a
compd
CB1
CB2
1
2
3
4
5
0.65 ( 0.12
86.4 ( 17.9
21.7 ( 7.1
2.17 ( 0.46
0.32 ( 0.08
136 ( 35
3.1 ( 0.13
65.6 ( 18.6
83.7 ( 19.2
3.3 ( 0.58
0.52 ( 0.17
50.4 ( 14.2
14
a
Affinities of the cannabinoid analogues for CB1 and CB2 were
determined using rat brain (CB1) or mouse spleen (CB2) mem-
branes and [3H]CP-55,940 as previously described.22 Ki values
were obtained from three independent experiments run in dupli-
cate and are expressed as the mean of the three values.
tions, giving 3,5-dimethoxy-1-(1′-hydroxyheptyl)resor-
cinol (10) (Scheme 2) in an 87% yield. Oxidation of 10
with J one’s reagent at room temperature resulted in the
formation of ketone 11 in an 80% yield, which upon
treatment with 1,2-ethanedithiol and boron trifluoride
etherate in methylene chloride gave the corresponding
thioketal 12 in a 97% yield. This was demethylated
with boron tribromide in methylene chloride at 0 °C for
12 h to afford resorcinol 13 in 84% yield. Close ana-
logues of 13 and 5 have been reported by Fahrenholtz.15
Compound 5 served as a starting point for several
side-chain analogues. Thus cleavage of the 1,3-dithio-
lane group with silver nitrate in aqueous 90% ethanol16
afforded the keto analogue 3, which was subsequently
converted to the corresponding alcohol 2 in 93% yield.
Finally the preparation of 4 was most efficiently achieved
using the Taylor protocol.17
Recep tor Bin d in g Stu d ies
The abilities of 1-5 and 14 to displace radiolabeled
CP-55,940 from purified rat forebrain synaptosomes and
mouse spleen synaptosomes were determined as de-
scribed in the methods section. Ki values calculated
from the respective displacement curves are listed in
Table 1 and serve as indicators for the affinities of these
∆8-THC analogues for the CB1 and CB2 receptors.
Resu lts a n d Discu ssion
The compounds included in this study are ∆8-THC
analogues in which the optimized seven-carbon side
chain was modified at the C1′ position. As can be
observed in Table 1, the range of Ki values of the six
analogues included in this study spans over 2 orders of
magnitude, indicating that structural modifications at
the benzylic position of the side chain of the ∆8-THC
skeleton can have a profound effect on the affinities of
these molecules for both the CB1 and CB2 receptors.
Our results confirm earlier findings9 clearly indicating
that a seven-carbon side chain on the tetrahydrocan-
nabinoid structure can lead to high-affinity analogues
for both cannabinoid receptors as is exemplified by 1,
4, and 5. Also in accordance with earlier structure-
activity relationships (SAR),7 the cannabidiol analogue
14 has considerably reduced afffinities.
Ma ter ia ls a n d Exp er im en ta l P r oced u r es
All reactions were carried out under scrupulously dry
conditions. Organic phases were dried over Na2SO4 and
evaporated under reduced pressure. Silica gel 60, 200-400
mesh, and ASTM, 150-230 mesh (E. Merck, Germany), were
used for flash and gravity column chromatography, respec-
tively. All compounds were demonstrated to be homogeneous
by analytical TLC on precoated silica gel TLC plates (grade
60, F254, E. Merck), and chromatograms were visualized by
phosphomolybdic acid staining. 1H NMR spectra were re-
corded on a Bruker AC 300 spectrometer operating at 300 MHz
and are reported in units of δ relative to internal CHCl3 at
7.24 ppm. All NMR spectra were recorded in CDCl3 unless
otherwise stated. Analyses indicated by the symbols of the
elements were carried out by the microanalytical section of
the Institute of Organic and Pharmaceutical Chemistry,
National Hellenic Research Foundation.
Introduction of a triple bond in the benzylic position
restricts rotation around the C1′-C2′ bond. The result-
ing ∆8-THC analogue 1 has a high affinity for CB1 as
well as a 5-fold selectivity for this receptor over its
subtype CB2. In a previous publication,9 using a high-
Vin ylic Dibr om id e 7. To a solution of carbon tetrabromide
(2 g, 12 mmol) in 28 mL of anhydrous methylene chloride at 0
°C was added triphenylphosphine (7.86 g, 30 mmol) portion-
wise so that the reaction temperature did not exceed 5 °C. The

1198 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7
Notes
mixture was stirred at 0 °C for an additional 30 min, and a
solution of 3,5-dimethoxybenzaldehyde (2 g, 12 mmol) in 7.5
mL of dry methylene chloride was added dropwise via syringe.
Stirring at 0 °C was continued until TLC showed that all of
the aldehyde had reacted (3 h). At completion, methylene
chloride was removed on a rotary evaporator, and the residue
was purified by flash column chromatography (20% diethyl
ether-petroleum ether as eluent) to afford 3.46 g (yield 99%)
of dibromide 7: 1H NMR (300 MHz, CDCl3) δ 7.41 (s, 1H), 6.68
saturated NH4Cl (2 × 10 mL) and brine (20 mL), dried (Na2-
SO4), and evaporated. Purification by flash column chroma-
tography (20% diethyl ether-petroleum ether as eluent)
provided 2.6 g of compound 10 (86%): 1H NMR (300 MHz,
CDCl3) δ 6.49 (d, J ) 2.1 Hz, 2H), 6.36 (t, J ) 2.1 Hz, 1H),
4.57 (t, J ) 5.7 Hz, 1H), 3.78 (s, 6H), 1.96 (brs, 1H, OH), 1.70
(m, 2H), 1.27 (bs, 8H), 0.87 (t, J ) 6.8 Hz, 3H). Anal.
(C15H24O3) C, H.
1-(3,5-Dim eth oxyp h en yl)-1-h ep ta n -1-on e (11). Resor-
cinol 10 (2.47 g, 9.8 mmol) was dissolved in acetone (25 mL).
To this cold (0 °C) solution was added a solution of J one’s
reagent (14 mL; prepared from 7 g of CrO3, 50 mL of H2O,
and 6.1 mL of concentrated H2SO4), and the reaction mixture
was stirred at room temperature for 0.5 h. Upon completion
the reaction was quenched by the addition of propan-2-ol, the
mixture diluted with ethyl acetate (80 mL), and the organic
phase washed with 20% aqueous sodium bisulfite (2 × 20 mL),
H2O (20 mL), and brine (25 mL), dried (Na2SO4), and evapo-
rated. Purification by flash column chromatography (30%
diethyl ether-petroleum ether) yielded compound 11 (1.95 g,
79.6%): 1H NMR (300 MHz, CDCl3) δ 7.09 (d, J ) 2.32 Hz,
2H), 6.64 (t, J ) 2.32 Hz, 1H), 3.84 (s, 6H), 2.91 (t, J ) 7.3 Hz,
2H), 1.71 (m, 2H), 1.33 (brs, 6H), 0.89 (t, J ) 6.7 Hz, 3H). Anal.
(C15H22O3) C, H.
2-(3,5-Dim et h oxyp h en yl)-2-h exyl-1,3-d it h iola n e (12).
Ketone 11 (1.9 g, 7.6 mmol) was dissolved in methylene
chloride (30 mL), and 1,2-ethanedithiol (1.3 g, 13.8 mmol) and
boron trifluoride etherate (0.272 mL, 2.3 mmol) were added.
The solution was stirred at room temperature overnight, and
at completion a saturated solution of NaHCO3 (10 mL) was
added. The mixture was diluted with diethyl ether; the
organic layer was washed with water (15 mL) and brine (2 ×
15 mL), dried (Na2SO4), and evaporated to afford 2.4 g of 12
(97%) sufficiently pure for the following step: 1H NMR (300
MHz, CDCl3) δ 6.86 (d, J ) 2.0 Hz, 2H), 6.33 (t, J ) 2.0 Hz,
1H), 3.79 (s, 6H), 3.38-3.19 (m, 4H), 2.33 (t, J ) 7.4 Hz, 2H),
1.21 (brs, 8H), 0.83 (t, J ) 6.9 Hz, 3H). Anal. (C17H26O2S2)
C, H.
2-(3,5-Dih ydr oxyph en yl)-2-h exyl-1,3-dith iolan e (13). Bo-
ron tribromide (0.47 mL, 4.93 mmol) was added to a solution
of 12 (0.6 g, 1.84 mmol) in methylene chloride (49 mL) at -78
°C under an argon atmosphere. Following the addition of
boron tribromide, the reaction temperature was gradually
raised over a period of 3 h to 0 °C. Stirring was continued at
that temperature until completion of the reaction (12 h).
Workup of the reaction mixture was performed as described
earlier for compound 9. Purification by flash column chroma-
tography (50% diethyl ether-petroleum ether as eluent) gave
460 mg (84%) of compound 13: 1H NMR (300 MHz, CDCl3) δ
6.76 (d, J ) 2.2 Hz, 2H), 6.21 (t, J ) 2.2 Hz, 1H), 4.95 (s, 2H),
3.36-3.16 (m, 4H), 2.25 (m, 2H), 1.19 (brs, 8H), 0.82 (t, J )
7.0 Hz, 3H). Anal. (C15H22O2S2) C, H.
(d, J ) 2.1 Hz, 2H), 6.44 (brs, 1H), 3.79 (s, 6H). Anal. (C10H10
-
Br2O2) C, H.
1,3-Dim eth oxy-5-(1′-h ep tyn yl)ben zen e (8). Dibromide
7 (2 g, 6.9 mmol) was dissolved in anhydrous THF (22 mL)
and cooled to -78 °C under an argon atmosphere. A 1.6 M
solution of n-butyllithium in hexanes (9.5 mL, 15.18 mmol)
was added over 15 min, and the reaction mixture was stirred
for 1 h at -78 °C. A solution of 1-bromopentane (0.95 mL,
7.59 mmol) in 15 mL of dry hexamethylphosphoramide was
then added dropwise, and stirring was continued at -78 °C
for 4.5 h, whereupon the reaction was quenched by the addition
of a saturated solution of NH4Cl. Workup under standard
conditions followed by flash column chromatography (5%
diethyl ether-petroleum ether as eluent) provided 950 mg
(yield 60%) of compound 8: 1H NMR (300 MHz, CDCl3) δ 6.55
(d, J ) 1.16 Hz, 2H), 6.39 (brs, 1H), 3.76 (s, 6H), 2.39 (t, J )
6.85 Hz, 2H), 1.7-1.3 (m, 6H), 0.92 (t, J ) 7.2 Hz, 3H). Anal.
(C15H20O2) C, H.
5-(1′-Hep tyn yl)r esor cin ol (9). Boron tribromide (1.28 g,
5.12 mmol) was added to a solution of 1,3-dimethoxy-5-(1-
heptynyl)benzene (0.54 g, 2.33 mmol) in methylene chloride
(77.5 mL) at -78 °C under an argon atmosphere. Following
the addition of BBr3, the reaction temperature was gradually
raised over a period of 2 h to -10 °C. Stirring was continued
at that temperature until completion of the reaction was
indicated by TLC (16 h). Unreacted boron tribromide was
destroyed by addition of methanol. The solvent was removed
in vacuo, and the residual oil was diluted with ethyl acetate.
The solution was washed with saturated sodium bicarbonate
(2 × 20 mL), water (2 × 10 mL), and brine (2 × 20 mL). The
organic layer was dried over Na2SO4, filtered, and concentrated
in vacuo. Purification by flash column chromatography (60%
diethyl ether-petroleum ether as eluent) gave 310 mg (yield
65%) of 5-(1-heptynyl)resorcinol (9): 1H NMR (300 MHz,
CDCl3) δ 6.46 (d, J ) 2.0 Hz, 2H), 6.29 (brs, 1H), 5.10 (brs,
2H), 2.36 (t, J ) 7 Hz, 2H), 1.65-1.25 (m, 6H), 0.91 (t, J ) 7
Hz, 3H). Anal. (C13H16O2) C, H.
(-)-(1′-Hep tyn yl)-∆8-THC (1). 5-(1-Heptynyl)resorcinol
(9) (150 mg, 0.736 mmol) was azeotroped with dry benzene (2
× 10 mL) and dissolved in dry benzene (7 mL). Dry p-
toluenesulfonic acid was added (26 mg, 0.137 mmol) followed
by the addition of (+)-cis/ trans-p-mentha-2,8-dien-1-ol (140
mg, 0.92 mmol). The reaction mixture was heated under dry
argon to 80 °C for 4 h. Upon completion, the mixture was
diluted with diethyl ether (40 mL) and the ethereal solution
washed successively with saturated aqueous NaHCO3 (2 × 5
mL), H2O (2 × 5 mL), and brine (2 × 10 mL) and dried over
Na2SO4. Filtration, concentration in vacuo, and purification
by flash column chromatography (10% diethyl ether-petro-
leum ether as eluent) afforded 62 mg of 1 (25%): 1H NMR (300
MHz, CDCl3) δ 6.78 (s, 1H, OH), 6.28 (d, J ) l.96 Hz, 1H),
6.09 (d, J ) 1.96 Hz, 1H), 5.43 (bs, 1H), 3.2 (dd, J ) 4, 12 Hz,
1H), 2.8-2.53 (m, 3H), 2.15 (m, 1H), 1.95-1.52 (m, 6H), 1.38
(s, 3H), 1.37-1.2 (bs, 6H), 1.09 (s, 3H), 0.90 (t, J ) 7 Hz, 3H).
Anal. (C23H30O2) C, H.
1-(3,5-Dim eth oxyph en yl)h eptan -1-ol (10). 3,5-Dimethoxy-
benzaldehyde (6) (2 g, 12 mmol) was dissolved in dry tetrahy-
drofuran (24 mL) under an argon atmosphere and the flask
cooled to -78 °C. Hexylmagnesium bromide [prepared from
1-bromohexane (5.94 g, 36 mmol) and Mg turnings (876 mg,
36 mmol) in dry tetrahydrofuran (72 mL)] was added, and
stirring continued for 4 h at -60 °C. Upon completion the
reaction was quenched by the addition of saturated aqueous
ammonium chloride (10 mL). The reaction mixture was
extracted with ethyl acetate (3 × 50 mL), washed with
(-)-2-(6a,7,10,10a-Tetr ah ydr o-6,6,9-tr im eth yl-1-h ydr oxy-
6H-d iben zo[b,d ]p yr a n yl)-2-h exyl-1,3-d ith iola n e (5). To a
solution of resorcinol 13 (0.46 g, 1.54 mmol) in dry benzene
(14.0 mL) at 25 °C under an argon atmosphere was added (+)-
cis/ trans-p-mentha-2,8-dien-1-ol (293 mg, 1.93 mmol) followed
by the addition of p-toluenesulfonic acid (54.5 mg, 0.29 mmol).
The reaction mixture was stirred at 25 °C for 0.5 h, at which
time TLC indicated the complete consumption of starting
material. The reaction mixture was diluted with ether. The
ethereal solution was washed with saturated NaHCO3, H2O,
and brine and dried (Na2SO4). Evaporation of the solvent
followed by flash column chromatography (10% diethyl ether-
petroleum ether) afforded 670 mg of cannabidiol 14: 1H NMR
(300 MHz, CDCl3) δ 6.72 (bs, 2H), 6.0 (s, 1H, OH), 5.55 (s,
1H), 4.9 (bs, 1H, OH), 4.61 (s, 1H), 4.55 (s, 1H), 3.85 (m, 1H),
3.4-3.2 (m, 5H), 2.5-2.0 (m, 6H), 1.7 (s, 3H), 1.40 (s, 3H), 1.25
(bs, 8H), 0.85 (t, J ) 7 Hz, 3H). Anal. (C25H36O2S2) C, H.
To a solution of 14 (0.67 g, 1.55 mmol) in anhydrous
dichloromethane (44 mL) was added boron trifluoride etherate
(0.69 mL, 5.55 mmol) at 0 °C. Following the addition the
reaction mixture was stirred at 25 °C for 4 h, at which time
TLC indicated the disappearance of starting material. The

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7 1199
reaction was quenched by the addition of a saturated solution
of NaHCO3, the mixture was concentrated in vacuo and diluted
with ethyl acetate, and the organic layer was washed with
water (15 mL) and brine (2 × 15 mL) and dried over Na2SO4.
Solvent evaporation and purification by flash column chro-
matography (10% diethyl ether-petroleum ether as eluent)
afforded 5. The overall yield from 13 was 422 mg (63%): 1H
NMR (300 MHz, CDCl3) δ 6.8 (d, J ) 1.98 Hz, 1H, H4), 6.6 (d,
J ) 1.98 Hz, 1H, H2), 5.45 (bs, 1H, H8), 4 75 (s, 1H, OH), 3.4-
3.2 (m, 4H, -S(CH2)2S-), 3.20 (m, 1H, H10R), 2.7 (br s, 1H, H10a),
from these membranes was used to determine the K50 values
for the test compounds. The assay was conducted in a 96-
well microfilter plate. The samples were filtered using a
Packard Filtermate 96 and Whatman GF/C filter plates, and
0.5% BSA was incorporated into the wash buffer. Radioactiv-
ity was detected using MicroScint 20 scintillation cocktail
added to the dried filter plates and was counted using a
Packard Instruments Top Count. Data were collected from
three independent experiments between 100% and 0% specific
binding for [3H]CP-55,940, determined using 0 and 100 nM
CP-55,940. The normalized data from three independent
experiments were combined and analyzed using a four-
parameter logistic equation to yield IC50 values which were
converted to Ki values using the assumptions of Cheng and
Prussoff.21
2.3 (m, 2H, 2′CH2), 2.15 (m, 1H, H7), 2.05-1.83 (m, 3H, H6R
,
H7, H10â), 1.7 (s, 3H), 1.4 (s, 3H), 1.25 (brs, 8H, -CH2-), 1.1 (s,
3H), 0.85 (t, J ) 7 Hz, 3H). Anal. (C25H36O2S2) C, H.
(-)-1-Hyd r oxy-6a ,7,10,10a -tetr a h yd r o-6,6,9-tr im eth yl-
6H-d iben zo[b,d ]p yr a n -3-yl 1′-Hexyl Keton e (3). To a
stirred solution of 1,3-dithiolane 5 (100 mg, 0.23 mmol) in 90%
ethanol (4 mL) at 25 °C was added a solution of AgNO3 (120
mg, 0.69 mmol) in water (0.5 mL), and the reaction mixture
stirred at room temperature for 3 h. At completion the
precipitate was removed and washed with ethyl acetate and
the filtrate further diluted with ethyl acetate, washed with
brine, and dried (Na2SO4). Solvent evaporation and purifica-
tion of the residue by flash column chromatography (15%
diethyl ether-petroleum ether as eluent) afforded 65 mg of 3
(79%): 1H NMR (300 MHz, CDCl3) δ 7.18 (d, J ) 1.4 Hz, 1H),
7.0 (d, J ) 1.4 Hz, 1H), 6.4 (s, 1H), 5.44 (d, J ) 4 Hz, 1H),
3.32 (dd, J ) 4, 13 Hz, 1H), 2.9 (t, J ) 7 Hz, 2H), 2.79 (m,
1H), 2.15 (m, 1H), 1.94-1.7 (m, 3H), 1.67 (s, 3H), 1.39 (s, 3H),
1.36 (bs, 8H), 1.08 (s, 3H), 0.88 (t, J ) 7 Hz, 3H). Anal.
(C23H32O3) C, H.
Ack n ow led gm en t. This work was supported by the
National Hellenic Research Foundation and by National
Institute on Drug Abuse (U.S.A.) grants DA-3801, DA-
7215, DA-9158, and DA-0152. We would like to thank
Dr. E. Kalatzis for providing us with the elemental
analysis data.
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1H NMR (300 MHz, CDCl3) δ 6.5 (d, J ) 1.5 Hz, 1H), 6.34 (d,
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1H), 4.87 (bs, 1H, OH), 3.23 (dd, J ) 4.14 Hz, 1H), 2.73 (m,
1H), 2.41 (t, J ) 7 Hz, 2H), 2.15 (m, 1H), 1.93-1.81 (m, 3H),
1.7 (s, 3H), 1.41 (s, 3H), 1.34 (bs, 8H), 1.11 (s, 3H), 0.86 (t, J
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