Journal of Medicinal Chemistry
Article
salicylaldehyde). The reaction vessel was subjected to microwave
irradiation and kept at a constant temperature of 110 °C for 50 min
(max. 200 W) while being stirred. After being cooled to rt, the reaction
was quenched by addition of water. The aqueous layer was extracted
with EtOAc, the combined organic phases were dried over sodium
sulfate, and the solvent was removed under reduced pressure. The
products were purified by flash column chromatography. Purity was
another jump between 27a and 26a, 28a, indicating that there
is an optimal size for the substituent at the 7-position.
Physicochemical Properties. Molecular weights, log P
values, and polar surface areas of selected coumarin derivatives
(19a, 21a, and 28b), which possess high affinity, were
calculated and compared to those of commercially available
CB receptor ligands some of which are therapeutically used
(see Supporting Information, Table S3). The physicochemical
properties of the new coumarin derivatives are in the same
range as those of commercially available CB ligands, indicating
that they may show similar in vivo behavior.
1
determined by H NMR, MS, and elemental analysis and was ≥95%.
5-Methoxy-3-(2-methylbenzyl)-7-pentyl-2H-chromen-2-one
(19a). Yield 56.3 mg, 36% (scale: 450 μmol). Rf (c-Hex/EtOAc 40:1)
= 0.06. mp: 173−175 °C. 1H NMR (400 MHz, CDCl3): δ/ppm = 0.92
(t, 3J = 6.9 Hz, 3 H, CH2-CH3), 1.32−1.39 (m, 4 H, 2 × CH2), 1.62−
1.68 (m, 2 H, CH2), 2.30 (s, 3 H, Car-CH3), 2.66 (t, 3J = 7.7 Hz, 2 H,
Car-CH2-CH2), 3.84 (s, 3 H, OCH3), 3.89 (s, 2 H, CH2), 6.50 (s, 1 H,
Har), 6.77 (s, 1 H, Har), 7.20−7.25 (m, 4 H, 4 × Har), 7.46 (s, 1 H,
CH). 13C NMR (100 MHz, CDCl3): δ/ppm = 14.0 (p, CH2-CH3),
19.5 (p, Car-CH3), 22.5 (s, CH2), 30.8 (s, CH2), 31.4 (s, CH2), 34.0 (s,
CH2), 36.6 (s, Car-CH2-CH2), 55.8 (p, OCH3), 105.5 (t, CarH), 108.0
(q, Car-CH), 108.4 (t, CarH), 125.1 (q, Car-CH2), 126.2 (t, Car-H),
127.0 (t, Car-H), 130.2 (t, Car-H), 130.5 (t, Car-H), 134.1 (t, CH),
136.1 (q, C-CH2), 136.9 (q, Car-CH3), 147.6 (q, Car-CH2CH2), 154.1
(q, Car-O-CO), 155.4 (q, Car-OCH3), 162.2 (q, CO). IR (DRIFT):
ν/cm−1 = 2924 (w), 2858 (w), 1725 (m), 1618 (m), 1573 (w), 1494
(w), 1455 (w), 1423 (w), 1352 (w), 1244 (w), 1167 (w), 1142 (w),
1117 (m), 1051 (w), 957 (w), 881 (w), 833 (w), 760 (w), 745 (w),
728 (w), 468 (w), 408 (w). EI-MS m/z (%): 351 (29) [M+ + H], 350
CONCLUSIONS
■
A series of 7-alkyl-3-benzylcoumarin derivatives was designed
and synthesized as high affinity CB1 and/or CB2 receptor
ligands, tested in radioligand binding studies, and functionally
characterized in cAMP accumulation assays. On the basis of the
obtained structure−activity relationships, the synthesized
compounds can be separated into two classes: 5-methoxy-
and the 5-hydroxy-substituted coumarins. The two groups
differ in their structure−activity relationships and their
functional properties. In particular, the SARs of 5-hydroxy-
coumarins correlate better with those of classical cannabinoids.
The physicochemical properties of the synthesized compounds
are comparable to those of commercially available and
therapeutically applied CB receptor ligands. The developed
series provides the advantage of high versatility, allowing us to
obtain potent CB receptor ligands with high affinity and
potency at either CB1 or CB2, or both receptor subtypes.
Furthermore fine-tuning of compound properties with regard
to affinity, selectivity, and efficacy could be achieved by small
modifications of the substitution pattern. Thus, 7-alkyl-3-
benzylcoumarins are highly versatile scaffolds for obtaining
potent CB receptor ligands. The relatively simple structures,
which do not possess any stereocenters, are easily accessible by
a straightforward one-pot synthetic procedure. Derivatives
which possess high potency at either CB1, or CB2, or both
receptor subtypes and a broad spectrum of efficacies at each
receptor subtype could be obtained. The most potent
compounds of the present series include 5-methoxy-3-(2-
methylbenzyl)-7-pentyl-2H-chromen-2-one (19a, PSB-SB-
1201), a potent and selective CB1 antagonist (Ki CB1 0.022
μM, 18-fold selective), 5-methoxy-3-(2-methoxybenzyl)-7-
pentyl-2H-chromen-2-one (21a, PSB-SB-1202), a potent dual
CB1/CB2 agonist (CB1 Ki 0.032 μM, EC50 0.056 μM; CB2 Ki
0.049 μM, EC50 0.014 μM), 5-hydroxy-3-(2-hydroxybenzyl)-7-
(2-methyloct-2-yl)-2H-chromen-2-one (25b, PSB-SB-1203), a
dual CB1/CB2 ligand that blocks CB1 but activates CB2
receptors (CB1 Ki 0.244 μM; CB2 Ki 0.210 μM, EC50 0.054
μM), and 7-(1-butylcyclopentyl)-5-hydroxy-3-(2-hydroxyben-
zyl)-2H-chromen-2-one (27b, PSB-SB-1204), which is a
selective CB2 receptor agonist (CB1 Ki 1.59 μM; CB2 Ki
0.068 μM, EC50 0.048 μM). Selected compounds of the
present series will be further investigated in animal models to
explore the pharmacological properties of these new
cannabinoid receptor ligands.
+
+
(100) [M+], 333 (21), 294 (19) [C19H18O3 ], 259 (22) [C16H19O3 ].
EI-HRMS (C23H26O3): calcd 350.1882, found 350.1885.
General Procedures for the Deprotection of Coumarin Deriva-
tives. Under an atmosphere of argon, 5.00 equiv BBr3 (1 M, CH2Cl2)
was added to a solution of 1.00 equiv of coumarin in dichloromethane
(20 mL/mmol coumarin) at −78 °C, and the resulting mixture was
stirred for 30 min at this temperature and for 24 h at rt. For work up,
saturated NaHCO3 solution was added at 0 °C, and the aqueous layer
was extracted with CH2Cl2. The combined organic phases were
washed with water and brine and were dried over sodium sulfate. The
solvent was removed under reduced pressure, and the product was
purified by flash column chromatography.
7-(1-Butylcyclopentyl)-5-hydroxy-3-(2-hydroxybenzyl)-2H-chro-
men-2-one (27b). Yield 317 mg, 99% (scale: 820 μmol). Rf (c-Hex/
EtOAc 7:1) = 0.12. mp: 67−70 °C. 1H NMR (400 MHz, CDCl3): δ/
3
ppm = 0.74 (t, J = 7.3 Hz, 3 H, CH3), 0.84−0.92 (m, 2 H, CH2),
1.07−1.16 (m, 2 H, CH2), 1.49−1.54 (m, 2 H, CH2), 1.56−1.61 (m, 2
H, CH2), 1.64−1.72 (m, 3 H, CH2), 1.74−1.85 (m, 3 H, CH2), 3.87 (s,
4
4
2 H, CH2), 6.69 (d, J = 1.4 Hz, 1 H, Har), 6.78 (d, J = 1.4 Hz, 1 H,
Har), 6.87 (ddd, 3J = 3J = 7.5 Hz, 4J = 1.2 Hz, 1 H, Har), 6.95 (dd, 3J =
8.1 Hz, 4J = 1.2 Hz, 1 H, Har), 7.13 (ddd, 3J = 3J = 8.1 Hz, 4J = 1.7 Hz,
1 H, Har), 7.23 (dd, 3J = 7.5 Hz, 4J = 1.7 Hz, 1 H, Har), 7.40 (bs, 1 H,
OH), 8.16 (s, 1 H, CH), 8.36 (bs, 1 H, OH). 13C NMR (100 MHz,
CDCl3): δ/ppm =13.9 (p, CH3), 23.1 (s, 2 × CH ), 23.2 (s, CH2),
2
27.4 (s, CH2), 32.1 (s, CH2), 37.5 (s, 2 × CH2), 41.4 (s, CH2), 51.6 (q,
C(CH2)3), 106.9 (t, Car-H), 107.2 (q, Car-CH), 109.4 (t, Car-H), 118.1
(t, Car-H), 121.1 (t, Car-H), 124.7 (q, C-CH2), 125.4 (q, Car-CH2),
128.6 (t, Car-H), 130.6 (t, Car-H), 136.6 (t, CH), 152.5 (q, Car-C),
153.7 (q, Car-O-CO), 154.2 (q, Car-OH), 165.6 (q, CO), 171.9 (q,
Car-OH). IR (ATR): ν/cm−1 = 3276 (w), 2927 (w), 2859 (w), 1674
(m), 1615 (m), 1489 (w), 1455 (m), 1422 (m), 1343 (w), 1234 (m),
1176 (m), 1054 (m), 933 (w), 845 (w), 751 (m), 732 (w), 671 (w),
523 (w). FAB-MS m/z (%): 393 (100) [M+ + H], 299 (82)
+
[C19H23O3 ], 107 (37) [C7H7O+]. FAB-HRMS (C25H28O4 + H+):
calcd 393.2066, found 393.2064.
Retroviral Transfection. CHO K1 cells stably transfected with the
human CB1 and CB2 receptor were generated with a retroviral
transfection system. Packaging cells (1.5 × 106 GP+envAM12 cells)
were plated into 25 cm2 cell culture flasks 24 h before the transfection
and grown in 5 mL of DMEM medium containing 10% FCS, 100 U/
mL penicillin, 100 μg/mL streptomycin, 1% ultraglutamine, and 0.2
mg/mL hygromycin B. A few hours before the transfection, the
medium was replaced with 6.25 mL of DMEM medium supplemented
with 10% FCS and 1% ultraglutamine without antibiotics. Receptor
EXPERIMENTAL SECTION
■
Syntheses. General Procedures for the Preparation of Coumarin
Derivatives. Under an atmosphere of argon, 1.00 equiv of substituted
salicylaldehyde, 1.20 equiv of potassium carbonate, 2.50 equiv of α,β-
unsaturated aldehyde, and 1.20 equiv of 1,3-dimethylimidazolium
dimethylphosphate were suspended in toluene (3.3 mL/mmol
7974
dx.doi.org/10.1021/jm3008213 | J. Med. Chem. 2012, 55, 7967−7977