Syntheses of 7-Substituted α-Cyperone Derivatives for Selective Sigma-1 Receptor over Cannabinoid-1 Receptor Binding Affinities

Experimental

Instruments and Chemicals. Melting points were obtained on a Fisher-Johns melting point apparatus. 1H and 13C NMR spectra were obtained on a Varian Gemini NMR spectrometer at 400 and 100 MHz, respectively. 1H chemical shifts were recorded relative to TMS (trimethylsilane, 0 ppm) and 13C chemical shifts relative to CDCl3 (77.0 ppm) and coupling constants J in Hz. Abbreviations for signal multiplicities are as follows: s (singlet), d (doublet), t (triplet) and m (multiplet). ESI-MS spectra were obtained by Shimadzu LCMS-2010EV.

(2R,4aS,7R)-1,4a-Dimethyl-7-(prop-1-en-2-yl)2,3,4,4a, 5,6,7,8-octahydronaphthalen-2-ol (2): Compound 2 was prepared by following the previously reported procedure,15 and obtained as a yellow oil (3.21 g, 56% yield). The spectral data of the product were consistent with the previously reported data.

(4aS,7R)-7-(3-Chloroprop-1-en-2-yl)-1,4a-dimethyl-4, 4a,5,6,7,8-hexahydronaphthalen-2(3H)-one (3): To a solution of α-cyperone 1 (50 mg, 0.4 mmol) in ethnaol (10 mL) at −18 ℃ was added NaBH4 (50 mg, 1.5 mmol). The reaction mixture was stirred at room temperature for 1 h. After the reaction mixture was quenched with 1 N aqueous HCl solution at 0 ℃, the solution was extracted with ethyl acetate. The organic layer was washed with water and brine, dried over Na2SO4 and concentrated in vacuo. The residue was purified with silica gel chromatography to afford the titled compound as a yellow oil (35 mg, 57% yield). The spectral data of the product were consistent with the previously reported data.20

(4aS,7R)-7-Isopropyl-1,4a-dimethyl-4,4a,5,6,7,8-hexahydronaphthalen- 2(3H)-one (4): Compound 4 was prepared by following the previously reported procedure,21 and obtained as a yellow oil (120 mg, 61% yield). The spectral data of the product were consistent with the previously reported data.

(4aS,7R)-7-(3-Methoxyprop-1-en-2-yl)-1,4a-dimethyl- 4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one (5): A solution of (4aS,7R)-7-(3-chloroprop-1-en-2-yl)-1,4a-dimethyl- 4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one 3 (100 mg, 0.45 mmol) and TEA (45 mg, 0.45 mmol) in MeOH (10 mL) was refluxed for 12 h. After being cooled to room temperature, the mixture was washed with water and brine, dried over Na2SO4 and concentrated in vacuo. The residue was purified with silica gel chromatography to afford the product as a colorless oil (37 mg, 40% yield). 1H NMR (CDCl3) δ 1.16 (s, 3H, 4aC-CH3), 1.70 (s, 3H, 1C-CH3), 3.27 (s, 3H, OCH3), 3.87 (s, 2H, CH2OCH3), 4.96 (s, 1H, C(CH2OCH3)=CHH), 5.03 (s, 1H, C(CH2OCH3)=CHH); 13C NMR (CDCl3) δ 198.75, 161.60, 149.34, 128.66, 110.94, 74.92, 58.00, 42.00, 41.67, 37.47, 35.90, 33.85, 33.21, 27.29, 22.58, 11.05.

(4aS,7R)-7-(3-Hydroxyprop-1-en-2-yl)-1,4a-dimethyl- 4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one (6): Compound 6 was prepared by following the previously reported procedure,21 and obtained as a colorless oil (60 mg, 82% yield). The spectral data of the product were consistent with the previously reported data.

2-((2R,4aS)-4a,8-Dimethyl-7-oxo-1,2,3,4,4a,5,6,7-octahydronaphthalen- 2-yl)acrylic acid (7): Compound 7 was prepared by following the previously reported procedure,21 and obtained as a colorless oil (45 mg, 51% yield). The spectral data of the product were consistent with the previously reported data.

(4aS,7R)-7-(3-(Diethylamino)prop-1-en-2-yl)-1,4a-dimethyl- 4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one (8): To a solution of (4aS,7R)-7-(3-chloroprop-1-en-2-yl)-1,4adimethyl- 4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one 3 (40.0 mg, 0.41 mmol) and TEA (0.20 mL, 0.50 mmol) in dichloromethane (10 mL) was added diethylamine (0.30 mL, 0.61 mmol) and refluxed for 8 h. After being cooled to room temperature, the mixture was washed with water and brine, dried over Na2SO4 and concentrated in vacuo. The residue was purified with silica gel chromatography to afford the title compound as colorless oil (20 mg, 39% yield). 1H NMR (CDCl3) δ 0.90-0.98 (t, 6H, J = 7.2 Hz, N(CH2CH3)2), 1.16 (s, 3H, 4aC-CH3), 2.36-2.46 (q, 4 H, N(CH2CH3)2), 2.95 (s, 2H, C(=CH2)CH2N), 4.87 (s, 1H, C(=CHH)CH2N), 4.94 (s, 1H, C(=CHH)CH2N); 13C NMR (CDCl3) δ 198.85, 162.37, 151.51, 128.38, 110.57, 58.53, 46.63, 42.07, 41.85, 37.42, 35.97, 33.84, 33.53, 27.26, 22.55, 11.79, 11.02; ESIMS: m/z 290.35 (M + H)+, 331.40 (M + ACN + H)+.

CB1 Receptor Binding Assay. Preparation of rat cerebral cortex membrane and binding assays for the sigma-1 receptor were performed using methods published previously in detail.2425 Each tube contained 40 μg membrane protein, TME buffer and 0.1 nM of [3H] CP-55,940 was incubated in total reaction volume of 500 μL for 60 min at 30 ℃. Nonspecific binding was determined in the presence of 10 μM CP-55,940. The incubation was terminated by rapid filtration through the presoaked filtermats by using the cell harvester. After being washed three times with the ice-cold Tris-HCl buffer, the filter was transferred to a liquid scintillation vial. After addition of EtOH and counting cocktail, the quantity of radioactivity was determined by liquid scintillation spectrometry.

Sigma-1 Receptor Binding Assay. Preparation of rat cortex membrane and binding assays for the CB1 receptor were performed using methods published previously in detail.2627 In brief, Each tube contained 300 μg membrane protein, Tris-HCl buffer (50 mM, pH 8.0) and 5 nM of [3H]pentazocine was incubated in total reaction volume of 500 μL for 60 min at 25 ℃. The incubation was terminated by rapid filtration through the presoaked filtermats by using the cell harvester. After being washed three times with the ice-cold Tris-HCl buffer, the filter was transferred to a liquid scintillation vial. After addition of EtOH and counting cocktail, the quantity of radioactivity was determined by liquid scintillation spectrometry.