N-Arylsulfonyl-2-vinyltryptamines as new 5-HT₆ serotonin receptor Ligands

Abstract

Several new 2-vinyl-N_b,N_b-dimethyltryptamines were prepared using Fischer indole synthesis followed by simple functional group transformations and evaluated on 5-HT₄, 5-HT₅, 5-HT₆ and 5-HT₇ serotonin receptors. It was found that 2-vinyl substitution conferred a potent and selective 5-HT₆ binding activity to these molecules which could be enhanced by N_a-arylsulfonyl substituents.

Keywords::

• 2-vinyl-N_b,N_b-dimethyltryptamines
• N_a-arylsulfonyl-tryptamines
• 5-HT₆ receptor inhibitors
• radioligand binding tests

Introduction

Serotonin (5-hydroxytryptamine, 5-HT) receptor family represents seven main classes (5-HT₁ to 5-HT₇) and within these classes fourteen different subtypes have been reported [1]. Among these, human 5-HT₆ receptors were recently identified as members of the G-protein superfamily, positively coupled to an adenyl cyclase second messenger system, and mainly localised in the central nervous system [2,3]. The observed high binding affinity of some therapeutically important antipsychotic and antidepressant agents at 5-HT₆ receptors suggested their implication in the treatment of schizophrenia, anxiety, depression and related disorders [4]. Recent studies pointed out that 5-HT₆ receptors might be involved in behavioural and memory dysfunctions [2,5].

After the discovery of the first bisaryl sulfonamide type 5-HT₆ selective antagonists 6-8, Glennon has recently reported several 2-substituted tryptamines as selective 5-HT₆ ligands [9]. Both 2-ethyl- and 2-phenyl-5-methoxy-N,N-dimethyltryptamines 1 and 2 were found to be highly potent ligands, displaying agonist and antagonist effect, respectively (Figure 1).

Figure 1 Structure of serotonin and some 2-substituted tryptamines.

As part of our research programme concerning the preparation and synthetic application of 2-vinylindoles [10], we were interested to know whether functionalized 2-vinyltryptamines 3 could act as 5-HT₆ receptor ligands. The vinyl moiety could be considered to possess similar steric and electronic character to that of ethyl and phenyl groups, respectively.

Here we describe the preparation and biological activity of new 2-vinyltryptamines showing promising 5-HT₆ binding activities.

Materials and methods

Chemistry

General

Melting points, determined on a Reichert hot plate apparatus, are uncorrected. IR spectra were recorded on a Bomem FTIR apparatus with Cosmic interferometer. UV spectra (in MeOH) were recorded on a Unicam 8700 spectrometer. ¹H- and ¹³C- NMR spectra, using TMS as internal standard, were measured on a Bruker AC 300 apparatus at 300 and 75 MHz, respectively. MS spectra were obtained on a VG Autospec (Fisons) spectrometer.

Synthesis

2-Methyl-2,3,4,5-tetrahydro-1h-pyrido[4,3-b]indole (7)

Prepared according to the described method [11]. Yield: 95%.

8-Methoxy-2-methyl-2,3,4,5-tetrahydro-1h-pyrido[4,3-b]indole (8)

To an ice-cooled solution of 4-methoxyphenylhydrazine hydrochloride (6.0 g, 34.38 mmol) in methanol saturated with HCl gas (100 mL) was added dropwise 1-methyl-4-piperidone (4.69 g, 41.46 mmol) and the reaction mixture was stirred at room temperature for 30 min. After evaporation of the solvent under reduced pressure, the residue was dissolved in water (40 mL), alkalinized under cooling with a 10% aqueous solution of NaOH to pH = 12–13, and extracted with dichloromethane (4 × 40 mL). The combined organic layers were washed with water (10 mL), dried over Na₂SO₄, and evaporated to dryness to afford 8 (7.0 g, 94%) as an amorphous solid. IR (KBr), cm^{− 1}: 3388 (NH), 2905, 1630 (C = C); ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.55 (s, 3H, NCH₃), 2.65–2.77 (m, 4H, CH₂-CH₂NCH₃), 3.65 (s, 2H, CH₂-NCH₃), 3.82 (s, 3H, OCH₃), 6.70 (dd, J = 7.8, 2.1, 1H, H-7), 6.83 (d, J = 2.1, 1H, H-9), 7.01 (d, J = 7.8, 1H, H-6), 8.70 (s, 1H, NH); ¹³C NMR (CDCl₃), δ, ppm: 23.5 (CH₂-CH₂NCH₃), 45.6 (NCH₃), 51.7 (CH₂-CH₂NCH₃), 52.3 (CH₂NCH₃), 55.8 (OCH₃), 99.8 (C-9), 107.8 (C-9b), 110.5 (C-6), 111.3 (C-7), 126.2 (C-9a), 131.3 (C-4a), 132.7 (C-5a), 153.7 (C-8); MS (m/z, %) 216 (M⁺, 25), 173 (100), 158 (55), 130 (9).

2,2-Dimethyl-2,3,4,5-tetrahydro-1h-pyrido[4,3-b]indol-2-ium Iodide (9)

Prepared according to the described method [11]. Yield: 95%.

2,2-Dimethyl-8-methoxy-2,3,4,5-tetrahydro-1h-pyrido[4,3-b]indol-2-ium Iodide (10)

A solution of 8 (7.0 g, 32.4 mmol) in methanol (70 mL) was stirred with methyl iodide (14.1 g, 6.2 mL, 97.2 mmol) at 35°C for 3 h. After evaporation of the solvent the residue was crystallized from diethyl ether to obtain white crystals (9.6 g, 83%) 10, m.p. 210°C (diethyl ether). IR (KBr), cm^{− 1}: 3240 (NH), 1625 (C = C); ¹H NMR (CDCl₃+CD₃OD), δ, ppm; J, Hz: 3.22 (t, J = 7.5, 2H, CH₂-CH₂N⁺), 3.35 (s, 6H, N(CH₃)₂), 3.74 (t, J = 7.5, 2H, CH₂-CH₂N⁺), 3.81 (s, 3H, OCH₃), 4.78 (s, 2H, CH₂N⁺), 6.81 (dd, J = 8.1, 2, 1H, H-8), 6.91 (d, J = 2, 1H, H-6), 7.31 (d, J = 8.1, 1H, H-9), 10.5 (s, 1H, NH); ¹³C NMR (CDCl₃+DMSO-d₆), δ, ppm: 19.2 (CH₂-CH₂N⁺), 50.9 (⁺N(CH₃)₂), 55.3 (OCH₃), 59.8 (CH₂-CH₂N⁺), 60.8 (-CH₂N⁺), 99.2 (C-9), 99.4 (C-9b), 110.3 (C-6), 111.7 (C-7), 124.6 (C-9a), 127.5 (C-4a), 131.4 (C-5a), 153.6 (C-8).

[2-(2-Dimethylaminoethyl)-1h-indol-3-yl]acetonitrile (11)

Prepared according to the described method [11]. Yield: 81%.

[2-(2-Dimethylaminoethyl)-5-methoxy- 1H-indol-3-yl]acetonitrile (12)

A solution of iodide 10 (9.0 g, 25.1 mmol) in ethanol (100 mL) was heated under reflux with a solution of potassium cyanide (8.9 g, 137 mmol) in water (30 mL) for 5 h. After evaporation of the solvent under reduced pressure, the residue was dissolved in water (30 mL), alkalinized (pH = 13) under cooling with a 10% aqueous solution of NaOH, and the mixture was extracted with dichloromethane (4 × 40 mL). The combined organic layers were washed with water (10 mL), dried over Na₂SO₄, filtered and concentrated to afford 12 (6.0 g, 93%), as white crystals, m.p. 101°C (dichloromethane). IR (KBr), cm^{− 1}: 3318 (NH), 2925, 2241 (CN), 1630 C = C); ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.35 (s, 6H, N(CH₃)₂), 2.65 (t, J = 7.4, 2H, CH₂-CH₂-NCH₃), 2.77 (t, J = 7.4, 2H, CH₂-CH₂-NCH₃), 3.71 (s, 2H, CH₂-CN), 3.85 (s, 3H, OCH₃), 6.82 (dd, J = 8.1, 1.8, 1H, H-6), 7.02 (d, J = 1.8, 1H, H-4), 7.25 (d, J = 8.1, 1H, H-7), 10.2 (s, 1H, NH); ¹³C NMR (CDCl₃), δ, ppm: 12.7 (-CH₂-N(CH₃)₂), 22.3 (CH₂-CH₂-N(CH₃)₂), 44.9 (N(CH₃)₂), 55.8 (OCH₃), 58.0 (CH₂-CH₂-N(CH₃)₂), 98.2 (C-3), 99.3 (C-4), 111.3 (C-7), 111.7 (C-6), 118.2 (CN), 127.2, 129.9, 137.7, 154.1; MS (m/z, %) 257 (M⁺, 25), 212 (100), 197 (57), 186 (18), 173 (16), 169 (41).

[2-(3-Cyanomethyl-1h-indol-2-yl)ethyl]trimethylammonium Iodide (13)

Prepared according to the described method [11]. Yield: 95%.

[2-(3-Cyanomethyl-5-methoxy-1h-indol-2-yl)ethyl]trimethylammonium Iodide (14)

A solution of 12 (6.00 g, 23.3 mmol) in dichloromethane (190 mL) and ethyl acetate (60 mL) was heated under reflux with methyl iodide (6.62 g, 46.6 mmol) for 4 h. After evaporation of the solvent the residue was crystallized from diethyl ether to give quaternary ammonium iodide 14 (9.1 g, 98%), as white crystals, m.p. 210°C (diethyl ether). IR (KBr), cm^{− 1}: 3358 (NH), 3220, 2942, 2244 (CN), 1625 (C = C); ¹H NMR (DMSO-d₆), δ, ppm; J, Hz: 3.21 (s, 9H, N⁺(CH₃)₃), 3.32 (t, J = 7.2, 2H, CH₂-CH₂-N⁺(CH₃)₃), 3.62 (t, J = 7.2, 2H, CH₂-CH₂-N⁺(CH₃)₃), 3.81 (s, 3H, OCH₃), 4.15 (s, 2H, CH₂-CN), 6.81 (dd, J = 8, 1.8, 1H, H-6), 7.12 (d, J = 1.8, 1H, H-4), 7.28 (d, J = 8, 1H, H-7), 11.2 (s, 1H, NH); ¹³C NMR (DMSO-d₆), δ, ppm: 12.4 (CH₂CN), 19.6 (CH₂-CH₂-N⁺(CH₃)₃), 52.6 (-N⁺(CH₃)₃), 55.6 (OCH₃), 64.1 (CH₂-CH₂-N⁺(CH₃)₃), 100.1 (C-4), 101.1 (C-3), 111.7 (C-7), 112.0 (C-6), 119.5 (CN), 127.4 (C-3a), 130.5 (C-2), 131.9 (C-7a), 153.7 (C-5).

(2-Vinyl-1h-indol-3-yl)acetonitrile (5A)

Prepared according to the described method [11]. Yield: 88%.

(5-Methoxy-2-vinyl-1h-indol-3-yl)acetonitrile (6A)

A solution of salt 14 (9.00 g, 22.5 mmol) in methanol (120 mL) and water (80 mL) was stirred with a 30% aqueous solution of NaOH (30 mL) at room temperature for 4 h. After evaporation of methanol under reduced pressure the residue was heated at 80°C for 20 min and then extracted with dichloromethane (4 × 30 mL). The combined organic layers were dried over Na₂SO₄, filtered, evaporated to dryness and purified by flash chromatography (eluent: CH₂Cl₂:MeOH 9:1) to afford 6a (4.2 g, 88%), as pale yellowish crystals, m.p. 127°C (methanol). IR (KBr), cm^{− 1}: 3340 (NH), 3220, 2935, 2220 (CN), 1622 (C = C); ¹H NMR (CDCl₃), δ, ppm; J, Hz: 3.71 (s, 2H, CH₂CN), 3.82 (s, 3H, OCH₃), 5.32 (d, J = 11.1, 1H, CH₂ = ), 5.51 (d, J = 18.2, 1H, CH₂ = ), 6.70 (dd, J = 18.2, 11.1, 1H, CH₂ = CH), 6.85 (dd, J = 8.1, 2.1, 1H, H-6), 7.02 (d, J = 2.1, 1H, H-4), 7.15 (d, J = 8.1, 1H, H-7), 8.41 (s, 1H, NH); ¹³C NMR (CDCl₃), δ, ppm 12.7 (CH₂-CN), 55.8 (OCH₃), 100.2 (C-4), 102.2 (C-3), 111.8 (C-7), 113.6 (CH = CH₂), 113.7 (C-6), 117.7 (CN), 124.3 (CH = CH₂), 127.7 (C-3a), 131.1 (C-2), 134.1 (C-7a), 154.6 (C-5). MS (m/z, %) 212 (M⁺, 100), 197 (48), 185 (11), 169 (26).

(1-Methyl-2-vinyl-1h-indol-3-yl)acetonitrile (5B)

To a stirred solution of 2-vinylindole 5a (300 mg, 1.64 mmol) in dichloromethane (20 mL) were added a solution of sodium hydroxide (35%, 1.32 mL, 16 mmol) tetrabutylammonium hydrogen sulfate (56 mg, 0.16 mmol) and iodomethane (0.25 mL, 570 mg, 4.01 mmol). Stirring was continued at room temperature until the disapperance of the starting material. The reaction mixture was extracted with dichloromethane (3 × 10 mL), the combined organic layers were dried (Na₂SO₄), filtered, evaporated and the residue was purified by chromatography (eluent: CH₂Cl₂/cyclohexane 6:4) affording 5b (293 mg, 91%), which was crystallized in diethyl ether, m.p. 91–92°C (diethyl ether).UV (MeOH), λ_max, nm: 210, 228, 301; IR (KBr), cm^{− 1}: 2938, 2238 (CN), 1626 (C = C), 1470; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 3.66 (s, 3H, NCH₃), 3.82 (s, 2H, CH₂N), 5.60 (d, J = 17.7, 1H, CH = CH₂), 5.68 (d, J = 11.6, 1H, CH = CH₂), 6.72 (dd, J = 17.7, 11.6, 1H, CH = CH₂), 7.11–7.30 (m, 3H, H-5, H-6, H-7), 7.62 (d, J = 7.8, 1H, H-4); ¹³C NMR (CDCl₃), δ, ppm: 13.8 (CH₂-CN), 30.4 (NCH₃), 101.1 (C-3), 109.4 (C-7), 118.1 (CN), 118.2 (C-4), 120.1 (C-5), 121.5 (CH = CH₂), 122.7 (C-6), 125.1 (CH = CH₂), 126.5 (C-3a), 136.0 (C-2), 136.8 (C-7a); MS (m/z, %) 196 (M⁺, 100), 181 (18), 169 (39), 156 (9), 154 (17), 144 (10), 140 (6), 127 (14). Anal. Calcd. for C₁₃H₁₂N₂: C, 79.56; H, 6.16; N, 14.27%; Found: C, 79.44; H, 6.19; N, 14.20%.

(1-Methoxymethyl-2-vinyl-1h-indol-3-yl)acetonitrile (5C)

To a stirred solution of 2-vinylindole 5a (690 mg, 3.79 mmol) in dichloromethane (40 mL) were added at 0°C a solution of sodium hydroxide (35%, 2.15 mL, 26 mmol) tetrabutylammonium hydrogensulfate (126 mg, 0.37 mmol) and methoxymethyl chloride (0.48 mL, 6.31 mmol). After 2 h stirring at room temperature the reaction mixture was diluted with water (15 mL) and, extracted with dichloromethane (3 × 30 mL). The combined organic layers were dried (Na₂SO₄), filtered, evaporated and the residue was purified by chromatography (eluent: cyclohexane/ethyl acetate 1:1 → 6:4) affording 5c (830 mg, 97%), as a viscous yellowish oil. UV (EtOH), λ_max, nm: 209, 224, 297; IR (film), cm^{− 1}: 2940, 2907, 2254 (CN), 1628 (C = C), 1464; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 3.24 (s, 3H, CH₂OCH₃), 3.82 (s, 2H, CH₂N), 5.38 (s, 2H, CH₂OCH₃), 5.68 (d, J = 12.1, 1H, CH = CH₂), 5.70 (d, J = 17.3, 1H, CH = CH₂), 6.80 (dd, J = 17.3, 12.1, 1H, CH = CH₂), 7.20 (dt, J = 8.2, 1.1, 1H, H-5), 7.28 (dt, J = 8.2, 1.1, 1H, H-6), 7.42 (d, J = 8.2, 1H, H-7), 7.63 (d, J = 8.2, 1H, H-4); ¹³C NMR (CDCl₃), δ, ppm: 13.6 (CH₂-CN), 55.8 (CH₂OCH₃), 74.2 (CH₂OCH₃), 102.9 (C-3), 109.6 (C-7), 117.8 (CN), 118.3 (C-4), 120.8 (C-5), 122.1 (CH = CH₂), 123.3 (C-6), 124.6 (CH = CH₂), 126.7 (C-3a), 136.0 (C-2), 136.9 (C-7a); MS (m/z, %) 226 (M⁺, 100), 183 (6), 169 (18), 160 (62). Anal. Calcd. for C₁₄H₁₄N₂O: C, 74.31; H, 6.24; N, 12.38%; Found: C, 74.11; H, 5.99; N, 12.71%.

2-(2-Vinyl-1h-indol-3-yl)ethylamine (15A)

Prepared according to the described method [11]. Yield: 82%.

2-(5-Methoxy-2-vinyl-1h-indol-3-yl)ethylamine (16A)

To a solution of nitrile 6a (0.60 g, 2.83 mmol) in diethyl ether (100 mL) and tetrahydrofuran (30 mL), lithium aluminium hydride (0.4 g, 10.54 mmol) was added in small portions and the reaction mixture was stirred at room temperature for 30 min. The excess of the reagent was decomposed at 0°C by careful addition of a saturated aqueous Na₂SO₄ solution; the precipitate was filtered, washed with dichloromethane (4 × 10 mL). The combined organic layers were washed with water (10 mL), dried (Na₂SO₄), filtered and evaporated to dryness to afford 16 (0.61 g, 99%), as an amorphous solid which was crystallized in diethyl ether, m.p. 106–108°C (diethyl ether); UV (MeOH), λ_max, nm: 209, 221, 308; IR (KBr), cm^{− 1}: 3428 (NH), 2936, 1632 (C = C), 1582, 1485; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 1.45 (sl, 2H, NH₂), 2.93 (m, 4H, CH₂CH₂N), 3.85 (s, 3H, OCH₃), 5.22 (d, J = 11.3, 1H, CH = CH₂), 5.62 (d, J = 17.7, 1H, CH = CH₂), 6.80 (m, 2H, CH = CH₂, H-6), 6.97 (s, 1H, H-4), 7.20 (d, J = 8.7, 1H, H-7), 9.65 (sl, 1H, NH); ¹³C NMR (CDCl₃), δ, ppm: 27.9 (CH₂-CH₂-NH₂), 42.6 (CH₂-CH₂-NH₂), 55.5 (OCH₃), 100.3 (C-4), 111.2 (CH = CH₂), 111.3 (C-6), 112.4 (C-7), 112.4 (C-3), 125.4 (CH = CH₂), 128.6 (C-3a), 131.5 (C-2), 134.0 (C-7a), 153.3 (C-5); MS (m/z, %) 216 (M⁺, 32), 186 (100), 171 (12), 154 (11), 143 (26). Anal. Calcd. for C₁₃H₁₆N₂O: C, 72.19; H, 7.45; N, 12.95%; Found: C, 72.31; H, 7.47; N, 13.18%.

Dimethyl-[2-(2-vinyl-1h-indol-3-yl)ethyl]amine (3A)

A solution of 2-vinylindole 5a (2.00 g, 10.98 mmol) in tetrahydrofuran (30 mL) and diethyl ether (20 mL) was stirred with lithium aluminium hydride (2.00 g, 52.70 mmol) at room temperature for 30 min. The excess of the reagent was decomposed at 0°C by careful addition of a saturated aqueous Na₂SO₄ solution; the precipitate was filtered, washed with dichloromethane (3 × 20 mL) and methanol (3 × 2 mL). The aqueous phase was extracted with dichloromethane (3 × 100 mL), the combined organic layers were dried (Na₂SO₄), filtered, and evaporated to dryness. To the obtained crude tryptamine, dissolved in methanol (100 mL), acetic acid (2.5 mL) and sodium cyanoborohydride (1.37 g, 21.80 mmol) were added. After 10 min stirring 37% formaldehyde (2.42 mL) in methanol (15 mL) was added dropwise at 0°C and stirring was continued for 1.5 h. After evaporation of the solvent the residue was partitioned between dichloromethane (60 mL) and 10% K₂CO₃ (60 mL). The aqueous phase was extracted with dichloromethane (3 × 30 mL), the combined organic layers were dried (Na₂SO₄), filtered, evaporated and the residue was purified by chromatography (eluent: CH₂Cl₂/MeOH 100:4 → 100:6/with five drops of NH₄OH). Dimethyl-2-vinyltryptamine 3a was obtained (1.92 g, 82%) as a yellowish amorphous solid. UV (MeOH), λ_max, nm: 208, 228, 303, 313; IR (film), cm^{− 1}: 3428 (NH), 3275–3055, 2944, 1634 (C = C), 1460; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.33 (s, 6H, N(CH₃)₂), 2.54 (m, 2H, CH₂N), 2.98 (m, 2H, CH₂CH₂N), 5.26 (d, J = 11.3, 1H, CH = CH₂), 5.46 (d, J = 17.7, 1H, CH = CH₂), 6.80 (dd, J = 17.7, 11.3, 1H, CH = CH₂), 7.09 (dt, J = 8.0, 1.0, 1H, H-5), 7.17 (dt, J = 8.0, 1.0, 1H, H-6), 7.26 (d, J = 8.0, 1H, H-7), 7.55 (d, J = 8.0, 1H, H-4), 8.32 (sl, 1H, NH); ¹³C NMR (CDCl₃), δ, ppm: 22.4 (CH₂-CH₂-N(CH₃)₂), 45.2 (N(CH₃)₂), 60.4 (CH₂-CH₂-N(CH₃)₂), 110.7 (C-7), 111.3 (CH = CH₂), 113.5 (C-3), 118.8 (C-4), 119.4 (C-5), 122.9 (C-6), 125.3 (CH = CH₂), 128.5 (C-3a), 132.4 (C-2), 136.2 (C-7a); MS (m/z, %) 214 (M⁺, 100), 183 (14), 168 (58), 159 (97), 143 (19), 128 (74). Anal. Calcd. for C₁₄H₁₈N₂: C, 78.46; H, 8.47; N, 13.07%; Found: C, 78.21; H, 8.89; N, 12.81%.

Dimethyl-[2-(1-methyl-2-vinyl-1h-indol-3-yl)ethyl]amine (3B)

A solution of 5b (276 mg, 1.41 mmol) in a mixture of tetrahydrofuran (4 mL) and diethyl ether (3 mL) was stirred with lithium aluminium hydride (267 mg, 7.02 mmol), at room temperature for 1.5 h. The excess of the reagent was decomposed at 0°C by careful addition of a saturated aqueous Na₂SO₄ solution, the precipitate was filtered, washed with dichloromethane (3 × 10 mL) and methanol (3 × 1 mL). The aqueous phase was extracted with dichloromethane (3 × 30 mL), the combined organic layers were dried (Na₂SO₄), filtered, and evaporated to dryness.

To the obtained crude product, dissolved in methanol (15 mL), acetic acid (0.22 mL) and sodium cyanoborohydride (132 mg, 2.10 mmol) were added. After 20 min stirring at 0°C, 37% formaldehyde (0.31 mL) in methanol (5 mL) was added dropwise and stirring was continued for 1.5 h. After evaporation of the solvent, the residue was partitioned between dichloromethane (20 mL) and 10% K₂CO₃ (20 mL). The aqueous phase was extracted with dichloromethane (3 × 10 mL), the combined organic layers were dried (Na₂SO₄), filtered, evaporated and the residue was purified by chromatography (eluent: CH₂Cl₂/MeOH 100:1->100:5/with five drops of NH₄OH). Dimethyl-2-vinyltryptamine 3b was obtained (92 mg, 29%), as a yellowish amorphous solid. UV (MeOH), λ_max, nm: 209, 228, 301; IR (film), cm^{− 1}: 2940, 1626, 1470; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.68 (s, 6H, N(CH₃)₂), 2.68 (m, 2H, CH₂N), 3.05 (m, 2H, CH₂CH₂N), 3.72 (s, 3H, NCH₃), 5.50 (dd, J = 11.7, 1.2, 1H, CH = CH₂), 5.59 (dd, J = 17.8, 1.2, 1H, CH = CH₂), 6.79 (dd, J = 17.8, 11.7, 1H, CH = CH₂), 7.10 (dd, J = 7.9, 1.3, 1H, H-5), 7.24 (m, 2H, H-6, H-7), 7.69 (d, J = 7.9, 1H, H-4); ¹³C NMR (CDCl₃), δ, ppm: 23.2 (CH₂-CH₂-N(CH₃)₂), 30.6 (NCH₃), 45.3 (N(CH₃)₂), 60.2 (CH₂-CH₂-N(CH₃)₂), 109.1 (C-7), 111.7 (C-3), 117.9 (CH = CH₂), 118.7 (C-4), 119.1 (C-5), 122.1 (C-6), 125.9 (CH = CH₂), 127.5 (C-3a), 134.4 (C-2), 138.8 (C-7a); MS (m/z, %) 228 (M⁺, 76), 197 (5), 184 (13), 170 (100), 154 (33), 128 (23), 115 (16). Anal. Calcd. for C₁₅H₂₀N₂: C, 78.90; H, 8.83; N, 12.27%; Found: C, 79.18; H, 9.05; N, 11.91%.

[2-(1-Methoxymethyl-2-vinyl-1h-indol-3-yl)ethyl]dimethylamine (3C)

To a stirred suspension of sodium hydride (60%, 84 mg, 2.10 mmol) in tetrahydrofuran (1.5 mL) was added dropwise a dimethylsulfoxide (1.5 mL) solution of 2-vinyldimethyltryptamine 3a (150 mg, 0.70 mmol). After 30 min stirring at 0°C under nitrogen, methoxymethyl chloride (MOMCl) (64 μL, 0.84 mmol) was added and stirring was continued at room temperature for a further 30 min. After evaporation of the solvent the residue was partitioned between dichloromethane (10 mL) and a 10% aqueous solution of NaHCO₃ (10 mL). The aqueous phase was extracted with dichloromethane (3 × 10 mL), the combined organic layers were dried (Na₂SO₄), filtered, evaporated and the crude product was purified by chromatography (eluent: CH₂Cl₂/MeOH 100:5/five drops of NH₄OH) to give 3c (56 mg, 30%), as an amorphous solid. UV (MeOH), λ_max, nm: 212, 227, 300; IR (film), cm^{− 1}: 3289 (NH), 2945, 1615 (C = C), 1464, 1346; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.63 (s, 6H, N(CH₃)₂), 2.89 (m, 2H, CH₂N), 3.23 (m, 2H, CH₂CH₂N), 3.31 (s, 3H, OCH₃), 5.44 (s, 2H, CH₂OCH₃), 5.60 (dd, J = 11.8, 1.3, 1H, CH = CH₂), 5.73 (dd, J = 17.8, 1.3, 1H, CH = CH₂), 6.85 (dd, J = 17.8, 11.8, 1H, CH = CH₂), 7.17 (dt, J = 7.8, 1.1, 1H, H-5), 7.25 (dt, J = 7.8, 1.1, 1H, H-6), 7.43 (d, J = 7.8, 1H, H-7), 7.63 (d, J = 7.8, 1H, H-4); ¹³C NMR (CDCl₃), δ, ppm: 21.4 (CH₂-CH₂-N(CH₃)₂), 43.8 (N(CH₃)₂), 55.7 (CH₂-OCH₃), 58.5 (CH₂-N(CH₃)₂), 74.3 (CH₂-OCH₃), 109.5 (C-7), 111.0 (C-3), 118.6 (C-4), 119.6 (CH = CH₂), 120.4 (C-5), 123.0 (C-6), 125.1 (CH = CH₂), 127.6 (C-3a), 134.9 (C-2), 137.5 (C-7a); MS (m/z, %) 259 (M+1, 100), 214 (13), 184 (4), 170 (3); Anal. Calcd. for C₁₆H₂₂N₂O: C, 74.38; H, 8.58; N, 10.84%; Found: C, 74.11; H, 8.35; N, 11.18%.

3-(2-Dimethylaminoethyl)-2-vinyl-1h-indole-1-carboxylic Acid Tert-butyl Ester (3D)

A solution of 3a (200 mg, 0.93 mmol) in acetonitrile (12 mL) was stirred with di-tert-butyl dicarbonate (480 mg, 2.20 mmol) and 4-(N,N-dimethylamino)-pyridine (10 mg, 0.08 mmol) at room temperature for 4 h. After evaporation of the solvent, the residue was partitioned between dichloromethane (20 mL) and a 10% aqueous solution of NaHCO₃ (20 mL) and the aqueous phase was extracted with dichloromethane (3 × 20 mL). The combined organic phases were dried (MgSO₄), filtered, the solvent was evaporated and the residue was purified by chromatography (eluent: CH₂Cl₂/MeOH 100:3) affording 3d (198 mg, 68%), as an amorphous solid. UV (MeOH), λ_max, nm: 212, 227, 300; IR (film), cm^{− 1}: 3342 (NH), 2972, 2945, 2774, 1730 (CO), 1458; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 1.66 (s, 9H, C(CH₃)₃), 2.36 (s, 6H, N(CH₃)₂), 2.57 (m, 2H, CH₂N), 2.98 (m, 2H, CH₂CH₂N), 5.39–5.42 (dd, J = 11.5, 1.8, 1H, CH = CH₂), 5.42–5.51 (dd, J = 17.7, 1.8, 1H, CH = CH₂), 6.95 (dd, J = 17.7, 11.5, 1H, CH = CH₂), 7.26 (m, 2H, H-5, H-6), 7.54 (dd, J = 7.2, 1.1, 1H, H-4), 8.08 (dd, J = 7.2, 1.1, 1H, H-7); ¹³C NMR (CDCl₃), δ, ppm: 23.0 (CH₂-CH₂-N(CH₃)₂), 28.1 (CO₂C(CH₃)₃), 45.2 (N(CH₃)₂), 59.7 (CH₂-CH₂-N(CH₃)₂), 83.7 (CO₂C(CH₃)₃), 115.5 (C-7), 116.9 (CH = CH₂), 117.7 (C-3), 118.6 (C-4), 122.8 (C-5), 124.3 (C-6), 129.0 (CH = CH₂), 130.0 (C-3a), 134.8 (C-2), 135.3 (C-7a), 150.4 (NCO₂C(CH₃)₃); MS (m/z, %) 314 (M⁺, 13), 272 (12), 239 (10), 214 (30), 183 (9), 168 (46), 154 (100). Anal. Calcd. for C₁₉H₂₆N₂O₂: C, 72.57; H, 8.33; N, 8.91%; Found: C, 72.81; H, 8.05; N, 9.18%.

[2-(5-Methoxy-2-vinyl-1h-indol-3-yl)ethyl]dimethylamine (4A)

To a solution of 16a (0.60 g, 2.78 mmol) in methanol (50 mL), acetic acid (0.41 mL) and sodium cyanoborohydride (0.3 g, 4.78 mmol) were added and after 10 min stirring 37% formaldehyde (0.58 mL) in methanol (10 mL) was added dropwise at 0°C and stirring was continued for 1.5 h. After evaporation of the solvent, the residue was partitioned between dichloromethane (20 mL) and a 10% aqueous solution of K₂CO₃ (20 mL). The aqueous phase was extracted with dichloromethane (3 × 10 mL), the combined organic layers were dried (Na₂SO₄), filtered, evaporated and the residue was purified by chromatography (eluent: CH₂Cl₂/MeOH 50:1 → 10:1) to give 4a (0.42 g, 59%), as an amorphous solid. UV (MeOH), λ_max, nm: 209, 219, 307; IR (film), cm^{− 1}: 3328 (NH), 2945, 1632 (C = C), 1487, 1466, 1437; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.36 (s, 6H, N(CH₃)₂), 2.52 (m, 2H, CH₂CH₂N), 2.95 (m, 2H, CH₂N), 3.86 (s, 3H, OCH₃), 5.24 (d, J = 11.3, 1H, CH = CH₂), 5.47 (d, J = 17.7, 1H, CH = CH₂), 6.76–6.87 (m, 2H, CH = CH₂, H-6), 7.00 (s, 1H, H-4), 7.19 (d, J = 8.7, 1H, H-7), 8.19 (s, 1H, NH); ¹³C NMR (CDCl₃), δ, ppm: 22.6 (CH₂-CH₂-N(CH₃)₂), 45.4 (N(CH₃)₂), 55.9 (OCH₃), 60.4 (CH₂-N(CH₃)₂), 100.8 (C-4), 111.0 (CH = CH₂), 111.4 (C-6), 112.9 (C-7), 113.5 (C-2), 125.4 (CH = CH₂), 128.9 (C-3), 131.4 (C-3a), 133.2 (C-7a), 153.9 (C-5); MS (m/z, %) 244 (M⁺, 82), 230 (20), 215 (62), 199 (35), 186 (100), 173 (36), 158 (30), 154 (39). Anal. Calcd. for C₁₅H₂₀N₂O: C, 73.73; H, 8.25; N, 11.47%; Found: C, 73.44; H, 8.01; N, 11.58%.

General method for the synthesis of arylsulfonyl tryptamines 3e-i and 4e

To a stirred suspension of sodium hydride (60%, 2.0–3.0 mmol) in tetrahydrofuran (1.5 mL) was added via a syringe a dimethylsulfoxide (1 mL) solution of 2-vinyldimethyltryptamines 3a or 4a (1.0 mmol). After 30 min stirring at 0°C under nitrogen a solution of arylsulfonylchloride (1.6–4.3 mmol) in tetrahydrofuran (1.5–2 mL) was added and stirring was continued at room temperature until the disappearance of the starting material. After evaporation of the solvent the residue was partitioned between dichloromethane (10 mL) and 10% aqueous NaHCO₃ (10 mL). The aqueous phase was extracted with dichloromethane (3 × 10 mL), the combined organic layers were dried (Na₂SO₄), filtered, evaporated and the crude product was purified by chromatography (eluent: CH₂Cl₂/MeOH 100:2 → 100:10) to give protected dimethyl-2-vinyltryptamines 3e-i, 4e.

[2-(1-Benzenesulfonyl-2-vinyl-1h-indol-3yl)ethyl]dimethyl Amine (3E)

Yield: 61%. Amorphous solid. UV (MeOH), λ_max, nm: 208, 222, 269, 275, 287; IR (film), cm^{− 1}: 3406 (NH), 2693, 2778, 1620 (C = C), 1149, 1371; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.30 (s, 6H, N(CH₃)₂), 2.45 (m, 2H, CH₂N), 2.91 (m, 2H, CH₂CH₂N), 5.45 (dd, J = 17.7, 1.7, 1H, CH = CH₂), 5.60 (dd, J = 11.4, 1.7, 1H, CH = CH₂), 7.11 (dd, J = 17.7, 11.4, 1H, CH = CH₂), 7.21–7.37 (m, 4H, H-5, H-6, H-PhSO₂), 7.47 (m, 2H, H-4, H-PhSO₂), 7.72 (d, J = 7.5, 2H, H-PhSO₂), 8.20 (d, J = 8.3, 1H, H-7); ¹³C NMR (CDCl₃), δ, ppm: 23.2 (CH₂-CH₂-N(CH₃)₂), 45.1 (N(CH₃)₂), 59.3 (CH₂-CH₂-N(CH₃)₂), 115.1 (C-7), 119.2 (C-4), 119.6 (CH = CH₂), 120.9 (C-3), 123.7 (C-5), 125.1 (C-6), 126.5 (CH_benzene), 127.4 (CH = CH₂), 128.7 (CH_benzene), 130.8 (C-3a), 133.4 (CH_benzene),135.1 (C-2), 136.2 (C_benzene-SO₂), 138.0 (C-7a); MS (m/z, %) 354 (M⁺, 11), 296 (5), 213 (39), 199 (8), 168 (30), 154 (100); HREIMS: calcd. 354.14021, found 354.14262.

{2-[1-(Tosyl-4-sulfonyl)-2-vinyl-1h-indol-3-yl]ethyl}dimethyl Amine (3F)

Yield: 51%. Amorphous solid. UV (MeOH), λ_max, nm: 204, 223, 270, 277, 285; IR (film), cm^{− 1}: 3312 (NH), 2945, 2776, 1622 (C = C), 1452, 1371; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.31 (s, 3H, CH₃), 2.43 (s, 6H, N(CH₃)₂), 2.60 (m, 2H, CH₂N), 3.00 (m, 2H, CH₂CH₂N), 5.45 (dd, J = 17.7, 1.6, 1H, CH = CH₂), 5.62 (dd, J = 11.4, 1.6, 1H, CH = CH₂), 7.08–7.18 (m, 3H, CH = CH₂, H-ArSO₂), 7.22–7.36 (m, 2H, H-5, H-6), 7.50 (d, J = 8.2, 1H, H-4), 7.61 (d, J = 8.3, 2H, H-ArSO₂), 8.20 (d, J = 8.2, 1H, H-7); ¹³C NMR (CDCl₃), δ, ppm: 21.4 (C_benzene-CH₃), 23.1 (CH₂-CH₂-N(CH₃)₂), 45.1 (N(CH₃)₂), 59.2 (CH₂-CH₂-N(CH₃)₂), 115.1 (C-7), 119.1 C-4), 119.5 (CH = CH₂), 120.5 (C-3), 123.6 (C-5), 125.0 (C-6), 127.6 (CH = CH₂), 129.4 (CH_benzene), 130.7 (C-3a), 135.0 (CH_benzene), 135.1 (C-2), 135.2 (C-7a), 136.1 (C_benzene-SO₂), 144.5 (C_benzene-CH₃); MS (m/z, %) 368 (M⁺, 26), 213 (100), 155 (22). Anal. Calcd. for C₂₁H₂₄N₂O₂S: C, 68.44; H, 6.56; N, 7.60%; Found: C, 68.81; H, 6.45; N, 7.37%.

{2-[1-(4-Chlorobenzenesulfonyl)-2-vinyl-1h-indol-3-yl]ethyl}dimethylamine (3 G)

Yield: 46%. Amorphous solid. UV (MeOH), λ_max, nm: 205, 228, 272, 277, 286; IR (film), cm^{− 1}: 3324 (NH), 2942, 2776, 1620 (C = C), 1452, 1375; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.29 (s, 6H, N(CH₃)₂), 2.43 (m, 2H, CH₂N), 2.90 (m, 2H, CH₂CH₂N), 5.47 (dd, J = 17.7, 1.7, 1H, CH = CH₂), 5.62 (dd, J = 11.4, 1.7, 1H, CH = CH₂), 7.10 (dd, J = 17.7, 11.4, 1H, CH = CH₂), 7.30 (m, 4H, H-5, H-6, H-ArSO₂), 7.47 (dd, J = 7.7, 1.1, 1H, H-4), 7.65 (dd, J = 6.8, 1.9, 2H, H-ArSO₂), 8.16 (d, J = 7.7, 1H, H-7); ¹³C NMR (CDCl₃), δ, ppm: 23.2 (CH₂-CH₂-N(CH₃)₂), 45.2 (N(CH₃)₂), 59.2 (CH₂-CH₂-N(CH₃)₂), 115.1 (C-7), 119.3 (C-4), 119.8 (CH = CH₂), 121.3 (C-3), 124.0 (C-5), 125.3 (C-6), 127.5 (CH = CH₂), 128.0 (CH_benzene), 129.1 (CH_benzene), 130.9 (C-3a), 135.0 (C-2), 136.1 (C-7a), 136.3 (C_benzene-SO₂), 140.1 (C_benzene-Cl),; MS (m/z, %) 388 (M⁺, 25), 390 (9), 213 (100), 168 (70), 154 (81). Anal. Calcd. for C₂₀H₂₁N₂ClO₂S: C, 61.76; H, 5.44; N, 7.20%; Found: C, 61.91; H, 5.59; N, 7.41%.

{2-[1-(2,4,6-Triisopropylbenzenesulfonyl)-2-vinyl-1h-indol-3-yl]ethyl}dimethylamine (3 H)

Yield: 25%. Amorphous solid. UV (MeOH) λ_max, nm: 209, 237, 283; IR (film), cm^{− 1}: 2961, 2866, 2774, 1458, 1373, 1346; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 1.01 (d, 12H, CH(CH₃)₂-oSO₂), 1.23 (d, 6H, CH(CH₃)₂-pSO₂), 2.34 (s, 6H, N(CH₃)₂), 2.52 (m, 2H, CH₂N), 2.90 (m, 3H, CH(CH₃)₂-pSO₂, CH₂CH₂N), 4.07 (m, 2H, CH(CH₃)₂-oSO₂), 5.52 (dd, J = 12.0, 1.1, 1H, CH = CH₂), 5.58 (dd, J = 16.9, 1.1, 1H, CH = CH₂), 6.54 (dd, J = 16.9, 12.0, 1H, CH = CH₂), 7.10 (s, 2H, H-ArSO₂), 7.27 (m, 2H, H-5, H-6), 7.52 (d, J = 7.6, 1H, H-4), 7.98 (d, J = 7.6, 1H, H-7); ¹³C NMR (CDCl₃), δ, ppm: 22.9 (CH₂-CH₂-N(CH₃)₂), 23.5 (CH(CH₃)₂), 24.2 (CH(CH₃)₂), 29.1 (CH(CH₃)₂), 34.1 (CH(CH₃)₂), 45.2 (N(CH₃)₂), 59.6 (CH₂-CH₂-N(CH₃)₂), 114.1 (C-7), 117.4 (C-3), 119.1 (C-4), 119.8 (CH = CH₂), 122.4 (C-5), 123.7 (CH_benzene), 124.6 (C-6), 126.0 (CH = CH₂), 129.1 (C-3a), 133.6 (C_benzene-SO₂), 134.8 (C-2), 136.2 (C-7a), 150.9 (C_benzene), 154.2 (C_benzene); MS (m/z, %) 481 (M+1), 467 (3), 436 (5), 398 (4), 348 (1), 259 (8). Anal. Calcd. for C₂₉H₄₀N₂O₂S: C, 72.45; H, 8.39; N, 5.83%; Found: C, 72.59; H, 8.71; N, 6.10%.

{2-[1-(Naphthyl-2-sulfonyl)-2-vinyl-1h-indol-3-yl]ethyl}dimethylamine (3I)

Yield: 53%. Amorphous solid. UV (MeOH), λ_max, nm: 207, 228, 278, 329; IR (film), cm^{− 1}: 2934, 1668, 1622, 1593, 1452, 1373; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.29 (s, 6H, N(CH₃)₂), 2.43 (m, 2H, CH₂N), 2.98 (m, 2H, CH₂CH₂N), 5.48 (dd, J = 17.7, 1.7, 1H, CH = CH₂), 5.65 (dd, J = 11.4, 1.7, 1H, CH = CH₂), 7.12–7.36 (m, 3H, CH = CH₂, H-5, H-6), 7.43 (d, J = 8.2, 1H, H-4), 7.50–7.64 (m, 3H, H-Ar), 7.72–7.80 (m, 2H, H-Ar), 7.87 (d, J = 7.8, 1H, H-Ar), 8.28 (d, J = 8.2, 1H, H-7), 8.36 (s, 1H, H-Ar); ¹³C NMR (CDCl₃), δ, ppm: 23.0 (CH₂-CH₂-N(CH₃)₂), 45.0 (N(CH₃)₂), 59.1 (CH₂-CH₂-N(CH₃)₂), 115.8 (C-7), 119.2 (C-4), 119.7 (CH = CH₂), 120.6 (C-3), 121.3 (CH_naphthalene), 123.7 (C-5), 125.1 (C-6), 127.5 (CH = CH₂), 127.6 (CH_naphthalene), 127.7 (CH_naphthalene), 128.3 (C_naphthalene), 129.1 (CH_naphthalene), 129.2 (CH_naphthalene), 129.3 (CH_naphthalene), 130.7 (C-3a), 131.6 (CH_naphthalene), 131.8 (C_naphthalene), 135.0 (C_naphthalene), 135.1 (C-2), 136.2 (C-7a); MS (m/z, %) 404 (M⁺, 40), 359 (6), 346 (21), 280 (7), 213 (13), 154 (26), 127 (100), 115 (18). Anal. Calcd. for C₂₄H₂₄N₂O₂S: C, 71.25; H, 5.98; N, 6.93%; Found: C, 71.07; H, 6.17; N, 7.01%.

2-(1-Benzensulfonyl-5-methoxy-2-vinyl-1h-indol-3-yl)ethyl]dimethylamine (4E)

Yield: 33%. Amorphous solid. UV (MeOH), λ_max, nm: 207, 218, 272, 312, 354; IR (film), cm^{− 1}: 3428, 2955, 1616, 1478; ¹H NMR (CDCl₃), δ, ppm; J, Hz: 2.22 (s, 6H, N(CH₃)₂), 2.45 (m, 2H, CH₂N), 2.89 (m, 2H, CH₂CH₂N), 3.84 (s, 3H, OCH₃), 5.45 (dd, J = 17.7, 1.3, 1H, CH = CH₂), 5.60 (dd, J = 11.4, 1.3, 1H, CH = CH₂), 6.91 (m, 2H, H-4, H-6), 7.10 (dd, J = 17.7, 11.4, 1H, CH = CH₂), 7.35 (dd, J = 8.0, 1.0, 2H, H-PhSO₂), 7.47 (dd, J = 8.0, 1.0, 1H, H-PhSO₂), 7.68 (d, J = 8.0, 2H, H-PhSO₂), 8.10 (d, J = 8.7, 1H, H-7); ¹³C NMR (CDCl₃), δ, ppm: 23.1 (CH₂-CH₂-N(CH₃)₂), 45.0 (N(CH₃)₂), 55.5 (OCH₃), 58.9 (CH₂-CH₂-N(CH₃)₂), 101.9 (C-4), 113.5 (C-6), 116.1 (C-7), 119.4 (CH = CH₂), 120.8 (C-3), 126.5 (CH_benzene), 127.6 (CH = CH₂), 128.7 (CH_benzene), 130.7 (C-7a), 131.9 (C-3a), 133.4 (CH_benzene), 135.9 (C-2), 137.7 (C_benzene-SO₂), 156.7 (C-5); MS (m/z, %) 384 (M⁺, 14), 243 (49), 199 (28), 185 (100), 170 (81); Anal. Calcd. for C₂₁H₂₄N₂O₃S: C, 65.59; H, 6.29; N, 7.29%; Found: C, 65.41; H, 6.01; N, 7.05%.

Pharmacology

Evaluation on 5-HT₄ receptors

Briefly, male guinea pigs (220–224 g, Iffa Credo, France) were subjected to euthanasia and decapitated. Brains were rapidly removed at 4°C and striatal regions carefully dissected and pooled. The tissues were then suspended in 10 volumes of HEPES buffer (50 mM, pH 7.4) at 4°C. After homogenization at 4°C (Ultra-Turrax, maximal speed, 15 s), and ultracentrifugation (23000 × g, 60 min, 4°C), the pellet was resuspended in HEPES buffer (50 mM, pH 7.4) at 4°C in order to obtain a tissue concentration of about 15 mg protein/ml. The protein concentrations were determined by the method of Lowry et al. [12] using bovine serum albumin as the standard. For radioligand binding studies, membrane preparations were incubated in duplicate (HEPES buffer: 50 mM, pH 7.4) at 37°C for 30 min with 0.6 nM [³H]-GR 113808 (Amersham, France) and fixed concentrations of compounds under study. Incubation was terminated by rapid filtration through 0.5% polyethylenimine-presoaked Whatman GF/B filters using a Brandel cell harvester [13]. Filters were subsequently washed three times with 4 ml of HEPES buffer (50 mM, pH 7.4) at 4°C. Non-specific binding of [³H]-GR 113808 was defined in the presence of 10 μM 5-HT. Results were expressed as the percentage of inhibition of the [³H]-GR 113808 binding (at 10^{− 6} and 10^{− 8} M of compounds under study, concentrations chosen to initially screen for intermediate and high affinity compounds).

Evaluation on 5-HT₅ receptors

In brief, 3 μg of proteins (CHO-K1 cells transiently expressing the human 5-HT₅ receptors, RB-HS5AM, Perkin Elmer Life Sciences) were incubated at 37°C for 60 min in duplicate in the absence or the presence of 10^{− 6} or 10^{− 8} M of each drug and 2 nM [³H]-LSD in 50 mM Tris-HCl buffer (pH 7.4) supplemented with 10 mM MgCl₂ and 0.5 mM EDTA according to Rees et al [14]. At the end of the incubation, homogenates were filtered through Whatman 934-AH filters presoaked with 0.5% polyethylenimine and washed 5 times with ice-cold 50 mM Tris-HCl buffer. Non-specific binding was evaluated in parallel in the presence of 500 μM serotonin. Radioactivity associated with proteins was then quantified in the presence of a scintillation cocktail and expressed as the percentage of inhibition for each concentration of drugs under study.

Evaluation on 5-HT₆ receptors

The compounds were evaluated in terms of their ability to compete with the binding of [³H]-LSD on membranes of sf9 cells transiently expressing the human 5-HT₆ receptor (CRM-044, Perkin-Elmer Life Science) according to Monsma et al. [15] In brief, 4 μg of proteins were incubated at 27°C for 90 min in duplicate in the absence or the presence of 10^{− 6} or 10^{− 8} M of each compound and 2 nM [³H]-LSD in 50 mM Tris-HCl buffer (pH 7.4) supplemented with 10 mM MgSO₄ and 0.5 mM EDTA. At the end of the incubation, the homogenates were filtered through Whatman GF/A filters and washed five times with ice-cold 50 mM Tris-HCl buffer. Non-specific binding was evaluated, in parallel, in the presence of 10^{− 5} M clozapine. Radioactivity associated with proteins was then quantified and expressed as the percentage of inhibition for each concentration of the compound under study.

Evaluation on 5-HT₇ receptors

All synthesized compounds were evaluated in terms of their ability to compete with the binding of [³H]-LSD on membranes of sf9 cells transiently expressing the human 5-HT₇ receptor (CRM 047, Perkin-Elmer Life Science) according to Shen et al. [16]. In brief, proteins were incubated at 27°C for 60 min in duplicate in the absence or the presence of 10^{− 6} or 10^{− 8} M of each drug and 2 nM [³H]-LSD in 50 mM Tris-HCl buffer (pH 7.4) supplemented with 10 mM MgSO₄ and 0.5 mM EDTA. At the end of the incubation, homogenates were filtered through Whatman GF/A filters presoaked with 0.5% polyethylenimine and washed 5 times with ice-cold 50 mM Tris-HCl buffer. Non-specific binding was evaluated in parallel in the presence of 250 μM clozapine. Radioactivity associated with proteins was then quantified in the presence of a scintillation cocktail and expressed as the percentage of inhibition for each concentration of drugs under study.

Results and discussion

Chemistry

The key intermediate 2-vinylindole 5a was prepared by a two step quaternization, Hofmann elimination procedure from 11. This dimethylaminoethyl indole derivative was obtained by cyanide cleavage of cyclic gramine derivative 7 [11]. Apart from some minor modifications, its 5-methoxy counterpart 6a was synthesized following the same way starting from the corresponding tetrahydro-γ-carboline 8 (Scheme 1).

Scheme 1 Synthesis of 2-vinylindoles 5a and 6a. Reagents: i: HCl-CH₃OH; ii: CH₃I; iii: KCN, EtOH-H₂O reflux; iv: NaOHaq.

Lithium aluminium hydride mediated reduction of nitriles 5a, 6a afforded the corresponding 2-vinyltryptamines 15a, 16a which were smoothly dimethylated to 3a, 4a according to the well-known method [17] (Scheme 2).

Scheme 2 Synthesis of 2-vinyltryptamines. Reagents: i: LiAlH₄; ii: CH₃I, CH₂Cl₂-NaOHaq; iii: MOMCl, CH₂Cl₂-NaOHaq; iv: NaH, MOMCl; v: Boc₂O, DMAP; vi: HCOHaq, NaBH₃CN, AcOH; vii: NaH, ArSO₂Cl.

To avoid the N_b-quaternization for the introduction of electron-donating substituents on the indole nitrogen, alkylation prior to nitrile reduction was preferred. By this way, N_a-methyl-N_b,N_b-dimethyl-2-vinyltryptamine 3b was prepared in a 29% yield, but as reduction and dimethylation of 5c could not be carried out in a satisfactory yield, the MOM derivative 3c was prepared starting from 3a by treatment with methoxymethyl chloride (MOMCl) in the presence of sodium hydride, in a 30% yield.

As for the electron-withdrawing substituents, t-butoxycarbonyl (Boc) and different arylsulfonyl groups were chosen. N_a-Arylsulfonyl-N_b,N_b-dimethyl-2-vinyltryptamines 3e-i, 4e were prepared by treating N_b,N_b-dimethyl-2-vinyltryptamine 3a or 4a with the appropriate arylsulfonyl chloride, using sodium hydride as a base in a mixture of anhydrous tetrahydrofuran and dimethylsulfoxide.

Pharmacology

All the synthesized compounds were evaluated on 5-HT₄, 5-HT₅, 5-HT₆ and 5-HT₇ receptors (Table I). Compounds 3a and 4a exhibited a moderate affinity for the 5-HT₆ receptor (77 and 79% of inhibition at 10^{− 6} M, respectively) showing that replacing the 2-ethyl or 2-phenyl group of the tryptamine by a vinyl retained affinity for this receptor. However, introduction of a 5-methoxy group (4a) had only a slight influence on binding. The presence of electron donating groups on the indole nitrogen induced significantly diminished affinity towards all types of investigated 5-HT receptors (3b, 3c vs. 3a).

Table I.  Inhibition values (%) of various 2-vinyltryptamines on 5-HT₆, 5-HT₄, 5-HT₅ and 5-HT₇ receptors

N°	R^1	5-HT6		5-HT4		5-HT5		5-HT7
		10^− 6 M	10^− 8 M	10^− 6 M	10^− 8 M	10^− 6 M	10^− 8 M	10^− 6 M	10^− 8 M
3a	H	77	1	7	0	27	10	55	2
4a	H	79	12	0	0	20	0	54	0
3b	CH3	25	0	22	17	0	0	17	0
3c	MOM	0	4	11	9	0	0	5	0
3d	Boc	53	26	44	0	35	0	24	0
3e	SO2Ph	97	45	22	1	29	25	18	0
3f	SO2C6H4p-CH3	90	39	nd	nd	45	14	22	16
3g	SO2C6H4p-Cl	97	27	16	5	2	0	18	0
3h	SO2C6H2(i-Pr)3	90	39	nd	nd	45	14	22	16
3i	SO2(2-naphtyl)	97	48	15	13	0	0	40	0
4e	SO2Ph	95	32	16	0	0	0	4	0
17		90	24	14	0	0	0	4	0

nd: not determined.

According to the findings of Glennon [18] and Russel [19], N_a substitution of tryptamine with a benzenesulfonyl group enhanced the 5-HT₆ receptor binding activity (ie. 3e). The substitution pattern of the phenyl group had little effect on affinity (ie. 3f-i) and introduction of a methoxy group in position 5 had no influence (ie. 4e), except for receptor selectivity. Compound 4e was found to have a more selective 5-HT₆ inhibitory activity compared to its non-methoxylated counterpart (3e). Generally, N_a-arylsulfonyl derivatives, especially 3 g and 3i displayed a good selectivity towards other tested receptors (ie. 5-HT₄, 5-HT₅ and 5-HT₇).

In order to compare our pharmacological data (inhibition %) with that of the literature (K_i), N_a-benzenesulfonyl-N_b,N_b-dimethyltryptamine 17 was prepared and submitted to affinity studies. This compound proved to be a potent and selective ligand of 5-HT₆ receptor in accord with its high affinity (K_i = 4.1 nM) reported by Glennon et al. [20]. Comparison of biological data of these different methods led to the conclusion that N_a-arylsulfonyl-N_b,N_b-dimethyltryptamines (3e-3i, 4a) were at least as potent as 17 and displayed about ten-fold higher affinity than 2-ethyl (1) or 2-phenyl (2) analogues (Figure 2).

Figure 2 Comparison of 5-HT₆ binding data.

These results showed that it was possible to replace an alkyl or aryl group in position 2 by a vinyl group without modification of the 5-HT₆ receptor affinity. The pharmacological profile of these compounds will be further evaluated.

Acknowledgements

Spectroscopic measurements by P. Sigaut (MS) and C. Petermann (NMR) are gratefully acknowledged.