Design, synthesis and pharmacological evaluation of conformationally restricted N-arylsulfonyl-3-aminoalkoxy indoles as a potential 5-HT₆ receptor ligands

Figures & data

Figure 1.  Chemical structures of compounds that bind to 5-HT₆R.

Table 1.  5-HT₆R binding affinities.

Compound	R1	R2	R3	5-HT6 Ki, nM	% Inhibition at 1 µM
8a	2-H	H	H	—	82.3
8b	3-Cl	H	H	—	97.2
8c	2-Cl	H	H	464	—
8d	2-OMe	H	H	127	—
8e	2-OiPr	H	H	—	67.35
8f	2-OMe	Me	H	—	68.26
8g	3-F	H	Me	—	74.13
8h	2-Cl	Me	H	—	48.15
8i	2-Cl	H	Me	—	61.07
8j	2-H	Me	H	—	74.28
8k	2-OEt	H	H	—	61.67
8l	2-H	H	Me	—	60.18
8m	3-F	Me	H	—	46.68
8n	2-OMe	H	Me	—	86.38
8o	1-F	H	H	>500	—

5-HT receptor binding studies carried out at Novascreen, USA.: Human recombinant/HEK293 cells; Radioligand: [³H] LSD (60–80 Ci/mmol). Final ligand concentration: 1.5 nM, non-specific determinant: Methiothepin mesylate: [0.1 M]; reference compound: Methiothepin mesylate, positive control: Methiothepin mesylate.

Note: The α- and β-methyl derivatives were tested as racemic mixture. The percent inhibition at 1 µM was an average of the assay conducted in duplicate. The K_i value reported was an average of the assay conducted in duplicate.

Table 2.  Selectivity profile of compounds on other receptors.

Compound	5-HT7	M1	5-HT4
		IC50 nM
8a	>10,000	>10,000	>10,000
8b	>10,000	>10,000	>10,000

Compounds were tested for IC₅₀ value in non-radioactive cell-based assay.

Figure 2.  Evaluation of compound 8b for 5-HT₇ receptor binding in cell-based assay.

Figure 3.  Evaluation of compound 8b for 5-HT₄ receptor binding in cell-based assay.

Figure 4.  Evaluation of compound 8b for M₁ receptor binding in cell-based assay.

Table 3.  Human cytochrome P450 inhibitory data and % surrogate metabolism for compounds 8a and 8b.

Compound	IC50 (µM)		Surrogate % metabolism
	2D6	3A4	Human	Wister rat
8a	7.65	>45	50.98	100
8b	5.06	37.05	95.59	77.54

The cytochrome P450 inhibitory potential was determined using isoform-selective assays and heterologously expressed human CYP2D6 and CYP3A4. These values are the mean of duplicate determinations. Microsomal metabolic stability in Wistar rat and human at 0.5 h, Con. 2.5 µM.

Table 4.  Pharmacokinetic profile of compound 8b in male Wister rats.

	Compound 8b
Dose mg/kg	10	10
Route	Oral	i.v.
n	3	3
Cmax (µg/ml)	0.31 ± 0.05	1.65 ± 0.13
Tmax (h)	0.67	0.08
AUCt (µg·h/ml)	1.2 ± 0.13	3.4 ± 0.27
AUCinf (µg·h/ml)	1.2 ± 0.14	3.4 ± 0.27
t1/2 (h)	1.49 ± 0.26	1.59 ± 0.28
CL (L/h/kg)	8.2	2.8
Vz (L/kg)	17.5	6.6
MRTlast	3.46	1.81
Cb/Cp (mg/kg/h)	9.04 ± 1.87
F (%)	35 ± 5

Fasted male Wistar rats, vehicle used: water for injection for both oral and i.v. routes.

Dosing volumes: 10 ml/kg for oral and 2 ml/kg for i.v.

Figure 5.  Latency to target in Morris water maze task. Data represents mean ± SEM of latency to target recorded as time taken to locate the hidden platform in water. Compound 8b at 10 mg/kg p.o. reversed scopolamine-induced deficit and significant difference from scopolamine-treated group is indicated with asterisk (unpaired t-test; *p < 0.05).

Figure 6.  Path length to target in Morris water maze task. Data represents mean ± SEM of path length recorded as path taken to locate the hidden platform in water. Compound 8b at 10 mg/kg p.o. reversed scopolamine-induced deficit and significant difference from scopolamine-treated group is indicated with asterisk (unpaired t-test *p < 0.05; **p < 0.01).

Scheme 1.  Reagents: (a) Glycine, water, NaOH; (b) DMF, NaOAc, Ac₂O; (c) Na₂SO₃, MeOH/water; (d) THF, K₂CO₃, Me₂NCH₂CH₂Cl, reflux; (e) NaOH, MeOH, reflux; (f) 2-Bromobenzenesulfonyl chloride, THF, KOH powder; (g) DMA, CH₃COOK, P(PPh₃)₄Pd, 120°C.