New 1,2,4-oxadiazole derivatives with positive mGlu₄ receptor modulation activity and antipsychotic-like properties

Figures & data

Figure 1. Chemical structures of various classes of mGlu₄ PAMs. Compounds 1 and 2 were the first ligands identified as PAMs for mGlu₄ receptor, 11 is currently in phase II clinical trials, and 12 has advanced as a preclinical development candidate.

Figure 2. Design of three new series of compounds generated via bioisosteric replacement.

Scheme 1. Reagents and conditions: (a) NH₂OH·HCl, NaOH_aq, EtOH, reflux, 1–5 h; (b) R₁COCl, toluene, K₂CO₃, MW 170 °C, 10 min; (c) Fe, CH₃COOH, EtOH, water, 60 °C, 1–2 h or SnCl₂, 5 N HCl, EtOH, reflux, 2 h; (d) R₂COCl, py, rt, overnight.

Scheme 2. Reagents and conditions: (a) NH₂OH·HCl, NaOH_aq, EtOH, reflux, 1–5 h; (b) 4-nitrobenzoyl chloride, toluene, K₂CO₃, MW 170 °C, 10 min; (c) Fe, CH₃COOH, EtOH, water, 60 °C, 1–2 h or Raney Ni, NH₂-NH₂ aq, MeOH/THF, 60 °C, 30 min; (d) R₂COCl, py, rt, overnight.

Scheme 3. Reagents and conditions: (a) py, rt, overnight; (b) NH₂OH·HCl, NaOH_aq, EtOH, reflux, 1–5 h; (c) R₂COCl, toluene, K₂CO₃, MW 170 °C, 10 min or rt, 30 min than reflux, 6 h.

Figure 3. Chemical optimisation strategy for compound 17d.

Table 1. In vitro mGlu₄ receptor PAM activity of 1,2,4-oxadiazole derivatives.

Cmpd	R1	R2	R3	EC50^a [nM]	GluMax [%]	Fold shift^b
17d	2-Cl	2-pyridyl	H	3700	116	1.8
28	2-Cl	3-pyridyl	H			NA^c
29	2-Cl	4-pyridyl				NA
30	2-Cl	Ph				NA
31	2-Cl	6-F-2-pyridyl				NA
32	2-Cl	6-Cl-2-pyridyl				NA
33	H	2-pyridyl	OMe	1830	130	5.3
34	2-Cl	2-pyridyl		656 (138)^d	114 (3.94)^d	13.4 (2.00)^d
35	3-Cl	2-pyridyl		5300	145	2.2
36	4-Cl	2-pyridyl		1980	157	2.0
37	2-F	2-pyridyl		393 (62)^d	116 (1.77)^d	3.68 (0.19)^d
38	2-Cl,4-F	2-pyridyl		1980	124	4.6
39	2-Cl	6-F-2-pyridyl		920	135	2.0
40	2-Cl	5-Cl-3-F-2-pyridyl				NA
41	2-Cl	6-Cl-2-pyridyl		1920	115	4.1
42	2-Cl	3-Cl-6-MeO-2-pyridyl				NA
43	2-Cl	4,6-diF-2-pyridyl		2500	134	5.0
44	2-Cl	6-F-2-pyridyl		780	135	6.2
45	2-Cl	4-pirymidyl		3100	118	3.1
46	2-Cl	2- thiazolyl		2200	126	3.6
47	2-F	6-F-2-pyridyl		890	121	6.9
48	2-F	3,6-diCl-2-pyridyl				NA
49	H	2-pyridyl	Cl	352 (60)^d	123 (3.24)^d	6.77 (0.53)^d
50	2-Cl	6-F-2-pyridyl				NA
51	2-Cl	6-Cl-2-pyridyl				NA
52	2-Cl	2-pyridyl		282 (46)^d	123 (3.18)^d	8.03 (0.76)^d
53	2-Cl,4-F	2-pyridyl		1350	119	2.1
54	2-MeO	2-pyridyl		750	111	2.2
55	H	2-pyridyl	F	2560	127	3.0
56	2-Cl	2-pyridyl				NA
57	2-Cl,4-F	2-pyridyl				NA
58	2-MeO	2-pyridyl				NA
59	H	2-pyridyl	CF3	740	150	7.6
60	2-Cl	2-pyridyl		390 (57)^d	120 (0.88)^d	2.94 (0.1)^d
61	H	2-pyridyl	Me	1650	128	5.1
62	2-Cl	2-pyridyl		308 (35)^d	135 (3.65)^d	3.3 (0.34)^d

^aValue determined in a presence of EC₂₀ (3 µM) concentration of L-Glu (PAM-mode) in a forskolin-stimulated cAMP assay in T-REx 293 cells expressing human mGlu₄ receptor; data are mean of two independent experiments; ^bFold shift of L-Glu dose-response curve determined in the presence of 10 µM of compound; ^cNA: non-active; ^dMean from at least three independent experiments with SEM value in bracket.

Figure 4. The activity of compounds 34, 37, 49, 52, 60, 62 and reference drugs MMPIP (a selective NAM of mGlu₇ receptor) and AZ12216052 (a PAM of mGlu₈ receptor) tested at a concentration of 10 μM in the cAMP accumulation assay in cells expressing mGlu₇ and mGlu₈ receptors. The percent activity refers to two extreme FRET signals: 0% corresponds to forskolin treatment alone and 100% to maximal FRET signal for the control cells (without any treatment). A/D – agonistic activity; B/E – PAM activity measured in the presence of L-Glu at the EC₂₀ concentration (0.1 mM for mGlu₇ receptor, and 1 μM for mGlu₈ receptor); C/F – NAM activity measured in the presence of L-Glu at the EC₈₀ concentration (1 mM for mGlu₇ receptor, 10 μM for Glu₈ receptor).

Figure 5. The time course of 52 after i.p. administration in mice: (A) plasma and (B) brain concentration-time profiles.

Table 2. Pharmacokinetic parameters in the mouse plasma and brain after a 10 mg/kg i.p. dose of 52.

Parameters	Plasma	Brain
Tmax^a	0.25	0.5
T1/2^b	1.10	2.26
Cmax^c	0.54	2.12
AUC^d	0.37	5.64

^aTime at maximum observed concentration [h]; ^bterminal elimination half-life after i.p administration [h]; ^cmaximum concentration after i.p administration [µM/L]; ^darea under the curve [µM/L × h].

Figure 6. The effects of compounds 52 and 62 on (A, B) stress-induced hyperthermia and (D, E) DOI-induced HTR. Doses are indicated as mg/kg. Bars represent the mean ± SEM ***p < 0.001 vs. vehicle. Compounds 52 and 62 at all doses significantly reduced the SIH response: 52 [F_(3.34) = 9.35; p < 0.001], 62 [F_(3.36)=17.12; p < 0.001]; and DOI-induced HTR: 52 [F_(3.36) = 28.14; p < 0.001]), 62 [F (3.16) = 38.24; p < 0.001]. The control drugs are presented in panels C (diazepam) and F (clozapine). ***p < 0.001 and **p < 0.01.