Discovery of Novel Diphenyl Acrylonitrile Derivatives That Promote Adult Rats' Hippocampal Neurogenesis

Abstract

We previously discovered WS-6 as a new antidepressant in correlation to its function of stimulating neurogenesis. Herein, several different scaffolds (stilbene, 1,3-diphenyl 1-propene, 1,3-diphenyl 2-propene, 1,2-diphenyl acrylo-1-nitrile, 1,2-diphenyl acrylo-2-nitrile, 1,3-diphenyl trimethylamine), further varied through substitutions of twelve amide substituents plus the addition of a methylene unit and an inverted amide, were examined to elucidate the SARs for promoting adult rat neurogenesis. Most of the compounds could stimulate proliferation of progenitors, but just a few chemicals possessing a specific structural profile, exemplified by diphenyl acrylonitrile 29b, 32a, and 32b, showed better activity than the clinical drug NSI-189 in promoting newborn cells differentiation into mature neurons. The most potent diphenyl acrylonitrile 32b had an excellent brain AUC to plasma AUC ratio (B/P = 1.6), suggesting its potential for further development as a new lead.

Keywords: SARs; differentiation; diphenyl acrylonitrile; neurogenesis; proliferation.

Figure 1

The compounds promoting neurogenesis in vivo.

Figure 2

Different substituents (R groups) for the target compounds 8, 9, 12, 18, 23, 24, 29, 32, 36, 39, and 42.

Scheme 1

Reagents and conditions (R groups were listed in Figure 2): (i) CH₃PPh₃Br, NaNH₂, Et₂O, −10–25 °C, 1 h, 32.9%; (ii) KOAc, Pd(OAc)₂, Bu₄NBr, DMF, 80 °C, 5 h, 49.2%; (iii) SnCl₂, EtOH, reflux, 2 h, 18.9–37.6%; (iv) (a) N,N-dimethylcarbamoyl chloride/phenylacetyl chloride/dimethylsulfamoyl chloride/cyclopropylsulfonyl chloride/benzenesulfonyl chloride, pyridine, DMAP, CH₂Cl₂, 0–25 °C, 40.4–41.4%; (b) Isobutyric anhydride/benzoic anhydride, pyridine, DMAP (4-dimethylaminopyridine), CH₂Cl₂, 0–25 °C, 6.9–84.9%; (c) Cyclobutanecarboxylic acid/1-cyanocyclopropylformic acid/2-picolinic acid, pyridine, DCC (N,N′-dicyclohexylcarbodiimide), DMAP, CH₂Cl₂, −15–25 °C, 21.2–73.5%.

Scheme 2

Reagents and conditions (R groups were listed in Figure 2): (i) LiOH•H₂O, MeOH, 25 °C, 3 h, 97.9–99.2%; (ii) NiCl₂, NaBH₄, MeOH, 25 °C, 5 min; (iii) PTSA (p-toluenesulfonic acid), toluene, reflux, 3 h, 14.3%; (iv) (a) Methanesulfonyl chloride, pyridine, DMAP, CH₂Cl₂, 0–25 °C, 32.7%; (b) Isobutyric anhydride, pyridine, DMAP, CH₂Cl₂, 0–25 °C, 47.5–57.8%.

Scheme 3

Reagents and conditions (R groups were listed in Figure 2): (i) CH₃ONa, MeOH, reflux, 3 h, 17.8–27.2%; (ii) (a) SnCl₂, EtOH, reflux, 2 h, 37.6%; (b) Fe, NH₄Cl, MeOH, 80 °C, 2 h, 82.8%; (iii) Acetic anhydride/isobutyric anhydride, pyridine, DMAP, CH₂Cl₂, 0–25 °C, 27.2–61.9%.

Scheme 4

Reagents and conditions: (i) NaBH₄, CHCl₃, 25 °C, 10 h, 58.7%; (ii) HCHO, HCOOH, CHCl₃, reflux, 3 h, 44.3%.

Scheme 5

Reagents and conditions: (i) CH₃PPh₃Br, NaNH₂, Et₂O, −10–25 °C, 1 h, 32.9%; (ii) P(o-MePh)₃, Pd(OAc)₂, Et₃N, CH₃CN, 60 °C for 1 h; then 90 °C for 24 h, 78.1–86.0%; (iii) (a) Pivaloyl chloride, pyridine, DMAP, isopropylamine, CH₂Cl₂, 0–25 °C, 59.1%. (b) Isobutyric anhydride, pyridine, DMAP, CH₂Cl₂, 0–25 °C, 86.6%.

Figure 3

SARs of compounds 8d, 8g, 8h, 8j, 8k, and 8l in the proliferation stage of neurogenesis. All compounds showed significant proliferation-promoting activity. Eleven-week-old rats (n = 2) were administered intraperitoneally at a dose of 4.0 mg/kg/day for 28 days, followed by a BrdU pulse. The rats were sacrificed 24 h after the BrdU injections. BrdU⁺ immunoreactivity demonstrated the number of newborn cells in the vehicle group and the drug treatment groups. Data are expressed as mean ± SEM (n = 8 slices). (V: vehicle group; *** p < 0.001; ** p < 0.01).

Figure 4

SARs of compounds 9b, 12f, 18b, and 23b in the proliferation stage of neurogenesis. Compounds 9b, 18b, and 23b (but not 12f) showed significant proliferation-promoting activity. Eleven-week-old rats (n = 2) were exposed to the compounds intraperitoneally at a dose of 4.0 mg/kg/day for 28 days, followed by a BrdU pulse. The rats were sacrificed 24 h after the BrdU injection. BrdU⁺ immunoreactivity demonstrated the number of newborn cells in the vehicle group and the drug treatment groups. Data are expressed as mean ± SEM (n = 8 slices). (V: vehicle group; *** p < 0.001; ** p < 0.01).

Figure 5

SARs of compounds 8e, 23i, 24b, 29b, and 36a in the proliferation stage of neurogenesis. Compounds 24b and 29b showed significant proliferation-promoting activity. Eleven-week-old rats (n = 2) were administrated intraperitoneally at a dose of 4.0 mg/kg/day for 28 days, followed by a BrdU pulse. The rats were sacrificed 24 h after the BrdU injections. BrdU⁺ immunoreactivity demonstrated the number of newborn cells in the control group, the vehicle group, and the drug treatment groups. Data are expressed as mean ± SEM (n = 8 slices). (C: control group; V: vehicle group; ** p < 0.01; * p < 0.05).

Figure 6

SARs of compounds 8c, 8d, 29b, 39b, and 42b in the proliferation stage of neurogenesis. Compounds 8c, 8d, 29b, and 39b (but not 42b) showed significant proliferation-promoting activity (The stilbene 8d and the diphenyl acrylonitrile 29b were repeated to check reproducibility). Eleven-week-old rats (n = 2) were administrated intraperitoneally at a dose of 4.0 mg/kg/day for 28 days, followed by a BrdU pulse. The rats were sacrificed 24 h after the BrdU injections. BrdU⁺ immunoreactivity demonstrated the number of newborn cells in the control group, the vehicle group, and the drug treatment groups. Data are expressed as mean ± SEM (n = 8 slices). (C: control group; V: vehicle group; *** p < 0.001; * p < 0.05).

Figure 7

SARs of compounds 8c, 8d, 8j, 8k, 18b, 23b, 24b, 29b, 39b, and 42b in the differentiation stage of neurogenesis. Compound 29b showed significant neurogenesis-promoting activity. Green fluorescent BrdU⁺ dots in the subgranular zone indicate newborn cells (white triangle), and yellow fluorescent BrdU⁺&NueN⁺ dots in the subgranular zone indicate newborn mature neurons (white triangle). Nine-week-old rats (n = 2) were administrated intraperitoneally at a dose of 4.0 mg/kg/day for 28 days, followed by a BrdU pulse. The rats were sacrificed 28 days instead of 24 h after the BrdU injections. (A) The number of BrdU⁺ cells; (B) the number of NeuN⁺ and BrdU⁺ cells. Data are expressed as mean ± SEM (n = 8 slices). (C: control group; V: vehicle group; *** p < 0.001; ** p < 0.01; * p < 0.05).

Figure 8

SARs of NSI-189, 29a, 29b, 32a, and 32b in the proliferation stage of neurogenesis. Compounds 29b, 32a, and 32b showed significant proliferation-promoting activity. Nine-week-old rats (n = 4) were administrated intraperitoneally at a dose of 4.0 mg/kg/day for 28 days, followed by a BrdU pulse. The rats were sacrificed 24 h after the BrdU injection. BrdU⁺ immunoreactivity demonstrated the number of positive cells in the control group, vehicle group, and NSI-189 and drug treatment groups. Data are expressed as mean ± SEM (n = 8 slices). (C: control group; V: vehicle group; ** p < 0.01; * p < 0.05).

Figure 9

SARs of compounds NSI-189, 29a, 29b, 32a, and 32b in the differentiation stage of neurogenesis. Compound 29b, 32a, and 32b showed significant neurogenesis-promoting activity. Green fluorescent BrdU⁺ dots in the subgranular zone indicate newborn cells (white triangle), and yellow fluorescent BrdU⁺&NeuN⁺ dots in the subgranular zone indicate newborn mature neurons (white triangle). Nine-week-old rats (n = 4) were administrated intraperitoneally at a dose of 4.0 mg/kg, and the rats were sacrificed 28 days instead of 24 h after the BrdU injections. (A) The number of BrdU⁺ cells; (B) the number of NeuN⁺ and BrdU⁺ cells. Data are expressed as mean ± SEM (n = 8 slices). (C: control group; V: vehicle group; ** p < 0.01).