Novel harmine derivatives as potent acetylcholinesterase and amyloid beta aggregation dual inhibitors for management of Alzheimer’s disease

Figures & data

Figure 1. Chemical structures of harmine and its derivatives.

Figure 2. Design strategy for the new series of harmine derivatives targeting AChE and Aβ_1-42 aggregation.

Scheme 1. Synthesis of compounds 11 − 15. Reagents and conditions: (i) NaH, DMF, rt; (ii) AcOH, HBr, reflux; (iii) Different acylbromides, EDCI, dry CH₂Cl₂, reflux; (iv) NaHCO₃, EtOH, reflux.

Scheme 2. Synthesis of compounds 17a − 17l. Reagents and conditions: (i) NaHCO₃, EtOH, reflux.

Table 1. Inhibition of hAChE, hBuChE, and Aβ_1 − 42 aggregation by the synthesised compounds.

Compound	IC50 (nM)^a or inhibition % at 1 μM		S.I.^b	IC50 (μM)^a for Aβ1 − 42 or inhibition % at 20 μM
	hAChE	hBuChE
11	36.35%	29.85 %	n.d.^c	21.35 %
12	49.69 ± 2.13	163.28 ± 7.73	3.3	38.64 %
13	58.76 ± 1.96	38.45 %	> 17.0	9.31 ± 0.36
14	156.52 ± 4.89	463.64 ± 22.57	2.9	47.61 %
15	285.62 ± 18.27	36.8%	> 3.5	18.33 ± 0.61
17a	12.57 ± 0.56	581.33 ± 23.51	6.5	6.74 ± 0.27
17b	35.82 ± 1.29	251.16 ± 10.88	2.4	30.95%
17c	15.73 ± 0.68	39.75 %	> 6.6	16.02 ± 0.47
17d	89.38 ± 4.62	584.34 ± 23.95	46.4	13.82 ± 0.51
17e	106.28 ± 4.98	17.28%	> 27.9	31.38 %
17f	149.81 ± 6.03	20.98 %	> 63.5	43.87%
17g	279.55 ± 11.82	673.82 ± 30.62	2.4	34.60%
17h	48.13 %	568.36 ± 24.64	< 0.6	20.34%
17i	116.45 ± 4.86	46.08%	> 8.5	31.85 %
17j	121.65 ± 4.15	203.51 ± 0.27	1.6	37.86 %
17k	748.24 ± 32.94	40.18 %	> 1.3	43.56%
17l	48.38 ± 2.35	356.50 ± 18.64	7.3	12.42 ± 0.37
Harmine	33.80%	25.68%	n.d.^c	29.43%
Tacrine	81.36 ± 3.47	12.52 ± 0.51	0.2	n.d. ^c
Donepezil	17.86 ± 0.76	22.54%	> 56.0	n.d. ^c
Resveratrol	n.d.^c	n.d. ^c	n.d.^c	11.51 ± 0.45
Curcumin	n.d.^c	n.d. ^c	n.d.^c	15.47 ± 0.62

^a Values are expressed as mean ± SD of five independent experiments.

^b Selectivity index for AChE is defined as IC₅₀ (hBuChE)/IC₅₀ (hAChE).

^c n.d.: Not determined.

Table 2. Physiochemical properties for some active compounds, tacrine, donepezil, resveratrol and curcumin.

Compound	MW	HBA	HBD	tPSA	Log P	n violation
13	496.28	5	0	50.60	4.67	0
15	524.32	6	0	50.60	5.52	2
17a	510.30	6	0	50.60	5.12	2
17c	510.30	6	0	50.60	5.20	2
17d	514.27	6	0	50.60	4.79	1
17l	564.27	6	0	50.60	5.45	2
Tacrine	198.12	2	2	38.91	2.87	0
Donepezil	379.21	4	0	38.77	4.19	0
Resveratrol	228.08	3	3	60.69	2.54	0
Curcumin	368.13	6	2	93.06	2.60	1
Acceptable value	≤ 500	≤ 10	≤ 5	≤ 90	≤ 5	≤1

MW: molecular weight; HBA: number of hydrogen acceptors; HBD: number of hydrogen donors; tPSA: total polar surface area; Log P: log octanol/water partition coefficient.

Table 3. Predicted ADME and toxicity results for some active compounds, tacrine, donepezil, resveratrol and curcumin.

Compound	Absorption				Distribution			Metabolism				Metabolism		Toxicity
	Caco − 2 log unit	MDCK ×10^−5cm/s	HIA	F30%	PPB %	BBB	VD L/Kg	CYP1A2 inhibitor	CYP2C19 inhibitor	CYP2C9 nhibitor	CYP2D6 inhibitor	CL mL/min/kg	T1/2	LD50 mg/kg	toxicity class
13	−5.00	1.8	−−−	−−−	93.8	+++	2.50	+	+	−−	+++	9.75	0.04	1000	4
17d	−5.02	1.8	−−−	−−−	94.3	+++	2.63	+	+	−−	+++	9.52	0.01	1000	4
Tacrine	−4.70	2.2	−−−	+++	63.8	+++	1.63	+++	−−	−−−	+	3.598	0.20	40	2
Donepezil	−4.79	2.1	−−−	−−−	87.7	+++	1.59	−−	−	−−−	+++	10.64	0.16	505	4
Resveratrol	−4.87	1.2	−−−	+++	96.0	−−−	0.71	+++	−−	−	+	14.41	0.90	1560	4
Curcumin	−4.85	1.3	−−−	+++	89.7	−−	0.32	++	−−	+	−−	12.80	0.94	2000	4

Caco − 2: Caucasian colon adenocarcinoma cell lines; MDCK: Madin–Darby canine kidney; HIA: human intestinal absorption; F: bioavailability; PPB: plasma proteinbinding; BBB: blood–brain barrier; VD: volume of distribution; CYP: cytochrome P450; CL: clearance; T1/2: half − life. For the classification endpoints, the prediction probability values are transformed into six symbols: 0 − 0.1(−−−), 0.1 − 0.3(−−), 0.3 − 0.5(−), 0.5 − 0.7(+), 0.7 − 0.9(++), and 0.9 − 1.0(+++).

Figure 3. AChE induced Aβ_1-42 aggregation inhibition by compounds 13 and 17d. *** p < 0.001 vs control group.

Figure 4. Neurotoxicity of compounds in SH-SY5Y cells. *p < 0.05, **p < 0.01 and *** p < 0.001 vs control group (untreated cells).

Figure 5. Neuroprotective effects of compounds 13 and 17d against Aβ_1-42-induced cell death in SH-SY5Y cells. ^# p < 0.05 and ^### p < 0.001 vs control group (untreated cells); *p < 0.05 and ***p < 0.001 vs Aβ_1-42-treated cells.

Figure 6. The Lineweaver-Burk plot of hAChE exhibits competitive inhibition with compound 13.

Figure 7. Proposed binding mode of compound 13 inside AChE active site, (A) 3D image, the blue dashed lines stand for π-π stacking, the red dashed lines represent hydrogen bondsnd and the black dashed lines mean hydrophobic interaction (B) 2D image.

Figure 8. Proposed binding mode of compound 13 inside Aβ_1-42 active site, (A) 3D image, the blue dashed lines stand for π-π stacking, the red dashed lines represent hydrogen bondsnd and the black dashed lines mean hydrophobic interaction, (B) 2D image.