Design and synthesis of new indole drug candidates to treat Alzheimer’s disease and targeting neuro-inflammation using a multi-target-directed ligand (MTDL) strategy

Figures & data

Figure 1. Examples of some drug candidates and natural products for the treatment of AD and anti-inflammatory agents and the design strategy for the novel derivatives.

Scheme 1. Synthetic routes for preparation of starting material 2, carboxylic acid derivatives 3a–c, and amide derivatives 4a–d. Reagents and conditions: (i) NaH, ClSO₃H, THF, stirring R.T., 3 h; (ii) phenyl acetic acid, p-chlorophenyl acetic acid or 3,4,5-trimethoxyphenyl acetic acid, K₂CO₃, Ac₂O, 90 °C, 4–6 h; (iii) the appropriate amine, HBTU, DMF, stirring 2–4 h.

Scheme 2. Synthetic routes for preparation of chalcone derivatives 5a–c and 6a,b. Reagents and conditions: (i) HBTU, DMF, stirring 8 h; (ii) NaOEt, EtOH abs., stirring R.T., 24 h; (iii) K₂CO₃, KI, acetone, reflux, 6–8 h; iv) KOH, MeOH, stirring R.T., 24 h.

Scheme 3. Synthetic routes for preparation of imine derivatives 7a–c, 8, 9a–c, and 10a,b. Reagents and conditions: (i) benzohydrazide, phenylacetic acid hydrazide, or p-chlorophenyl acetic acid hydrazide, gl. acetic acid, reflux 3–5 h; (ii) cyanoacetic acid hydrazide, abs. ethanol, reflux 3 h; (iii) the appropriate arylidine derivative, abs. EtOH, reflux 4–6 h; (iv) ethyl/or phenyl isothiocyanate, S, abs. EtOH, TEA, reflux 10–12 h.

Figure 2. Acetylcholinesterase and butyrylcholinesterase (AChE and BuChE) inhibition activities for synthesised target compounds and reference drugs.

Table 1. Values of inhibition of Aβ1–42 self-induced aggregation for tested compounds and tacrine.

Compounds	IC50 (uM)
3c	6.91
4a	22.40
4b	13.75
4d	8.76
5b	2.50
6b	4.94
7c	14.92
10b	5.16
Tacrine	3.50

Figure 3. Nitric oxide (NO) assessment for compounds 5b and 6b and a positive control.

Figure 4. Cyclooxygenase-2 (COX-2) assessment for compounds 5b and 6b and a positive control.

Figure 5. Interleukin-1β (IL-1β) assessment for compounds 5b and 6b and a positive control.

Figure 6. Tumour necrosis factor-α (TNF-α) assessment for compounds 5b and 6b and positive control.

Figure 7. Cytotoxicity of synthetic compounds 5b and 6b and positive control on SH-SY5Y and THLE2 human cell lines.

Figure 8. Binding interactions of the most active compound 5b inside rhAChE active site, (A) 3D image, 5b is described as white colour line and the ligand as yellow colour line, (B) 2D image.

Figure 9. Binding interactions of the most active compound 5b inside hBuChE active site, (A) 3D image, 5b is described as white colour line and ligand as yellow colour line, (B) 2D image.

Table 2. Molecular modelling data for selected test compounds and ligands into rhAChE and hBuChE active sites.

Compd. No.	AChE			BuChE
	Energy score (Kcal/mol)	Binding interaction	Amino acid	Energy score (Kcal/mol)	Binding interaction	Amino acid
3c	−17.4815	–SO2Me arene-H	Trp86	–	–	–
4a	–	–	–	−17.9970	p-Cl-Ph arene-H p-Cl-Ph arene-H	Trp82 Gly116
4b	–	–	–	−17.3823	Pyridine arene-H	Thr120
4d	–	–	–	−19.5390	Indole-Ph arene-H	Trp82
5b	−31.6883	–SO2Me –CH = CH–CO–	Tyr124 Phe225	−19.5216	Ph arene-arene Pyrrol arene-arene CO-Ph arene-arene	Trp82 Trp82 Tyr332
6b	−28.3927	–CH2–Ph arene-arene Pipridine–CH2– arene-H –NH–Ph arene-arene	Trp86 Tyr341 Trp286	−12.9466	-CH2-Ph arene-H Pipridine CH2 arene-H SO2Me arene-H SO2Me	Trp82 Trp82 Ile69 Gln71
7c	−17.0177	SO2Me arene-H	Trp286	−17.4498	p-Cl-Ph arene-arene	Trp82
10b	−18.4817	Pyrrole arene-H Pyrrole arene-arene Thiazole arene-H C=S	Tyr341 Trp286 His447 Gly448	−20.7428	Indole-Ph arene-H	Trp82
Ligand/ AChE	−17.2793	Dimethoxyphenyl arene-arene Pipridine–CH2– arene-H –CH2–Ph arene-arene	Trp286 Tyr341 Trp86	–	–	–
Ligand/ BuChE	–	–	–	−16.4403	C=O –CH2–OMe Pipridine-NH+ arene-cation	Gly116 Trp82 Tyr332

Table 3. Predicted physicochemical properties and drug-likeness for some active compounds, donepezil and tacrine.

Compd. no.	^aMW	^bnON	^cnOHNH	^dlogP (o/w)	^enrotb	^fTPSA	^g%Abs	n violation
Acceptable value	˂500	˂10	˂5	˂5	≤10	˂160	100%	≤1
3c	431.47	8	1	2.29	7	104.08	73.10	0
4a	442.97	5	0	4.35	4	59.38	88.52	0
4b	451.94	6	1	3.82	5	81.07	81.04	0
4d	533.09	5	0	6.02	6	59.38	88.52	2
5b	492.98	6	1	4.88	7	85.25	79.59	0
6b	555.70	7	1	5.38	9	88.48	78.48	2
7c	389.86	6	1	3.46	5	80.54	81.22	0
10b	471.59	8	3	2.60	5	111.50	70.54	0
Donepezil	379.50	4	0	4.10	6	38.78	95.63	0
Tacrine	198.27	2	2	3.05	0	38.91	95.58	0

^aMolecular weight, ^bnumber of hydrogen-bond acceptors, ^cnumber of hydrogen-bond donors, ^doctanol/water partition coefficient, ^enumber of rotable bonds, ^ftopological polar surface area, ^gabsorbtion (%).

Table 4. In silico ADME prediction results for some active compounds, donepezil and tacrine.

Compd. no.	^aHIA	^bCaCo-2	^cMDCK	^dPPB	^eBBB	^fSkinP
Acceptable value	70–100%	>90		>90%	>0.40	≥ −3	Solubility mg/L
3c	99.78	3.74	0.04	100	0.07	–1.78	5.07
4a	97.77	19.12	0.04	92.73	0.02	–1.66	0.39
4b	97.30	10.86	0.04	95.71	0.01	–2.13	0.48
4d	98.26	21.50	0.04	90.70	0.09	–1.59	0.01
5b	97.47	10.29	0.06	93.68	0.21	–2.04	0.01
6b	97.52	17.47	0.43	96.63	0.22	–1.95	0.01
7c	96.61	2.07	0.07	100.00	0.01	–2.15	1.13
10b	98.00	0.60	0.04	100.00	0.05	–2.44	0.00
Donepezil	97.95	55.51	0.13	84.61	0.187	–3.04	6.23
Tacrine	96.51	25.85	38.45	95.39	0.86	–3.04	41.09

^aHuman intestinal absorbtion (%), ^bin vitro CaCo cell permeability (nm/sec), ^cin vitro MDCK cell permeability (nm/s), ^din vitro plasma protein binding (%), ^ein vitro blood–brain barrier penetration (C. brain/C. blood), and ^fSkin permeability.

Table 5. Predicted toxicity properties results for some active compounds, donepezil and tacrine.

Compd. no.	AMES	Carcino-Mouse	Carcino-Rat	hERG-inhibition
3c	Mutagen	Negative	Negative	Medium-risk
4a	Non-mutagen	Negative	Negative	Medium-risk
4b	Non-mutagen	Negative	Negative	Medium-risk
4d	Non-mutagen	Negative	Negative	Medium-risk
5b	Non-mutagen	Positive	Negative	Medium-risk
6b	Non-mutagen	Negative	Negative	Medium-risk
7c	Mutagen	Negative	Negative	Low-risk
10b	Non-mutagen	Positive	Negative	Ambiguous
Donepezil	Mutagen	Negative	Negative	Medium-risk
Tacrine	Mutagen	Positive	Negative	Medium-risk

Table 6. Metabolism prediction results for some active compounds, donepezil and tacrine.

Compd. No.	CYP1A2 inhibitor	CYP2C19 inhibitor	CYP2C9 inhibitor	CYP2D6 inhibitor	CYP3A4 inhibitor	P-gp substrate
3c	No	Yes	Yes	No	No	No
4a	No	Yes	Yes	No	Yes	No
4b	No	Yes	Yes	No	Yes	No
4d	No	No	Yes	No	Yes	Yes
5b	No	Yes	Yes	No	Yes	No
6b	No	No	Yes	No	Yes	Yes
7c	No	Yes	Yes	No	No	No
10b	No	Yes	Yes	No	Yes	No
Donepezil	No	No	No	Yes	Yes	Yes
Tacrine	Yes	No	No	No	Yes	Yes

Data availability statement

The data supporting the findings of this study are available within the article [and/or] its supplementary materials.