Dual functional cholinesterase and MAO inhibitors for the treatment of Alzheimer’s disease: synthesis, pharmacological analysis and molecular modeling of homoisoflavonoid derivatives

Figures & data

Figure 1. Structure of tacrine, donepezil, rivastigmine and galanthamine.

Figure 2. Chemical structures of ladostigil and rasagiline.

Figure 3. Design strategy for homoisoflavonoid derivatives.

Scheme 1. Reagents and conditions: (a) 3-chloropropionic acid trifluoromethanesulfonic acid; (b) NaOH, 0 °C; (c) p-methoxybenzaldehyde, piperidine, 80 °C; (d) α,ω-dibromo alkane, K₂CO₃, KI, butanone, rt; (e) amines, acetonitrile, reflux.

Table 1. In vitro inhibition IC₅₀ (μM) and selectivity of compounds 4, 9–18 on ChEs and MAOs.

			IC50^a (µM)
Compound	R	n	AChE^b	BuChE^c	MAO-A^d inhibition rate at 50 μM^f	MAO-B^e IC50^a (µM)
		–	>100	>100	24.1%	1.06 ± 0.01
9		2	0.74 ± 0.01	16.62 ± 1.30	8.0%	>25
10		3	3.94 ± 0.05	9.21 ± 0.63	24.7%	3.44 ± 0.04
11		4	5.73 ± 0.41	9.48 ± 0.26	28.5%	1.63 ± 0.06
12		5	14.1 ± 0.65	8.45 ± 0.64	30.0%	0.65 ± 0.05
13		3	3.78 ± 0.07	40.50 ± 4.90	19.1%	8.37 ± 0.80
14		3	2.45 ± 0.26	23.88 ± 2.39	20.0%	11.11 ± 0.25
15		3	7.47 ± 0.17	21.47 ± 0.35	22.4%	11.44 ± 1.54
16		3	2.83 ± 0.40	9.10 ± 0.02	24.8%	6.93 ± 0.49
17		3	8.51 ± 0.33	5.01 ± 0.40	37.9%	8.96 ± 0.77
18		3	27.86 ± 0.68	34.15 ± 3.05	1.3%	24.75 ± 0.76
Rivastigmine	–	–	5.10 ± 0.13	3.11 ± 0.04	n.t.^g	n.t.^g
Ladostigil	–	–	50.0 ± 4.8	n.t.^g	n.t.^g	37.1 ± 3.1
Clorgyline	–	–	n.t.^g	n.t.^g	4.1 ± 0.2 nM	n.t.^g
Pargyline	–	–	n.t.^g	n.t.^g	n.t.^g	0.19 ± 0.01

^aMean ± SD of at least three independent measurements.

^bAChE from electric eel was used.

^cBuChE from horse serum was used.

^dHuman Recombinant MAO-A was used.

^eHuman Recombinant MAO-B was used.

^fTest concentration is 50 μM.

^gn.t. = not tested.

Figure 4. Steady state inhibition by compound 10 of AChE hydrolysis of ACh; the plots show mixed-type inhibition for compound 10 on AChE.

Figure 5. Docking models of the compound–enzyme complex. (a) stereoviews looking down the gorge of TcAChE binding with 10 (yellow). (b) 10 docked into the catalytic gorge of TcAChE, highlighting the protein residues belonging to ACS and PAS that establish the main interactions.

Table 2. Reversibility and irreversibility of hMAO-B inhibition of hybrid 10 and pargyline^a.

	% hMAO-B inhibition^b
Compound	Before washing	After repeated washing
10 (3 µM)	40.3 ± 1.33	34.5 ± 089
10 (5 µM)	75.2 ± 3.84	65.9 ± 1.351
Pargyline (200 nM)	64.4 ± 5.21	51.7 ± 3.94

^aPargyline is an irreversible hMAO-B inhibitor.

^bData are the mean ± SD of three independent experiments.

Figure 6. Docking pose of derivative 10 (yellow) into human MAO-B (2V60) highlighting the protein residues that establish the main interactions with 10. The FAD cofactor was depicted using space fill representation.