Multipotent cholinesterase/monoamine oxidase inhibitors for the treatment of Alzheimer's disease: design, synthesis, biochemical evaluation, ADMET, molecular modeling, and QSAR analysis of novel donepezil-pyridyl hybrids

Abstract

The design, synthesis, and biochemical evaluation of donepezil-pyridyl hybrids (DPHs) as multipotent cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors for the potential treatment of Alzheimer's disease (AD) is reported. The 3D-quantitative structure-activity relationship study was used to define 3D-pharmacophores for inhibition of MAO A/B, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) enzymes and to design DPHs as novel multi-target drug candidates with potential impact in the therapy of AD. DPH14 (Electrophorus electricus AChE [EeAChE]: half maximal inhibitory concentration [IC50] =1.1±0.3 nM; equine butyrylcholinesterase [eqBuChE]: IC50 =600±80 nM) was 318-fold more potent for the inhibition of AChE, and 1.3-fold less potent for the inhibition of BuChE than the reference compound ASS234. DPH14 is a potent human recombinant BuChE (hBuChE) inhibitor, in the same range as DPH12 or DPH16, but 13.1-fold less potent than DPH15 for the inhibition of human recombinant AChE (hAChE). Compared with donepezil, DPH14 is almost equipotent for the inhibition of hAChE, and 8.8-fold more potent for hBuChE. Concerning human monoamine oxidase (hMAO) A inhibition, only DPH9 and 5 proved active, compound DPH9 being the most potent (IC50 [MAO A] =5,700±2,100 nM). For hMAO B, only DPHs 13 and 14 were moderate inhibitors, and compound DPH14 was the most potent (IC50 [MAO B] =3,950±940 nM). Molecular modeling of inhibitor DPH14 within EeAChE showed a binding mode with an extended conformation, interacting simultaneously with both catalytic and peripheral sites of EeAChE thanks to a linker of appropriate length. Absortion, distribution, metabolism, excretion and toxicity analysis showed that structures lacking phenyl-substituent show better druglikeness profiles; in particular, DPHs13-15 showed the most suitable absortion, distribution, metabolism, excretion and toxicity properties. Novel donepezil-pyridyl hybrid DPH14 is a potent, moderately selective hAChE and selective irreversible hMAO B inhibitor which might be considered as a promising compound for further development for the treatment of AD.

Keywords: 3D-QSAR; ADMET; ChE; MAO; donepezil-pyridyl hybrids; molecular modeling.

Figure 1

General structure of donepezil, ASS234, and donepezil-pyridyl hybrids (DPHs) (l) described here. Abbreviations: Bn, benzyl; Me, methyl; Ph, phenyl.

Figure 2

Recently reported donepezil-pyridyl hybrids (DPHs1–8). Note: Data from Samadi A, Chioua M, Bolea I, et al. Synthesis, biological assessment and molecular modeling of new multipotent MAO and cholinesterase inhibitors as potential drugs for the treatment of Alzheimer’s disease. Eur J Med Chem. 2011;46(9):4665–4668. Abbreviations: Bn, benzyl; Me, methyl; Ph, phenyl.

Figure 3

Synthesis of target DPHs 9, 13, and 14. Abbreviation: Bn, benzyl; DPHs, donepezil-pyridyl hybrids; EtOH, ethanol; Me, methy; Ph, phenyl; TEA, triethylamine; THF, tetrahydrofuran.

Figure 4

Synthesis of target DPHs10–12, 15, and 16. Abbreviation: Bn, benzyl; DPHs, donepezil-pyridyl hybrids; EtOH, ethanol; Ph, phenyl; TEA, triethylamine; THF, tetrahydrofuran.

Figure 5

Assessment of reversibility of hMAO B activity inhibited by DPH14 (50 μM) and R-deprenyl (500 nM). Notes: hMAO B was pre-incubated with each inhibitor for 30 minutes and remaining activity was measured prior and following a rapid 100-fold dilution with 1 mM tyramine. No changes were observed in enzyme inhibition by DPH14 revealing an irreversible inhibitory behavior. Bars expressed as mean ± standard error of the mean of at least three different experiments. Abbreviations: hMAO B, human monoamine oxidase B; DPH, donepezil-pyridyl hybrid; Depr, R-deprenyl; NT, non-treated.

Figure 6

Binding mode of inhibitor DPH14 at the active site of EeAChE. Notes: (A) Mode I, compound DPH14 is illustrated in violet. (B) Mode II, compound DPH14 is illustrated in blue. Ligands are rendered as balls and sticks and the side chains conformations of the mobile residues are illustrated in the same color as the ligand. Different sub-sites of the active site were colored: catalytic triad (CT) in green, oxyanion hole (OH) in pink, anionic sub-site (AS) in orange, except Trp86, acyl binding pocket (ABP) in yellow, and PAS in light blue. Black dashed lines are drawn among atoms involved in hydrogen bond interactions. Abbreviations: DPH, donepezil-pyridyl hybrid; PAS, peripheral anionic site; EeAChE, Electrophorus electricus acetylcholinesterase.

Figure 7

Complexes of compound DPH14 and eqBuChE homology built 3D-model. Notes: (A) Mode I, compound DPH14 is illustrated in violet (B) Mode II, compound DPH14 is illustrated in blue. Compound DPH14 is rendered as sticks. Abbreviations: DPH, donepezil-pyridyl hybrid; eqBuChE, equine serum butyrylcholinesterase; CAS, catalytic active site; PAS, peripheral anionic site.

Figure 8

Docking pose of inhibitor DPH14 into hMAO A. Notes: (A) Crystal structure of hMAO A represented in ribbon diagram. Compound DPH14 is represented as green sticks. (B) Amino acid residues of the binding site are color-coded. The flavin adenine dinucleotide cofactor (FAD) and the six water molecules are represented as an integral part of the hMAO A structure model and are rendered as orange sticks and red balls, respectively. Green dashed lines are drawn among atoms involved in hydrogen bond interactions. Abbreviations: DPH, donepezil-pyridyl hybrid; hMAO A, human monoamine oxidase A.

Figure 9

Docking pose of inhibitor DPH14 into hMAO B. Notes: (A) The protein structure of hMAO B is rendered as a blue cartoon model. Compound DPH14 is represented as pink sticks. (B) Amino acid residues of the binding site are color-coded. The flavin adenine dinucleotide cofactor (FAD) and the six water molecules are represented as an integral part of the hMAO B structure model and are rendered as orange sticks and red balls, respectively. Abbreviations: DPH, donepezil-pyridyl hybrid; hMAO B, human monoamine oxidase B.