1,2,3,4-Tetrahydrobenzo[h][1,6]naphthyridines as a new family of potent peripheral-to-midgorge-site inhibitors of acetylcholinesterase: Synthesis, pharmacological evaluation and mechanistic studies

Abstract

[1,6]naphthyridines differently substituted at positions 1, 5, and 9 have been designed from the pyrano[3,2-c]quinoline derivative 1, a weak inhibitor of acetylcholinesterase (AChE) with predicted ability to bind to the AChE peripheral anionic site (PAS), at the entrance of the catalytic gorge. Fourteen novel benzonaphthyridines have been synthesized through synthetic sequences involving as the key step a multicomponent Povarov reaction between an aldehyde, an aniline and an enamine or an enamide as the activated alkene. The novel compounds have been tested against Electrophorus electricus AChE (EeAChE), human recombinant AChE (hAChE), and human serum butyrylcholinesterase (hBChE), and their brain penetration has been assessed using the PAMPA-BBB assay. Also, the mechanism of AChE inhibition of the most potent compounds has been thoroughly studied by kinetic studies, a propidium displacement assay, and molecular modelling. We have found that a seemingly small structural change such as a double O → NH bioisosteric replacement from the hit 1 to 16a results in a dramatic increase of EeAChE and hAChE inhibitory activities (>217-and >154-fold, respectively), and in a notable increase in hBChE inhibitory activity (> 11-fold), as well. An optimized binding at the PAS besides additional interactions with AChE midgorge residues seem to account for the high hAChE inhibitory potency of 16a (IC50 = 65 nM), which emerges as an interesting anti-Alzheimer lead compound with potent dual AChE and BChE inhibitory activities. recombinant AChE (hAChE), and human serum butyrylcholinesterase (hBChE), and their brain penetration has been assessed using the PAMPA-BBB assay. Also, the mechanism of AChE inhibition of the most potent compounds has been thoroughly studied by kinetic studies, a propidium displacement assay, and molecular modelling.We have found that a seemingly small structural change such as a double O → NH bioisosteric replacement from the hit 1 to 16a results in a dramatic increase of EeAChE and hAChE inhibitory activities (>217-and >154-fold, respectively), and in a notable increase in hBChE inhibitory activity (> 11-fold), as well. An optimized binding at the PAS besides additional interactions with AChE midgorge residues seem to account for the high hAChE inhibitory potency of 16a (IC 50 = 65 nM), which emerges as an interesting anti-Alzheimer lead compound with potent dual AChE and BChE inhibitory activities.

Tetrahydrobenzo[h][1,6]naphthyridine-6-chlorotacrine hybrids as a new family of anti-Alzheimer agents targeting β-amyloid, tau, and cholinesterase pathologies

“…Molecular dynamics (MD) simulations confirmed the expected binding of the tricyclic moiety of 4 at the AChE PAS (cation-π / π-π interactions with Trp286) and hydrogen bond between the protonated pyridine nitrogen atom and the hydroxyl group of the PAS residue Tyr72) as well as additional interactions of the amide function at position 9 with midgorge residues (hydrogen bond between the amide NH group and the hydroxyl group of Tyr124) [10].…”

“…The 3,4-dihydro-2H-pyrano [3,2-c]quinoline derivatives 1 and 3, as well as 6-chlorotacrine, 2, were also evaluated under the same assay conditions as reference compounds. Also, the reported activity of compound 4 [10] was considered for comparison purposes.…”

“…For the synthesis of hybrids 5a-d, we used as starting material the N-Boc-protected tetrahydrobenzo[h] [1,6]naphthyridine 6, readily available by a multicomponent Povarov reaction between dihydro-2H-pyridine under the catalysis of Sc(OTf) 3 in acetonitrile [12], followed by DDQ oxidation [13] of the resulting diastereomeric mixture of octahydrobenzo[h] [1,6]naphthyridines [10]. Saponification of ester 6, followed by treatment of the resulting carboxylate with an Et 2 O solution of HCl afforded the corresponding carboxylic acid, which was isolated as the naphthyridine hydrochloride.…”

“…Indeed, the most potent compound of the series, 4 (Fig. 1), resulting from a double O → NH bioisosteric replacement from ester 1 at position 1 and at the side chain in position 9, exhibited a nanomolar hAChE inhibitory activity (IC 50 = 65 nM) [10].…”

“…With the aim of optimizing this tricyclic scaffold as a PAS-binding moiety, we recently designed a family of tetrahydrobenzo [h] [1,6]naphthyridines, which mainly resulted from the substitution of the oxygen atom at position 1 of the 3,4-dihydro-2H-pyrano [3,2-c]quinoline system of ester 1 by an amine nitrogen atom [10]. The rationale behind this structural modification was that the increased basicity of the pyridine nitrogen atom would enable i) its protonation at physiological pH, and hence, ii) the establishement of cation-π interactions, apart from π-π stacking, with the aromatic PAS residues.…”