Chemical and Pharmacological Studies on Enantiomerically Pure p‐Methoxytacripyrines, Promising Multi‐Target‐Directed Ligands for the Treatment of Alzheimer’s Disease

Abstract

Alzheimer's disease (AD) is an age-related neurodegenerative process characterized by progressive memory loss and other cognitive impairments.[1] Although the etiology of AD is not well known, several factors such as amyloid-b (Ab) [2] deposits, t-protein aggregation, oxidative stress or low levels of acetylcholine [3] are thought to play significant roles in the pathophysiology of the disease.[4] In spite of the continuous efforts of the pharmaceutical industry and academia, an efficient strategy for the treatment of AD is still lacking. This is partially related to the complexity of the pathology, in which multiple factors contribute to the final scenario. The multifactorial nature of AD has given rise to the rational basis for the development of the most current innovative therapeutic approaches based on the "one molecule, multiple targets" paradigm. [5][6][7][8][9] The multitarget approach [10] has been widely explored leading to the development of several multi-target-direct ligands (MTDLs), which include novel tacrine-melatonin hybrids, [11] dual inhibitors of acetylcholinesterase (AChE) and monoamine oxidase, [12] or serotonin transporters, [13] potent cholinesterase inhibitors with antioxidant and neuroprotective properties, [14] gallamine-tacrine hybrids binding at cholinesterases and M 2 muscarinic receptors, [15] or NO-donor-tacrine hybrids as hepatoprotective anti-AD drugs. [16] Based on the multitarget approach, some years ago we designed and synthesized novel multipotent molecules, called tacripyrines (I), by combination of tacrine and nimodipine, as reference agents with a multipotent cholinergic and calcium antagonism profile, respectively, for the treatment of AD. [17,18] Racemic tacripyrines exhibited potent and selective AChE inhibition, high calcium-channel blocking activity, as well as neuroprotective/antioxidant properties, able to cross the bloodbrain barrier.Particularly, (R/S)-p-methoxytacripyrine (ethyl 5-amino-4-(4-methoxyphenyl)-2-methyl-1, 4,6,7,8,9-hexahydrobenzo[b] [1,8] naphthyridine-3-carboxylate; (R/S)-1), one of the most potent cholinergic tacripyrines (IC 50 = 105 AE 15 nm against human AChE), at 100 mm showed 30.7 AE 8.6 % inhibition of the pro-aggregating action of AChE on Ab peptide (230 mm); furthermore, (R/S)-1 was also a moderate inhibitor of b-amyloid selfaggregation (34.9 AE 5.4 % at [I] = 50 mm).[18] Overall, these results prompted us to consider 1 as an appropriate hit compound in this project, and consequently, to undertake the pharmacological analysis of both enantiomers. The detailed investigation of chiral discrimination has enormous importance in medicinal chemistry as a means to better elucidating the mechanisms of interaction and to identify structural features involved in ligand-target recognition.The synthesis of (R/S)-1 was scaled up for this study, but essentially followed the general protocol previously described. [18] Briefly, starting from a mixture of E/Z-isomers of ethyl 2-(4-methoxybenzylidene)-3-oxobutanoate (2), [19] and reacting it with[a] Dr.

Structure–Activity Relationships of Organofluorine Inhibitors of β‐Amyloid Self‐Assembly

“…In a recent work it was stated that chirality was an important feature of methoxytacripyrines as inhibitors. [35] Analyzing the published data, however, led us to the conclusion that the activity differences between the enantiomers or racemic mixtures, while considerably high for h AChE inhibition, were rather insignificant (<10 %) for Aβ assembly given the experimental error of the fibril growing and analytical processes. Chiral compounds in our current set of molecules are included in Groups II and V. The results obtained with these compounds support our earlier conclusions.…”

Synthesis, Pharmacological Assessment, and Molecular Modeling of Acetylcholinesterase/Butyrylcholinesterase Inhibitors: Effect against Amyloid-β-Induced Neurotoxicity

“…The AutoDock Vina docking procedure used was previously validated. 62 Molecular Docking of Inhibitors 16 and 18 into eqBuChE and hBuChE. The horse BuChE model has been retrieved from the SWISS-MODEL Repository.…”

Tacrines as Therapeutic Agents for Alzheimer's Disease. IV. The Tacripyrines and Related Annulated Tacrines

“…Hence, the investigation of the activity profile of single enantiomers is of mandatory importance in order to elucidate the mechanisms of interaction and identify structural features involved in ligand‐target recognition. In the light of these considerations, in 2011 some of the authors published a new work in which they described the production of single enantiomers with high enantiomeric excess (ee>98 %) by chiral resolution of the ( R / S )‐4′‐methoxytacripyrine ITH122 , using a semi‐preparative high‐performance liquid chromatography (HPLC) approach on a chiral stationary phase . The absolute configuration at C4 was assigned by the X‐ray diffraction analysis of the two isolated fractions.…”

“…In the light of these considerations, in 2011 some of the authors published a new work in which they described the production of single enantiomers with high enantiomeric excess (ee > 98 %) by chiral resolution of the (R/S)-4'-methoxytacripyrine ITH122, using a semi-preparative high-performance liquid chromatography (HPLC) approach on a chiral stationary phase. [16] The absolute configuration at C4 was assigned by the X-ray diffraction analysis of the two isolated fractions. The 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 evaluation of the anti-ChE activity of the two enantiomers revealed that chirality at the stereocenter C4 modulated the activity toward both ChEs, resulting the (S)-enantiomer ten folds more potent on AChE than the (R)-enantiomer.…”

“…In previous accounts [11][12][13] dedicated to our contributions to this topic, we have reviewed the work and results on: (a) pyranotacrines of type (I) (Figure 1), and identified the hittacrine ethyl 5-amino-4-(4-methoxyphenyl)-2-methyl-6,7,8,9-tetrahydro-4H-pyrano [2,3-b]quinoline-3-carboxylate (2, Figure 1) a potent VDCC blocking compound (blocking the K + -induced Ca 2 + entry by 49.7 %), potent reversible, non-competitive AChEI (IC 50 = 0.87 AE 0.40 mM), showing also a moderate BuChE inhibition (IC 50 = 6.2 AE 0.6 mM); [11] (b) (benzo)chromenopyranotacrines of type (II) (Figure 1), the most relevant tacrine in this series being 14-(3,4dimethoxyphenyl)-9,11,12,14-tetrahydro-10H-benzo [5,6] chromeno [2,3-b]quinolin-13-amine (3), a mixed-type, selective human AChEI (hAChEI) (IC 50 = 0.083 AE 0.024 mM), less toxic than tacrine, and endowed with neuroprotective activity (Figure 2), [12] and (c) pyridotacrines (III) (Figure 1), whose most attractive tacrine analogue was pyridotacrine (4) ( Figure 1) which acted as a submicromolar inhibitor of hAChE (0.78 AE 0.08 mM) and a micromolar inhibtor of equine BuChE (12 AE 1 mM) and was able to significantly mitigate the reduction of cell viability (SH-SY5Y cell line) upon exposure to okadaic acid, a known inhibitor of the enzyme phosphoprotein phosphatase 2A, which is the main dephosphorylating enzyme of the tau protein. [13] The present account focuses on the review of the achievements related to tacripyrines (IV, Figure 2), which are compounds resulting from the hybridization oftacrine and 1,4-dihydropyridine (1,4-DHP) scaffold, [14][15][16][17][18][19][20][21][22][23][24][25] pyrimidotacripyrines (V, Figure 2), [26] and related simplified annulated tacrines, such as the hupertacrines (VI, Figure 2)...…”