Synthesis and cholinesterase inhibitory activity study of new piperidone grafted spiropyrrolidines.

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder, which affected 35 million people in the world. The most practiced approach to improve the life expectancy of AD patients is to increase acetylcholine neurotransmitter level at cholinergic synapses by inhibition of cholinesterase enzymes. A series of unreported piperidone grafted spiropyrrolidines 8(a-p) were synthesized and evaluated in vitro for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities. Therein, compounds 8h and 8l displayed more potent AChE enzyme inhibition than standard drug with IC50 values of 1.88 and 1.37 µM, respectively. Molecular docking simulations for 8l possessing the most potent AChE inhibitory activities, disclosed its interesting binding templates to the active site channel of AChE enzymes. These compounds are remarkable AChE inhibitors and have potential as AD drugs.

Efficient Synthesis and Discovery of Schiff Bases as Potent Cholinesterase Inhibitors.

BACKGROUND: The search for new cholinesterase inhibitors is still a promising approach for management of Alzheimer`s disease. Schiff bases are considered as important class of organic compounds, which have wide range of applications including as enzyme inhibitors. In the present study, a new green ionic liquid mediated strategy was developed for convenient synthesis of two series of Schiff bases 3(a-j) and 5(a-j) as potential cholinesterase inhibitors using aromatic aldehydes and primary amines in [bmim]Br. METHODS: The synthesized compounds were evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory potential by modified Ellman's method. The molecular interactions between the most active compound and the enzyme were analyzed by molecular docking. RESULTS: Among them, 3j displayed higher inhibitory activities than reference drug, galanthamine, with IC50 values of 2.05 and 5.77 µM, for AChE and BChE, respectively. Interestingly, all the compounds except 3b displayed higher BChE inhibitions than galanthamine with IC50 values ranging from 5.77 to 18.52 µM. Molecular docking of compound 3j inside the TcAChE and hBChE completely coincided with the inhibitory activities observed. The compound forms strong hydrogen bonding at the peripheral anionic site of AChE whereas on BChE, it had hydrophobic and mild polar interactions. CONCLUSION: An efficient and eco-friendly synthetic methodology has been developed to synthesize Schiff bases in a very short reaction time and excellent yields in ionic solvent, whereby the compounds from series 3 showed promising cholinesterase inhibitory activity.

New Indole Alkaloids from the Bark of Rauvolfia Reflexa and their Cholinesterase Inhibitory Activity.

BACKGROUND/AIMS: Rauvolfia reflexa is a member of the Apocynaceae family. Plants from the Apocynaceae family have been traditionally used in the treatment of age-related brain disorders Methods and Results: Two new indole alkaloids, rauvolfine C (1) and 3-methyl-10,11-dimethoxy-6-methoxycarbonyl-ß-carboline (2), along with five known, macusine B (3), vinorine (4), undulifoline (5), isoresrpiline (6) and rescinnamine (7) were isolated from the bark of Rauvolfia reflexa. Cholinesterase inhibitory assay and molecular docking were performed to get insight of the inhibitory activity and molecular interactions of the compounds. The compounds showed good to moderate cholinesterase inhibitory activity with IC50 values in the range of 8.06 to 73.23 µM. Compound 7 was found to be the most potent inhibitor of both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Compounds 1, 2, 5 and 6 were found to be selective towards BChE, while compounds 3, 4 and 7 were dual inhibitors, having almost equal inhibitory activity on both AChE and BChE. Molecular docking revealed that compounds 6 and 7 interacted differently on AChE and BChE, by means of hydrophobic interactions and hydrogen bonding. In AChE, the indole moiety of both compounds interacted with the residues lining the peripheral anionic site, whereas in BChE, their methoxy groups are primarily responsible for the strong inhibitory activity via interactions with residues at the active site of the enzyme. CONCLUSION: Two new and five known indole alkaloids were isolated from R. reflexa. Among the compounds, 7 and 6 showed the most potent and promising cholinesterase inhibitory activity, worthy for further investigations.

An expedient synthesis, acetylcholinesterase inhibitory activity, and molecular modeling study of highly functionalized hexahydro-1,6-naphthyridines.

A series of hexahydro-1,6-naphthyridines were synthesized in good yields by the reaction of 3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones with cyanoacetamide in the presence of sodium ethoxide under simple mixing at ambient temperature for 6-10 minutes and were assayed for their acetylcholinesterase (AChE) inhibitory activity using colorimetric Ellman's method. Compound 4e with methoxy substituent at ortho-position of the phenyl rings displayed the maximum inhibitory activity with IC50 value of 2.12 µM. Molecular modeling simulation of 4e was performed using three-dimensional structure of Torpedo californica AChE (TcAChE) enzyme to disclose binding interaction and orientation of this molecule into the active site gorge of the receptor.

A facile ionic liquid promoted synthesis, cholinesterase inhibitory activity and molecular modeling study of novel highly functionalized spiropyrrolidines.

A series of novel dimethoxyindanone embedded spiropyrrolidines were synthesized in ionic liquid, [bmim]Br and were evaluated for their inhibitory activities towards cholinesterases. Among the spiropyrrolidines, compound 4f exhibited the most potent activity with an IC50 value of 1.57 µM against acethylcholinesterase (AChE). Molecular docking simulation for the most active compound was employed with the aim of disclosing its binding mechanism to the active site of AChE receptor.

Ionic liquid mediated synthesis and molecular docking study of novel aromatic embedded Schiff bases as potent cholinesterase inhibitors.

Novel aromatic embedded Schiff bases have been synthesized in ionic liquid [bmim]Br and evaluated in vitro for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes inhibitory activities. Among the newly synthesized compounds, 5f, 5h and 7j displayed higher AChE enzyme inhibitory activities than standard drug, galanthamine, with IC50 values of 1.88, 2.05 and 2.03µM, respectively. Interestingly, all the compounds except for compound 5c displayed higher BChE inhibitories than standard with IC50 values ranging from 3.49 to 19.86µM. Molecular docking analysis for 5f and 7j possessing the most potent AChE and BChE inhibitory activities, disclosed their binding interaction templates to the active site of AChE and BChE enzymes, respectively.

Synthesis and discovery of highly functionalized mono- and bis-spiro-pyrrolidines as potent cholinesterase enzyme inhibitors.

Novel mono and bis spiropyrrolidine derivatives were synthesized via an efficient ionic liquid mediated, 1,3-dipolar cycloaddition methodology and evaluated in vitro for their AChE and BChE inhibitory activities in search for potent cholinesterase enzyme inhibitors. Most of the synthesized compounds displayed remarkable AChE inhibitory activities with IC50 values ranging from 1.68 to 21.85 µM, wherein compounds 8d and 8j were found to be most active inhibitors against AChE and BChE with IC50 values of 1.68 and 2.75 µM, respectively. Molecular modeling simulation on Torpedo californica AChE and human BChE receptors, showed good correlation between IC50 values and binding interaction template of the most active inhibitors docked into the active site of their relevant enzymes.

Ionic liquid mediated synthesis of mono- and bis-spirooxindole-hexahydropyrrolidines as cholinesterase inhibitors and their molecular docking studies.

One pot, three-component reaction of 1-acryloyl-3,5-bisarylmethylidenepiperidin-4-ones with isatin and sarcosine in molar ratios of 1:1:1 and 1:2:2 furnished to mono- and bis-spiropyrrolidine heterocyclic hybrids comprising functionalized piperidine, pyrrolidine and oxindole structural motifs. Both mono and bis-spiropyrrolidines displayed good inhibitory activity against acetylcholinesterase (AChE) with IC50 values of 2.36-9.43 µM. For butyrylcholinesterase (BChE), mono-cycloadducts in series 8 with IC50 values of lower than 10 µM displayed better inhibitory activities than their bis-cycloadduct analogs in series 9 with IC50 values of 7.44-19.12 µM. The cycloadducts 9j and 8e were found to be the most potent AChE and BChE inhibitors with IC50 values of 2.35 and 3.21 µM, respectively. Compound 9j was found to be competitive inhibitor of AChE while compound 8e was a mixed-mode inhibitor of BChE with calculated Ki values of 2.01 and 6.76 µM, respectively. Molecular docking on Torpedo californica AChE and human BChE showed good correlation between IC50 values and free binding energy values of the synthesized compounds docked into the active site of the enzymes.

An expedient synthesis and screening for antiacetylcholinesterase activity of piperidine embedded novel pentacyclic cage compounds.

The aim of this study was to synthesize and evaluate diazapentacyclic analogs for their acetylcholinesterase (AChE) inhibitory activity. The pentacyclic analogs were synthesized by one-pot three-component domino reactions in a microwave synthesizer. Most of the compounds exhibited moderate to good AChE inhibitory activity, compound 5i showed potent inhibitory activity with IC50 1.12 ± 0.01 µM and this may provide a new lead for developing potential inhibitors for Alzheimer's disease.

An efficient ionic liquid mediated synthesis, cholinesterase inhibitory activity and molecular modeling study of novel piperidone embedded α,ß-unsaturated ketones.

A series of hitherto unreported piperidone embedded α,ß-unsaturated ketones were synthesized efficiently in ionic solvent and evaluated for cholinesterase inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Most of the synthesized compounds displayed good enzyme inhibition; therein compounds 7i and 7f displayed significant activity against AChE with IC50 values of 1.47 and 1.74 µM, respectively. Compound 6g showed the highest BChE inhibitory potency with IC50 value of 3.41 µM, being 5 times more potent than galanthamine. Molecular modeling simulation was performed using AChE and BChE receptors extracted from crystal structure of human AChE and human BChE to determine the amino acid residues involved in the binding interaction of synthesized compounds and their relevant receptors.

Cholinesterase inhibitory activity versus aromatic core multiplicity: a facile green synthesis and molecular docking study of novel piperidone embedded thiazolopyrimidines.

Novel thiazolopyrimidine derivatives have been synthesized via microwave assisted, domino cascade methodology in ionic liquid and evaluated in vitro for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities. Among the newly synthesized compounds 6d, 6a, 6e and 6b displayed higher AChE inhibitory activity than standard drug, galanthamine, with IC50 values of 0.53, 1.47, 1.62 and 2.05µM, respectively. Interestingly, all the compounds except for 6m-r and 6x displayed higher BChE inhibitory potentials than galanthamine with IC50 values ranging from 1.09 to 18.56µM. Molecular docking simulations for 6d possessing the most potent AChE and BChE inhibitory activities, disclosed its binding interactions at the active site gorge of AChE and BChE enzymes.

An expedient, ionic liquid mediated multi-component synthesis of novel piperidone grafted cholinesterase enzymes inhibitors and their molecular modeling study.

Series of hitherto unreported piperidone grafted pyridopyrimidines synthesized through ionic liquid mediated multi-component reaction. These compounds were evaluated for their inhibitory activities against AChE and BChE enzymes. All the compounds displayed considerable potency against AChE with IC50 values ranging from 0.92 to 9.11 µM, therein compounds 6a, 6h and 6i displayed superior enzyme inhibitory activities compared to standard drug with IC50 values of 0.92, 1.29 and 2.07 µM. Remarkably, all the compounds displayed higher BChE inhibitory activity compared to galantamine with IC50 values of 1.89-8.13 µM. Molecular modeling, performed for the most active compounds using three dimensional crystal structures of TcAChE and hBChE, disclosed binding template of these inhibitors into the active site of their respective enzymes.

A facile chemo-, regio- and stereoselective synthesis and cholinesterase inhibitory activity of spirooxindole-pyrrolizine-piperidine hybrids.

A series of novel hybrid spiro heterocycles comprising pyrrolizine, spiroxindole and piperidine moieties was synthesized chemo-, regio- and stereoselectively in good yields from 1,3-dipolar cycloaddition reaction of a series of 1-acryloyl-3,5-bisarylmethylidenepiperidin-4-ones with azomethine ylides generated in situ from 5-choloroisatin and l-proline in methanol. These cycloadducts displayed significant cholinesterase inhibitory activity. Among the compounds screened, 8g and 8e, showed maximum inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinestrase (BChE) with IC50 values of 3.33 and 3.13µM, respectively.

Microwave assisted synthesis, cholinesterase enzymes inhibitory activities and molecular docking studies of new pyridopyrimidine derivatives.

A series of hitherto unreported pyrido-pyrimidine-2-ones/pyrimidine-2-thiones were synthesized under microwave assisted solvent free reaction conditions in excellent yields and evaluated in vitro for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes inhibitory activity. Among the pyridopyrimidine derivatives, 7e and 7l displayed 2.5- and 1.5-fold higher enzyme inhibitory activities against AChE as compared to standard drug, galanthamine, with IC50 of 0.80 and 1.37 µM, respectively. Interestingly, all the compounds except 6k, 7j and 7k displayed higher inhibitory potential against BChE enzyme in comparison to standard with IC50 ranging from 1.18 to 18.90 µM. Molecular modeling simulations of 7e and 7l was performed using three-dimensional structure of Torpedo californica AChE (TcAChE) and human butyrylcholinesterase (hBChE) enzymes to disclose binding interaction and orientation of these molecule into the active site gorge of respective receptors.

Synthesis and discovery of novel piperidone-grafted mono- and bis-spirooxindole-hexahydropyrrolizines as potent cholinesterase inhibitors.

Three-component reaction of a series of 1-acryloyl-3,5-bisbenzylidenepiperidin-4-ones with isatin and L-proline in 1:1:1 and 1:2:2 molar ratios in methanol afforded, respectively the piperidone-grafted novel mono- and bisspiro heterocyclic hybrids comprising functionalized piperidine, pyrrolizine and oxindole ring systems in good yields. The in vitro evaluation of cholinesterase enzymes inhibitory activity of these cycloadducts disclosed that monospiripyrrolizines (8a-k), are more active with IC50 ranging from 3.36 to 20.07 µM than either the dipolarophiles (5a-k) or bisspiropyrrolizines (9a-k). The compounds, 8i and 8e with IC50 values of 3.36 and 3.50 µM, respectively showed the maximum inhibition of acethylcholinesterase (AChE) and butrylylcholinestrase (BuChE). Molecular modeling simulation, disclosed the binding interactions of the most active compounds to the active site residues of their respective enzymes. The docking results were in accordance with the IC50 values obtained from in vitro cholinesterase assay.

Cholinesterase enzymes inhibitors from the leaves of Rauvolfia reflexa and their molecular docking study.

Plants of the Apocynaceae family have been traditionally used in the treatment of age-related brain disorders. Rauvolfia reflexa, a member of the family, has been used as an antidote for poisons and to treat malaria. The dichloromethane, ethanol and methanol extracts from the leaves of Rauvolfia reflexa showed potential acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities, with IC50 values in the 8.49 to 52.23 g/mL range. Further cholinesterase inhibitory-guided isolation of these extracts afforded four bioactive compounds, namely: (E)-3-(3,4,5-trimethoxyphenyl)acrylic acid (1), (E)-methyl 3-(4-hydroxy-3,5-dimethoxyphenyl) acrylate (2), 17-methoxycarbonyl-14-heptadecaenyl-4-hydroxy-3-methoxycinnamate (3) and 1,2,3,4-tetrahydro-1-oxo-ß-carboline (4). The isolated compounds showed moderate cholinesterase inhibitory activity compared to the reference standard, physostigmine. Compounds 1 and 2 showed the highest inhibitory activity against AChE (IC50 = 60.17 µM) and BChE (IC50 = 61.72 µM), respectively. Despite having similar molecular weight, compounds 1 and 2 were structurally different according to their chemical substitution patterns, leading to their different enzyme inhibition selectivity. Compound 2 was more selective against BChE, whereas compound 1 was a selective inhibitor of AChE. Molecular docking revealed that both compounds 1 and 2 were inserted, but not deeply into the active site of the cholinesterase enzymes.

(3E,5E)-3,5-Bis(4-methyl-benzyl-idene)-1-[3-(piperidin-1-yl)propano-yl]piperidin-4-one.

In the title compound, C(29)H(34)N(2)O(2), the central piperidine ring adopts a half-chair conformation, whereas the terminal one adopts a chair conformation. The mean plane of the central piperidine ring [maximum deviation = 0.384 (2) Å] makes dihedral angles of 64.82 (13) and 17.55 (13)° with the benzene rings. In the crystal, mol-ecules are linked into a tape along the b axis via C-H⋯O inter-actions, generating R(2) (2)(20) and R(2) (1)(6) graph-set motifs. C-H⋯π inter-actions are observed between the tapes.

(3E,5E)-3,5-Bis(naphthalen-1-yl-methyl-idene)piperidin-4-one.

In the title compound, C(27)H(21)NO, the piperidine ring adopts a chair conformation. The mean plane through the piperidine ring makes dihedral angles of 49.27 (5) and 63.07 (5)° with the naphthalene ring systems. In the crystal, mol-ecules are linked into dimers via pairs of inter-molecular C-H⋯O inter-actions, generating ten-membered R(2) (2)(10) ring motifs. C-H⋯π inter-actions further stabilize the crystal structure.

(3E,5E)-3,5-Dibenzyl-idene-1-[3-(piperidin-1-yl)propano-yl]piperidin-4-one.

The asymmetric unit of the title compound, C(27)H(30)N(2)O(2), comprises two independent mol-ecules. The dihedral angles between the phenyl rings in the two mol-ecules are 55.59 (8) and 55.39 (8)°. The piperidine rings adopt chair conformations. The crystal structure is stabilized by weak inter-molecular C-H⋯O and C-H⋯N hydrogen bonds. The crystal studied was a non-merohedral twin with a domian ratio of 0.75 (2):0.25 (2).

(E)-2-(4-Methylbenzylidene)hydrazinecarboxamide.

The title compound, C(9)H(11)N(3)O, was synthesized by the reaction of 4-methyl-benzaldehyde with semicarbazide. The mol-ecule adopts an E configuration about the central C=N double bond and the dihedral angle between the mean planes of the benzene ring and the carboxamide groups is 17.05 (9)°. The hydrazine N atoms are twisted slightly out of the plane of the carboxamide group [C-C-N-N torsion angle = 178.39 (14)°] and an intra-molecular N-H⋯N bond generates an S(5) ring. In the crystal, adjacent mol-ecules are connected via a pair of N-H⋯O hydrogen bonds, generating R(2) (2)(8) loops, resulting in supra-molecular [001] ribbons.