A facile synthesis, antibacterial, and antitubercular studies of some piperidin-4-one and tetrahydropyridine derivatives

Design, Synthesis, and Biological Evaluation of quinoxaline bearing tetrahydropyridine derivatives as anticancer, antioxidant, and anti-tubercular agents

BACKGROUND

Quinoxaline and Tetrahydropyridine derivatives showed various biological properties. The combination of these two scaffolds may contribute to good biological activity and may give novel and efficacious bioactive candidates.

OBJECTIVE

The present study aimed to identify bioactive agents with quinoxaline bearing tetrahydropyridine derivatives possessing anticancer, antioxidant, and anti-tubercular agents.

METHOD

A series of novel quinoxaline bearing tetrahydropyridine derivatives have been designed and synthesized in good yields. The synthetic protocol involves three-component Povarov reactions of 6-amino quinoxaline, propenyl guaethol, and substituted aldehydes using BF3•OEt2 as catalyst. The newly synthesized molecules were evaluated for their anticancer activity against four cell lines, i.e. A-549, MCF-7, PC-3, and HepG2.

RESULTS

The results from in vitro assay indicated that compound 4a proved to be as potent as the standard drug adriamycin against all cell lines with GI50 values <10 μg/ml. Compounds 4b, 4f, and 4i exhibited good cytotoxicity against A-549 cell line. All synthesized molecules were evaluated for their antioxidant activity and the results revealed that the compounds 4a, 4b, and 4i showed promising antioxidant activities against DPPH and H2O2 scavenging. In addition, the anti-mycobacterial activity of the synthesized compounds against MTB H37Rv strain was determined using MABA method. The results indicate that the compounds 4a, 4b, 4g, and 4i showed better anti-mycobacterial activity than the standard drugs pyrazinamide, ciprofloxacin and streptomycin with MIC value 1.6 μg/ml. Furthermore, molecular docking studies and ADME properties showed good pharmacokinetic profile and drug-likeness properties.

CONCLUSION

These studies showed that a series of novel quinoxaline bearing tetrahydropyridine derivatives exhibit anticancer, anti-mycobacterial, and antioxidant activities.

Cervicovaginal microbiota isolated from healthy women exhibit probiotic properties and antimicrobial activity against pathogens isolated from cervical cancer patients

Abnormal cervicovaginal microbiota play an important role in HPV persistence and progression to cervical cancer. The present study aimed at isolating and identifying potential probiotics from vaginal swabs of healthy women and evaluating their activity against vaginal pathogens isolated from cervical cancer patients. Based on probiotic, acid-bile tolerance and antimicrobial properties, 13 lactic acid bacteria (LAB) from the healthy group were identified by MALDI TOF MS (Matrix Assisted Laser Desorption and Ionisation, Time Of Flight Mass Spectrometry). Among these, four strains, Lactobacillus gasseri P36Mops, Limosilactobacillus fermentum P37Mws, Lactobacillus delbrueckii P31Mcs and Enterococcus faecium P26Mcm, exhibited significant antimicrobial activity against 8 vaginal pathogens (Staphylococcus haemolyticus P41Tcs, Escherichia coli P30Tcs, E. coli P79Bcm, Enterococus faecalis P29Mops, E. faecalis P50Tws, E. faecalis P68Tcb, S. haemolyticus P48Bcb and S. haemolyticus P58Bcb) isolated from precancerous and cervical cancer patients. 16S rRNA sequencing of four potential probiotics revealed congruency with the MALDI-TOF MS identification and phylogenetic analysis showed genetic relationship with previously reported LAB strains. The selected LAB showed strain specific hydrophobicity (35.88-56.70%), auto-aggregation (35.26-61.39%) and antibiotic susceptibility. Interestingly, L. gasseri P36Mops was resistant to five standard antibiotics routinely used against urogenital or vaginal infections. LCMS (Liquid Chromatography Mass Spectrometry) analyses of the CFS (cell-free supernatant) of the four potential probiotics revealed the presence of metabolites such as N-(1-deoxy-1-fructosyl)valine, hygroline, acetoxy-2-hydroxy-16-heptadecen-4-one, avocadyne 4-acetate, avocadyne 2-acetate, taraxinic acid glucosyl ester, 6-hydroxypentadecanedioic acid, with reported antimicrobial activity. The overall data suggest the bio-therapeutic potential of the identified vaginal probiotics against cervical cancer-associated pathogens.

Recent Advances in Chemistry and Biological Activity of 2,6-Diphenyl Piperidines

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The review discusses different methods for preparation of 2,6-diphenyl-piperidin-4-one derivatives. 2,6-Diphenyl-piperidin-4-one is prepared from aromatic aldehyde and acetone in ammonium acetate. Reaction of 1-phenylsulfinylpropan-2-one or 1-(4-chlorophenylsulfinyl)propan-2-one, aromatic aldehyde and ammonium acetate gives a series of 2,6-diaryl-2,3-dihydro-1H-pyridin-4-one 6a,b. 4-Phenyl-2-amino-1,3-butadienes reacts with N-allyl benzaldimine through Diels-Alder reaction to afford 2,6-diphenyl-4-piperidinone derivative 7. Also, reactions of 2,6-diphenyl-piperdin-4-one are discussed. The reactions of latter compounds can be on nitrogen atom or carbonyl function group or methylene group adjacent to carbonyl group. In addition, different applications of 2,6-diphenyl-piperidin-4-one are summarized.

Design, docking, and DFT investigations of 2,6-bis(3,4-dihydroxyphenyl)-3-phenethylpiperidin-4-one

In the present investigation, a totally of 673 newly designed 2,6-diphenyl piperidin-4-one derivatives are docked with 2B7N protein of Helicobacter pylori which causes peptic ulcer disease. The docking studies revealed that 2,6-bis(3,4-dihydroxyphenyl)-3-phenethylpiperidin-4-one (BDPO) is identified as the most promising new compound with active nature against 2B7N with a binding affinity value of -8.0 Kcal/mol. The molecular structure of BDPO has been analyzed by DFT based theoretical calculations at the B3LYP/6-311++G(d,p) level of theory using the Gaussian 16W program package. The molecular electrostatic potential, Frontier molecular energy gap, and Mulliken population analysis have been used to understand the reactive site of the molecule. The stability and hyper-conjugative interactions were studied by natural bond orbital analysis (NBO) based on a second-order perturbation approach. The thermodynamic properties like thermal energy, specific heat capacity, and entropy at different temperatures were also calculated. The calculated first-order hyper polarizability results show that the title compound is 25.3 times greater than that of standard reference material, urea. So the title molecule is a good non-linear material. Also, this molecule has Van der Waals attraction and steric effect. It undergoes local excitation for the first five excitations.

Allyl piperidine-1-carbodiothioate and benzyl 1H-imidazole 1 carbodithioate: two potential agents to combat against mycobacteria

AIMS

The emergence of multidrug resistant strains of Mycobacterium tuberculosis has made tuberculosis more difficult to manage clinically. With the aim of obtaining new and effective anti-mycobacterial agent(s), this study investigated the anti-mycobacterial activity of several imidazole and piperidine derivatives.

METHODS AND RESULTS

Towards obtaining new anti-mycobacterial agents, Mycobacterium smegmatis cells were treated with different compounds for their growth inhibitory activity. Among these, benzyl 1H-imidazole-1-carbodithioate and allyl piperidine-1-carbodiothioate exhibited better inhibition than the others. Thereafter, anti-biofilm property of these two was examined by treating M. smegmatis with these agents before and after the formation of biofilm. The result showed that both the compounds at their sublethal dose inhibited the formation of biofilm as well as dispersed preformed biofilm. Consistently, they augmented the activity of isoniazid or rifampicin against biofilm-encapsulated cells. MTT assay was performed to examine the toxic effects of this combinatorial therapy on different cell lines. Results exhibited a low cytotoxicity for this combinatorial treatment. The activity of these two was also verified against dormant mycobacterial cells and was found to be effective.

CONCLUSION

The present study identified two compounds that exhibited anti-mycobacterial activities against both planktonic and dormant cells. These two also exhibited anti-biofilm activity at their sublethal dose and augmented the activity of isoniazid and rifampicin against biofilm encapsulated cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current study provides two new agents that have the potential to be used in anti-mycobacterial therapy and may help in public health management.

Identification of a 3,3-difluorinated tetrahydropyridinol compound as a novel antitumor agent for hepatocellular carcinoma acting via cell cycle arrest through disturbing CDK7-mediated phosphorylation of Cdc2

Tetrahydropyridinol derivatives were recently reported to exhibit good biological activities, and the incorporation of fluorine into organic molecules may have profound effects on their physical and biological properties. Therefore, we investigated the anticancer activities of six fluorinated tetrahydropyridinol derivatives that we synthesized previously. We found that only one compound, 3,3-difluoro-2,2-dimethyl-1,6-diphenyl-5-tosyl-1,2,3,6-tetrahydropyridin-4-ol, showed significant antiproliferative activity on human hepatocellular carcinoma HepG2 and HMCCLM3 cells (the IC₅₀ values were 21.25 and 29.07 μM, respectively). We also found that this compound mediated cell cycle arrest in the G0/G1 phase at 30-40 μM. Western blot analysis demonstrated that the cell cycle arrest induced by this compound in HepG2 and HMCCLM3 cells was associated with a significant decrease in Cdc2 and cyclin B1, which led to the accumulation of the phosphorylated-Tyr¹⁵ (inactive) form of Cdc2 and low expression of M phase-promoting factor (cyclin B1/Cdc2). Moreover, cells treated with this compound exhibited decreased expression of cyclin-dependent kinase (CDK)-activating kinase (CDK7/cyclin H). This compound also induced cell apoptosis via activation of caspase-3. A xenograft model in nude mice demonstrated anti-liver cancer activity and the mechanism of action of this compound. These findings indicated that the anticancer effect of this compound was partially due to G0/G1 cell cycle arrest via inhibition of CDK7-mediated expression of Cdc2, and this compound may be a promising anticancer candidate for further investigation.

Targeting HIV-TB coinfection by developing novel piperidin-4-substituted imines: Design, synthesis, in vitro and in silico studies

Tuberculosis is the "Achilles heel" of the human immunodeficiency (HIV) ministration. HIV-positive people are 16-27 times more prone to contract tuberculosis. But the adverse interaction between antiretroviral drugs and antitubercular drugs has made it necessary to look for a single drug regimen for HIV-TB coinfection. Piperidine derivatives have been reported as anti-HIV and anti-TB agents. This inspired us to design, synthesize, and characterize a series of 3,5-bis(furan-2-ylmethylidene)-piperidin-4-substituted imines (R1-R25) and these were further screened for in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv and anti-HIV activity. Molecular docking studies showed energetically favorable binding interactions with both EACP reductase (1ZID.pdb) and reverse-transcriptase (1REV.pdb) targets. The compounds R7, R12, R17, R18, R19, R20 were found to be more potent as anti-TB agents than ethambutol (MIC 3.125 μg/ml). Compound R7 was found to be moderately active with an IC₅₀ of 2.1 ± 0.04 μM in multicycle infection assays, in comparison with the standard drug, zidovudine (IC₅₀  = 5.7 ± 0.04 nM), used as anti-HIV drug. The cytotoxicity assay was done on Vero, MT-2, and TZM-bl cells to assess the safety of these compounds and they were found to be safe. From the above results, R7 seems to be a promising lead for anti-HIV and anti-TB activity.

C(sp3)–H dehydrogenation and C(sp2)–H alkoxy carbonylation of inactivated cyclic amines towards functionalized N-heterocycles

A novel and efficient synthesis of tetrahydropyridine-, dihydropyrrole-, and tetrahydroazepine-3-carboxylates via cascade reactions of cyclic amines with CO and alcohols is presented. To our knowledge, this should be the first example in which functionalized N-heterocycles were prepared through Pd-catalyzed C(sp³)–H dehydrogenation and C(sp²)–H carbonylation of cyclic amines.

Hydrogen bonding in 2,6-bis(4-fluorophenyl)-3,5-dimethylpiperidin-4-one methanol solvate

The crystal structure analysis of a 2,6-diaryl 4-piperidone derivative, isolated as a mono-methanol solvate, reveals that both the piperidone and the methanol molecule lie on a crystallographic mirror plane. A chair conformation is found for the piperidone ring with the aryl and methyl groups in equatorial positions. The most prominent feature of the molecular packing is the formation of supramolecular zigzag chains mediated by amine-N–H···O(methanol) and hydroxyl-O–H···N(amine) hydrogen bonds, i.e. the methanol molecule serves as a bridge between piperidone molecules. The molecular structure is compared with that determined in an unsolvated form and the gas-phase equilibrium structure, obtained using density-functional theory (DFT); differences relate, in the main, to the relative dispositions of the aryl rings. An analysis of the Hirshfeld surfaces of the experimental structures indicates very similar relative contributions with the notable exception being the contribution by O···H/H···O which at 13.7% in the methanol solvate is >8.5% in the unsolvated form.

Design, development, drug-likeness, and molecular docking studies of novel piperidin-4-imine derivatives as antitubercular agents

Tuberculosis remains one of the major grievous diseases worldwide. The emergence of resistance to antituberculosis drugs emphasize the necessity to discover new therapeutic agents for preferential tuberculosis therapy. In this study, various novel 1-(1H-benzimidazol-2-ylmethyl) piperidin-4-imine derivatives were developed and checked for favorable pharmacokinetic parameters based on drug-likeness explained by Lipinski’s rule of five. All 20 of the novel chemical entities were found to possess a favorable pharmacokinetic profile since they were not violating Lipinski’s rule of five. The title compounds were also synthesized, characterized, and tested for ex vivo antitubercular activity against Mycobacterium tuberculosis H37Rv (ATCC27294). The results revealed that four compounds (2-[1-(1H-benzimidazol-2-ylmethyl)piperidin-4-ylidene] hydrazinecarbothioamide, 2-[1-(1H-benzimidazol-2-ylmethyl)piperidin-4-ylidene]-N-hydroxy-hydrazinecarbo-thioamide, 1-[1-(1H-benzimidazol-2-ylmethyl)piperidin-4-ylidene]guanidine, and 2-[1-(1H-benzimidazol-2-ylmethyl)piperidin-4-ylidene]hydrazinecarboxamide) were the most potent (minimum inhibitory concentration 6.25 µg/mL) antitubercular agents, with less toxicity (selectivity index more than 10). The molecules were also subjected to three-dimensional molecular docking on the crystal structure of enoyl-acyl carrier protein (EACP) reductase enzyme (code 1ZID, Protein Data Bank), which represents a good prediction of the interactions between the molecules and EACP reductase with minimum binding energy.

Differential effects of tetrahydropyridinol derivatives on β-catenin signaling and invasion in human hepatocellular and breast carcinoma cells

In continuation of previous efforts to investigate the biological potency of tetrahydropyridinol derivatives, the present study synthesized three target compounds: N-(bromoacetyl)-3-carboxyethyl-2,6-diphenyl-4-O-(pentafluorobenzoyl)-Δ3-tetra-hydropyridine (5a), N-(chloroacetyl)-3-carboxyethyl-2,6-diphenyl-4-O-(pentafluorobenzoyl)-Δ3-tetrahydropyridine (5b) and N-(2-bromopropanoyl)-3-carboxyethyl-2,6-diphenyl-4-O-(pentafluorobenzoyl)-Δ3-tetrahydropyridine (5c), and examined their anticancer potency. Experiments were performed using the Sk-Hep1 and Hep3B human hepatocellular carcinoma cell lines and MDA-MB-231 breast adenocarcinoma cell line. Among the three compounds, 5a and 5b were comparably and significantly cytotoxic to the Sk-Hep1, Hep3B and MDA-MB-231 cells. The highest level of cytotoxicity was detected in theSk-Hep1 cells with half maximal inhibitory concentrations for compounds 5a and 5b at 12 and 6 µM, respectively. These two compounds induced cell cycle arrest in the Sk-Hep1 and MDA-MB-231 cells through the downregulation of β-catenin and upregulation of glycogen synthase kinase-3β and E-cadherin. By contrast, 5a and 5b induced G1 arrest in the Hep3B cells by modulating the p21 and p27 cell cycle regulatory molecules and cyclin-dependent kinase 2. In addition, 5a and 5b significantly inhibited the invasion of Sk-Hep1 and MDA-MB-231 cells. These results suggested that the 5a and 5b compounds induce cell cycle arrest by suppressing Wnt/β-catenin signaling in highly invasive Sk-Hep1 and MDA-MB-231 cells, and by inducing p53 independent cell cycle arrest in Hep3B cells.

Crystal structure of 4-chloro-N-[2-(piperidin-1-yl)eth-yl]benzamide monohydrate

In the title compound, C14H19ClN2O2·H2O, the piperdine ring adopts a chair conformation. The dihedral angle between the mean plane of the piperidine ring and that of the phenyl ring is 41.64 (1)°. In the crystal, mol-ecules are linked by O-H⋯N, N-H⋯O and C-H⋯O hydrogen bonds involving the water mol-ecule, forming double-stranded chains propagating along [010].

Synthesis, Spectral Analysis, In Vitro Microbiological Evaluation, and Molecular Docking Studies of Some Novel 1-(1-Aryl-1H-tetrazol-5-yl)-2-(piperidin-1-yl)ethanone Derivatives

A new series of novel heterocyclic compounds containing both tetrazoles and piperidine nuclei together, namely, 1-(1-aryl-1H-tetrazol-5-yl)-2-(piperidin-1-yl)ethanone (22–28), were synthesized by the treatment of the respective 2-chloro-1-(1-aryl-1H-tetrazol-5-yl)ethanone (15–21) with piperidine in acetonitrile for 6 h. A series of novel tetrazole substituted piperidine derivatives were synthesized and evaluated for their antimicrobial activity using serial dilution method. The structures of the synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, mass spectral data, and elemental analysis. Evaluation of antimicrobial activity shows that several compounds exhibit good activity when compared with the reference drug candidates and thus could be promising new lead molecules.

A novel amalgamation of 1,2,3-triazoles, piperidines and thieno pyridine rings and evaluation of their antifungal activity

It is the first report of the novel amalgamation of 1,2,3-triazoles, piperidines, thieno pyridine rings and evaluation of their antifungal activity. The synthesized compounds showed interesting moderate to good antifungal activity, wherein they were able to discriminate between the two species Aspergillus flavus and Aspergillus niger of the same genus. In addition, the main highlight of this series is the sensitivity of the fungal strain Cryptococcus neoformans to the compounds having p-chlorobenzoyl (9h), methane sulfonyl (9i) and p-methylbenzene sulfonyl (9j) attached to the piperazine nitrogen.

Synthesis and structure-activity relationship studies of 4-arylthiosemicarbazides as topoisomerase IV inhibitors with Gram-positive antibacterial activity. Search for molecular basis of antibacterial activity of thiosemicarbazides

1-(indol-2-carbonyl)-4-(4-nitrophenyl)-thiosemicarbazide was synthesized and antibacterial and type IIA topoisomerases (DNA gyrase and topoisomerase IV) activity was evaluated. It was found that it shows activity against Gram-positive bacteria with MICs of 50 μg/mL and inhibitory action against topoisomerase IV with an IC(50) of 14 μM. Although modification of its structure resulted in molecules with a lower biological profile, our observations strongly implicate that thiosemicarbazide derivatives participate in at least two different mechanisms of antibacterial activity; one is connected with the inhibition of topoisomerase IV, while the nature of the other cannot be elucidated from the limited data collected thus far. The differences in bioactivity further investigated by the molecular modeling approach and docking studies suggest that inhibitory activity of 4-arylthiosemicarbazides is connected with electronic structure rather than the geometry of the molecule.

Recent advances in the design and synthesis of heterocycles as anti-tubercular agents

Due to the unusual structure and chemical composition of the mycobacterial cell wall, effective tuberculosis (TB) treatment is difficult, making many antibiotics ineffective and hindering the entry of drugs. With approximately 33% of infection, TB is still the second most deadly infectious disease worldwide. The reasons for this are drug-resistant TB (multidrug resistant and extensively drug resistant), persistent infection (latent TB) and synergism of TB with HIV; furthermore no new chemical entity has emerged in last 40 years. New data available from the recently sequenced genome of the mycobacterium and the application of methods of modern drug design promise much for the fight against this disease. In this review, we present an introduction to TB, followed by an overview of new heterocyclic anti-tubercular moieties published during the last decade.

1-(2-Azido-acet-yl)-3-methyl-2,6-diphenyl-piperidin-4-one

In the title compound, C(20)H(20)N(4)O(2), the piperidine ring adopts a distorted boat conformation. The two phenyl rings form dihedral angles of 82.87 (1) and 84.40 (1)° with respect to the piperidine ring. The crystal packing is stabilized by inter-molecular C-H⋯O and C-H⋯N inter-actions.

Synthesis, antimicrobial evaluation and QSAR studies of novel piperidin-4-yl-5-spiro-thiadiazoline derivatives

In an attempt to find a new class of antimicrobial agents, a series of new 1,3,4-thiadiazolines were synthesized from 2,6-diarylpiperidin-4-ones, via the corresponding 4'-phenylthiosemicarbazones. All the synthesized compounds (23-39) were virtually screened against bacterial (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi) and fungal strains (Candida albicans, Rhizopus sp, Aspergillus niger and Aspergillus flavus) by serial dilution method. QSAR study indicated that the increase in weakly polar component of solvent accessible surface area will favour antibacterial activity while increase in polarizability and decrease in ionisation potential and hydrogen bond donor will favour antifungal activity.

Ethyl 4-hydroxy-2,6-diphenyl-1-(2-thiomorpholinoacetyl)-1,2,5,6-tetrahydropyridine-3-carboxylate

In the title compound, C₂₆H₃₀N₂O₄S, the thio­morpholine ring adopts a chair conformation whereas the tetra­hydro­pyridine ring is in a half-chair conformation. The dihedral angle between the two phenyl rings is 33.3 (2)°. A strong intra­molecular O—H⋯O hydrogen bond generates an S(6) motif. In the crystal, mol­ecules are linked by inter­molecular C—H⋯O hydrogen bonds, generating a ribbon-like structure propagating along the a axis.

Ethyl 4-hy-droxy-2,6-diphenyl-1-[2-(piperidin-1-yl)acet-yl]-1,2,5,6-tetra-hydro-pyridine-3-carboxyl-ate

In the title compound, C₂₇H₃₂N₂O₄, the piperidine and tetra­hydro­pyridine rings adopt chair and half-chair conformations, respectively. The dihedral angle between the two phenyl rings is 32.9 (1)°. The mol­ecular structure is stabilized by a strong intra­molecular O—H⋯O hydrogen bond, generating an S(6) motif. In the crystal, inter­molecular C—H⋯O inter­actions form a ribbon-like structure along the a axis.