Letters in Drug Design & Discovery - Volume 16, Issue 3, 2019

Background: The synthesis of high value risedronic acid is not fully resolved, as, for the time being, the best method based on the preparation from 3-pyridylcarboxylic acid by reaction with phosphorus trichloride in methanesulfonic acid gives risedronic acid in a good yield, but in an unpure form. Methods: Alternative protocols realizing the synthesis in sulfolane as the solvent and/or in the presence of suitable IL additive were developed to obtain the target dronic acid in a pure form. Results & Conclusion: Using phosphorus trichloride and phosphorous acid in two equivalents quantities together with 0.6 equivalents of [bmim][BF4] without any solvent, the method afforded the target dronic acid in a yield of 66% in a pure form.

Background: (±)-6,8-Dihydroxy-3-undecyl-3,4-dihydroisochromen-1-one is one of the structural analog of several substituted undecylisocoumarins isolated from Ononis natrix (Fabaceae), has been successfully synthesized by direct condensation of homopthalic acid (1) with undecanoyl chloride yields isochromen-1-one (2). Methods: Alkaline hydrolysis of (2) gave the corresponding keto-acid (3), which is then reduced to hydroxy acid (4) then its cyclodehydration was carried out with acetic anhydride to afford 3,4- dihydroisochromen-1-one (5). Followed by demethylation step, the synthesis of target 6,8- dihydroxy-7-methyl-3-undecyl-3,4-dihydroisocoumarin (6) was achieved. Results: In vitro antibacterial screening of all the synthesized compounds were carried out against ten bacterial strains by agar well diffusion method. Conclusion: Newly synthesized molecules exhibited moderate antibacterial activity and maximum inhibition was observed against Bacillus subtilus and Salmonella paratyphi.

Background: The role of small molecules as antioxidants to prevent the oxidation of other molecules and inhibit them from radical formation is the area of much interest to cure disease especially cancer. Moreover, the antioxidants play important role as stabilizers to prevent oxidation of fuels and lubricants. Methods: In the present study, fifteen tetrakis-Schiff&'s bases derivatives (1-15) were synthesized and screened for their antioxidant activities. Compounds 1-15 were synthesized by continuous stirring of reaction mixture of 1,4-bis (hydrazonomethyl)benzene (1 mmol) with various substituted aromatic aldehydes (2 mmol) in distilled water using acetic acid as catalyst at room temperature for 2-10 min. Results: Our present study showed that all compounds are better ferrous ion-chelating agents except compound 1,4-bis((E)-((E)-(3,4-dimethoxybenzylidene)hydrazono)methyl)benzene (6) (IC50 = 329.26 ± 4.75 μM) which has slightly low activity than the standard EDTA (IC50 = 318.40 ± 5.53 μM). In addition, DPPH radical scavenging activity of eleven compounds showed higher activity than the standard. However, remaining four compounds showed comparable radical scavenging activity to the standard DPPH (IC50 = 257.77 ± 4.60 μM). Conclusion: The series of fifteen Schiff's bases (1-15) were synthesized and evaluated as antioxidants. From both assays, it has been demonstrated that most of the tetrakis-Schiff's bases have potential to serve as leads for the development of antioxidant agents for future research.

Background: Alkaline Phosphatase (AP) is a physiologically important metalloenzyme that belongs to a large family of ectonucleotidase enzymes. Over-expression of tissue non-specific alkaline phosphatase has been linked with ectopic calcification including vascular and aortic calcification. In Vascular Smooth Muscles Cells (VSMCs), the high level of Reactive Oxygen Species (ROS) resulted in the up-regulation of TNAP. Accordingly, there is a need to identify highly potent and selective inhibitors of APs for treatment of disorders related to hyper activity of APs. Methods: Herein, a series of coumarinyl alkyl/aryl sulfonates (1-40) with known Reactive Oxygen Species (ROS) inhibition activity, was evaluated for alkaline phosphatase inhibition against human Tissue Non-specific Alkaline Phosphatase (hTNAP) and Intestinal Alkaline Phosphatase (hIAP). Results: With the exception of only two compounds, all other compounds in the series exhibited excellent AP inhibition. For hIAP and hTNAP inhibition, IC50 values were observed in the range 0.62-23.5 μM, and 0.51-21.5 μM, respectively. Levamisole (IC50 = 20.21 ± 1.9 μM) and Lphenylalanine (IC50 = 100.1 ± 3.15 μM) were used as standards for hIAP and hTNAP inhibitory activities, respectively. 4-Substituted coumarinyl sulfonate derivative 23 (IC50 = 0.62 ± 0.02 μM) was found to be the most potent hIAP inhibitor. Another 4-substituted coumarinyl sulfonate derivative 16 (IC50 = 0.51 ± 0.03 μM) was found to be the most active hTNAP inhibitor. Some of the compounds were also found to be highly selective inhibitors of APs. Detailed Structure-Activity Relationship (SAR) and Structure-Selectivity Relationship (SSR) analysis were carried out to identify structural elements necessary for efficient and selective AP inhibition. Molecular modeling and docking studies were carried out to rationalize the most probable binding site interactions of the inhibitors with the AP enzymes. In order to evaluate drug-likeness of compounds, in silico ADMETox evaluation was carried out, most of the compounds were found to have favorable ADME profiles with good predicted oral bioavailability. X-ray crystal structures of compounds 38 and 39 were also determined. Conclusion: Compounds from this series may serve as lead candidates for future research in order to design even more potent, and selective inhibitors of APs.

Background: Quinoline scaffold acts as “privileged structure” for anticancer drug design. Certain derivatives showed good results through different mechanisms as topoisomerase 1 and kinase inhibition. Methods: A new series of 2-chloro-3-(2-amino-3-cyano-4H-chromene, 4H-pyranyl and fused 1- cyclohexen-4-yl)quinoline structures (3-5, 6 and 7) were designed, synthesized, and evaluated for their in vitro antitumor activity. All compounds were tested by MTT assay against a panel of four different human tumor cell lines. The inhibitory activity of selected compounds was assessed on topoisomerase 1 and epidermal growth factor receptor tyrosine kinase via ELISA. In addition, compounds 7b and 3a were docked into the X-ray crystal structure of Topo 1 and EGFR enzymes, respectively to explain the molecular basis of the potent activity. Results: Compounds 3a, 3b and 7b showed characteristic efficacy profile. 7b showed the best cytotoxic activity on all types of tested cell lines with IC50 range (15.8±1.30 to 28.2±3.37 μM), relative to 5-fluoruracil of IC50 range (40.7±2.46 to 63.8±2.69 μM). Via ELISA, 7b and 3a showed characteristic inhibition profile on Topo 1 and EGFR-TK respectively. In addition, 7b has scored binding energy (101.61 kcal/mol) and six hydrogen bonds with amino acids conserved residues in the enzyme pocket. Conclusion: Analysis of results revealed that compounds 7a and 7b mainly were Topo 1 inhibitors while 3a was mainly EGFR inhibitor. This property may be exploited to design future quinoline derivatives as antitumor agents with enhanced selectivity towards either of the two molecular targets.

Background: Several strategies have been reported for the synthesis of thiazole derivatives. Methods: However, many of these methods suffer from several drawbacks. Several modifications have been made to counter these problems. Here, we have synthesized a new series of 2-(2-((1HImidazol- 4-yl)methylene)hydrazinyl)-4-(4-substitutedphenyl)thiazoles without using the catalyst at room temperature. Results: The structures of synthesized compounds have been confirmed by spectral analysis, such as Mass, IR, 1H NMR and 13C NMR. All synthesized compounds were screened for in vitro antibacterial activity against some gram-positive and gram-negative bacteria. Conclusion: The thiazole derivatives, with a pharmacologically potent group, discussed in this article may provide valued therapeutic important in the treatment of microbial diseases, especially against bacterial and fungal infections.

Background: Combined in-silico and in-vitro approaches were adopted to investigate the antiplasmodial activity of Catharanthus roseus and Tylophora indica plant extracts as well as their isolated components (vinblastine, vincristine and tylophorine). Methods: We employed molecular docking to prioritize phytochemicals from a library of 26 compounds against Plasmodium falciparum multidrug-resistance protein 1 (PfMDR1). Furthermore, Molecular Dynamics (MD) simulations were performed for a duration of 10 ns to estimate the dynamical structural integrity of ligand-receptor complexes. Results: The retrieved bioactive compounds viz. tylophorine, vinblastin and vincristine were found to exhibit significant interacting behaviour; as validated by in-vitro studies on chloroquine sensitive (3D7) as well as chloroquine resistant (RKL9) strain. Moreover, they also displayed stable trajectory (RMSD, RMSF) and molecular properties with consistent interaction profile in molecular dynamics simulations. Conclusion: We anticipate that the retrieved phytochemicals can serve as the potential hits and presented findings would be helpful for the designing of malarial therapeutics.

Background: Development of novel antimalarial agents has been one of the sought areas in medicinal chemistry. In this study the same was done by virtual screening of in-house database on developed QSAR model. Methods: A six point pharmacophore model was generated (AADHRR.56) from 41 compounds using PHASE module of Schrodinger software and used for pharmacophore based search. Docking studies of the obtained hits were performed using GLIDE. Most promising hit was synthesized & biologically evaluated for antimalarial activity. Result: The best generated model was found to be statistically significant as it had a high correlation coefficient r2= 0.989 and q2 =0.76 at 3 component PLS factor. The significance of hypothesis was also confirmed by high Fisher ratio (F = 675.1) and RMSE of 0.2745. The model developed had good predicted coefficient (Pearson R = 0.8826). The virtual screening on this model resulted in six hits, which were docked against FP-2 enzyme. The synthesized compound displayed IC50 value of 0.27μg/ml against CQS (3D7) and 0.57μg/ml against CQR (RKL9). Conclusion: 3D QSAR studies reviled that hydrophobic groups are important for anti-malarial activity while H-donor is less desirable for the same. Electron withdrawing groups at R1 position favours the activity. The biological activity data of the synthesized hit proved that the pharmacophore hypothesis developed could be utilized for developing novel anti-malarial drugs.

Background: Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic infections in immunocompromised patients. The inhibition of Quorum Sensing (QS) system has been recognized as an attractive strategy for the treatment of P. aeruginosa infections. In the present study, a series of novel 2-methyl-3-[4-(substituedaminosulfonyl)phenyl]-4(3H)-quinazolinones (1-8) were synthesized and tested for their biofilm formation and swarming motility inhibitory activities in P. aeruginosa PA01. Findings: These compounds were found to reduce biofilm formation by 20-32% and swarming motility by 51-62% in P. aeruginosa PA01 at a concentration of 12.5μM. Molecular docking studies were also performed to elucidate the possible key interactions of these compounds with the active site of the P. aeruginosa QS receptor LasR. Furthermore, some molecular properties related to drug likeness and ADME were predicted. Results and Conclusion: Results of this study demonstrated that compounds 1-8 can influence QS-regulated biofilm formation and swarming motility in P. aeruginosa PA01 by binding LasR protein and could be developed as anti-biofilm agents to treat chronic biofilm associated infections caused by P. aeruginosa and other clinically significant pathogens.

Background: Structural similarity in Chalcone and Pyrazoline brought our intention for the analysis of such compounds. This study involved the synthesis of chalcones and their pyrazoline derivatives and their screening as cholinesterase inhibitors. The newly synthesized compounds were also investigated for their antioxidant potential. Methods: Chalcones were synthesized by well-established methods of synthesis and their structural elucidation was carried out by H-NMR, 13C-NMR, Mass spectrometry and FTIR. For the determination of inhibition potency of synthesized compounds, spectrophotometric method was applied whereas, DPPH free radical scavenging method was used to check the antioxidant ability. Results: Chalcones and their pyrazoline derivatives were synthesized and characterised by 1HNMR, 13C-NMR, Mass spectrometry and FTIR. The compounds were screened for their anti- Alzheimer activity, which exhibited that compounds 1g, 1c and 1h, 1g showed strong inhibitory potency against acetylcholinesterase and butyrylcholinesterase, respectively. DPPH radical scavenging method was applied to check anti-oxidant potential of synthesized compounds and results explored that among all the synthesized compounds only compounds 1c and 1b showed strong scavenging potential. Conclusion: Chalcone and their pyrazoline derivatives were synthesized and screened for their anti-Alzheimer and antioxidant potential. The experimental results of anti-Alzheimer activity were compared with molecular docking studies, which showed that compounds 1g, 1c and 1h, 1g were active against AChE and BChE, respectively. Among the synthesized compounds 1c and 1b were found to be most potent antioxidants. These results suggest that compound 1b, 1c, 1g and 1h may further be explored for further developments.

Background: Aurones, (Z)-2-benzylidenebenzofuran-3-one derivatives, are naturallyoccurring structural isomers of flavones, with promising pharmacological potential. Methods: In this study, the structural requirements for the inhibition of porcine pancreatic α- amylase by hydroxylated or methoxylated aurone derivatives were investigated by assessing their in vitro biological activities against porcine pancreatic α-amylase. Results: The structure-activity relationship of these inhibitors based on both in vitro and in silico findings showed that the hydrogen bonds between the OH groups of the A or B ring of (Z)- benzylidenebenzofuran-3-one derivatives and the catalytic residues of the binding site are crucial for their inhibitory activities. Conclusion: It seems that the OH groups in aurones inhibit α-amylase in a manner similar to that of OH groups in flavones and flavonols.

Background: Benzimidazole and piperidine rings are important pharmacophore groups for drug design studies. Objective: In this study, we aimed to investigate the antidepressant-like activity of some 2-(4- substituted-phenyl)-1-[2-(piperidin-1-yl)ethyl]-1H-benzimidazole derivatives. Methods: Tail-suspension Test (TST) and Modified Forced Swimming Tests (MFST) were used to assess antidepressant-like activities of the test compounds. Moreover, locomotor activity performances of the animals were evaluated by an activity cage device. Results: In the TST and MFST, compounds 2c-2h (10 mg/kg) and the reference drug fluoxetine (20 mg/kg) significantly reduced the immobility time of mice indicating the antidepressant-like activities of these compounds. Further, in MFST, the same compounds induced significant enhancement in the duration of active swimming behaviors without affecting the climbing performance of the animals. This prolongation in the swimming time, similar to fluoxetine, pointed out that antidepressant- like activity of the compounds 2c-2h might be related to the serotonergic rather than noradrenergic mechanisms. Besides, results of the activity cage tests demonstrated that none of the tested compounds caused an alteration in the locomotor activities of mice, signifying that antidepressantlike effects presented in this study were specific. Conclusion: In conclusion, results of this present study supported the previous papers reporting the therapeutic potential of compounds carrying benzimidazole and/or piperidine rings in their structure and emphasized, once again, the importance of these pharmacophore groups in drug design studies.

Background: N-Acetylserotonin (NAS, N-acetyl-5-hydroxytryptamine) is the immediate precursor of the neurohormone melatonin (MT, N-acetyl-5-methoxytryptamine), which regulates sleep and wake cycles. NAS is produced by the N-acetylation of serotonin and is converted to melatonin via the action of Acetylserotonin O-methyltransferase (ASMT). Like melatonin, NAS acts as an agonist on the melatonin receptors MT1, MT2, and MT3. However, as NAS is abundant in specific brain areas, separate from serotonin and melatonin, it may also have discrete central effects. Indicatively, it has been reported that NAS may play a role in the antidepressant effects of Selective Serotonin Reuptake Inhibitors (SSRIs) and Monoamine Oxidase Inhibitors (MAOIs). Objective: To decipher the controlled release characteristics of the active substances (NAS and MT) in a quick initial pace, aiming at a satisfactory sleep-onset related anti-depressive profile and prolonged release, thereafter, targeting at coping with poor sleep quality problems. Methods: A series of hydrophilic matrix tablets involving as excipients, hydroxypropylmethylcellulose (HPMC) K15M, low viscosity sodium alginate, lactose monohydrate, and polyvinylpyrrolidone (PVP) M.W.: 10.000 and 55.000) was developed and tested at two dissolution media (pH 1.2 and 7.4). Results: The results showed that commonly used excipients with different physicochemical properties govern the controlled release of NAS and MT from solid matrix systems. Conclusions: We have demonstrated how broadly used excipients affect the in vitro controlled release of NAS and MT from solid pharmaceutical formulations. Currently, we extend our studies on the controlled release of these drugs using various other biopolymers/formulants of different physicochemical characteristics, which will help to highlight the discrete release profiles of NAS and MT.

Background: A phytochemical study on medicinal plants used for the treatment of fever and malaria in Africa yielded metabolites with potential antiplasmodial activity, many of which are Anthraquinones (AQ). AQs have similar sub-structure as naphthoquinones and xanthones, which were previously reported as novel antiplasmodial agents. Objective: The present study aimed to investigate the structural requirements of 9,10- anthraquinones with hydroxy, methoxy and methyl substituents to exert strong antiplasmodial activity and to investigate their possible mode of action. Methods: Thirty-one AQs were synthesized through Friedel-Crafts reaction and assayed for antiplasmodial activity in vitro against Plasmodium falciparum (3D7). The selected compounds were tested for toxicity and probed for their mode of action against β-hematin dimerization through HRP2 and lipid catalyses. The most active compounds were subjected to a docking study using AutoDock 4.2. Results: The active AQs have similar common structural characteristics. However, it is difficult to establish a structure-activity relationship as certain compounds are active despite the absence of the structural features exhibited by other active AQs. They have either ortho- or meta-arranged substituents and one free hydroxyl and/or carbonyl groups. When C-6 is substituted with a methyl group, the activity of AQs generally increased. 1,3-DihydroxyAQ (15) showed good antiplasmodial activity with an IC50 value of 1.08 μM, and when C-6 was substituted with a methyl group, 1,3- dihydroxy-6-methylAQ (24) showed stronger antiplasmodial activity with an IC50 value of 0.02 μM, with better selectivity index. Compounds 15 and 24 showed strong HRP2 activity and mild toxicity against hepatocyte cells. Molecular docking studies showed that the hydroxyl groups at the ortho (23) and meta (24) positions are able to form hydrogen bonds with heme, of 3.49 Å and 3.02 Å, respectively. Conclusion: The activity of 1,3-dihydroxy-6-methylAQ (24) could be due to their inhibition against the free heme dimerization by inhibiting the HRP2 protein. It was further observed that the anthraquinone moiety of compound 24 bind in parallel to the heme ring through hydrophobic interactions, thus preventing crystallization of heme into hemozoin.

Background: Antimicrobial resistance is a major threat to human health. So this manuscript describes the synthesis of five different 3,5-disubstituted 4,5-dihydroisoxazoles with antimicrobial activity. Methods: They were obtained from nitrile oxide cycloaddition derived from 2-furaldehyde and 5- nitro-2-furaldehyde to different dipolarophiles (acrylamide, ethyl acrylate and styrene). All heterocycles were isolated (30-50 %) and characterized by FTIR, MS, 1H and 13C NMR, as they were also evaluated against Gram-positive and Gram-negative bacteria. Results and Conclusion: All products showed bioactivity against all bacteria, however, the heterocycle 3-(5-nitro-2-furanyl)-5-carboxylamide-4,5-dihydroisoxazole (6b) presented the lowest value for the minimum inhibition concentration (MIC - 14 μg/mL).