Medicinal Chemistry - Volume 14, Issue 8, 2018

Background: Viscum album (the European mistletoe) is a semi-parasitic plant, which is of high medical interest. It is widely found in Europe, Asia, and North America. It contains at least three distinct lectins (i.e. ML-I, II, and III), varying in molecular mass and specificity. Among them, ML-I is in focus of medical research for various activities, including anti-cancer activities. To understand the molecular basis for such medical applications, a few studies have already addressed the structural and functional analysis of ML-I in complex with ligands. In continuation of these efforts, we are reporting the crystal structure of ML from Viscum album in complex with the nucleic acid oxidation product 4-N-furfurylcytosine (FC) refined to 2.85 Šresolution. FC is known to be involved in different metabolic pathways related to oxidative stress and DNA modification. Methods: X-ray suitable hexagonal crystals of the ML-I/FC complex were grown within four days at 294 K using the hanging drop vapor diffusion method. Diffraction data were collected up to a resolution of 2.85 Ů The ligand affinity was verified by in-silico docking. Results: The high-resolution structure was refined subsequently to analyze particularly the active site conformation and a binding epitope of 4-N-furfurylcytosine. A distinct 2Fo-Fc electron density at the active site was interpreted as a single FC molecule. The specific binding of FC is achieved also through hydrophobic interactions involving Tyr76A, Tyr115A, Glu165A, and Leu157A of the ML-I A-chain. The binding energy of FC to the active site of ML-I was calculated as well to be -6.03 kcal mol-1. Conclusion: In comparison to other reported ML-I complexes, we observed distinct differences in the vicinity of the nucleic acid base binding site upon interaction with FC. Therefore, data obtained will provide new insights in understanding the specificity, inhibition, and cytotoxicity of the ML-I A-chain, and related RIPs.

Background: Influenza is still a serious threat to human health with significant morbidity and mortality, so it is desirable to develop novel anti-flu drug agents with novel structures. Objective: The main purpose of this research was to explore broad-spectrum anti-flu agents and provide antiviral stockpiles in response to potential future influenza pandemics. Methods: Fifteen novel 12N-substituted tricyclic matrinic derivatives were synthesized and evaluated for their anti-influenza activities against H1N1 subtype taking 12N-p-cyanobenzenesulfonyl matrinane (1) as the lead. All prepared compounds were characterized by 1H NMR, 13C NMR and ESI-HRMS. The pharmacokinetics (PK) profile of the key compound was also examined in this study. Result: The structure-activity relationship study indicated that suitable benzyl groups on 12N atom might be beneficial for the activity. Among them, 12N-p-carboxybenzyl matrinic butane (17g) exhibited the most promising activity with an IC50 value of 16.2 μM and a selective index (SI) value of over 33.4. In addition, compound 17g displayed a good in vivo pharmacokinetic profile with an area under the curve (AUC0-∞) value of 9.89 μM·h. Conclusion: We consider tricyclic matrinic butane derivatives to be a new class of anti-influenza agents and this study provided useful information on further optimization.

Background: In our previous work, several piperazine derived bis(dialkylaminethiocarbonyl) disulfides and disulfide esters of dithiocarbamic acid have been synthesized and evaluated for their spermicidal and microbicidal efficacy. These studies have provided some promising compounds for developing a dually active vaginal microbicidal contraceptive which is under pre-clinical stage. Objective: The main objective of this study was the design synthesis and biological evaluation of bis(dialkylaminethiocarbonyl) disulfides (4–15) and 2,2'-disulfanediylbis (3-(substituted-1-yl) propane-2,1-diyl) disubstituted-1-carbodithioates (19-28) as non-surfactant molecules capable of eliminating Trichomonas vaginalis as well as irreversibly immobilizing 100% human sperm promptly. Method: Spermicidal, anti-trichomonas, cytotoxicity and biocompatibility study of the synthesized compounds was done as per the reported methodologies. Result: Among bis(dialkylaminethiocarbonyl) disulfides (4-15, Table 1), compound 4 (MEC 0.02 mM) was found to be the most desirable for spermicidal activity as it was 40 times more active than Nonoxynol-9 (N-9), and also active against Trichomonas vaginalis (MIC 0.02 &1.10 mM). 2, 2'-disulfanediylbis (3-(substituted- 1-yl) propane-2, 1-diyl) disubstituted-1-carbodithioates (19-28, Table 2), and compounds (19, 22, 23, and 24 MEC 0.05 mM) were sixteen times more active than N-9 with promising Trichomonacidal activity. Conclusion: This study suggested that the disulfide linkage alone and dithiocarbamate along with disulfide group within the same chemical entity impart the desired multiple activities of compounds.

Background: Several species of the genus Erythrina have been used as sedative, antidepressant, and anticonvulsant. Erythrina crista-galli is native to the Pampa Biome and is widely used for medicinal purposes. Erythrinan alkaloids exhibit a range of pharmacological properties. Objective: The aim of this study was to evaluate the basic fractions and the alkaloids isolated from E. crista-galli bark against a collection of bacteria and fungi for the first time. Methods: Erythrina crista-galli stem bark was extracted with MeOH under reflux. The crude extract was dissolved in water, acidified and extracted with diethyl ether. Basification of the aqueous solution followed by diethyl ether and ethyl acetate extractions gave the basic ether and basic ethyl acetate fractions. Chromatographic purification of these fractions afforded five known alkaloids: erytharbine (1), erysotrine (2), erysotramidine (3), erysotrine N-oxide (4) and erythratidine (5) along with a new alkaloid named here erythratidine N-oxide (6). Alkaloids 1-6 were investigated against a collection of bacteria and fungi using the broth micro dilution method. Results: In this work, a new alkaloid was isolated from E. crista-galli. The most significant bacterial inhibitory effect of alkaloidal fractions was observed against the Gram-negative Pseudomas aeroginosa (MIC values of 31.25 μg.mL-1). Basic ether fraction displayed good antimicrobial activity against Shigella sonnei with MIC= 62.5 μg.mL-1. Isolated alkaloids 1-6 showed inhibitory activity against all bacteria tested (MIC values of 50-100 μg.mL-1). In addition, the crude extract and alkaloids 1, 2, and 5 also showed good antifungal potential against Candida krusei (MICs between 12.5 and 31.25 μg.mL-1). The previously undescribed alkaloid 6 presented MIC values between 50 and 100 μg.mL-1 against all tested microorganisms. Conclusion: In general, as with a considerable number of phytochemicals with antimicrobial activity, alkaloids 1-6 may be considered with potential as antibacterial/antifungal agents. The MIC values of the extract, alkaloidal fractions and compounds 1-6 indicate that, at least in part, the isolates were responsible for the antimicrobial activity observed.

Background: Viral diseases are considered main threats that face the humanity worldwide. The emergence of new viruses like influenza viruses emphasizes the significance of designing novel antiviral drugs. Method: The aim of this work is to synthesize a new set of nucleoside and non-nucleoside cyanopyridine, characterized and evaluated for their in vitro antiviral properties against various strains. Conclusion: More of the compounds showed variable antiviral potential against a panel of eighteen DNA and RNA viruses. The screening data suggested that the order of activity of the active compounds are in the order of O-glycosyl > O-alkyl > N-alkyl > S-alkyl derivatives. In addition, the 4-fluoro substituted compounds are more effective among the O- and N-alkyl analogs, whereas remarkable antiviral activity was ascribed to the methoxylated O-glycosyl derivatives. Most of the active compounds proved to be more selective towards the inhibition of the replication of DNA rather than the RNA-viruses. The analogs 1a, 2a, 12b, 14b and 16b possessed broad spectrum and noticeable antiviral potential against most of the tested DNA- and RNA-viruses (EC50 ≈ 0.8-20 μM), accompanied with considerably low cytotoxic margin (MCC ≈ 4-20 μM), and comparable with reference standard antiviral agents.

Background: Alzheimer's Disease (AD) is the leading cause of dementia among the aging population. This devastating disorder is generally associated with the gradual memory loss, specified by a decrease of acetylcholine level in the cortex hippocampus of the brain due to hyperactivation of cholinesterases (acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)). Objective: Therefore, inactivation of AChE and BChE by inhibitors can increase the acetylcholine level and hence may be an encouraging strategy for the treatment of AD and related neurological problems. Method: In this contribution, two series of chromenone-based derivatives were tested by Ellmann's calorimetric method for AChE and BChE inhibition. Results: All the compounds showed inhibitory activity against cholinesterases and some of them exhibited dual inhibition of AChE as well as BChE. The most potent inhibitor of AChE was 2l having an IC50 value of 0.08 ± 0.03 μM, while 3q inhibited the BChE with an IC50 value of 0.04 ± 0.01 μM. In case of dual inhibition, 3h showed an inhibitory concentration of 0.15 ± 0.01 μM for AChE, and 0.09 ± 0.01 μM for BChE. Molecular docking studies were performed to explore the probable binding modes of the most potent dual inhibitors. Conclusion: It can be hypothesized that the inhibitors are able to target cholinesterase pathways and may emerge as a suitable outset for the further development process.

Background: Glucuronidation is essential for the metabolism and excretion of toxic substances. β-Glucuronidase enzyme slows down the process of glucuronidation, and thus plays an important role in the on-set of colorectal carcinoma, and many other diseases. Inhibition of β- glucuronidase activity is thus identified as an important approach for the treatment of several diseases. Objective: Current study was aimed to synthesize a library of 2-oxo-1,2,3,4-tetrahydropyrimidine and to evaluate their β-glucuronidase inhibitory activity, and their mode of enzyme inhibition. Method: We synthesized a series of 2-oxo-1,2,3,4-tetrahydropyrimidines 1-25 by fusing urea, ethyl acetoacetate, and a variety of aldehydes using copper nitrate trihydrate as catalyst. All synthesized compounds were evaluated for their in vitro β-glucuronidase inhibitory activity. In addition, molecular docking studies were also performed by using MOE docking tools. Results: Eighteen compounds showed inhibitory activity better than the standard D-saccharic acid 1,4-lactone, a well known β-glucuronidase inhibitor (IC50 = 45.75 ± 2.16 μM). Compound 20 (IC50 = 1.36 ± 0.03 μM) showed an excellent inhibitory activity, thirty-five folds superior to the standard. Docking results highlighted the role of various chemical moieties at different positions on 2- oxo-1,2,3,4-tetrahydropyrimidine skeleton in enzyme inhibitory activity. Conclusion: This study has identified a class of potent β-glucuronidase inhibitors with the potential to be investigated further.

Background: Histone deacetylases (HDAC) enzymes are emerging as potential targets for cancer treatments. In this study, several series of novel hydroxamic acids incorporating 1-((1H- 1,2,3-triazol-4-yl)methyl)-3-substituted-2-oxoindolines were explored. Methods: The compounds were designed using Autodock Vina program, then synthesized and evaluated in vitro and in silico for their inhibitory activity against HDACs. The cytotoxicity was measured by SRB method. The enzyme inhibitory effects of the compounds were evaluated by the fluorescent assay. Results: Biological evaluation showed that these hydroxamic acids were generally cytotoxic against four human cancer cell lines (SW620, colon; PC-3, prostate; AsPC-1, pancreas; NCI-H23, lung). Several compounds, e.g. 7g, 11c, and 11g, displayed up to 10-fold more potent than SAHA (suberoylanilide hydroxamic acid, vorinostat) in term of cytotoxicity. The synthesized compounds were also comparably potent to SAHA in inhibiting HDAC2. In particular, compound 11c displayed potential inhibitory effects against HDAC1, HDAC2, HDAC6, and HDAC8 with comparable or slightly higher potency than SAHA. Docking results on four class I and IIB isoenzymes indicated that these compounds tightly bound to HDACs at the active site with binding affinities much higher than that of SAHA. Finally, chemo-informatics approaches were employed to assess the pharmacokinetic and toxicity profiles of 7g and 11c. We identified degradation via phase II metabolism and toxicity two of the most serious problems that need further optimization. Conclusion: Taking altogether our findings are encouraging and current hydroxamate derivatives are worth being considered as potential HDAC inhibitors and could be useful for further research on the development of new anti-cancer agents.

Background: The Hantzsch ester, diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5- dicarboxylate, has been used as a hydride donor and its various biological effects have been reported. To identify chemotherapeutic agents with apoptotic effects, 21 diethyl 2,6-dimethyl-1,4- dihydropyridine-3,5-dicarboxylates were designed and synthesized; they have not been reported as apoptosis inducers thus far. Their structure-cytotoxicity relationships were investigated. Further biological experiments were performed on the title compound. Methods: The cytotoxicities of the current synthetic compounds were measured using a clonogenic assay in HCT116 human colon cancer cells. An annexin V staining assay was used to confirm if the title compound induced apoptosis. To identify the synthetic compounds, Nuclear Magnetic Resonance (NMR) spectroscopy and high-resolution mass spectrometry (HR-MS) were conducted. As molecular symmetry was observed in the NMR spectroscopic data, the three dimensional structures were determined from ab initio calculations and X-ray crystallography. Results: The results obtained from NMR spectroscopy, ab initio calculations, and X-ray crystallography revealed that the diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate derivatives synthesized in this research have symmetric structures. The cytotoxicities of the 21 derivatives were tested in the HCT116 human colon cancer cell lines, and their half-maximal cell growth inhibitory concentrations ranged between 16.29 and 68.88 μM. Structure-cytotoxicity relationships demonstrated that bulky substitutions were preferred, para-positioned substituents tended to have better cytotoxic values, and the polarity may have a function as well. The cytotoxicity of the title compound in HCT116 colon cancer cells was mediated through apoptotic cell death. Conclusion: To obtain chemotherapeutic agents that induce apoptosis, 21 diethyl 2,6-dimethyl- 1,4-dihydropyridine-3,5-dicarboxylates were designed and synthesized. NMR spectroscopy, ab initio calculations, and X-ray crystallography demonstrated that the diethyl 2,6-dimethyl-1,4- dihydropyridine-3,5-dicarboxylate derivatives synthesized in this research had symmetric structures. Even if the half-maximal cell growth inhibitory concentrations of the 21 derivatives did not show dramatic inhibitory activity against HCT116 human colon cancer cells, small changes in the structure affected the anticancer activities. Treatment with diethyl 4-(4-chlorophenyl)-2,6- dimethyl-1,4-dihydropyridine-3,5-dicarboxylate substantially reduced the cell viability and the cytotoxicity against HCT116 colon cancer cells was mediated through apoptotic cell death. As the ability of diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylates to induce apoptosis has not been previously reported, we have now reported their design, synthesis, cytotoxicity, and structureactivity relationships.