Medicinal Chemistry - Volume 9, Issue 7, 2013

Tuberculosis, caused by Mycobacterium tuberculosis, is amongst the foremost infectious diseases. Treatment of tuberculosis is a complex process due to various factors including a patient’s inability to persevere with a combined treatment regimen, the difficulty in eradicating the infection in immune-suppressed patients, and multidrug resistance (MDR). Extensive research circumscribing molecules to counteract this disease has led to the identification of many inhibitory small molecules. Among these are chalcone derivatives along with curcumin analogs. In this review article, we summarize the reported literature regarding anti tubercular activity of chalcone derivatives and synthetic curcumin analogs. Our goal is to provide an analysis of research to date in order to facilitate the synthesis of superior antitubercular chalcone derivatives and curcumin analogs.

A new dihydropyranexanthone derived from the natural xanthone lichexanthone (1) was synthesised and, together with other 18 derivatives including ω-bromo and ω-aminoalkoxylxanthones (containing methyl, ethyl, propyl, tertbutylamino and piperidinyl moieties), were tested against Mycobacterium tuberculosis. Nine ω-aminoalkoxylxanthones showed good antimycobacterial activity, and their in vitro cytotoxicity was determined using VERO cells in order to calculate the selectivity index (SI). One of these nitrogenated xanthone derivatives showed very promising results, with MIC of 2.6 µ;M and SI of 48. This MIC is comparable to values found in “first and second line” drugs commonly used to treat TB. In order to understand better about this compound, it was evaluated together with two other ones that showed good SI, against resistant clinical strains of M. tuberculosis to verify the existence of cross-resistance. A chemometrical approach was useful to establish a pattern of antitubercular activity among the group of ω-aminoalkoxylxanthones, according to some structural and chemical features.

A 30-membered piperidine ring-fused aromatic sulfonamide library was synthetized, including N-arylsulfonyl 1,2,3,4-tetrahydroquinolines, 1,2,3,4-tetrahydroisoquinolines and 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indoles. The compounds induced oxidative stress and glutathione depletion in HT168 melanoma and K562 leukemia cells and in micromolar concentrations exerted cytotoxic effects. Among the tested sulfonamides, compounds 21, 22, 23, 35 and 41 exhibited 100% cytotoxic effects with low (< 10 µM) EC50 values on K562 cells. The cytotoxicity of lead compound 22 was investigated in 24 different cancer cell lines, and it was found to be active against leukemia, melanoma, glioblastoma, and liver, breast and lung cancer cells, as confirmed by classical biochemical and holographic microscopic analyses.

Based on the structure of 23-hydroxybetulinic acid (1), a series of 28-amide derivatives were synthesized. Biological evaluation in vitro for their antitumor activities against five cell lines (A549, BEL-7402, SF-763, B16 and HL-60) has indicated that compound 6g possesses the most effective antitumor activity with an IC50 value of 10.47 µM when treated with HL-60 cells. In vivo testing has also shown a comparable activity of 6g to cyclophosphamide against H22 liver tumor in mice and 5-fluorouracil against B16 melanoma, respectively.

Acetogenins are among the most potent of the known inhibitors of complex I (NADH-ubiquinone oxidoreductase) in mitochondrial electron transfer system. Elucidation of the dynamic function of the alkyl spacer linking the two toxophores (i.e., the hydroxylated tetrahydrofuran and the γ-lactone rings) is critical for fully understanding their inhibition mechanism. To this end, using molecular dynamics simulations a structure-activity relationship study of a series of acetogenins was performed for the first time using this approach. Our results clearly indicated that both, the length and the molecular flexibility of the spacer, were crucial for taking an active conformation. A partially folded conformation with an optimal length (bis-tetrahydrofuran rings and 13 carbon atoms) of about 16 Å with a high molecular flexibility might depict an active form of the spacer. In addition, we demonstrated that the bis-tetrahydrofuran derivatives are able to overcome the shortage of the length of the spacer more efficiently than the mono-tetrahydrofuran derivatives with the help of the additional tetrahydrofuran, which acts as a pseudospacer. Our results obtained from molecular dynamics calculations supported the use of a combined decane/water system as a good solvent model to simulate the biological environment of acetogenins acting as inhibitor of complex I.

A series of novel imidazolone derivatives were designed and synthesized via a rational drug design strategy. These compounds were obtained from 3-substituted imidazolidine-2,4-dione through alkylation, formylation, dehydration, and amination. The structures were characterized by 1H NMR, 13C NMR, and MS. All target compounds were screened for their DPP-4 inhibitory activity in vitro. The results revealed that some imidazolone derivatives showed potent DPP-4 inhibition. Compound 5b had an IC50 value of 2.21 µM inhibitory activity against DPP-4. As a promising lead compound, compound 5b with DPP-4 binding mode was further studied by docking analysis. The expected interaction mode was obtained.

A series of ferulic acid amides with extended P1' groups were synthesized and tested for their inhibitory activities on matrix metalloproteinase (MMP)-1, MMP-2, and MMP-9. Preliminary structure–activity relationship analysis and docking studies indicated that ferulic acid amides with electron-donating groups at the amino phenyl ring showed better inhibitory activities and selectivity than those with electron-withdrawing groups. Compound 3e, which had a hydroxyl group at meta-position of amino phenyl ring, showed considerable inhibitory activities against MMP-2, MMP-9 and best selectivity over MMP-1. The findings of this study would provide information for the exploitation and utilization of ferulic acid as MMP inhibitor for metastatic tumor treatment.

The emergence of mutant virus in drug therapy for HIV-1 infection has steadily risen in the last decade. Inhibition of reverse transcriptase enzyme has emerged as a novel target for the treatment of HIV infection. The aim to decipher the structural features that interact with receptor, we report a quantitative structure activity relationship (QSAR) study on a dataset of thirty seven compounds belonging to bisphenylbenzimidazoles (BPBIs) as reverse transcriptase inhibitors using enhanced replacement method (ERM), stepwise multiple linear regression (Stepwise-MLR) and genetic function approximation (GFA) method for selecting a subset of relevant descriptors, developing the best multiple linear regression model and defining the QSAR model applicability domain boundaries. The enhanced replacement method was found to give better results r2=0.8542, Q2(loo) = 0.7917, r2pred = 0.7812) at five variables as compared to stepwise MLR and GFA method, evidenced by internal and external validation parameters. The modified r2 (r2m) of the training set, test set and whole data set were calculated and are in agreement with the enhanced replacement method. The results of QSAR study rationalize the structural requirement for optimum binding of ligands. The developed QSAR model shows that hydrophobicity, flexibility, three dimensional surface area, volume and shape of molecule are important parameters to be considered for designing new compounds and to decipher reverse transcriptase enzyme inhibition activity of these compounds at molecular level. The applicability domain was defined to find the similar analogs with better prediction power.

A series of novel 1,2,4-triazole thioacetanilide derivatives has been designed, synthesized and evaluated for their anti-HIV activities in MT-4 cells. Half of these compounds showed moderate to potent activities against wild-type HIV-1 with an EC50 ranging from 38.0 µ;M to 4.08 µM. Among them, 2-(4-(2-fluorobenzyl)-5-isopropyl-4H-1,2,4-triazol- 3-ylthio)-N-(2-nitrophenyl)acetamide 7d was identified as the most promising compound (EC50 = 4.26 µM, SI = 49). However, no compound was active against HIV-2. The preliminary structure-activity relationships among the newly synthesized congeners are discussed.

Breast cancer is one of the most high-profile malignant diseases in modern society. Among postmenopausal women affected by the disease, a substantial portion has breast tumors that are estrogen-receptor positive. A common therapeutic intervention for this type of cancer is through endocrine therapy. Endocrine agents can act by either diminishing the availability or inhibiting the binding of estrogens to ER. Aromatase catalyzes the conversion of androgens to estrogens in the final step of the biosynthesis of estrogens and is therefore an attractive therapeutic target for inhibition. 3DQSAR pharmacophore modeling studies were undertaken for biphenyl derivatives as aromatase inhibitors in JEG-3 cell lines. A four-point pharmacophore with two H-bond acceptors and two aromatic rings as pharmacophoric features was developed. The pharmacophore hypothesis yielded a statistically significant 3D-QSAR model, with a correlation coefficient of R2 = 0.977 for training set molecules. The generated model showed excellent predictive power, with a correlation coefficient of Q2 = 0.946 for an external test set. The 3D-QSAR plots illustrated insights into the structure activity relationship of these compounds which may help in the design and development of potent biphenyl derivatives as new aromatase inhibitors.

Xylose is one of the most abundant carbohydrates in nature, and widely used to produce bioethanol via fermentation in industry. Xylulose can produce two key enzymes: xylose reductase and xylitol dehydrogenase. Owing to the disparate cofactor specificities of xylose reductase and xylitol dehydrogenase, intracellular redox imbalance is detected during the xylose fermentation, resulting in low ethanol yields. To overcome this barrier, a common strategy is applied to artificially modify the cofactor specificity of xylose reductase. In this study, we utilized molecular simulation approaches to construct a 3D (three-dimensional) structural model for the NADP-dependent Pichia stipitis xylose reductase (PsXR). Based on the 3D model, the favourable binding modes for both cofactors NAD and NADP were obtained using the flexible docking procedure and molecular dynamics simulation. Structural analysis of the favourable binding modes showed that the cofactor binding site of PsXR was composed of 3 major components: a hydrophilic pocket, a hydrophobic pocket as well as a linker channel between the aforementioned two pockets. The hydrophilic pocket could recognize the nicotinamide moiety of the cofactors by hydrogen bonding networks, while the hydrophobic pocket functioned to position the adenine moiety of the cofactors by hydrophobic and Π-Π stacking interactions. The linker channel contained some key residues for ligand-binding; their mutation could have impact to the specificity of PsXR. Finally, it was found that any of the two single mutations, K21A and K270N, might reverse the cofactor specificity of PsXR from major NADP- to NADdependent, which was further confirmed by the additional experiments. Our findings may provide useful insights into the cofactor specificity of PsXR, stimulating new strategies for better designing xylose reductase and improving ethanol production in industry.

L-type calcium channel (LTCC) blockers are used as cardiac antiarrhythmics or antihypertensives. In our previous research, we have reported a furanocoumarin, imperatorin, which exhibited potent vasodilatory effects. The possible mechanism might involve with inhibition against LTCC. In order to further investigate the pharmacologic mechanism of imperatorin for interaction with LTCC, the homology modeling of LTCC was performed using MODELLER 9.9 program with potassium channels as templates. The binding mode of imperatorin to LTCC was further investigated by molecular docking. Molecular docking results indicated that imperatorin occupied the same binding site as verapamil and hydrogen bond interaction played important role in blocker-channel binding. Docking studies provided useful information to understand the action mechanism of imperatorin. The results described here will be helpful in the development of novel potential LTCC blockers.

Curcumin bioconjugates, with folic acid, fatty acids and dipeptide, have shown much lower MIC than curcumin against clinically isolated Gram-positive, S.viridians, and Gram-negative bacterial strains, E. coli, P. mirabilis and K. pneumoniae. Polynomial regression analysis was performed to establish a correlation between lipophilicity (logP) and antibacterial activity (pMIC), which showed the efficacy of these molecules against the bacterial strains in the following order: E. coli > S viridans = K. pneumoniae > P. mirabilis. The regression coefficients (R2 = 0.62 to 0.91) derived for each strain were correlated significantly and led to a conclusion that it was the amphiphilic nature that governed the antibacterial activity. Thus, the bioconjugate 2, having folic acid attached at active methylene site of curcumin with free phenolic hydroxyls, showed the best result.

Ibuprofen is one of the most popular NSAIDs for the last three decades but also known for its gastrointestinal side effects similar to other NSAIDs. To overcome this problem, we have designed and synthesized ibuprofen - antioxidant (thymol, guaiacol, eugenol, and menthol) hybrids (6-13) with and without spacer as gastro sparing agents. The hybrids have been found to be chemically stable, biolabile and exhibited retention of anti-inflammatory and analgesic activity with significant reduced ulcerogenicity as compared to the ibuprofen and ibuprofen + antioxidant physical mixture. The absence of ulcerogenicity may be attributed to antioxidants and improved physicochemical properties of these hybrid molecules.