Revealing the Binding Process of New 3-Alkylpyridine Marine Alkaloid Analogue Antimalarials and the Heme Group: An Experimental and Theoretical Investigation.

Synthetic 3-alkylpyridine marine alkaloid (3-APA) analogues have shown good antimalarial activity against Plasmodium falciparum. However, despite their structural originality, their molecular target was unknown. Herein, we report a proposal for the antimalarial mechanism of action of 3-APA analogues through interference with the process of hemozoin (Hz) formation. The interaction between 3-APA analogues and heme groups was investigated employing an in silico approach and biophysical techniques such as ultraviolet-visible light (UV-vis) titration and electrospray ionization-mass spectrometry (ESI-MS). The in silico approach was performed based on pure ab initio electronic structure methods in order to obtain insights at the molecular level concerning the binding process of antimalarial drugs at their target site, the heme group. In silico results showed that the formation of heme:3-APA complexes at a molecular ratio of 2:1 are more stable than 1:1 complexes. These results were further confirmed by experimental techniques, such as UV-vis and high-resolution mass spectrometry (ESI-TOF), for two of the most active 3-APA analogues.

LEISHMANICIDAL ACTIVITY in vivo OF A MILTEFOSINE DERIVATIVE IN Mesocricetus auratus.

Visceral leishmaniasis (VL) is a chronic and systemic disease; if untreated, it can cause death in a large number of cases. The therapy is based on the use of antimonials, which have been used for over 50 years. However, cases of resistance have been reported in some countries. In this context, miltefosine (MIL) was introduced to treat antimonial unresponsive cases. Nonetheless, in recent years MIL unresponsive and relapse cases of VL have increasingly been reported. In the current study, the therapeutic potential of compound 5-(4-(3-methanesulfonatepropyl)-1H-1,2,3-triazol-1-yl)dodecyl methanesulfonate (C11), an MIL derivative, was assessed in an experimental VL hamster model. For this purpose, golden hamsters (Mesocricetus auratus) were infected with Leishmania (L.) infantum chagasi and treated daily for 10 days with C11 and MIL administered orally; in addition, Glucantime (GLU), peritoneal route, were administered at 15, 10, 50 mg/kg body weight/day, respectively. Twenty four hours after the end of treatment the animals were euthanatized; and the specimens were collected to evaluate the relative mRNA expression of cytokines IFN-γ, TNF-α, IL-17, TGF-ß, IL-4 and IL-10 in fragments of the spleen and liver; moreover, the parasitism in these organs was evaluated as well as the main histopathological alterations. The C11-treated animals showed greater expression of IL-17 and TNF-α cytokines and reduced expression of IL-10 in the spleen in comparison to the infected untreated group (UTG) (p <0.05). The C11 and GLU groups showed a significant reduction in the IgG levels in comparison to the UTG group (p <0.05). Moreover, the C11-treated animals had fewer parasites in the spleen than the UTG animals (reduction of 95.9%), as well as a greater preservation of white pulp architecture in the spleen than the UTG, GLU and MIL groups (p <0.05). For the liver, the animals from the C11 and MIL groups showed a significant increase in TNF-α relative expression in comparison to the UTG animals, which would explain the increase in the number of granulomas and the reduction in the parasitic load (p <0.05). Combined, these findings indicate that C11 is an interesting compound that should be considered for the development of new drugs against VL, mainly due to its leishmanicidal effect and immunostimulating action.

Catalytic mechanism for the conversion of salicylate into catechol by the flavin-dependent monooxygenase salicylate hydroxylase.

Salicylate hydroxylase (NahG) is a flavin-dependent monooxygenase that catalyzes the decarboxylative hydroxylation of salicylate into catechol in the naphthalene degradation pathway in Pseudomonas putida G7. We explored the mechanism of action of this enzyme in detail using a combination of structural and biophysical methods. NahG shares many structural and mechanistic features with other versatile flavin-dependent monooxygenases, with potential biocatalytic applications. The crystal structure at 2.0 Šresolution for the apo form of NahG adds a new snapshot preceding the FAD binding in flavin-dependent monooxygenases. The kcat/Km for the salicylate reaction catalyzed by the holo form is >105 M-1 s-1 at pH 8.5 and 25 °C. Hammett plots for Km and kcat using substituted salicylates indicate change in rate-limiting step. Electron-donating groups favor the hydroxylation of salicylate by a peroxyflavin to yield a Wheland-like intermediate, whereas the decarboxylation of this intermediate is faster for electron-withdrawing groups. The mechanism is supported by structural data and kinetic studies at different pHs. The salicylate carboxyl group lies near a hydrophobic region that aids decarboxylation. A conserved histidine residue is proposed to assist the reaction by general base/general acid catalysis.

Synthesis of new heterocyclic derivatives of alpha,alpha-trehalose.

Several novel N-1, N-2, and S-5 tetrazole and 1,3,4-oxadiazole derivatives of alpha,alpha-trehalose disubstituted at C-6,6', with potential synthetic and pharmacological interest were prepared from commercial tetrazoles and 1,3,4-oxadiazoles in reaction with hexa-O-benzyl-6,6'-di-O-triflyl-alpha,alpha-trehalose.

Novel Symmetrical 1,4-Disubstituted-bis-1,2,3-Triazoles: Synthesis by Double CuAAC and Cytotoxicity Evaluation.

BACKGROUND: A series of symmetrical 1,4-disubstituted bis-1,2,3-triazoles was prepared by double copper catalyzed Azide-alkyne Cycloaddition (CuAAC) from aliphatic bis-azides and a tetraethylene glycol bis-azide derivative. The eighteen novel compounds were evaluated in vitro for their cytotoxic activity against two human tumor cell lines: Human breast adenocarcinoma (MDA-MB 231) and ovarian adenocarcinoma (TOV-21G). RESULTS AND CONCLUSION: The results of colorimetric MTT assays showed that compounds 4j and 4q exhibited a better selectivity index and cell viability comparable with the standard drug doxorubicin. These compounds induced apoptosis in both tested cell lines, as assessed by BrdU assay. The results suggest that these structurally simple compounds may be promising prototypes for antitumoral agents.

A UBI 31-38 Peptide-coumarin Conjugate: Photophysical Features, Imaging Tracking and Synergism with Amphotericin B Against Cryptococcus.

Cryptococcosis is a fungal disease of global significance for which new effective treatments are needed. The conjugation of the synthetic antimicrobial peptide fragment UBI 31-38 to a coumarin derivative showed to be an effective approach for the design of a novel anticryptococcal agent. In addition to antifungal activity, the conjugate exhibited intense fluorescence, which could be valuable for mechanistic investigations of this molecule. In this work, we studied the photophysical properties of the conjugate and confocal scanning laser microscopy was used to inspect the distribution of the peptide-coumarin conjugate in Cryptococcus cell. The synergism of this compound with amphotericin B or fluconazole against C. gattii and C. neoformans strains was also investigated. The results indicated that the fluorescent conjugate alone as well as its combination with amphotericin B are promising tools against cryptococcosis.

Studies on free radical scavenging, cancer cell antiproliferation, and calf thymus DNA interaction of Schiff bases.

Thirty-nine Schiff bases were synthesized by performing microwave-assisted condensation of the corresponding aldehydes and aromatic amines. Their reactive nitrogen species (RNS) scavenging activity and inhibitory effects against cancer cell growth were then subsequently investigated. Additionally, the interaction between the calf thymus DNA (ctDNA) and selected Schiff bases was evaluated using fluorescence spectroscopy, and their binding parameters were determined. The yields of the various compounds ranged from moderate to excellent (43-99%) after only a 2-min reaction. The hydroxylated Schiff bases 2, 8, 15, 16, 18, 20, 29, 32, 34, and 37 were found to be potent scavengers of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals with half-maximal scavenging concentration (SC50) values lower than that of the positive control, resveratrol. The presence of hydroxyl substituents on the aromatic rings also proved essential to the cytotoxicity of the compounds. The binding constants (Kb) obtained using fluorescence spectroscopy ranged from 0.37 to 3.07×105Lmol-1, and were strongly influenced by the structure and hydroxylation degree. Schiff bases 3 and 8 showed promising cytotoxic activity, with half-maximal growth inhibitory (GI50) values in the same order of magnitude as those exhibited by the reference drug, doxorubicin against various cell lines. Interestingly, these compounds also showed the highest Kb, suggesting that the cytotoxic activity could be related to their interaction with the DNA of the tumor cells. The results of this study highlighted some Schiff bases as potential lead compounds for the design of new free radical scavengers and anticancer agents.

Synthesis, antiproliferative activities, and computational evaluation of novel isocoumarin and 3,4-dihydroisocoumarin derivatives.

A series of novel isocoumarin derivatives were synthesized using Castro-Stephens cross-coupling. Moreover, novel 3,4-dihydroisocoumarin derivatives were obtained by catalytic hydrogenation of the corresponding isocoumarin precursors. The antiproliferative activity of all compounds was evaluated in vitro in different tumor cells. Furthermore, docking calculations were performed for the kallikrein 5 (KLK5) active site to predict the possible mechanism of action of this series of compounds. Theoretical findings indicate that the 3,4-dihydroisocoumarin derivative 10a forms hydrogen bonds with Ser190 and Gln192 residues of KLK5. This derivative was the most active compound in the series with potent antiproliferative activity and high selectivity index (SI > 378.79) against breast cancer cells (MCF-7, GI50 = 0.66 µg mL(-1)). This compound represents a promising matrix for developing new antiproliferative agents.

Synthesis of a New Peptide-Coumarin Conjugate: A Potential Agent against Cryptococcosis.

Antimicrobial peptides (AMPs) are currently being investigated as potential sources of novel therapeutics against an increasing number of microorganisms resistant to conventional antibiotics. The conjugation of an AMP to other bioactive compounds is an interesting approach for the development of new derivatives with increased antimicrobial efficiency and broader spectra of action. In this work, the synthesis of a new peptide-coumarin conjugate via copper(I)-catalyzed azide-alkyne cycloaddition is described. The conjugate was assayed for in vitro cytotoxicity and displayed antifungal activity against Cryptococcus gattii and Cryptococcus neoformans. Additionally, the conjugate exhibited increased antifungal efficacy when compared with the individual peptide, coumarin, or triazole moieties. Treatment of C. gattii with the peptide-coumarin conjugate enhanced the production of reactive oxygen species, suggesting that the oxidative burst plays an important role in the mechanism of action of the conjugate.

Synthesis and antiproliferative activity of 8-hydroxyquinoline derivatives containing a 1,2,3-triazole moiety.

Twelve novel 8-hydroxyquinoline derivatives were synthesized with good yields by performing copper-catalyzed Huisgen 1,3-dipolar cycloaddition ("click" reaction) between an 8-O-alkylated-quinoline containing a terminal alkyne and various aromatic or protected sugar azides. These compounds were evaluated in vitro for their antiproliferative activity on various cancer cell types. Protected sugar derivative 16 was the most active compound in the series, exhibiting potent antiproliferative activity and high selectivity toward ovarian cancer cells (OVCAR-03, GI50 < 0.25 µg mL(-1)); this derivative was more active than the reference drug doxorubicin (OVCAR-03, GI50 = 0.43 µg mL(-1)). In structure-activity relationship (SAR) studies, the physico-chemical parameters of the compounds were evaluated and docking calculations were performed for the α-glucosidase active site to predict the possible mechanism of action of this series of compounds.

Design of new drugs for the treatment of Alzheimer's disease based on tacrine structure.

Tacrine was the first drug approved by FDA for the treatment of Alzheimer's disease. However, its use was restricted in function of side effects observed in some patients. Investigations on the structural basis by which tacrine inhibits cholinesterases activity brought new perspectives for the design of more potent analogs with fewer side effects. This review discusses the recent advances on the development of tacrine-structure-based compounds capable to target multiple molecules involved in Alzheimer's disease. Detailed information on strategies of molecular modifications commonly used in medicinal chemistry, such as bioisosterism, hybridization, dimerization and simplification is presented as well.

Effect of 3-alkylpyridine marine alkaloid analogues in Leishmania species related to American cutaneous leishmaniasis.

A series of oxygenated analogues of marine 3-alkylpyridine alkaloids were synthesized, and their leishmanicidal activity was assayed. All compounds were prepared from 3-pyridinepropanol in few steps and in good yields. The key step for the synthesis of these compounds was a classic Williamson etherification under phase-transfer conditions. Besides toxicity in peritoneal macrophages, the compounds exhibited a significant leishmanicidal activity. Of twelve compounds tested, five showed a strong leishmanicidal activity against promastigote forms of Leishmania amazonensis and L. braziliensis with IC50 below 10 µm. Compounds 11, 14, 15, and 16 showed a strong leishmanicidal activity on intracellular amastigotes (IC50 values of 2.78; 0.27; 1.03, and 1.33 µm, respectively), which is unlikely to be owing to the activation of nitric oxide production by macrophages.

Synthesis and evaluation of antimalarial activity of oxygenated 3-alkylpyridine marine alkaloid analogues.

A series of new oxygenated analogues of marine 3-alkylpyridine alkaloids were prepared from 3-pyridinepropanol in few steps and in good yields. The key step for the synthesis of these compounds was a Williamson etherification under phase-transfer conditions. All new compounds were evaluated for their antiplasmodial activity and cytotoxicity. A significant reduction in parasitaemia was observed for some of the prepared compounds, and the majority of them exhibited a selectivity index (SI) ranging from 2.78 to 15.58, which suggests that these compounds may be a promising class of substances with antimalarial activity.

Synthesis of aryl aldimines and their activity against fungi of clinical interest.

Aldimines are aldehyde-derived compounds that contain a C=N group. Besides its broad industrial applications, this class of non-naturally occurring compounds are found to possess antibacterial, antifungal, antimalarial, antiproliferative, anti-inflammatory, antiviral, and antipyretic properties. Based on this, six aryl aldimines were synthesized from the condensation of aromatic amines with benzaldehydes. The antifungal activities of synthesized compounds were evaluated against nineteen fungal strains that included Candida and Aspergillus species, Cryptococcus neoformans. The aryl aldimines 2-(benzylideneamino)phenol (3) and 4-(benzylideneamino)phenol (8) were the most active compounds against the fungi studied. Compounds 3 and 8 efficiently inhibited the metabolism of C. neoformans mature biofilm.

Diterpenoids from the aerial parts of Plectranthus ornatus.

Phytochemical investigation of a hexane extract of the aerial parts of Plectranthus ornatus yielded three new neoclerodane diterpenoids (1-3), two labdane diterpenes (4 and 5) obtained for the first time as natural products, and several previously known substances. The structures and relative stereochemistry of 1-5 were established mainly on the basis of NMR spectroscopic studies and by comparison with related compounds.