An investigation of the predominant structure of antibiotic azithromycin in chloroform solution through NMR and thermodynamic analysis.

Azithromycin (AZM) is a well-known macrolide-type antibiotic that has been used in the treatment of infections and inflammations. Knowledge of the predominant molecular structure in solution is a prerequisite for an understanding of the interactions of the drug in biological media. Experimental structural determination can be carried out for samples in solid-state (X-ray diffraction technique) and gas phase (electron diffraction experiment). In solution, spectroscopic methods can be used to extract valuable information which combined with quantum chemical calculations can lead to the determination of the preferred molecular structures to be observed when a given solute is dissolved in each solvent. That is precisely the aim of this work. We used experimental NMR chemical shift data (in CDCl3) as a reference for comparison with Density Functional Theory (DFT) NMR calculations, with geometry optimized having as guess input two crystallographic structures available in the literature with the configuration of all chiral carbon atoms inverted, named here A and B. The Polarizable Continuum Model (PCM) was used to describe the solvent effects (chloroform) including five explicit CHCl3 solvent molecules, which we believe can account for short and long-range solute-solvent interactions. Analysis of calculated thermodynamic, NMR chemical shift, MAE (Mean Absolute Error), and spin-spin coupling constant values revealed that both supposable C3R-C5S (named M2-A) and C3S-C5R (named M2-B) structures are equally probable to exist in chloroform solution. In addition, we found that the heavy atoms' conformation is reasonably similar in the solid-state and chloroform solution; however, regarding the OH groups, the spatial orientations are rather different with intramolecular OH⋯N and OH⋯O hydrogen bonds present in solution and with some of them being absent in the X-ray structure probably due to crystal packing effects.

Water Solvent Effect on Theoretical Evaluation of 1H NMR Chemical Shifts: o-Methyl-Inositol Isomer.

In this paper, density functional theory calculations of nuclear magnetic resonance (NMR) chemical shifts for l-quebrachitol isomer, previously studied in our group, are reported with the aim of investigating in more detail the water solvent effect on the prediction of 1H NMR spectra. In order to include explicit water molecules, 20 water-l-quebrachitol configurations obtained from Monte Carlo simulation were selected to perform geometry optimizations using the effective fragment potential method encompassing 60 water molecules around the solute. The solvated solute optimized geometries were then used in B3LYP/6-311+G(2d,p) NMR calculations with PCM-water. The inclusion of explicit solvent in the B3LYP NMR calculations resulted in large changes in the 1H NMR profiles. We found a remarkable improvement in the agreement with experimental NMR profiles when the explicit hydrated l-quebrachitol structure is used in B3LYP 1H NMR calculations, yielding a mean absolute error (MAE) of only 0.07 ppm, much lower than reported previously for the gas phase optimized structure (MAE = 0.11 ppm). In addition, a very improved match between theoretical and experimental 1H NMR spectrum measured in D2O was achieved with the new hydrated optimized l-quebrachitol structure, showing that a fine-tuning of the theoretical NMR spectra can be accomplished once solvent effects are properly considered.

General method for the preparation of active esters by palladium-catalyzed alkoxycarbonylation of aryl bromides.

A useful method was developed for the synthesis of active esters by palladium-catalyzed alkoxycarbonylation of (hetero)aromatic bromides. The protocol was general for a range of oxygen nucleophiles including N-hydroxysuccinimide (NHS), pentafluorophenol (PFP), hexafluoroisopropyl alcohol (HFP), 4-nitrophenol, and N-hydroxyphthalimide. A high functional group tolerance was displayed, and several active esters were prepared with good to excellent isolated yields. The protocol was extended to access an important synthetic precursor to the HIV-protease inhibitor, saquinavir, by formation of an NHS ester followed by acyl substitution.

Quantum chemical investigation of predominant conformation of the antibiotic azithromycin in water and DMSO solutions: thermodynamic and NMR analysis.

Azithromycin (AZM) is a macrolide-type antibiotic used to prevent and treat serious infections (mycobacteria or MAC) that significantly inhibit bacterial growth. Knowledge of the predominant conformation in solution is of fundamental importance for advancing our understanding of the intermolecular interactions of AZM with biological targets. We report an extensive density functional theory (DFT) study of plausible AZM structures in solution considering implicit and explicit solvent effects. The best match between the experimental and theoretical nuclear magnetic resonance (NMR) profiles was used to assign the preferred conformer in solution, which was supported by the thermodynamic analysis. Among the 15 distinct AZM structures, conformer M14, having a short intramolecular C6-OH … N H-bond, is predicted to be dominant in water and dimethyl sulfoxide (DMSO) solutions. The results indicated that the X-ray structure backbone is mostly conserved in solution, showing that large flexible molecules with several possible conformations may assume a preferential spatial orientation in solution, which is the molecular structure that ultimately interacts with biological targets.

An isoniazid analogue promotes Mycobacterium tuberculosis-nanoparticle interactions and enhances bacterial killing by macrophages.

Nanoenabled drug delivery systems against tuberculosis (TB) are thought to control pathogen replication by targeting antibiotics to infected tissues and phagocytes. However, whether nanoparticle (NP)-based carriers directly interact with Mycobacterium tuberculosis and how such drug delivery systems induce intracellular bacterial killing by macrophages is not defined. In the present study, we demonstrated that a highly hydrophobic citral-derived isoniazid analogue, termed JVA, significantly increases nanoencapsulation and inhibits M. tuberculosis growth by enhancing intracellular drug bioavailability. Importantly, confocal and atomic force microscopy analyses revealed that JVA-NPs associate with both intracellular M. tuberculosis and cell-free bacteria, indicating that NPs directly interact with the bacterium. Taken together, these data reveal a nanotechnology-based strategy that promotes antibiotic targeting into replicating extra- and intracellular mycobacteria, which could actively enhance chemotherapy during active TB.

Rhodium-catalyzed intramolecular formation of N-sulfamoyl 2,3-aziridino-γ-lactones and their use for the enantiospecific synthesis of α,ß-diamino acid derivatives.

4-Hydroxymethylbutenolide 4 was transformed into its sulfamoyl derivative 5, which upon treatment with iodosobenzene diacetate and magnesium oxide in the presence of a rhodium catalyst afforded the product of intramolecular aziridination 6. Reaction of 6 with primary or secondary amines in DMA led to regioselective opening of the aziridine ring at C2 to give the corresponding bicyclic derivatives 7a-7g in good to excellent yields. Methanolysis of the lactone ring of the N-benzyl-N-methyl derivative 7c followed by protection of the resulting secondary hydroxy group and treatment of the product with Boc anhydride provided the activated cyclic sulfamates 13 and 14. The latter then reacted with a second nucleophile (azide or thiophenol) to give the corresponding difunctionalized α,ß-diamino methyl esters 15-18, 20.

(1) H NMR analysis of O-methyl-inositol isomers: a joint experimental and theoretical study.

Density functional theory (DFT) calculations of (1) H NMR chemical shifts for l-quebrachitol isomers were performed using the B3LYP functional employing the 6-31G(d,p) and 6-311 + G(2d,p) basis sets. The effect of the solvent on the B3LYP-calculated NMR spectrum was accounted for using the polarizable continuum model. Comparison is made with experimental (1) H NMR spectroscopic data, which shed light on the average uncertainty present in DFT calculations of chemical shifts and showed that the best match between experimental and theoretical B3LYP (1) H NMR profiles is a good strategy to assign the molecular structure present in the sample handled in the experimental measurements. Among four plausible O-methyl-inositol isomers, the l-quebrachitol 2a structure was unambiguously assigned based only on the comparative analysis of experimental and theoretical (1) H NMR chemical shift data. The B3LYP infrared (IR) spectrum was also calculated for the four isomers and compared with the experimental data, with analysis of the theoretical IR profiles corroborating assignment of the 2a structure. Therefore, it is confirmed in this study that a combined experimental/DFT spectroscopic investigation is a powerful tool in structural/conformational analysis studies.

Preparation, cytotoxic activity and DNA interaction studies of new platinum(II) complexes with 1,10-phenanthroline and 5-alkyl-1,3,4-oxadiazol-2(3H)-thione derivatives.

This work describes the synthesis, characterization and in vitro anticancer activity of two platinum(II) complexes of the type [Pt(L1)2(1,10-phen)] 1 and [Pt(L2)2(1,10-phen)] 2, where L1 = 5-heptyl-1,3,4-oxadiazole-2-(3H)-thione, L2 = 5-nonyl-1,3,4-oxadiazole-2-(3H)-thione and 1,10-phen = 1,10-phenanthroline. As to the structure of these complexes, the X-ray structural analysis of 1 indicates that the geometry around the platinum(II) ion is distorted square-planar, where two 5-alkyl-1,3,4-oxadiazol-2-thione derivatives coordinate a platinum(II) ion through the sulfur atom. A chelating bidentate phenanthroline molecule completes the coordination sphere. We tested these complexes in two breast cancer cell lines, namely, MCF-7 (a hormone responsive cancer cell) and MDA-MB-231 (triple negative breast cancer cell). In both cells, the most lipophilic platinum compound, complex 2, was more active than cisplatin, one of the most widely used anticancer drugs nowadays. DNA binding studies indicated that such complexes are able to bind to ct-DNA with Kb values of 104 M-1. According to data from dichroism circular and fluorescence spectroscopy, these complexes appear to bind to the DNA in a non-intercalative, probably via minor groove. Molecular docking followed by semiempirical simulations indicated that these complexes showed favorable interactions with the minor groove of the double helix of ct-DNA in an A-T rich region. Thereafter, flow cytometry analysis showed that complex 2 induced apoptosis and necrosis in MCF-7 cells.

Ethyl 2-[(carbamoyl-amino)-imino]-propano-ate hemihydrate.

The title compound, C(6)H(11)N(3)O(3)·0.5H(2)O, has two independent mol-ecules and one mol-ecule of water in the asymmetric unit. The crystal packing is stabilized by inter-molecular N-H⋯N, O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds. These inter-actions form a two-dimensional array in the ab plane with a zigzag motif which has an angle close to 35° between the zigzag planes. The hydrogen bonding can be best described using the graph-set notation as N(1) = C(10)R(2) (2)(10)R(2) (2)(8) and N(2) = R(6) (4)(20)R(2) (2)(8).

Ethyl 2-[(carbamothioyl-amino)-imino]-propano-ate.

The title compound, C(6)H(11)N(3)O(2)S, consists of a roughly planar mol-ecule (r.m.s deviation from planarity = 0.077 Šfor the non-H atoms) and has the S atom in an anti position to the imine N atom. This N atom is the acceptor of a strongly bent inter-nal N-H⋯N hydrogen bond donated by the amino group. In the crystal, mol-ecules are arranged in undulating layers parallel to (010). The mol-ecules are linked via inter-molecular amino-carboxyl N-H⋯O hydrogen bonds, forming chains parallel to [001]. The chains are cross-linked by N(carbazone)-H⋯S and C-H⋯S inter-actions, forming infinite sheets.

Preclinical Gold Complexes as Oral Drug Candidates to Treat Leishmaniasis Are Potent Trypanothione Reductase Inhibitors.

The drugs currently used to treat leishmaniases have limitations concerning cost, efficacy, and safety, making the search for new therapeutic approaches urgent. We found that the gold(I)-derived complexes were active against L. infantum and L. braziliensis intracellular amastigotes with IC50 values ranging from 0.5 to 5.5 µM. All gold(I) complexes were potent inhibitors of trypanothione reductase (TR), with enzyme IC50 values ranging from 1 to 7.8 µM. Triethylphosphine-derived complexes enhanced reactive oxygen species (ROS) production and decreased mitochondrial respiration after 2 h of exposure, indicating that gold(I) complexes cause oxidative stress by direct ROS production, by causing mitochondrial damage or by impairing TR activity and thus accumulating ROS. There was no cross-resistance to antimony; in fact, SbR (antimony-resistant mutants) strains were hypersensitive to some of the complexes. BALB/c mice infected with luciferase-expressing L. braziliensis or L. amazonensis and treated orally with 12.5 mg/kg/day of AdT Et (3) or AdO Et (4) presented reduced lesion size and parasite burden, as revealed by bioimaging. The combination of (3) and miltefosine allowed for a 50% reduction in miltefosine treatment time. Complexes 3 and 4 presented favorable pharmacokinetic and toxicity profiles that encourage further drug development studies. Gold(I) complexes are promising antileishmanial agents, with a potential for therapeutic use, including in leishmaniasis caused by antimony-resistant parasites.

JVA, an isoniazid analogue, is a bioactive compound against a clinical isolate of the Mycobacterium avium complex.

Bacteria belonging to Mycobacterium avium complex are organisms of low pathogenicity that infect immunosuppressed individuals. Infection is treated with an antimicrobial macrolide, Clarithromycin (CAM) or Azitromycin, associated with Ethambutol and Rifabutin during 12 months. Regimen long duration and side effects hinder patient's commitment to treatment favoring emergence of antibiotic resistance. In this present study, we evaluated the activity of JVA, an Isoniazid (INH) derivative, against M. avium 2447, a clinical isolate. We demonstrated that JVA reduces M. avium 2447 growth in macrophages, more efficiently than CAM and INH. In order to explore JVA mechanism of action, we investigated compound properties and performed pH-dependent stability studies. Our results suggest an enhanced ability of JVA to cross biological membranes. Furthermore, we suggest that in acidic conditions of macrophages' phagosomes, where mycobacteria replicate, JVA would be promptly hydrolyzed to INH, delivering the adduct INH-nicotinamide adenine dinucleotide and thus inhibiting M. avium 2447 growth.

In vitro anti-Trypanosoma cruzi activity of ternary copper(II) complexes and in vivo evaluation of the most promising complex.

In order to improve the previously observed antichagasic activity of Cu(II) complexes containing 2-chlorobenzhydrazide (2-CH), we report herein the synthesis and anti-Trypanosoma cruzi activity of novel copper complexes containing 2-methoxybenzhydrazide (2-MH), 4-methoxybenzhydrazide (4-MH) and three α-diimine ligands, namely, 1,10-phenanthroline (phen), 2,2-bipyridine (bipy) and 4-4'-dimethoxy-2-2'-bipyridine (dmb). Two of these complexes showed higher in vitro anti-Trypanosoma cruzi activity when compared to benznidazole, the main drug used in Chagas disease treatment. One of them, the copper complex with 4-MH and dmb, [Cu(4-MH)(dmb)(ClO4)2], exhibited a higher selectivity index than that recommended for preclinical studies. Considering this observation, complex [Cu(4-MH)(dmb)(ClO4)2] was selected for preliminary in vivo assays, which verified that this compound was able to reduce parasitemia by 64% at the peak of infection. Further investigations were performed on all compounds. The Cu(II) complexes bind to ct-DNA with Kb values in the range of 103-104 M-1, with [Cu(4-MH)(dmb)(ClO4)2] showing the highest Kb value (1.45 × 104 M-1). Molecular docking simulations predicted that [Cu(4-MH)(dmb)(ClO4)2] binds in the minor groove of the double helix of ct-DNA and forms one hydrogen bond.

Antileishmanial activity of aldonamides and N-acyl-diamine derivatives.

A number of lipophilic N-acyl-diamines and aldonamides have been synthesized and tested for their in vitro antiproliferative activity against Leishmania amazonensis and L. chagasi. Ribonamides, having one amino group, displayed good to moderate inhibition of parasite growth. The best result was obtained for compounds 10 and 15 with IC50 against L. chagasi below 5 microM.

Preparation and antitubercular activities of alkylated amino alcohols and their glycosylated derivatives.

A series of N- and C-alkylated amino alcohols and of their protected galactopyranosyl derivatives was synthesized and evaluated for antitubercular activity. Five of these compounds displayed good activity, with a MIC below 12.5mug/mL. The presence of the carbohydrate slightly affected the antibacterial activity.

Novel gold(I) complexes with 5-phenyl-1,3,4-oxadiazole-2-thione and phosphine as potential anticancer and antileishmanial agents.

The current anticancer and antileishmanial drug arsenal presents several limitations concerning their specificity, efficacy, costs and the emergence of drug-resistant cells lines, which encourages the urgent need to search for new alternatives. Inspired by the fact that gold(I)-based compounds are promising antitumoral and antileishmanial drug candidates, we synthesized novel gold(I) complexes containing phosphine and 5-phenyl-1,3,4-oxadiazole-2-thione and evaluated their anticancer and antileishmanial activities. Synthesis was performed by reacting 5-phenyl-1,3,4-oxadiazole-2-thione derivatives with chloro(triphenylphosphine)gold(I) and chloro(triethylphosphine)gold(I). The novel compounds were characterized by infrared, Raman, 1H, 13C nuclear magnetic resonance, high-resolution mass spectra, and x-ray crystallography. The coordination of the ligands to gold(I) occurred through the exocyclic sulfur atom. All gold(I) complexes were active at low micromolar or nanomolar range with IC50 values ranging from <0.10 to 1.66 µM against cancer cell lines and from 0.9 to 4.2 µM for Leishmania infantum intracellular amastigotes. Compound (6-A) was very selective against murine melanoma B16F10, colon cancer CT26.WT cell lines and L. infantum intracellular amastigotes. Compound (7-B) presented the highest anticancer activity against both cancer cell lines while the promising antileishmanial lead was compound (6-A). Tiethylphosphine gold(I) complexes were more active than the conterparts triphenylphosphine derivatives for both anticancer and antileishmanial activities. Triethylphosphine gold(I) derivatives presented antimony cross-resistance in L. guyanensis demonstrating their potential to be used as chemical tools to better understand mechanisms of drug resistance and action. These findings revealed the anticancer and antileishmanial potential of gold(I) oxadiazole phosphine derivatives.

Synthesis and evaluation of antibacterial and antitumor activities of new galactopyranosylated amino alcohols.

Three series of d-galactose derivatives linked to a lipophilic aminoalcohol moiety were synthesized and their antibacterial activity was evaluated against Mycobacterium tuberculosis and representative species of Gram positive and Gram negative bacteria. Five out of the thirteen tested compounds displayed activity against M. tuberculosis, with a minimal inhibitory concentration (MIC) of 12.5 µg/mL and seven compounds were active against the four bacterial strains tested. The best results were obtained for amino alcohols 10 and 11 against Staphylococcus epidermidis (MIC = 2 µg/mL). The antitumor activity was evaluated against three tumor cell lines (MCF-7, HeLa and MO59J) and compared to the normal cell line GM07492A. The results showed that the lowest IC50 values were observed for the amino alcohol 16 against MCF-7 (11.9 µM) and MO59J (10.0 µM).

Synthesis of acyl carbamates via four component Pd-catalyzed carbonylative coupling of aryl halides, potassium cyanate, and alcohols.

A simple and mild method is demonstrated for assembling acyl carbamates through a base-free four-component Pd-catalyzed carbonylation of aryl halides in the presence of potassium cyanate and alcohols in a two-chamber system. This approach produces a wide range of aryl acyl carbamates in good to excellent yields from the corresponding aryl bromides or iodides with near-stoichiometric carbon monoxide. In addition, the method can be extended to the synthesis of primary amides thereby expanding the usefulness of cyanate as an ammonia equivalent.

Biological activity and synthetic metodologies for the preparation of fluoroquinolones, a class of potent antibacterial agents.

In this present review we report different synthetic methodologies for the preparation of fluoroquinolones and their biological properties. The appearance of the fluoroquinolones, a new class of antibacterial agents (based on nalidixic acid, 4-quinolone-3-carboxylates), in early 1980's, gave a new impulse for the international competition to synthesize more effective drugs. Fluoroquinolones have a broad spectrum of activity against Gram-positive, Gram-negative and mycobacterial organisms as well as anaerobes. The fluoroquinolone ciprofloxacin hydrochloride is an important bioterrorist weapon and also an antibiotic used to treat bacterial infection in many different parts of the body, approved for use in patients who have been exposed to the inhaled form of anthrax.

Synthesis of genistein coupled with sugar derivatives and their inhibitory effect on nitric oxide production in macrophages.

The isoflavone genistein 1 and some derivatives modulate IL-12, TNF-α and NO production by macrophages and lung cancer cell lines, and improve the clinical signs of experimental autoimmune encephalomyelitis (EAE). Seven genistein derivatives connected at C-6 position of a sugar, such as d-glucose and d-galactose, were synthesized. The ability to modulate macrophage response was evaluated, showing variable inhibition capacity of NO and TNF-α production in J774.A1 and RAW 264.7. Five of the seven compounds were non-cytotoxic; compound 8 was more effective to inhibit NO and TNF-α production, without affecting cell viability.