Marcos Serrou do Amaral

A diaryl sulfide, sulfoxide, and sulfone bearing structural similarities to combretastatin A-4

Studies examining various spacer groups that link the two aromatic rings of combretastatin A-4 (CA4) have shown that the biological activity of analogs does not require the cis-stilbene configuration of CA4. Oxygen or nitrogen, carbonyl, methylene and ethylene spacers, for example, are present in CA4 analogs that show good activity. Up to now sulfur was not tested for this purpose. In this article we describe the synthesis of sulfide, sulfoxide and sulfone spacers between two aromatic rings comparable to those of CA4. We also compared them with CA4 for inhibitory effects on cell growth, tubulin polymerization, and the binding of [(3)H]colchicine to tubulin. We found that the sulfide is highly active and may be a lead compound for the preparation of antitumor compounds.

Development and validation of UV spectrophotometric method for determination of levofloxacin in pharmaceutical dosage forms

The objective of this research was to develop and validate an alternative analytical method for quantitative determination of levofloxacin in tablets and injection preparations. The calibration curves were linear over a concentration range from 3.0 to 8.0 μg mL-1. The relative standard deviation was below 1.0% for both formulations and average recovery was 101.42 ± 0.45% and 100.34 ± 0.85% for tablets and injection formulations, respectively. The limit of detection and limit of quantitation were 0.08 and 0.25 μg mL-1, respectively. It was concluded that the developed method is suitable for the quality control of levofloxacin in pharmaceuticals formulations.

Stability-indicating HPLC-DAD method for the simultaneous determination of fluoroquinolones and corticosteroids in ophthalmic formulations

The aim of this study is to develop and validate a stability-indicating assay method for simultaneous determination of gatifloxacin and prednisolone acetate, or of ciprofloxacin hydrochloride and dexamethasone in combination and in the presence of degradation products. Reverse-phase high-performance liquid chromatography is used. All analyses were carried out on a Kinetex C18 column and acetronitrile–water (50 : 50 v/v) pH 3.0 mobile phase with 0.30 mL min−1 flow rate. Efficient chromatographic separation of these drugs and their forced degradation products is achieved in less than 6 min and with a peak purity match factor higher than 950. The method shows linearity in the concentration range of 1.2 to 9.6 μg mL−1 for gatifloxacin (r = 0.9995), 2.0 to 16.0 μg mL−1 for prednisolone acetate (r = 0.9997), 2.5 to 25.0 μg mL−1 for both ciprofloxacin hydrochloride (r = 0.9993) and dexamethasone (r = 0.9998), precision (relative standard deviation lower than 2%), accuracy (mean recovery 100 ± 2%), and robustness, according to ICH and AOAC guidelines. This method is able to determine simultaneous ophthalmic combinations of these drugs and to separate the drug peaks from their forced degradation products. Additionally, the optimized chromatographic conditions can contribute to minimize waste of organic solvent .

A Critical Review of Properties and Analytical Methods for the Determination of Oxytetracyline in Biological and Pharmaceutical Matrices

ABSTRACT Antibiotics have an unquestionable importance in the treatment of many infections. Oxytetracycline is an antibiotic belonging to the class of tetracyclines, available for use in human and veterinary medicine. Development of analytical methods that prove the quality and efficacy of these drugs is fundamentally important to the pharmaceutical industry. In this context, the research presents an overview of the analytical profile of oxytetracycline, describing its chemical and pharmacological properties, and analytical methods for quantification of this drug in biological samples and pharmaceutical products. Oxytetracycline can be analyzed in these matrices by many types of methodologies. However, high-performance liquid chromatography is the most widely used, being recommended by official compendia. This kind of study can be useful to support the development of new efficient and sustainable analytical methods that may be utilized in the quality control routine of oxytetracycline in pharmaceutical products and pharmacokinetic monitoring in biological samples.

Synthesis and biological evaluation of biaryl analogs of antitubulin compounds

This paper reports the synthesis of methanones and esters bearing different substitution patterns as spacer groups between aromatic rings. This series of compounds can be considered phenstatin analogs. Two of the newly synthesized compounds, 5a and 5c, strongly inhibited tubulin polymerization and the binding of [(3)H] colchicine to tubulin, suggesting that, akin to phenstatin and combretastatin A-4, they can bind to tubulin at the colchicine site.

Modeling and molecular dynamics indicate that snake venom phospholipase B-like enzymes are Ntn-hydrolases

ABSTRACT Phospholipase‐B‐like (SVPLB‐like) enzymes are present in relatively small amounts in a number of venoms, however, their biological function and mechanisms of action are un‐clear. A three‐dimensional model of the SVPLB‐like enzyme from Crotalus adamanteus was generated by homology modeling based on the crystal structures of bovine Ntn‐hydrolyases and the modeled protein possesses conserved domains characteristic of Ntn‐hydrolases. Molecular dynamics simulations indicate that activation by autocatalytic cleavage results in the removal of 25amino acids which increases accessibility to the active site. SVPLB‐like enzymes possess a highly reactive cysteine and are hence amidases that to belong to the N‐terminal nucleophile (Ntn) hydrolase family. The Ntn‐hydrolases (N‐terminal nucleophile) form a superfamily of diverse enzymes that are activated autocatalytically; wherein the N‐terminal catalytic nucleophile is implicated in the cleavage of the amide bond. HIGHLIGHTSMolecular modeling and dynamics of phospholipase B‐like enzymes.Activation and proteolysis mechanisms.Classification as Ntn‐hydrolases.

Redox potential replica exchange molecular dynamics at constant pH in AMBER: Implementation and validation

Redox processes are important in chemistry, with applications in biomedicine, chemical analysis, among others. As many redox experiments are also performed at a fixed value of pH, having an efficient computational method to support experimental measures at both constant redox potential and pH is very important. Such computational techniques have the potential to validate experimental observations performed under these conditions and to provide additional information unachievable experimentally such as an atomic level description of macroscopic measures. We present the implementation of discrete redox and protonation states methods for constant redox potential Molecular Dynamics (CEMD), for coupled constant pH and constant redox potential MD (C(pH,E)MD), and for Replica Exchange MD along the redox potential dimension (E-REMD) on the AMBER software package. Validation results are presented for a small system that contains a single heme group: N-acetylmicroperoxidase-8 (NAcMP8) axially connected to a histidine peptide. The methods implemented allow one to make standard redox potential (Eo) predictions with the same easiness and accuracy as pKa predictions using the constant pH molecular dynamics and pH-REMD methods currently available on AMBER. In our simulations, we can correctly describe, in agreement also with theoretical predictions, the following behaviors: when a redox-active group is reduced, the pKa of a near pH-active group increases because it becomes easier for a proton to be attached; equivalently, when a pH-active group is protonated, the standard redox potential (Eo) of an adjacent redox-active group rises. Furthermore, our results also show that E-REMD is able to achieve faster statistical convergence than CEMD or C(pH,E)MD. Moreover, computational benchmarks using our methodologies show high-performance of GPU (Graphics Processing Unit) accelerated calculations in comparison to conventional CPU (Central Processing Unit) calculations.

Inhibition of thioredoxin A1 from Corynebacterium pseudotuberculosis by polyanions and flavonoids

In pathogens, the thioredoxin system forms part of the defense against oxidative stress and ensures the formation of the proper disulfide bonds to ensure protein function. In Corynebacterium pseudotuberculosis, the role and mechanism of TrxA1 has not been elucidated, but, the significant homology among different Trxs and the conservation of the residues that form their active sites underline the importance of the Trx systems. Proteins involved in redox metabolism and low molecular weight thiols, which might interact with them, become attractive targets to modulate the activity of pathogens. The activity of the protein was investigated using a turbidimetric assay system. The influence of different pH and low molecular weight thiols were tested. Additionally, this assay was used to investigate the inhibitory potential of ligands from different molecular families, such as, polyanions (suramin and heparin) and flavonoids (hesperetin and hesperidin). All four compounds showed inhibition of the protein activity by approximately 80%. The interactions between these compounds and Cp-TrxA1 were investigated using CD spectroscopy, NMR, molecular docking and dynamics. Our results demonstrate that suramin and hesperetin can serve as lead molecules for the development of specific inhibitors for the C. pseudotuberculosis TrxA1.

Design, Synthesis and Anticancer Biological Evaluation of Novel 1,4-Diaryl- 1,2,3-triazole Retinoid Analogues of Tamibarotene (AM80)

We report herein the design and synthesis via click chemistry of twelve novel triazole retinoid analogues of tamibarotene (AM80) and the evaluation of their anticancer activities against six cancer cell lines: HL60, K562, 786, HT29, MCF7 and PC3. Among the synthesized compounds, two were more potent than tamibarotene against solid tumor cells, and one of them had similar potency to tamibarotene against HL60 cells. The bioisosteric exchange between the amide group and the 1,2,3-triazole core in the retinoid agent tamibarotene (AM80) reported in this work is a valid strategy for the generation of useful compounds against cancer.