Marcos Pivatto

Ruthenium(II) Complexes Containing Anti-Inflammatory Drugs as Ligands: Synthesis, Characterization and in vitro Cytotoxicity Activities on Cancer Cell Lines

The synthesis, characterization and cytotoxic activity of cis-[Ru(dicl)(dppm)2]PF6 and cis-[Ru(ibu)(dppm)2]PF6, (dppm = 1,1-bis(diphenylphosphine)methane; dicl = diclofenac anion and ibu = ibuprofen anion), are described in this work. Complexes were characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), UV-Vis, 31P{1H} nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRESIMS). X-ray structure of cis-[Ru(ibu)(dppm)2]PF6 is also described. Preliminary calf thymus DNA (ct-DNA) binding studies were carried out by UV-Vis and viscosity experiments, with results suggesting the existence of electrostatic interactions between ruthenium complexes and ct-DNA. Cytotoxicity assays were carried out on a panel of human cancer cell lines and a human normal cell line. Complexes displayed a high to moderate cytotoxicity with IC50 ranging from 5 to 47 µmol L-1. cis-[Ru(ibu) (dppm)2]PF6 was found to be the most active, with IC50 values lower than cisplatin. The degree of cytotoxicity was maintained for the normal cell line, although cis-[Ru(ibu)(dppm)2]PF6 exhibited a similar selectivity to that of cisplatin but with a higher activity for at least two tumor cell lines which evidences a promising anticancer candidate and selects this complex for further experiments.

Antimalarial activity of piperidine alkaloids from Senna spectabilis and semisynthetic derivatives

In our continuing work looking for new anti-infective lead compounds from Brazilian biomes, the two known piperidine alkaloids ( - )-cassine and ( - )-spectaline were isolated from the flowers of Senna spectabilis (syn. Cassia spectabilis). Their structures were elucidated using a combination of spectroscopic and spectrometric data analysis. Further, these compounds were acetylated yielding the derivatives ( - )-3-O-acetylcassine and ( - )-3-O-acetylspectaline. All compounds were screened against P. falciparum-infected red blood cells (RBC) in culture, aiming to identify antimalarial prototypes. Among all compounds screened, the first two alkaloids (IC50 1.82 µM and IC50 2.76 µM) were more effective than the derivatives (IC50 24.47 µM and IC50 25.14 µM) in comparison to the standard compound chloroquine (IC50 0.30 µM). These data show that piperidine alkaloids constitute a class of natural products that feature a broad spectrum of biological activities, and are, therefore, important templates for drug design, including antimalarial.

In vitro evaluation of the schistosomicidal effect of the extracts, fractions and major 3-hydroxy-2,6-dialkyl-substituted piperidine alkaloids from the flowers of Senna spectabilis (Fabaceae)

In this work, we present the in vitro schistosomicidal activity evaluation of the most active dichloromethane fraction (FDm) (ED50=83.5μg/mL) and of a mixture of the major alkaloids ((-)-cassine/(-)-spectaline, C/E) (ED50=37.4μg/mL) from the flowers of Senna spectabilis against adult worms and cercariae. We also demonstrate other toxic effects including paralysis of the adult worms, inhibition of the secretory activity, tegument lesions and cercaricidal activity. In the association test of Praziquantel (PZQ)-C/E, we observed up to 80% mortality of Schistosoma mansoni in comparison to PZQ monotherapy. Due to the diversity of the toxic effects, the schistosomicidal activity of C/E is likely a result of a multitarget mechanism involving the tegument, secretory system and neuromotor action.

Pyridinic analog of the natural product (-)-spectaline as potential adjuvant for the treatment of central nervous system disorders

Previously we designed a series of pyridinic anticholinesterasic compounds based on molecular hybridization between tacrine and the natural piperidine alkaloid (-)-3-O-acetylspectaline isolated from Senna spectabilis. Based on the information that the cholinergic system has an important role in the treatment of schizophrenia and depression, we herein report the evaluation of a series of pyridinic compounds in animal models for antipsychotic and antidepressant-like activities. Compound 2 decreased the immobility time of mice in the forced swimming test (5 and 10mg/kg p.o.) and prevented the climbing behavior induced by apomorphine (10mg/kg, p.o.), without impairing animals locomotor activity.

Mass spectrometry for characterization of homologous piperidine alkaloids and their activity as acetylcholinesterase inhibitors

RATIONALE Piperidine alkaloids from Senna spectabilis constitute a rare class of natural products with several biological activities. However, the absence of chromophores makes their structural elucidation by conventional methods a great challenge. In this context, mass spectrometry emerges as a powerful tool for metabolomics studies. METHODS The piperidine alkaloids (-)-cassine and (-)-spectaline and the semisynthetic derivatives (-)-3-O-acetylcassine and (-)-3-O-acetylspectaline were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in the positive mode and electron ionization mass spectrometry (EI-MS). ESI fragmentation studies were performed with a quadrupole time-of-flight instrument; N2 was used as collision gas. The acetylcholinesterase inhibitory activity of the investigated compounds was evaluated by bioautography and microplate screening assays. RESULTS ESI-MS/MS and EI-MS provided valuable and complementary information about the structure of the piperidine compounds. Collision-induced dissociation experiments (MS/MS) revealed that neutral elimination of water or acetic acid is the major fragmentation pathway, which agrees with the stereochemistry proposed for (-)-cassine and (-)-spectaline and the semisynthetic derivatives (-)-3-O-acetylcassine and (-)-3-O-acetylspectaline. CONCLUSIONS The ESI-MS/MS and EI-MS studies allowed us to propose fragmentation mechanisms for piperidine alkaloids and derivatives. Therefore, mass spectrometry is an important tool for characterizing the structure of these compounds and for supporting further metabolomics studies.

Three new platinum complexes containing fluoroquinolones and DMSO: Cytotoxicity and evaluation against drug-resistant tuberculosis

This work describes the synthesis, characterization and biological evaluation of three platinum complexes of the type [Pt(DMSO)(L)Cl]Cl, in which L represents a fluoroquinolone, namely, ciprofloxacin (cpl), ofloxacin (ofl), or sparfloxacin (spf). The new complexes were characterized by elemental analysis, high-resolution mass spectrometry (HRESIMS) and 1H, 13C and 195Pt NMR (nuclear magnetic resonance). The spectral data suggest that the fluoroquinolones act as bidentate ligands coordinated to Pt(II) through the nitrogen atoms of the piperazine ring. Microbiological assays against wild type Mycobacterium tuberculosis (ATCC 27294) showed that all complexes have been very potent, exhibiting antitubercular potency at concentrations <2 μM, although none of the complexes presented higher potency than established anti-TB drugs. As to the resistant strains, the complex with sparfloxacin, [Pt(DMSO)(spf)Cl]Cl exhibited the best potential against most Mycobacterium tuberculosis clinical isolates. The cytotoxicity of these compounds was also evaluated in three breast cell lines: MCF-10 (a healthy cell), MCF-7 (a hormone responsive cancer cell) and MDA-MB-231 (triple negative breast cancer cell). In both tumor cell lines, [Pt(DMSO)(spf)Cl]Cl was more active and more selective than cisplatin. Flow cytometry analysis revealed that [Pt(DMSO)(spf)Cl]Cl induced late apoptotic cell death in MDA-MB-231 cells.