Cleiton M. da Silva

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.

From Nature to Market: Examples of Natural Products that Became Drugs

Nature is an irrefutable source of inspiration for the modern man in many aspects. The observation and understanding of nature have allowed the development of new materials, new sources of energies, new drugs etc. Specifically, natural products provide a great contribution to the development of new agents for the treatment of infections and antitumor agents. However, obtaining natural products directly from animals, fungi, bacteria, plants etc has been considered not enough to attend the high demand by pharmaceutical industries. In this regard, various strategies based on biotechnological processes or synthetic approaches have been developed. In this scenario the total synthesis can be undoubtedly a useful and powerful tool for obtaining higher amounts of natural products and/or structural modifications thereof. Herein, we emphasize successful examples of total synthesis of galanthamine, morphine, paclitaxel and podophyllotoxin - natural products approved as pharmaceuticals.

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.

Solvatomorphs of 25,26,27,28-tetrahydroxycalix[4]arene and 5,11,17,23-tetramino-25,26,27,28-tetrabutoxycalix[4]arene: quenching photoluminescence through switching the guest

Here, we have disclosed two solid state forms of 5,11,17,23-tetramino-25,26,27,28-tetrabutoxycalix[4]arene (1) and two solid state forms of the non-functionalized 25,26,27,28-tetrahydroxycalix[4]arene (2). This is the first structural knowledge of a tetra-amino functionalized calixarene derivative, even though this compound is well known and used as a precursor of several other functionalized calix[4]arenes. The two solid forms of 1 differ by the presence of either water or water/dimethylsulfoxide (DMSO) solvent molecules entrapped in the major calixarene cavity, even though the pinched conformation is adopted in both forms as a consequence of the contacts between solvent molecules and phenyl rings. Likewise, the switch from water to DMSO in the cone cavity of 1 has abrogated the photoluminescence (PL) found only in the dihydrate form. Frontier molecular orbital calculations at the B3LYP/6-31G* level of theory support a short-range electron transfer between guest (DMSO) and host (1) molecules quenching the solid state photoluminescence when DMSO is entrapped in the cone. This solvatomorphism approach for PL search in calixarenes opens a perspective on tuning and even increasing the performance of calixarenes through changing the guest solvent molecule. Similarly, the two crystal forms of 2 entrap either methyl alcohol or DMSO in their cones, which, as well as both crystal forms of 1, are packed into sheets through different fashions and contact patterns.

Copper(II) Nitroaromatic Schiff Base Complexes: Synthesis, Biological Activity and Their Interaction with DNA and Albumins

Copper(II) complexes of the Schiff base ligands 2-((5-nitrofuran-2-yl)methyleneamino)phenol (HL1) and 2-(4-nitrobenzylideneamino)phenol (HL2) were prepared and characterized using physicochemical and spectroscopic techniques. In these complexes the Schiff base ligands acted as a bidentate donor bound to Cu2+ through the oxygen and nitrogen atoms in the deprotonated form. The electron paramagnetic resonance spectra, carried out on [CuCl(L1)(phen)].0.5H2O and [CuCl(L2)(phen)].2H2O complexes, showed the presence of only mononuclear forms. The Cu2+ complexes and ligands were evaluated for their in vitro trypanocidal activity. The complex [CuCl(L1)(phen)].0.5H2O was more active than the free Schiff base and also presented a superior effect to benznidazole, the reference drug. The antiproliferative activity of the Schiff bases and Cu2+ complexes were evaluated for their effect on seven tumor cell lines and showed a cytostatic and in some cases a cytotoxic effect. These compounds also presented binding properties to deoxyribonucleic acid (DNA) and moderate ability to quench the intrinsic fluorescence of albumins.

Lower rim dimerization of a calixarene through the encapsulation of sodium ions

Here we report the tail-to-tail dimerization of tetra(carboxymethoxy)calix[4]arene in both solution and solid state phases using ESI-orbitrap UHRMS, 1H-NMR and single-crystal X-ray diffraction techniques. Three sodium ions are encapsulated into the dimeric structure which is also stabilized by hydrogen bonds between carboxyl moieties undergoing partial deprotonation.

Highly functionalized piperidines: Free radical scavenging, anticancer activity, DNA interaction and correlation with biological activity

Graphical abstract

Synthesis, in vitro and in vivo anti-Trypanosoma cruzi and toxicological activities of nitroaromatic Schiff bases

Chagas disease is a major health problem not only in Latin America but also in Europe and North America due to the spread of this disease into nonendemic areas. In terms of global burden, this major tropical infection is considered to be one of the most neglected diseases, and there are currently only two available chemotherapies: benznidazole and nifurtimox. Unfortunately, although these chemotherapies are beneficial in the acute phase of the disease, benznidazole and nifurtimox lead to significant side effects, including hepatitis and neurotoxicity. Therefore, the search for and development of more effective, safe and inexpensive anti-Trypanosoma cruzi drugs are required. In this work, a series of 10 nitroaromatic Schiff bases bearing different (nitro) aromatic rings-was synthesized. Subsequently, the in vitro and in vivo anti-T. cruzi activities of the Schiff bases were investigated, as well as the in vivo toxicity and the biological effects. The basic structure of the most promising in vivo Schiff base, 10 would be useful in the synthesis of new compounds for Chagas disease treatment.