From the recent development of catalytically controlled C-H activation with amenable synthetic routes obviating many challenges, the demand for this strategy has raised significantly to perform complex organic transformations. The impact of the achieved results in both homogeneous and heterogeneous catalysis reflects its efficacy in modern synthetic chemistry. A consolidated report and guidance of the methodologies involved in the previous and ongoing research in this domain would be very useful for the researchers to focus on more specific and selective C-H activation reactions to access desired complex molecular scaffolds. The perspective of this review is to contribute to the scientific community with examples, tips and details of modern development in this field and with a complete illustration of the routes which may be effective for planning of the ubiquitous C-H bond activation and its use for synthesis of relevant organic molecules.

Fifteen naphthoquinones, sixteen phenazines and fifteen aryl triazoles were synthesized and evaluated against Mycobacterium tuberculosis. Twenty five substances are reported here for the first time and, among all of the compounds evaluated, six presented MIC (minimal inhibitory concentration) values < 6.25 µg mL-1. These substances are promising antimycobacterial prototypes.

A doença de Chagas causada pelo Trypanosoma cruzi afeta cerca de oito milhões de pessoas em países em desenvolvimento, sendo classificada como uma doença tropical negligenciada pela Organização Mundial da Saúde. A quimioterapia disponível para esta doença é baseada em dois nitro-heterocíclicos, nifurtimox e benznidazol, ambos com graves efeitos colaterais e eficácia variável, e assim novos medicamentos visando um tratamento mais eficiente são necessários com urgência. Nos últimos 20 anos, temos desenvolvido em colaboração com grupos focados em química medicinal, um programa de quimioterapia experimental da doença de Chagas, investigando a eficácia, seletividade, toxicidade, alvos celulares e mecanismos de ação de diferentes classes de compostos sobre T. cruzi. Neste artigo, apresentamos uma visão geral desses estudos, enfocando protótipos naftoquinoidais e derivados, examinando a sua síntese, a atividade e mecanismo de ação, o que foi realizado e o que precisa ser abordado, avaliando e discutindo possíveis melhorias. Esta mini-revisão discute nosso esforço continuado visando a caracterização biológica e a síntese de compostos naftoquinoidais, auxiliando no desenvolvimento de um novo arsenal de drogas candidatas com eficácia contra o T. cruzi.

Chagas disease is caused by the parasite Trypanosoma cruzi and affects approximately eight million individuals in the developing world; it is also classified as a neglected tropical disease by the World Health Organization. The available therapy for this disease is based on two nitroheterocycles, nifurtimox and benznidazole, both of which exhibit severe side effects and variable efficacy; therefore, new drugs and better treatment schedules are urgently needed. For the past 20 years, we have been collaborating with groups focused on medicinal chemistry to produce experimental therapies for Chagas disease by investigating the efficacy, selectivity, toxicity, cellular targets and mechanisms of action of different classes of compounds against T. cruzi. In this report, we present an overview of these studies, focusing on naphthoquinonoid prototypes and discuss their synthesis, activity and mechanisms of action. Furthermore, we summarise the research that has been performed to date and suggest future research directions while assessing and discussing potential improvements. This mini-review discusses our continued efforts toward the biological characterisation and synthesis of naphthoquinoidal compounds, aiming to contribute to the development of a new arsenal of candidate drugs that exhibit effective anti-T. cruzi activity

Due to the recent advances of atovaquone, a naphthoquinone, through clinical trials as treatment for malarial infection, 19 quinone derivatives with previously reported structures were also evaluated for blood schizonticide activity against the malaria parasite Plasmodium falciparum. These compounds include 2-hydroxy-3-methylamino naphthoquinones (2-9), lapachol (10), nor-lapachol (11), iso-lapachol (12), phthiocol (13) and phenazines (12-20). Their cytotoxicities were also evaluated against human hepatoma and normal monkey kidney cell lines. Compounds 2 and 5 showed the highest activity against P. falciparum chloroquine-resistant blood-stage parasites (clone W2), indicated by their low inhibitory concentration for 50% (IC50) of parasite growth. The therapeutic potential of the active compounds was evaluated according to the selectivity index, which is a ratio of the cytotoxicity minimum lethal dose which eliminates 50% of cells and the in vitro IC50. Naphthoquinones 2 and 5, with activities similar to the reference antimalarial chloroquine, were also active against malaria in mice and suppressed parasitaemia by more than 60% in contrast to compound 11 which was inactive. Based on their in vitro and in vivo activities, compounds 2 and 5 are considered promising molecules for antimalarial treatment and warrant further study.

O presente estudo descreve a acentuada atividade citotóxica da nor-β-lapachona, seus derivados arilamino substituídos, naftoquinonas iodadas e metilada, além de nor-β-lapachonas 1,2,3-triazólicas, contra quatro linhagens de células de leucemia humana (HL-60, K562, Molt-4 e Jurkat). Nor-β-lapachonas arilamino substituídas foram identificadas com potente atividade, revelando-se como potenciais protótipos contra as linhagens tumorais descritas. Estudos utilizando o ensaio cometa evidenciaram danos ao ácido desoxirribonucleico (ADN) causado pelos derivados arilamino substituídos devido o aumento dos níveis intracelulares de espécies reativas de oxigênio (ERO's). Células de HL-60 foram selecionadas para a continuidade dos estudos de mecanismos moleculares subjacentes e apoptose induzida pelos derivados quinoidais foi observada por análise de citometria de fluxo. Cepas de Saccharomyces cerevisiae foram utilizadas para uma investigação preliminar sobre o mecanismo de ação em topoisomerases de ADN. Os estudos sugerem que, aparentemente, a citotoxidade dos compostos não envolve a inibição de topoisomerases, mas que o tratamento prejudica a atividade de reparação do ADN, provocando assim a morte celular. A capacidade em induzir apoptose e aberrações cromossômicas em fibroblastos de pulmão de hamster chinês (células V79) também foi investigada. Núcleos apoptóticos foram observados e nossos estudos indicam uma correlação entre dano ao ADN e apoptose.

The current study describes that nor-β-lapachone and its arylamino derivatives, iodinated and methylated naphthoquinones and nor-β-lapachone-based 1,2,3-triazoles exhibited pronounced cytotoxic effects against four human leukemia cell lines (HL-60, K562, Molt-4 and Jurkat). Nor-β-lapachones arylamino substituted with potent activity were identified, revealing themselves as potential prototypes against tumor cell lines. Moreover, cells treated with these compounds showed DNA damage according to the standard comet assay, a finding that was, at least in part, due to increased intracellular levels of ROS. HL-60 cells were chosen to study the underlying molecular mechanisms of cytotoxicity. Drug-induced apoptosis in HL-60 cells was observed by flow cytometry analyses. Strains of Saccharomyces cerevisiae were used for a preliminary investigation into the mechanism of drug action on DNA topoisomerases. These results suggested that the cytotoxicity of these compounds apparently does not involve topoisomerase inhibition, but that treatment impairs DNA repair activity, thus triggering cell death. Considering their pro-oxidant properties, we investigated the ability of these compounds to induce apoptosis and chromosomal aberrations as micronuclei in Chinese hamster lung fibroblasts (V79 cells). Morphological apoptotic nuclei and micronuclei induction following drug treatment were observed, suggesting a correlation between DNA damage and apoptosis.

A atividade citotóxica de cinco derivados 1,2,3-triazólicos da nor-²-lapachona e do precursor azidonaftoquinona, foi avaliada contra seis linhagens de células neoplásicas: SF-295 (sistema nervoso central), HCT-8 (cólon), MDAMB-435 (melanoma), HL-60 (leucemia), PC-3 (próstata) e B-16 (melanoma murino). Valores de IC50 entre 0,43 e 9,48 µM foram obtidos. A 3-(4-(1-hidróxicicloexil)-1H-1,2,3-triazol-1-il)-2,2-dimetilnaftol[1,2-b]furan-4,5-dione apresentou-se altamente citotóxica contra MDAMB-435, com IC50 menor do que o encontrado para doxorubicina (controle positivo). Na tentativa de obter correlação entre parâmetros físico-químicos (potencial de redução e clog P) e atividade citotóxica, estudos eletroquímicos foram realizados em tampão acetato, pH 4,5, em eletrodo de carbono vítreo, e valores de log P calculados (clog P). Apesar da ausência de interação estrutural conjugativa entre o sistema quinônico e o anel triazólico, observou-se a influência do anel heterocíclico no comportamento voltamétrico, com deslocamento anódico dos potenciais de redução. Não se verificou correlação entre os parâmetros eletroquímicos (EpIc) e a atividade citotóxica. Por outro lado, a comparação de EpIc com atividades tripanocidas, já descritas, reafirmou a tendência de maior atividade biológica para quinonas mais eletrofílicas (> EpIc). Apesar da ausência de correlação direta, foi possível verificar que clog P influencia a atividade citotóxica: quanto menor a lipofilia (< clog P), menor a citotoxicidade (> IC50).

The cytotoxicities of five nor-²-lapachone-based 1,2,3-triazoles and the precursor azidonaphthoquinone were assayed against six neoplasic cancer cell lines: SF-295 (central nervous system), HCT-8 (colon), MDAMB-435 (melanoma), HL-60 (leukaemia), PC-3 (prostate) and B-16 (murine melanoma). IC50 values ranging from 0.43 to 9.48 µM were obtained. 3-(4-(1-hydroxycyclohexyl)-1H-1,2,3-triazol-1yl)-2,2-dimethylnaphtho[1,2-b]furan-4,5-dione proved highly cytotoxic to MDAMB-435, with IC50 even lower than the one from doxorubicin (positive control). In an attempt to correlate physicochemical parameters (reduction potentials and calculated log P) with cytotoxic activity, electrochemical studies were conducted in acetate buffer, pH 4.5, using a vitreous carbon electrode and calculated log P values were obtained. Despite the absence of a structural conjugative interaction between the two systems (quinone and triazole), the heterocyclic group was found to influence the voltammetric behaviour, as indicated by anodic shifts in the reduction potentials. No correlation was found between EpIc and cytotoxicity. In contrast, a comparison of EpIc with previously reported trypanocidal activities reconfirmed the trend for higher activity coupled with better quinone electrophilicity (> EpIc).A leading term in the correlation of cytoxicity, despite the absence of a linear correlation, was the calculated log P: the lower the lipophilicity, the lower the cytoxicity (> IC50).