Design, synthesis and biological evaluation of novel 5-bromo derivatives of indole phytoalexins

The increasing diversity of small molecule libraries is a major source for the discovery of new drug candidates. In term of this trend, we report the synthesis five series 5-bromosubstituted derivatives of indole phytoalexins Type A-E using straightforward synthetic approach. Novel compounds were screened in vitro for antiproliferative/cytotoxic activity against seven human cancer cell lines by MTT assay. Evaluation of their antiproliferative potency showed that the activity of some analogues was better or comparable to that of cisplatin and at the same time the toxicity of these compounds on 3T3 cells was lower than that of cisplatin. We found that all 5-bromosubstituted analogues of indole phytoalexins Type A-E exhibited lower or approximately the same activities as a previously studied corrensponding non-brominated compounds.

Mechanochemical Synthesis and Isomerization of N-Substituted Indole-3-carboxaldehyde Oximes †

Performing solution-phase oximation reactions with hydroxylamine hydrochloride (NH2OH·HCl) carries significant risk, especially in aqueous solutions. In the present study, four N-substituted indole-3-carboxaldehyde oximes were prepared from the corresponding aldehydes by solvent-free reaction with NH2OH·HCl and a base (NaOH or Na2CO3) using a mechanochemical approach, thus minimizing the possible risk. In all cases, the conversion to oximes was almost complete. The focus of this work is on 1-methoxyindole-3-carboxaldehyde oxime, a key intermediate in the production of indole phytoalexins with useful antimicrobial properties. Under optimized conditions, it was possible to reach almost 95% yield after 20 min of milling. Moreover, for the products containing electron-donating substituents (-CH3, -OCH3), the isomerization from the oxime anti to syn isomer under acidic conditions was discovered. For the 1-methoxy analog, the acidic isomerization of pure isomers in solution resulted in the formation of anti isomer, whereas the prevalence of syn isomer was observed in solid state. From NMR data the syn and anti structures of produced oximes were elucidated. This work shows an interesting and possibly scalable alternative to classical synthesis and underlines environmentally friendly and sustainable character of mechanochemistry.

The Indole Phytoalexin Derivatives Induced a Significant Inhibition on Src Kinase Activity of Human Cancer Cells

The Src, a protein kinase, is a family of protein tyrosine kinases (SFKs), and this protein catalyses the phosphorylation of tyrosine. The studies have revealed its key roles in regulating signal transduction from cell surface receptors. The Src kinases act as cytoplasmic signalling machinery through regulating various cellular processes, such as cell growth, differentiation, migration, and survival. The pleiotropic functions of the Src family emphasise the importance of family members which have also been accepted as cellular oncogenes. Indole phytoalexins, which have been identified in various plants, have a structure with indole nucleus with the side chain or a heterocycle containing nitrogen and sulphur atoms. The antiproliferative effects of some phytoalexins have been demonstrated in various cancers. Among the members of phytoalexins, brassinin is known with a dithiocarbamate moiety and S-alkyl piece linked to indole core, and camalexin has an indole structure substituted at position 3 by the 1,3-thiazol-2-yl group. The inhibitory effects of these compounds on cancer cell proliferation have been reported. The aim of this study is to evaluate the effects of compounds on Src kinase activity. Human MCF-7 breast carcinoma and SW480 colorectal carcinoma cells were treated with compounds, and the effects of compounds on Src kinase activity were evaluated by Src-tyrosine kinase assay. The data were also compared with the growth inhibitory potential of compounds. The results have shown that both brassinin and camalexin have significantly inhibited the activity of Src kinase at 10 mM and higher concentrations in MCF-7 and SW480 cell lines (p < 0.05). In conclusion, this study is the first to evaluate the role of indole phytoalexins on the Src kinase activity of cancer cells. The data obtained have proven that the indole phytoalexin structure can show anticancer activity as Src mediated. It is thought that existing data will shed light on novel anticancer drug development studies.