Cadiolide analogues and their precursors as new inhibitors of bacterial quorum sensing and biofilm formation.

Bacterial quorum sensing (QS) and biofilm formation are promising targets for developing new therapies to treat chronic infections. Herein, we report the stereoselective synthesis of 18 new analogs of natural cadiolides. Among the new compounds, substances 8b, 8f, 8i, 9a, 9b and 9e completely inhibited the biofilm formation of Escherichia coli RP347 in vitro. In addition, compound 8b interfered acyl-homoserine lactone (AHL) mediated QS, while 9e interrupted the QS via autoinducer-2 (AI-2). Biological assays also revealed that synthetic intermediates alkynones are potent inhibitors of AI-2 and AHL-mediated QS. These results indicate that cadiolides and alkynones are good candidates for further structural modification for a new generation of more potent antimicrobial agents.

Natural product-inspired profluorophores for imaging NQO1 activity in tumour tissues.

Herein we designed a collection of trimethyl-lock quinone profluorophores as activity-based probes for imaging NAD(P)H:quinone oxidoreductase (NQO1) in cancer cells and tumour tissues. Profluorophores were prepared via synthetic routes from naturally-occurring quinones and characterised in vitro using recombinant enzymes, to be further validated in cells and fresh frozen canine tumour tissues as potential new tools for cancer detection and imaging.

Synthesis of Selenium-Quinone Hybrid Compounds with Potential Antitumor Activity via Rh-Catalyzed C-H Bond Activation and Click Reactions.

In continuation of our quest for new redox-modulating catalytic antitumor molecules, selenium-containing quinone-based 1,2,3-triazoles were synthesized using rhodium-catalyzed C-H bond activation and click reactions. All compounds were evaluated against five types of cancer cell lines: HL-60 (human promyelocytic leukemia cells), HCT-116 (human colon carcinoma cells), SF295 (human glioblastoma cells), NCIH-460 (human lung cells) and PC3 (human prostate cancer cells). Some compounds showed good activity with IC50 values below 1 µM. The cytotoxic potential of the naphthoquinoidal derivatives was also evaluated in non-tumor cells, exemplified by L929 cells. Overall, these compounds represent promising new lead derivatives and stand for a new class of chalcogenium-containing derivatives with potential antitumor activity.

Imidazoles from nitroallylic acetates and α-bromonitroalkenes with amidines: synthesis and trypanocidal activity studies.

Cascade reactions of amidines with nitroallylic acetates and α-bromonitroalkenes provide potentially bioactive imidazoles in good to excellent yields in most cases. While 2,4-disubstituted imidazol-5-yl acetates are formed in the first case, 2,4-disubstituted imidazoles, bearing no substituent at position 5, are the products in the second case. These two series of imidazoles, viz. 2,4,5-trisubstituted and 2,4-disubstituted, were screened for their activity against the protozoan parasite Trypanosoma cruzi which is responsible for Chagas disease. As many as three compounds were as active as the standard benznidazole and two others were 2-3-fold more active highlighting the potential of substituted imidazoles, easily accessible from nitroalkenes, as possible anti-parasitic agents.

Synthesis of imidazoles via cascade reaction of nitroallylic acetates with amidines and studies on their trypanocidal activity.

A one-pot, two step synthesis of highly substituted imidazoles has been carried out in good to excellent yields for the first time via a cascade intermolecular aza-SN2'-intramolecular aza-Michael addition involving a variety of Morita-Baylis-Hillman acetates of nitroalkenes and amidines in the presence of DABCO at room temperature. The synthetic and biological utility of the products has been demonstrated. In particular, some of the imidazoles exhibited potent activity against T. cruzi, the etiological agent of Chagas disease.

1,2,3-triazole-, arylamino- and thio-substituted 1,4-naphthoquinones: potent antitumor activity, electrochemical aspects, and bioisosteric replacement of C-ring-modified lapachones.

1,2,3-Triazole-, arylamino- and thio-substituted naphthoquinones (24, 8, and 2 representatives, respectively) were synthesized in moderate yields and evaluated against several human cancer cell lines (blood, ovarian, breast, central nervous system, colon, and prostate cancers and melanoma), showing, for some of them, IC50 values below 2 µM. The cytotoxic potential of the tested naphthoquinones was also assayed on non-tumor cells such as human peripheral blood mononucluear cells (PBMC) and two murine fibroblast lines (L929 and V79 cells). α-Lapachone- and nor-α-lapachone-based 1,2,3-triazoles and arylamino-substituted naphthoquinones showed potent cytotoxicity against different cancer cell lines. The compounds may represent promising new lead derivatives for anticancer drug development. The electrochemical properties of selected compounds were evaluated in an attempt to correlate them with antitumor activity.

Synthesis and anti-Trypanosoma cruzi activity of naphthoquinone-containing triazoles: electrochemical studies on the effects of the quinoidal moiety.

In our continued search for novel trypanocidal compounds, twenty-six derivatives of para- and ortho-naphthoquinones coupled to 1,2,3-triazoles were synthesized. These compounds were evaluated against the infective bloodstream form of Trypanosoma cruzi, the etiological agent of Chagas disease. Compounds 17-24, 28-30 and 36-38 are described herein for the first time. Three of these novel compounds (28-30) were found to be more potent than the standard drug benznidazole, with IC50/24h values between 6.8 and 80.8µM. Analysis of the toxicity to heart muscle cells led to LC50/24h of <125, 63.1 and 281.6µM for 28, 29 and 30, respectively. Displaying a selectivity index of 34.3, compound 30 will be further evaluated in vivo. The electrochemical properties of selected compounds were evaluated in an attempt to find correlations with trypanocidal activity, and it was observed that more electrophilic quinones were generally more potent.

It takes two to tango: synthesis of cytotoxic quinones containing two redox active centers with potential antitumor activity.

We report the synthesis of 47 new quinone-based derivatives via click chemistry and their subsequent evaluation against cancer cell lines and the control L929 murine fibroblast cell line. These compounds combine two redox centers, such as an ortho-quinone/para-quinone or quinones/selenium with the 1,2,3-triazole nucleus. Several of these compounds present IC50 values below 0.5 µM in cancer cell lines with significantly lower cytotoxicity in the control cell line L929 and good selectivity index. Hence, our study confirms the use of a complete and very diverse range of quinone compounds with potential application against certain cancer cell lines.

Synthesis of quinone imine and sulphur-containing compounds with antitumor and trypanocidal activities: redox and biological implications.

Ortho-Quinones represent a special class of redox active compounds associated with a spectrum of pronounced biological activities, including selective cytotoxicity and antimicrobial actions. The modification of the quinone ring by simple nitrogen and sulphur substitutions leads to several new classes of compounds with their own, distinct redox behaviour and equally distinct activities against cancer cell lines and Trypanosoma cruzi. Some of the compounds investigated show activity against T. cruzi at concentrations of 24.3 and 65.6 µM with a selectivity index of around 1. These results demonstrate that simple chemical modifications on the ortho-quinone ring system, in particular, by heteroatoms such as nitrogen and sulphur, transform these simple redox molecules into powerful cytotoxic agents with considerable "potential", not only in synthesis and electrochemistry, but also, in a broader sense, in health sciences.

Hybrid compounds with two redox centres: modular synthesis of chalcogen-containing lapachones and studies on their antitumor activity.

Chalcogen-containing ß-lapachone derivatives were synthesized using a straightforward methodology and evaluated against several cancer cell lines (leukaemia, human colon carcinoma, prostate, human metastatic prostate, ovarian, central nervous system and breast), showing, in some cases, IC50 values below 1 µM. The cytotoxic potential of the lapachones evaluated was also assayed using non-tumor cells: human peripheral blood mononuclear cells, two murine fibroblast lines (L929 and V79 cells) and MDCK (canine kidney epithelial cells). These compounds could provide promising new lead derivatives for anticancer drug development. This manuscript reports important findings since few authors have described C-3 substituted ß-lapachone with potent antitumor activity. The methodology employed allowed the preparation of the compounds from lapachol within a few minutes in a green approach.

Potent naphthoquinones against antimony-sensitive and -resistant Leishmania parasites: synthesis of novel α- and nor-α-lapachone-based 1,2,3-triazoles by copper-catalyzed azide-alkyne cycloaddition.

Continuing our screening program for novel anti-parasite compounds, we synthesized seven 1,4-naphthoquinones coupled to 1,2,3-triazoles, five nor-ß-lapachone-based 1,2,3-triazoles and ten α-lapachone-based 1,2,3-triazoles. These and other naphthoquinonoid compounds were evaluated for their activity against promastigote forms of antimony-sensitive and -resistant strains of Leishmania infantum (syn. Leishmania chagasi) and Leishmania amazonensis. The toxicity of these compounds to mammalian cells was also examined. The substances were more potent than an antimonial drug, with IC50 values ranging from 1.0 to 50.7 µM. Nor-α-lapachone derivatives showed the highest antileishmanial activity, with selectivity indices in the range of 10-15. These compounds emerged as important leads for further investigation as antileishmanial agents. Additionally, one of these compounds exhibited cross-resistance in Sb-resistant Leishmania and could provide a molecular tool for investigating the multidrug resistance mechanisms in Leishmania parasites.

On the search for potential anti-Trypanosoma cruzi drugs: synthesis and biological evaluation of 2-hydroxy-3-methylamino and 1,2,3-triazolic naphthoquinoidal compounds obtained by click chemistry reactions.

Five 2-hydroxy-3-substituted-aminomethyl naphthoquinones, nine 1,2,3-triazolic para-naphthoquinones, five nor-ß-lapachone-based 1,2,3-triazoles, and several other naphthoquinonoid compounds were synthesized and evaluated against the infective bloodstream form of Trypanosoma cruzi, the etiological agent of Chagas disease, continuing our screening program for new trypanocidal compounds. Among all the substances, 16-18, 23, 25-29 and 30-33 were herein described for the first time and fifteen substances were identified as more potent than the standard drug benznidazole, with IC(50)/24h values in the range of 10.9-101.5 µM. Compounds 14 and 19 with Selectivity Index of 18.9 and 6.1 are important structures for further studies.