Synthesis of a polyprenyl-type library containing 1,4-disubstituted-1,2,3-triazoles with anti-biofilm activities against Pseudoalteromonas sp

Natural Product-Based 1,2,3-Triazole/Sulfonate Analogues as Potential Chemotherapeutic Agents for Bacterial Infections

Despite the vast availability of antibiotics, bacterial infections remain a leading cause of death worldwide. In an effort to enhance the armamentarium against resistant bacterial strains, 1,2,3-triazole (5a-x) and sulfonate (7a-j) analogues of natural bioactive precursors were designed and synthesized. Preliminary screening against two Gram-positive (Streptococcus pneumoniae and Enterococcus faecalis) and four Gram-negative bacterial strains (Pseudomonas aeruginosa, Salmonella enterica, Klebsiella pneumoniae, and Escherichia coli) was performed to assess the potency of these analogues as antibacterial agents. Among all triazole analogues, 5e (derived from carvacrol) and 5u (derived from 2-hydroxy 1,4-naphthoquinone) bearing carboxylic acid functionality emerged as potent antibacterial agents against S. pneumoniae (IC₅₀: 62.53 and 39.33 μg/mL), E. faecalis (IC₅₀: 36.66 and 61.09 μg/mL), and E. coli (IC₅₀: 15.28 and 22.57 μg/mL). Furthermore, 5e and 5u also demonstrated moderate efficacy against multidrug-resistant E. coli strains and were therefore selected for further biological studies. Compound 5e in combination with ciprofloxacin displayed a synergistic effect on multidrug-resistant E. coli MRA11 and MRC17 strains, whereas compound 5u was selective against E. coli MRA11 strain. Growth kinetic studies on S. pneumoniae and E. coli treated with 5e and 5u showed an extended lag phase. 5e and 5u did not show significant cytotoxicity up to 100 μg/mL concentration on human embryonic kidney (HEK293) cells. Transmission electron microscopic (TEM) analysis of bacterial cells (S. pneumoniae and E. coli) exposed to 5e and 5u clearly showed morphological changes and damaged cell walls. Moreover, these compounds also significantly inhibited biofilm formation in S. pneumoniae and E. coli strains, which was visualized by scanning electron microscopic (SEM) analysis. Treatment of larvae of Galleria mellonella (an in vivo model for antimicrobial studies) with 5e and 5u did not cause an alteration in the hemocyte density, thereby indicating lack of an immune response, and were nontoxic up to a concentration of 2.5 mg/mL.

Antitrypanosomal and antileishmanial activity of prenyl-1,2,3-triazoles

A series of prenyl 1,2,3-triazoles were prepared from isoprenyl azides and different alkynes. The dipolar cycloaddition reaction provided exclusively primary azide products as regioisomeric mixtures that were separated by column chromatography and fully characterized. Most of the compounds displayed antiparasitic activity against Trypanosoma cruzi and Leishmania donovani. The most active compounds were assayed as potential TcCYP51 inhibitors.

Experimental and theoretical studies of the [3,3]-sigmatropic rearrangement of prenyl azides

[3,3]-Sigmatropic rearrangement of isoprenyl azides has been extensively investigated in an experimental and theoretical level.

Screening of bromotyramine analogues as antifouling compounds against marine bacteria

Rapid and efficient synthesis of 23 analogues inspired by bromotyramine derivatives, marine natural products, by means of CuSO4-catalysed [3+2] alkyne-azide cycloaddition is described. The final target was then assayed for anti-biofilm activity against three Gram-negative marine bacteria, Pseudoalteromonas ulvae (TC14), Pseudoalteromonas lipolytica (TC8) and Paracoccus sp. (4M6). Most of the synthesised bromotyramine/triazole derivatives are more active than the parent natural products Moloka'iamine (A) and 3,5-dibromo-4-methoxy-β-phenethylamine (B) against biofilm formation by the three bacterial strains. Some of these compounds were shown to act as non-toxic inhibitors of biofilm development with EC50 < 200 μM without any effect on bacterial growth even at high concentrations (200 μM).

Triazole-based inhibitors of geranylgeranyltransferase II

A small set of triazole bisphosphonates has been prepared and tested for the ability to inhibit geranylgeranyltransferase II (GGTase II). The compounds were prepared through use of click chemistry to assemble a central triazole that links a polar head group to a hydrophobic tail. The resulting compounds were tested for their ability to inhibit GGTase II in an in vitro enzyme assay and also were tested for cytotoxic activity in an MTT assay with the human myeloma RPMI-8226 cell line. The most potent enzyme inhibitor was the triazole with a geranylgeranyl tail, which suggests that inhibitors that can access the enzyme region that holds the isoprenoid tail will display greater activity.

Designing 2-aminoimidazole alkaloids analogs with anti-biofilm activities: structure-activities relationships of polysubstituted triazoles

In order to discover novel probes that may help in the investigation and the control of bacterial biofilms, we have designed a library of triazole-based analogs of 2-aminoimidazole marine alkaloids: naamine A and isonaamine A. Twenty-two compounds were screened for their biofilm inhibitory activity against two strains of Gram-negative bacteria. Four compounds were shown to act as non-toxic inhibitors of biofilm development without effect on bacterial growth even at high concentrations (100 μM).

Potential of medicinal plants from the Brazilian semi-arid region (Caatinga) against Staphylococcus epidermidis planktonic and biofilm lifestyles

ETHNOPHARMACOLOGICAL RELEVANCE

Medicinal plants from the Caatinga, a Brazilian xeric shrubland, are used in folk medicine to treat infections. These ethnopharmacological data can contribute to obtaining new antimicrobial/antibiofilm extracts and natural product prototypes for the development of new drugs. The aim of this study was to investigate the antibiofilm and antibacterial activities of 45 aqueous extracts from 24 Caatinga plant species.

MATERIALS AND METHODS

The effect of aqueous extracts on planktonic cells and on biofilm formation by Staphylococcus epidermidis was studied by the OD(600) absorbance and by the crystal violet assay, respectively. Scanning electron microscopy (SEM) was used to generate comparative images of extract-treated and untreated biofilms. Chromatographic analyses were performed to characterize the active extracts.

RESULTS

The in vitro screening, at 0.4 mg/mL and 4.0mg/mL, showed 20 plants effective in preventing biofilm formation and 13 plants able to inhibit planktonic bacterial growth. SEM images demonstrated distinct profiles of bacterial adhesion, matrix production and cell morphology according to different treatments and surfaces. The phytochemical analysis of the selected active extracts indicates the polyphenols, coumarins, steroids and terpenes as possible active compounds.

CONCLUSION

This study describes the first antibiofilm and antibacterial screening of Caatinga plants against S. epidermidis. The evaluation presented in this study confirms several ethnopharmacological reports and can be utilized to identify new antibiofilm and antibacterial products against S. epidermidis from traditional Brazilian medicine.

Antifouling activity of commercial biocides vs. natural and natural-derived products assessed by marine bacteria adhesion bioassay

Biofilm formation is a key step during marine biofouling, the natural colonization of immersed substrata, leading to major economic and ecological consequences. Consequently, bacteria have been used for the screening of new non-toxic antifoulants: the adhesion of five strains isolated on three French locations was monitored using a fluorescence-based assay and toxicity was also evaluated. Nine biocides including commercial, natural and natural-derived products were tested. The commercial antifoulants, TBTO and Sea Nine showed low EC(50) but high toxicity. The non-commercial products TFA-Z showed significant anti-adhesion activities and appeared to be non-toxic, suggesting a specific anti-adhesion mechanism. In addition, the strains could be classified depending on their sensitivity to the molecules used even if strain sensitivity also depended on the molecules tested. In conclusion, TFA-Z would be a promising candidate as non-toxic antifoulant and our results strengthen the need to perform antifouling bioassays with a panel of strains showing different response profiles.