Synthesis and Biological Properties of Fluorescent Strigolactone Mimics Derived from 1,8-Naphthalimide.

Strigolactones (SLs) have potential to be used in sustainable agriculture to mitigate various stresses that plants have to deal with. The natural SLs, as well as the synthetic analogs, are difficult to obtain in sufficient amounts for practical applications. At the same time, fluorescent SLs would be useful for the mechanistic understanding of their effects based on bio-imaging or spectroscopic techniques. In this study, new fluorescent SL mimics containing a substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive furan-2-one moiety were prepared. The structural, spectroscopic, and biological activity of the new SL mimics on phytopathogens were investigated and compared with previously synthetized fluorescent SL mimics. The chemical group at the C-6 position of the naphthalimide ring influences the fluorescence parameters. All SL mimics showed effects similar to GR24 on phytopathogens, indicating their suitability for practical applications. The pattern of the biological activity depended on the fungal species, SL mimic and concentration, and hyphal order. This dependence is probably related to the specificity of each fungal receptor-SL mimic interaction, which will have to be analyzed in-depth. Based on the biological properties and spectroscopic particularities, one SL mimic could be a good candidate for microscopic and spectroscopic investigations.

An ecotoxicological assessment of a strigolactone mimic used as the active ingredient in a plant biostimulant formulation.

A risk assessment on the aquatic toxicity of the plant biostimulant strigolactone mimic (2-(4-methyl-5-oxo-2,5-dihydro-furan-2-yloxy)-benzo[de]isoquinoline-1,3-dione (SL-6) was performed using a suite of standardised bioassays representing different trophic groups and acute and chronic endpoints. In freshwater, three trophic groups of algae, crustacea and fish were used. Whilst in seawater, algae (unicellular and macroalgae), Crustacea and Mollusca were employed. In addition, the genotoxicity of SL-6 was determined with the comet assessment performed on unicellular marine algae, oysters, and fish embryos. This was the first time ecotoxicity tests have been performed on SL-6. In freshwater, the lowest LOEC was measured in the unicellular algae at 0.31 mg/L SL-6. Although, similar LOEC values were found for embryo malformations and impacts on hatching rate in zebrafish (LOEC 0.31-0.33 mg/L). Consistent malformations of pericardial and yolk sac oedemas were identified in the zebrafish embryos at 0.31 mg/L. In marine species, the lowest LOEC was found for both Tisbe battagliai mortality and microalgae growth at an SL-6 concentration of 1.0 mg/L. Significant genotoxicity was observed above control levels at 0.0031 mg/L SL-6 in the unicellular algae and 0.001 mg/L SL-6 in the oyster and zebrafish larvae. When applying the simple risk assessment, based on the lowest NOECs and appropriate assessment factors, the calculated predicted no effect concentration (PNEC), for the ecotoxicity and the genotoxicity tests were 1.0 µg/L and 0.01 µg/L respectively.

Novel Strigolactone Mimics That Modulate Photosynthesis and Biomass Accumulation in Chlorella sorokiniana.

In terrestrial plants, strigolactones act as multifunctional endo- and exo-signals. On microalgae, the strigolactones determine akin effects: induce symbiosis formation with fungi and bacteria and enhance photosynthesis efficiency and accumulation of biomass. This work aims to synthesize and identify strigolactone mimics that promote photosynthesis and biomass accumulation in microalgae with biotechnological potential. Novel strigolactone mimics easily accessible in significant amounts were prepared and fully characterized. The first two novel compounds contain 3,5-disubstituted aryloxy moieties connected to the bioactive furan-2-one ring. In the second group of compounds, a benzothiazole ring is connected directly through the cyclic nitrogen atom to the bioactive furan-2-one ring. The novel strigolactone mimics were tested on Chlorella sorokiniana NIVA-CHL 176. All tested strigolactones increased the accumulation of chlorophyll b in microalgae biomass. The SL-F3 mimic, 3-(4-methyl-5-oxo-2,5-dihydrofuran-2-yl)-3H-benzothiazol-2-one (7), proved the most efficient. This compound, applied at a concentration of 10-7 M, determined a significant biomass accumulation, higher by more than 15% compared to untreated control, and improved the quantum yield efficiency of photosystem II. SL-F2 mimic, 5-(3,5-dibromophenoxy)-3-methyl-5H-furan-2-one (4), applied at a concentration of 10-9 M, improved protein production and slightly stimulated biomass accumulation. Potential utilization of the new strigolactone mimics as microalgae biostimulants is discussed.

Synthesis and Solvent Dependent Fluorescence of Some Piperidine-Substituted Naphthalimide Derivatives and Consequences for Water Sensing.

Novel fluorescent strigolactone derivatives that contain the piperidine-substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive 3-methyl-furan-2-one unit were synthesized and their spectroscopic properties investigated. The solvatochromic behavior of these piperidine-naphthalimides was monitored in solvents of different polarity using the electronic absorption and fluorescence spectra. These compounds exhibited a strong positive solvatochromism taking into account the change of solvent polarity, and the response mechanism was analyzed by fluorescence lifetime measurements. According to Catalan and [f(n), f(ε), ß, α] solvent scales, the dipolarity and polarizability are relevant to describe the solute-solvent interactions. The emission chemosensing activity was discussed in order to determine the water content in organic environments. The emission intensity of these compounds decreased rapidly in dioxane, increasing water level up to 10%. Measuring of quantum yield indicated that the highest values of quantum efficiency were obtained in nonpolar solvents, while in polar solvents these derivatives revealed the lowest quantum yield. The fluorescence decay can be described by a monoexponential model for low water levels, and for higher water contents a biexponential model was valid.

Schiff bases containing a furoxan moiety as potential nitric oxide donors in plant tissues.

Stable Schiff bases containing a furoxan moiety are synthesized as single regioisomers by the reaction of 3-methyl-2-oxy-furazan-4-carbaldehydewith various amino compounds at room temperature. The structures of synthesized compounds were fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The effect of synthesized Schiff bases containing a furoxan moiety on biological generation of reactive oxygen species and nitric oxide in plant tissues was investigated for the first time by fluorescence microscopy and the released NO identified as nitrite with Griess reagent. There is a good correlation between the biological generation of NO determined by fluorescence microscopy and with Griess reagent. Some of the synthesized compounds exhibited both nitric oxide and reactive oxygen species generation abilities and represent potential NO donors in plant tissues.

New Strigolactone Mimics as Exogenous Signals for Rhizosphere Organisms.

The importance of strigolactones in plant biology prompted us to synthesize simplified strigolactone mimics effective as exogenous signals for rhizosphere organisms. New strigolactone mimics easily derived from simple and available starting materials in significant amounts were prepared and fully characterized. These compounds contain an aromatic or heterocyclic ring, usually present in various bioactive molecules, connected by an ether link to a furan-2-one moiety. The new synthesized strigolactone mimics were confirmed to be active on plant pathogenic fungi and parasitic weed seeds.

Isoxazole derivatives as new nitric oxide elicitors in plants.

Several 3,5-disubstituted isoxazoles were obtained in good yields by regiospecific 1,3-dipolar cycloaddition reactions between aromatic nitrile oxides, generated in situ from the corresponding hydroxyimidoyl chlorides, with non-symmetrical activated alkynes in the presence of catalytic amounts of copper(I) iodide. Effects of 3,5-disubstituted isoxazoles on nitric oxide and reactive oxygen species generation in Arabidopsis tissues was studied using specific diaminofluoresceine dyes as fluorescence indicators.

Indolizines and pyrrolo[1,2-c]pyrimidines decorated with a pyrimidine and a pyridine unit respectively.

The three possible structural isomers of 4-(pyridyl)pyrimidine were employed for the synthesis of new pyrrolo[1,2-c]pyrimidines and new indolizines, by 1,3-dipolar cycloaddition reaction of their corresponding N-ylides generated in situ from their corresponding cycloimmonium bromides. In the case of 4-(3-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine the quaternization reactions occur as expected at the pyridine nitrogen atom leading to pyridinium bromides and consequently to new indolizines via the corresponding pyridinium N-ylides. However, in the case of 4-(2-pyridyl)pyrimidine the steric hindrance directs the reaction to the pyrimidinium N-ylides and, subsequently, to the formation of the pyrrolo[1,2-c]pyrimidines. The new pyrrolo[1,2-c]pyrimidines and the new indolizines were structurally characterized through NMR spectroscopy. The X-ray structures of two of the starting materials, 4-(2-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine, are also reported.

New highlights of the syntheses of pyrrolo[1,2-a]quinoxalin-4-ones.

The one-pot three-component reactions of 1-substituted benzimidazoles with ethyl bromoacetate and electron-deficient alkynes, in 1,2-epoxybutane, gave a variety of pyrrolo[1,2-a]quinoxalin-4-ones and pyrrolo[1,2-a]benzimidazoles. The influence of experimental conditions on the course of reaction was investigated. A novel synthetic pathway starting from benzimidazoles unsubstituted at the five membered ring, alkyl bromoacetates and non-symmetrical electron-deficient alkynes in the molar ratio of 1:2:1, in 1,2-epoxybutane at reflux temperature, led directly to pyrrolo[1,2-a]quinoxalin-4-ones in fair yield by an one-pot three-component reaction.

Fast and green one-pot multicomponent synthesis of a library of pyrrolo [1,2-c] pyrimidines under microwave irradiation.

A simple, clean and rapid one-pot three component, microwave-assisted synthesis of pyrrolo[1,2-c]pyrimidine derivatives starting from various substituted pyrimidines, 2-bromoacetophenones and nonsymmetrical, electron deficient alkynes in 1,2-epoxybutane which acts both as solvent and acid scavenger is reported. This one-pot three component synthesis implies short reaction times being at the same time highly cost-effective and environmental friendly.

Synthesis of pyrrolo[2,1-a]isoquinolines by multicomponent 1,3-dipolar cycloaddition.

Pyrrolo[2,1-a]isoquinoline derivatives were synthesized by one-pot three-component reactions starting from isoquinoline, 2-bromoacetophenones and different non-symmetrical acetylenic dipolarophiles using 1,2-epoxypropane as solvent. The structure of the compounds was assigned by IR and NMR spectroscopy.

Efficient one-pot, three-component synthesis of a library of pyrrolo[1,2-c]pyrimidine derivatives.

Herein is reported a simple and efficient one-pot three-component synthesis of pyrrolo[1,2-c]pyrimidine derivatives starting from various substituted pyrimidines, 2-bromoacetophenones, and electron deficient alkynes in epoxides acting both as reaction medium and HBr scavanger. This method proved to be very lucrative and avoids formation of ylide inactivation products. The synthesis represents an environmentally benign alternative to classical methods. The new library of compounds was briefly characterized regarding the improved Lipinski rule to asses the potential drug-likeness of the compounds. The majority of compounds are statisfing the Lipinski rule.