RESUMO
The initial objective of our work was to synthesize a series of 2-amino-4H-pyran-3-carbonitriles to be tested for their antifungal activities against economically relevant phytopathogenic fungi. Fourteen compounds were prepared in up to 94% yield and shown percentages of Botrytis cinerea inhibition above 70%. Despite the promising biological results, we observed that stock solutions prepared for biological tests showed color changing when kept for a few days on the laboratory bench, under room conditions, illuminated by common LED daylight tubes (4500-6000 k). This prompted us to investigate the possible photo-induced degradation of our compounds. FT-IR ATR experiments evidenced variations in the expected bands for functional of -amino-4H-pyran-3-carbonitriles stored under LED daylight. Following, HPLC-UV analysis showed reductions in the intensity of chromatographic peaks of 2-amino-4H-pyran-3-carbonitriles, and but not for solutions kept in the dark. A solution of (E)-2-amino-8-(4-nitrobenzylidene)-4-(4-nitrophenyl)-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile underwent 84.4% of conversion after 72 h of exposure to continuous LED daylight in a BOD chamber, and the reaction product was isolated in 36% yield and characterized as (E)-7-cyano-5-(4-nitrobenzylidene)-8-(4-nitrophenyl)bicyclo[4.2.0]oct-1(6)-ene-7-carboxamide (7*). Despite freshly prepared solutions of 2-amino-4H-pyran-3-carbonitriles produced antifungal activities, these solutions lost biological activity when left on the bench for a week. Besides, compound 7* formed from photo-induced degradation of 7 also showed no antifungal activity. With this, we hope to bring two contributions: (1) production of cyclobutenes through photochemical reactions of 2-amino-4H-pyran-3-carbonitriles can be carried out through exposure to simple white LED daylight; (2) biological applications of such 2-amino-4H-pyran-3-carbonitriles may be impaired by their poor photostability.
Assuntos
Antifúngicos/farmacologia , Botrytis/efeitos dos fármacos , Luz , Piranos/química , Antifúngicos/síntese química , Antifúngicos/química , Cromatografia Líquida de Alta Pressão , Conformação Molecular , Fotólise/efeitos da radiação , Piranos/síntese química , Piranos/farmacologia , Espectrofotometria UltravioletaRESUMO
Assessment of photochemical stability is essential for evaluating quality and the shelf life of vegetable oils, which are very important aspects of marketing and human health. Most of conventional methods used to investigate oxidative stability requires long time experimental procedures with high consumption of chemical inputs for the preparation or extraction of sample compounds. In this work we propose a time-resolved thermal lens method to analyze photostability of edible oils by quantitative measurement of photoreaction cross-section. An all-numerical routine is employed to solve a complex theoretical problem involving photochemical reaction, thermal lens effect, and mass diffusion during local laser excitation. The photostability of pure oil and oils with natural and synthetic antioxidants is investigated. The thermal lens results are compared with those obtained by conventional methods, and a complete set of physical properties of the samples is presented.