Preparation and Promotion of Fruit Growth in Kiwifruit of Fluorinated N-Phenyl-N‘-1,2,3-thiadiazol-5-yl Ureas

Abstract

Seventeen phenyl-fluorinated analogues of thidiazuron [N-phenyl-N'-(1,2,3-thiadiazol-5-yl)urea, TDZ] have been prepared and characterized. The effects of each fluorinated urea on growth and quality of kiwifruits (Actinidia deliciosa) were evaluated by comparison with untreated (control) and TDZ-treated fruits. The results obtained showed a clear dependence of the growth-promoting activity of these fluorinated ureas on the pattern and degree of fluorine substitution in the phenyl ring. The most effective for promoting fruit growth was N-(2,3,5,6-tetrafluorophenyl)-N'-(1',2',3'-thiadiazol-5'-yl)urea at 25 ppm (at harvest, treated fruits were 58% heavier than untreated ones) followed by N-(3,5-difluorophenyl)-N'-(1',2',3'-thiadiazol-5'-yl)urea at 10 ppm (50%). Comparatively, TDZ-treated fruits were 31% (10 ppm) and 38% (25 ppm) heavier than untreated ones. The results also indicate that the effects of the more active phenyl-fluorinated ureas on some standard quality parameters of fruits, for example, percent of fruit dry matter content, soluble solids contents, total titratable acids, shape, and internal structure, are similar to those of TDZ. Quantitative structure-activity relationships have been derived for the fruit growth promoting activity of the phenyl-fluorinated analogues of TDZ.

1H,13C and19F NMR spectroscopy of polyfluorinated ureas. Correlations involving NMR chemical shifts and electronic substituent effects

“…It was assumed that in the solvent used for recording their NMR data (DMSO-d 6 solutions) all the ureas exist as monomers, which probably consist of an equilibrium mixture of conformers around the ureido moiety, predominated by the Z,Z (trans, trans) form, which is likely to be strongly stabilized by formation of a three-centre bond between the ureido protons (NH) and the oxygen atom of the sulfoxide moiety. 5 This situation is in agreement with the fact that although these ureas are practically insoluble in low-polarity solvents such as CDCl 3 or benzene-d 6 , they readily dissolve in them upon addition of 1-2 equiv. of DMSO-d 6 , to give 1 H NMR spectra similar to those recorded in DMSO-d 6 solutions.…”

“…5 This situation is in agreement with the fact that although these ureas are practically insoluble in low-polarity solvents such as CDCl 3 or benzene-d 6 , they readily dissolve in them upon addition of 1-2 equiv. of DMSO-d 6 , to give 1 H NMR spectra similar to those recorded in DMSO-d 6 solutions. The fact that no significant variations were observed in the chemical shifts of the ureido hydrogen atoms with the concentration of the fluorinated diphenylureas (over a fourfold concentration range) also supports the above postulate.…”

“…The fact that no significant variations were observed in the chemical shifts of the ureido hydrogen atoms with the concentration of the fluorinated diphenylureas (over a fourfold concentration range) also supports the above postulate. The picture was different when the NMR data were recorded in less coordinating solvents than DMSO-d 6 , e.g. acetone-d 6 , in which fairly complex 1 H, 13 C, and 19 F NMR spectra were obtained, probably attributable to the formation of aggregates promoted by self-association of the urea in this solvent.…”

“…One-dimensional 1 H, 19 F and 13 C spectra were recorded in DMSO-d 6 solutions at 23°C at a concentration of 0.023-0.034 mmol ml 1 IR spectra were measured as KBr pellets using a Nicolet Avatar 320 spectrometer. High-resolution mass spectra were recorded with a VG AutoSpec spectrometer using the electron ionization (EI) mode (70 eV).…”

“…We consider that a quantitative structure-activity relationship analysis of the activity of these compounds could probably be accomplished using the 1 H NMR chemical shift of the ureido protons, 6 an indirect measure of their acidity, as one of the variables. Several quantitative structure-activity relationships (QSAR) studies have been realized, using physicochemical substituent parameters and multiple regression analysis, in order to understand the main factors governing variations in the interaction of different diaryl and related ureas with the target site of action.…”