Giuseppe Placucci

New isatin derivatives with antioxidant activity

The reaction between isatin and 2,5-dimethoxyaniline is described. The main product was identified as 3,3-bis(4-amino-2,5-dimethoxyphenyl)-1,3-dihydroindol-2-one. The antioxidant activity of the compounds isolated was evaluated with two methods. Three published antitumor E-3-(2-chloro-3-indolylmethylene)1,3-dihydroindol-2-ones entered the same tests to search whether they are endowed with antioxidant activity too. 3,3-Bis(4-amino-2,5-dimethoxyphenyl)-1,3-dihydroindol-2-one and the three antitumor agents showed a good chemical antioxidant activity.

Unsupervised Principal Component Analysis of NMR Metabolic Profiles for the Assessment of Substantial Equivalence of Transgenic Grapes (Vitis vinifera)

Substantial equivalence is a key concept in the evaluation of unintended and potentially harmful metabolic impact consequent to a genetic modification of food. The application of unsupervised multivariate data analysis to the metabolic profiles is expected to improve the effectiveness of such evaluation. The present study uses NMR spectra of hydroalcoholic extracts, as holistic representations of the metabolic profiles of grapes, to evaluate the effect of the insertion of one or three copies of the DefH9-iaaM construct in plants of Silcora and Thompson Seedless cultivars. The comparison of the metabolic profiles of transgenic derivatives with respect to their corresponding natural lines pointed out that the overall metabolic changes occur in the same direction, independent of the host genotype, although the two cultivars are modified to different extents. A higher number of copies not only produces a larger effect but also modifies the whole pattern of perturbed metabolites.

Reactions of alkanethiyl and alkoxyl radicals with unsaturated cyclic ethers

Abstract Methanethiyl radicals (CH3S.) are shown to react with cyclic ethers containing double bonds to give addition and hydrogen abstraction from the allylic positions. The esr spectra of the corresponding radicals have been determined. In some cases radicals arising from a rearrangement (probably 1,4 H-shift) were observed. t-Butoxyl radicals also give abstraction and addition with the same substrates. In two cases the barriers to ring inversion for six-membered ring radicals have been determined.

Lanthanide induced shift as a tool for isomer assignment in esters of unsaturated fatty acids

Abstract Addition of Yb(fod) 3 to methyl oleate ( cis ) and methyl elaidate ( trans ) shifts the carboxylic lines of their 13 C-NMR spectra to different extents; that of the cis isomer less than that of the trans isomer, as is to be expected. On the same theoretical ground it can be anticipated that the opposite will occur for C-17: an effect that has been confirmed experimentally. The method is thus proposed as a means of aiding in the assignment of the cis and trans configuration in esters of fatty acids with one double bond.

Evidence of restricted rotation in the phenyl thiaxanthyl radical

The 9-phenyl thiaxanthyl radical has been obtained from the corresponding cation. A complete analysis of its E.S.R. spectrum has been achieved by using some deuterated derivatives as well as computer simulated spectra. The unusual ratio of the ortho/para hyperfine splittings (✠) has been interpreted as due to the occurrence of restricted rotation of the phenyl ring. Molecular orbital calculations indicate that the experimental results may be interpreted by assuming the phenyl ring to be twisted from the heterocyclic plane by an angle of about 72°. No significant differences were observed between the values of the spin density distribution calculated with standard p and d models.

Conformational studies by dynamic nmr. Part 18. Restricted rotation in nitrosobenzene and phenylhydrazine

The barriers to Ph-N rotation in the title compounds have been determined by C-13 NMR. The values are 7.6 and 6.9 kcal mol−1 respectively.

Stereodynamics and conformation of furan-3-aldehyde and of its corresponding furoyl σ-radical.

Abstract NOE measurements, combined with MM-2 calculations, predict that the proportion of the Z conformer in the title compound is high enough (14% at room temperature) as to give line broadening effects due to E,Z exchange. Line shape analysis of the dynamic C-13 NMR signals at variable temperature yielded a free energy of activation of 8.3 Kcal/mol. One of the lines of the spectrum of the Z conformer was also directly observed (0.8% at −140°C, corresponding to 11% at room temperature if the entropy difference is assumed zero). ESR spectra and INDO calculations show that also the σ-radical (obtained by H-abstraction from the HCO moiety of the title compound) essentially adopts the E conformation.

Conformation of α-substituted cycloalkyl radicals

Radicals obtained by addition of Et3Si˙ to the double bond of methylenecycloalkanes have been detected by e.s.r. at low temperature. The three-, four-, five-, and six-membered rings have been investigated. In the last case different splitting constants were detected for axial and equatorial hydrogens at low temperatures whereas a single average value is observed at higher temperatures. In the intermediate range line broadening effects allowed ΔG‡ 5.2 kcal mol–1 for the ring reversal process to be developed. In the case of the five-membered ring experimental evidence for a non-planar conformation has been also obtained. On the other hand the four-membered ring seems to be planar, at least within the approximation involved in these determinations.

Stereodynamical processes in β-substituted symmetric isopropyl radicals

Addition of trimethylsilyl (Me3Si·) and methylthiyl (MeS·) radical to Me3SiCH2–CHCH2 and MeSCH2–CHCH2 yields, respectively, the radicals Me3SiCH2ĊHCH2SiMe3(I) and MeSCH2ĊHCH2SMe (II) which were observed by e.s.r. spectroscopy. Restricted rotation about the ·CH–CH2 bonds was detected below –100 °C and the free energy of activation determined [3.4 for (I) and 2.85 kcal mol–1 for (II), respectively]. The features of the line shapes also showed that the conformation of (I) is symmetric whereas that of (II) is asymmetric. The geometry of these conformations was also assessed and the angle ϕ between the 2pz orbital of ·CH and the C–X bond was found to be 4–5°§ when X = SiMe3(I) and 10–11° when X = MeS (II). The dependence of the β-splitting on the conformation and on the electronic properties of silicon and sulphur was studied by INDO calculations and the hypothesis that sulphur-containing radicals must be distorted to account for their low aHβ splitting is challenged.

Heterocyclic azallyl badicals

Abstract Methyl-thlyl radical selectively abstracts allylic hydrogens from oxazolyn and thiazolin derivatives, yielding nitrogen centered azallyl radicals.