Effect of cyclodextrins on the thermal epimerization of tea catechins

金沢大学理工研究域物質化学系The epimerization reaction of tea catechins was investigated at pH 5.5 and 120°C in the absence/presence of cyclodextrins (CDs). In the absence of CDs, a considerable quantity (∼20%) of products originating from reactions other than the epimerization ("other products") was formed during the epimerization of gallated catechins. In the case of (-)-EGCg, addition of β-CD to the reaction solution reduced the quantity of these other products to just a few percent, but other CDs with different cavity sizes had little effect. Generally, the addition of β-CD increased the ratio of non-epi type catechins, that is, [non-epi type catechin] / ([epi type catechin]+[non-epi type catechin]). Molecular orbital (MO) calculations using the PM3 method suggested that non-epi type catechins are more thermodynamically stable than their epi-type counterparts, moving the equilibrium position in favor of non-epi type catechins in the epimerization process

Crystal structures of racemic and enantiomeric 5-isopropyl-5-methylhydantoin

Crystal structures of racemic and enantiomeric 5-isopropyl-5-methylhydantoin (IPrMH) have been determined by single crystal X-ray diffraction. Melting temperatures and solid state infrared spectra are also measured. Racemic IPrMH has a lower melting temperature than the pure enantiomer by 25 °C. The infrared spectrum of racemic IPrMH is identical with that of the pure enantiomer. Nevertheless, the racemic IPrMH doesn’t crystallize as a conglomerate but as a racemic compound. The racemic and the enantiomeric crystals are very similar to each other in molecular geometries and intermolecular interactions. In the both cases, the molecules are connected via N−H···O hydrogen bonds to form R22(8) rings, and these rings are linked into infinite one-dimensional tapes. In the racemic crystal, a single tape is composed of single enantiomer and itself is homochiral

Spectroscopic characterization of thiol adducts formed in the reaction of 4-methylcatechol with DPPH in the presence of N-acetylcysteine

Nucleophiles such as thiol compounds have enhancing effects on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of polyphenols. Several authors have suggested that regeneration of the catechol structure from o-quinone plays a key role in enhanced radical scavenging activity. We therefore explored the reaction of 4-methyl catechol (MC) with DPPH in the presence of N-acetylcysteine (NACys) to clarify the mechanism underlying activity enhancement. Four types of NACys adducts were isolated and purified by preparative HPLC after the reactions reached equilibrium and their structures were characterized spectroscopically using UV-Vis absorption, NMR, and LC-MS. Oxidation of MC using a periodate resin and subsequent reaction with NACys were also studied. LC-MS analyses revealed that a mono-NACys adduct is produced as the major product in the reaction of MC quinone with NACys, and direct reduction by NACys occurs in reactions with NACys MC quinones

Crystal Structure of 5-Phenyl-2-thioxo-4-imidazolidinone

The crystal structure of 5-phenyl-2-thioxo-4-imidazolidinone has been determined by X-ray diffraction. The crystal, C9H8N2OS, belongs to space group P1 with cell dimensions of a = 8.971(3)Å, b = 9.651(3)Å, c = 10.497(3)Å, α = 82.39(2)°, β = 80.15(2)°, γ = 79.16(2)°. The final R value is 0.045 for 2683 reflections (I > 2.00σ(I)). There are two independent molecules, A and B, in the asymmetric unit. The molecules differ mainly in the orientation of the phenyl ring with respect to the five-membered ring. In crystals, the thioamide groups of molecules A and B form centrosymmetric dimers A-A and B-B via the N-H…S hydrogen bonds. The amide groups of two neighboring molecules, A and B, form pseudo-centrosymmetric dimers A-B through N-H…O hydrogen bonds

1-Acetyl-5-(4-fluorophenyl)-2-sulfanylideneimidazolidin-4-one

In the title compound, C11H9FN2O2S, the 2-sulfanylideneimidazolidin-4-one moiety is essentially planar, with a maximum deviation of 0.0183 (14) Å. The mean plane of this moiety is approximately coplanar with the attached acetyl group and perpendicular to the benzene ring, making dihedral angles of 9.70 (14) and 86.70 (6)°, respectively. In the crystal, molecules are linked by N—H...O hydrogen bonds between the amide NH and acetyl C=O groups, forming a C(6) chain along the a-axis direction