DPPH (= 2,2-Diphenyl-1-picrylhydrazyl = 2,2-Diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) Radical-Scavenging Reaction of Protocatechuic Acid Esters (= 3,4-Dihydroxybenzoates) in Alcohols: Formation of Bis-alcohol Adduct
作者:Shizuka Saito、Hong Gao、Jun Kawabata
DOI:10.1002/hlca.200690074
日期:2006.4
unclear why protocatechuicacidesters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuicacid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcoholadduct, 3,4-dihydroxy-2-methoxybenzoic acid methyl ester (4), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate (1) in MeOH, was oxidized by the DPPH radical
The stereoselective synthesis of (−)-pericosine B, which is the antipode of the cytotoxic metabolite of the fungus Periconia byssoides OUPS-N133 separated from the sea hare, was accomplished in 9 steps in 12% total yield from (−)-quinic acid, together with the synthesis of its epimer. Every crucial step of this total synthesis, including ring opening of a β-epoxide and NaBH4reduction of an unstable
The invention relates to benzoxazines useful as inhibitors of ion channels. The invention also provides pharmaceutically acceptable compositions comprising the compounds of the invention and methods of using the compositions in the treatment of various disorders.
Effects of electron-withdrawing substituents on DPPH radical scavenging reactions of protocatechuic acid and its analogues in alcoholic solvents
作者:Shizuka Saito、Jun Kawabata
DOI:10.1016/j.tet.2005.06.040
日期:2005.8
The DPPH (2,2-diphenyl-l-picrylhydrazyl) radical scavenging activity of protocatechuic acid (3,4-dihydroxybenzoic acid) and its related catechols was examined. Compounds possessing strong electron-withdrawing substituents showed high activity. NMR analysis of the reaction mixtures of catechols and DPPH radical in methanol showed the formation of methanol adducts. The results suggest that high radical scavenging activity of catechols in alcohol is due to a nucleophilic addition of an alcohol molecule on o-quinones, which leads to a regeneration of a catechol structure. Furthermore, the radical scavenging activity in alcohols would largely depend on the electron-withdrawing/donating substituents, Since they affect the susceptibility toward nucleophilic attacks on o-quinone. (c) 2005 Elsevier Ltd. All rights reserved.
A Novel Oxidative Dimer from Protocatechuic Esters: Contribution to the Total Radical Scavenging Ability of Protocatechuic Esters
作者:Shizuka SAITO、Jun KAWABATA
DOI:10.1271/bbb.80130
日期:2008.7.23
A novel oxidative dimer was isolated as a major product from a reaction mixture of methyl protocatechuate and DPPH radical in methanol. Its unusual benzobicyclo[3.2.1]octane structure was elucidated by extensive spectral analysis. This result suggests that the regeneration of catechol structures by the nucleophilic addition of an alcohol molecule on o-quinones and subsequent dimerization is one of