Preparation and behavior of simple quinone metnides

Electrophilic Reactivities of Vinyl p-Quinone Methides

The electrophilic reactivity of a series of 8-arylated vinyl p-quinone methides (pVQMs) was determined by analyzing the kinetics of their reactions with carbanions in DMSO at 20 °C according to the linear free energy relationship log k = s_N(N + E). The electrophilicity parameters E for pVQMs were used to successfully predict Michael-additions with structurally diverse C-, N-, S-, and H-nucleophiles.

Photochemical formation and chemistry of long-lived adamantylidene-quinone methides and 2-adamantyl cations

Hydroxymethylphenols strategically substituted with the 2-hydroxy-2-adamantyl moiety, AdPh 8-10, were synthesized, and their photochemical reactivity was investigated. On excitation to the singlet excited state, AdPh 8 undergoes intramolecular proton transfer coupled with a loss of H(2)O giving quinone methide 8QM. The presence of 8QM has been detected by laser flash photolysis (CH(3)CN-H(2)O 1:1, tau = 0.55 s) and UV-vis spectroscopy. Singlet excited states of AdPh 9 and 10 in the presence of H(2)O dehydrate giving 9QM and 10QM. Photochemically formed QMs are trapped by nucleophiles giving the addition products (e.g., Phi for methanolysis of 8 is 0.55). In addition, the zwitterionic 9QM undergoes an unexpected rearrangement involving transformation of the 2-phenyl-2-adamantyl cation into the 4-phenyl-2-adamantyl cation (Phi approximately 0.03). An analogous rearrangement was observed with methoxy derivatives 9a and 10a. Zwitterionic 9QM was characterized by LFP in 2,2,2-trifluoroethanol (tau = 1 mus). In TFE, in the ground state, AdPh 10 is in equilibrium with 10QM, which allowed for recording the (1)H and (13)C NMR spectra of the QM. Introduction of the adamantyl substituent into the o-hydroxymethylphenol moiety increased the quantum yield of the associated QM formation by up to 3-fold and significantly prolonged their lifetimes. Furthermore, adamantyl substituent made the study of the alkyl-substituted quinone methides easier by LFP by prolonging their lifetimes and increasing the quantum yields of formation.

The role of 2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone (BHT quinone methide) in the metabolism of butylated hydroxytoluene

Male rats were fed 5.45 mmol/100 g diet butylated hydroxytoluene (BHT) or 2,6-di-tert-butyl-4-hydroxymethylphenol (BHT alcohol) in either a standard or purified diet for 1 wk, after which their livers were analysed for levels of unconjugated BHT metabolites and their blood clotting times were assayed. The BHT quinone methide, 2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone, was only found in appreciable concentrations (6-9 micrograms/g liver) in the livers of rats given BHT. For rats fed the purified diet, BHT and BHT alcohol caused significant reductions of the prothrombin index to 23 and 70%, respectively, of the control value, though rats fed the standard diet were not similarly affected. Liver concentrations of BHT in rats fed BHT alcohol also varied according to diet, indicating that the metabolic pathway may be affected by diet. Biliary excretion of the quinone methide was observed in rats given 140 mg BHT alcohol ip.

On the mechanism of covalent binding of butylated hydroxytoluene to microsomal protein

The structures of cysteine conjugates of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) and the binding sites of BHT metabolites on microsomal protein were investigated by 13C nuclear magnetic resonance (13C-NMR) and gas-liquid chromatography/mass spectrometry. The cysteine conjugates of 2,6-di-tert-butyl-4-hydroxymethylphenol (BHT-alcohol) and 2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone (quinone methide), which are metabolites of BHT found in rat liver and specifically reacts with thiol compounds, were prepared as alcoholic aqueous solutions. The molecular structure of the cysteine conjugate of BHT-alcohol agreed completely with that of quinone methide in 13C-NMR spectra or mass spectra. These spectra of both conjugates further showed that the conjugates are due to thioether binding between the 4-methyl group of metabolites and the sulfhydryl group of cysteine. When [14C]BHT-bound microsomes prepared in vitro were enzymatically hydrolyzed with Pronase E, the major radioactive material that eluted with methanol from a column of Amberlite XAD-2 and gave a positive ninhydrin reaction was identified as a cysteine conjugate of BHT by comparing its Rf values on TLC and mass spectrum. On the basis of the results, it was apparent that the binding site of activated substituents of BHT on protein was mainly the sulfhydryl group of cysteine residue.