Oxidative Oligomerization of DBL Catechol, a potential Cytotoxic Compound for Melanocytes, Reveals the Occurrence of Novel Ionic Diels-Alder Type Additions

The exposure of human skin to 4-(4-hydroxyphenyl)-2-butanone (raspberry ketone, RK) is known to cause chemical/occupational leukoderma. RK is a carbonyl derivative of 4-(4-hydroxyphenyl)-2-butanol (rhododendrol), a skin whitening agent that was found to cause leukoderma in skin of many consumers. These two phenolic compounds are oxidized by tyrosinase and the resultant products seem to cause cytotoxicity to melanocytes by producing reactive oxygen species and depleting cellular thiols through o-quinone oxidation products. Therefore, it is important to understand the biochemical mechanism of the oxidative transformation of these compounds. Earlier studies indicate that RK is initially oxidized to RK quinone by tyrosinase and subsequently converted to a side chain desaturated catechol called 3,4-dihydroxybenzalacetone (DBL catechol). In the present study, we report the oxidation chemistry of DBL catechol. Using UV–visible spectroscopic studies and liquid chromatography mass spectrometry, we have examined the reaction of DBL catechol with tyrosinase and sodium periodate. Our results indicate that DBL quinone formed in the reaction is extremely reactive and undergoes facile dimerization and trimerization reactions to produce multiple isomeric products by novel ionic Diels-Alder type condensation reactions. The production of a wide variety of complex quinonoid products from such reactions would be potentially more toxic to cells by causing not only oxidative stress, but also melanotoxicity through exhibiting reactions with cellular macromolecules and thiols.

Correction: A new phosphotungstate-supported rhenium carbonyl derivative: synthesis, characterization and catalytic selective oxidation of thiophenes

Correction for ‘A new phosphotungstate-supported rhenium carbonyl derivative: synthesis, characterization and catalytic selective oxidation of thiophenes’ by Jingkun Lu et al., CrystEngComm, 2019, 21, 7322–7328.

A new phosphotungstate-supported rhenium carbonyl derivative: synthesis, characterization and catalytic selective oxidation of thiophenes

We synthesized a new phosphotungstate-supported rhenium carbonyl derivative, [N(CH3)4]6H4[P2W17O62{Re(CO)3}2]·25H2O, existing the first {Re2} fragment. Moreover, it also exhibits high efficiency for the selective oxidation of thiophenes.

Synthesis, characterization and catalytic epoxidation properties of a new tellurotungstate(iv)-supported rhenium carbonyl derivative

We synthesized a new tellurotungstate(iv)-supported rhenium carbonyl derivative, Na2H2[(CH3)4N]6[Te2W20O70{Re(CO)3}2]·20H2O (1). Additionally, compound 1 showed excellent catalytic activity in the selective epoxidation of alkenes under comparatively mild reaction conditions.

An isotetramolybdate-supported rhenium carbonyl derivative: synthesis, characterization, and use as a catalyst for sulfoxidation

We successfully synthesized an isotetramolybdate-supported rhenium carbonyl derivative, [(CH3)4N]4[{Re(CO)3}4(Mo4O16)]·H2O, which showed excellent catalytic activity in the selective oxidation of sulfides under comparatively mild reaction conditions.

Isopentatungstate-supported metal carbonyl derivative: synthesis, characterization, and catalytic properties for alkene epoxidation

An isopentatungstate-supported metal carbonyl derivative has been synthesized and characterized, and can efficiently catalyze alkene epoxidation with high activity.