Chromatographic-mass spectrometric analysis of the urinary metabolite profile of chlorphenesin observed after dermal application of chlorphenesin-containing sunscreen

RATIONALE

Chlorphenesin is an approved biocide frequently used in cosmetics, and its carbamate ester is an approved skeletal muscle relaxant in certain countries for the treatment of discomfort related to skeletal muscle trauma and inflammation. A major urinary metabolite is 4-chlorophenoxy acetic acid (4-CPA), also known as para-chlorophenoxyacetate, which is also employed as a target analyte in sports drug testing to detect the use of the prohibited nootropic stimulant meclofenoxate. To distinguish between 4-CPA resulting from chlorphenesin, chlorphenesin carbamate, and meclofenoxate, urinary metabolite profiles of chlorphenesin after legitimate use were investigated.

METHODS

Human administration studies with commercially available sunscreen containing 0.25% by weight of chlorphenesin were conducted. Six study participants dermally applied 8 g of sunscreen and collected urine samples before and up to 7 days after application. Another set of six study participants applied 8 g of sunscreen on three consecutive days, and urine samples were also taken for up to 5 days after the last dosing. Urine specimens were analyzed using liquid chromatography-high resolution (tandem) mass spectrometry, and urinary metabolites were identified in accordance with literature data by accurate mass analysis of respective precursor and characteristic product ions.

RESULTS

In accordance with literature data, chlorphenesin yielded the characteristic urinary metabolites, chlorphenesin glucuronide, chlorphenesin sulfate, and 3-(4-chlorophenoxy)-2-hydroxypropanoic acid (4-CPP), as well as the common metabolite 4-CPA. 4-CPA and 4-CPP were observed at similar abundances, with urinary concentrations of 4-CPA reaching up to ~1500 and 2300 ng/mL after single and multiple sunscreen applications, respectively.

CONCLUSION

4-CPA is a common metabolite of meclofenoxate, chlorphenesin, and chlorphenesin carbamate. Monitoring the diagnostic urinary metabolites of chlorphenesin provides conclusive supporting evidence of whether chlorphenesin or the prohibited nootropic meclofenoxate was administered.

The synthesis of amphipathic prodrugs of 1,2-diol drugs with saccharide conjugates by high regioselective enzymatic protocol

A facile, high regioselective enzymatic synthesis approach for the preparation of amphipathic prodrugs with saccharides of mephenesin and chlorphenesin was developed. Firstly, transesterification of two drugs with divinyl dicarboxylates with different carbon chain length was performed under the catalysis of Candida antarctica lipase acrylic resin and Lipozyme in anhydrous acetone at 50 degrees C, respectively. A series of lipophilic derivatives with vinyl groups of mephenesin and chlorphenesin were prepared. The influences of different organic solvents, enzyme sources, reaction time, and the acylation reagents on the synthesis of vinyl esters were investigated. And then, protease-catalyzed high regioselective acylation of D-glucose and D-mannose with vinyl esters of mephenesin and chlorphenesin gave drug-saccharide derivatives in good yields. The studies of lipophilicity and hydrolysis in vitro of prodrugs verified that drug-saccharide derivatives had amphipathic properties, and both lipophilic and amphipathic drug derivatives had obvious controlled release characteristics.

β-Galactosidase Catalyzed Selective Galactosylation of Aromatic Compounds

A new approach to galacto-oligosaccharides and galacto-conjugates synthesis performed by the beta-galactosidase from Kluyveromyces lactis is reported. The enzymatic galactosylation of eight kinds of adsorbed aromatic primary alcohols, in particular the two drugs guaifenesin and chlorphenesin, gave the corresponding beta-D-galacto-pyranosides in yields ranging between approximately 10% and 96%. For the first time, we have showed that the adsorption of acceptor substrates onto solid supports such as silica gel influences the yield and the selectivity of galacto-conjugates synthesis. In particular, we observed that adsorption of acceptor favored the synthesis of digalactosylated compounds.