Biotransformation of diethenylbenzenes, V. Identification of urinary metabolites of 1,2-diethenylbenzene in the rat.

Abstract

1. Biotransformation of 1,2-diethenylbenzene (1) in rat was studied. Five urinary metabolites were isolated by extraction of acid hydrolysed urine and identified by nmr and mass spectroscopy, namely, 1-(2-ethenylphenyl)ethane-1,2-diol (2) 2-ethenylmandelic acid (3), 2-ethenylphenylglyoxylic acid (4), 2-ethenylphenylacetylglycine (5) N-acetyl-S-[1-(2-ethenylphenyl)-2-hydroxyethyl]cysteine (6) and N-acetyl-S-[2-(2-ethenylphenyl)-2-hydroxy-ethyl]cysteine (7). 2. In addition, minor metabolites, namely, 2-ethenylbenzoic acid (8) and 2-ethenylphenyl-acetic acid (9) were identified by glc-mass spectral analysis of the hydrolysed urine extract treated subsequently with diazomethane, hydroxylamine and a trimethyl-silylating reagent. Several compounds, which could arise from biotransformation of both ethenyl groups in the molecule of 1, were detected but not identified unequivocally. 3. A glucuronide was detected by tlc analysis of urine as a blue spot after spraying with naphthoresorcinol. Compounds showing molecular fragments indicating the glucuronide moiety were also detected by glc-mass spectroscopy in non-hydrolysed urine samples. 4. The total thioether excretion amounted to 5.3 +/- 2.4, 5.1 +/- 3.4 and 5.0 +/- 1.9% of the dose at 500, 300 and 100 mg/kg, respectively (mean +/- SD; n = 5). 5. Like styrene and other diethenylbenzene isomers, 1,2-diethenylbenzene is metabolically activated to a reactive epoxide intermediate, 2-ethenylphenyloxirane (10), which is further converted to the urinary metabolites mentioned above. The main detoxification pathways are hydrolysis to the glycol 2 followed by several oxidation steps, and conjugation with glutathione. The latter reaction is both regioselective and stereoselective. 6. The ratio of mercapturic acids 6:7 was 83:17. Each regioisomer consists of two diastereomers which show distinct resonance signals in the 13C-nmr. The diastereomer ratio was 82:28 and 79:21 for 6 and 7 respectively.