Identification of a bioactive impurity in a commercial sample of 6-methyl-2-p-tolylaminobenzo[d][1,3]oxazin-4-one (URB754)

Ann Chim. 2007 Sep;97(9):887-94. doi: 10.1002/adic.200790073.


The compound URB754 was recently identified as a potent inhibitor of the endocannabinoid-deactivating enzyme monoacylglycerol lipase (MGL) by screening of a commercial chemical library. Based on HPLC/MS, NMR and EI/MS analyses, the present paper shows that the MGL-inhibitory activity attributed to URB754 is in fact due to a chemical impurity present in the commercial sample, identified as bis(methylthio)mercurane. Although this organomercurial compound is highly potent at inhibiting MGL (IC50 = 11.9 +/- 1.1 nM), its biological use is prohibited by its toxicity and target promiscuity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aniline Compounds / analysis*
  • Benzoxazines / analysis*
  • Chromatography, High Pressure Liquid
  • Magnetic Resonance Spectroscopy
  • Spectrometry, Mass, Electrospray Ionization


  • Aniline Compounds
  • Benzoxazines
  • URB 754