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Open Access Publications from the University of California

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

  • Author(s): Tarzia, Giorgio
  • Antonietti, Francesca
  • Duranti, Andrea
  • Tontini, Andrea
  • Mor, Marco
  • Rivara, Silvia
  • Traldi, Pietro
  • Astarita, Giuseppe
  • King, Alvin
  • Clapper, Jason R
  • Piomelli, Daniele
  • et al.

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.

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