Isolation and identification of 3-carbamoyloxy-2-phenylpropionic acid as a major human urinary metabolite of felbamate.

A new metabolite of felbamate, isolated from the polar metabolite fraction of a human urine sample, was identified as 3-carbamoyloxy-2-phenylpropionic acid (CPPA) by electron impact and CI/MS of the methyl ester in the isolated fraction. Its presence in the unconjugated free form in two different human urine samples was confirmed by HPLC comparison of retention times with authentic synthetic CPPA and by on-line negative ion HPLC thermospray tandem mass spectrometric techniques. The amount of CPPA in 0-4 hr postdose human urine was estimated to be approximately 12% of the drug-derived substances present in the urine. Some CPPA was also found to be present in dog urine.