Patent ID: 7582801

Claim:
A labeled compound of the formula wherein C* is each independently selected from the group consisting of 13 C and 12 C with the proviso that at least one C* is 13 C, the methylene group includes zero, one or two deuterium atoms, the methyl group includes either zero or three deuterium atoms, Q is selected from the group consisting of sulfide, sulfinyl, and sulfone, and Z is an aryl group selected from the group consisting of 1-naphthyl, substituted 1-naphthyl, 2- naphthyl, substituted 2-naphthyl, and phenyl groups with the structure wherein R 1 , R 2 , R 3 , R 4 and R 5 are each independently selected from the group consisting of hydrogen, a C 1 -C 4 lower alkyl, a halogen, and an amino group selected from the group consisting of NH 2 , NHR and NRR′ where R and R′ are each independently selected from the group consisting of a C 1 -C 4 lower alkyl, a phenyl, and an alkoxy group.