The present invention is directed to labeled compounds, of the formulae wherein C* is each independently selected from the group consisting of 13C and 12C with the proviso that at least one C* is 13C, each
hydrogen of the
methylene group can independently be either
hydrogen or
deuterium, the
methyl group includes either zero or three
deuterium atoms, Q is from the group of
sulfide, sulfinyl, and
sulfone, Z is an
aryl group from the group of 1-naphthyl, substituted 1-naphthyl, 2-naphthyl, substituted 2-naphthyl, and phenyl groups with the structure wherein R1, R2, R3, R4 and R5 are each independently from the group of
hydrogen, a C1-C4 lower
alkyl, a
halogen, and an amino group from the group of NH2, NHR and NRR′ where R and R′ are each independently from the group of a C1-C4 lower
alkyl, a phenyl, and an
alkoxy group, and the
methyl group can include either zero or three
deuterium atoms. The present invention is also directed to labeled compounds of the formula where X is from the group of —NR6R7 and —OR8 where R6 and R7 are each independently selected from the group of C1-C4 lower
alkyl, alkoxy and
aryl and R8 is from the group of C1-C4 lower alkyl, alkoxy and
aryl, T is from the group of —CH3, —CD3, —CH2—S—R9, —CH2—S(O)—R9, and —CH2—(O)S(O)—R9, J is from the group of —CH(OH)—CH2—S—R9, —CH(OH)—CH2—S(O)—R9, and —CH(OH)—CH2—(O)S(O)—R9 where R9 is an aryl group from the group of 1-naphthyl, substituted 1-naphthyl, 2-naphthyl, substituted 2-naphthyl, and phenyl groups with the structure wherein R1, R2, R3, R4 and R5 are each independently from the group of hydrogen, a C1-C4 lower alkyl, a
halogen, and an amino group from the group of NH2, NHR and NRR′ where R and R′ are each independently from the group of a C1-C4 lower alkyl, a phenyl, and an
alkoxy group, and C* are each independently selected from the group consisting of 13C and 12C with the proviso that at least one C* is 13C.