Patent ID: 7307169

Claim:
An isotopically enriched N-substituted piperazine compound of the formula: or a salt thereof wherein; Y is a straight chain or branched C1-C6 alkyl group or a straight chain or branched C1-C6 alkyl ether group wherein the carbon atoms of the alkyl group or alkyl ether group are each independently optionally substituted with deuterium or fluorine atoms; and each Z is independently hydrogen, fluorine, chlorine, bromine, iodine, an amino acid side chain, a straight chain or branched C1-C6 alkyl group that may optionally contain a substituted or unsubstituted aryl group wherein the carbon atoms of the alkyl and aryl groups are each independently optionally substituted with fluorine atoms, a straight chain or branched C1-C6 alkyl ether group that may optionally contain a substituted or unsubstituted aryl group wherein the carbon atoms of the alkyl and aryl groups are each independently optionally substituted with fluorine atoms or a straight chain or branched C1-C6 alkoxy group that may optionally contain a substituted or unsubstituted aryl group wherein the carbon atoms of the alkoxy and aryl groups are each independently optionally substituted with fluorine atoms; wherein the N-methyl piperazine is isotopically enriched with one or more 13 C and/or 15 N atoms.