Patent ID: 8461298

Claim:
A compound of the formula: wherein: each of X and X′ is independently: (a) H; (b) one or two halogen atoms (e.g., bromo, chloro, fluoro, iodo); (c) —W—(CH 2 ) n —Z, wherein n is an integer from 1-4; wherein W, if present, is O, N, or S; and wherein Z is nitro, cyano, sulfonic acid, or a halogen; (d) —(CH 2 ) n —W—(CH 2 ) m —Z, wherein n and m are each independently 1 or 2; wherein W is O, N, S, or sulfonyl; with the proviso that if W is O, N, or S, then Z is nitro, cyano, or halogen; and with the proviso that if W is sulfonyl, then Z is H; or (e) —(CH 2 ) n —Z, wherein n is an integer from 1-4; and wherein Z is nitro, cyano, sulfonic acid, or a halogen; Y is a drug, a toxin, a peptide, a polypeptide, an epitope tag, or a member of a specific binding pair; and R 1 is selected from a carboxylic acid, an alkyl ester, an aryl ester, a substituted aryl ester, an aldehyde, an amide, an aryl amide, an alkyl halide, a thioester, a sulfonyl ester, an alkyl ketone, an aryl ketone, a substituted aryl ketone, a halosulfonyl, a nitrile, and a nitro.