Patent ID: 6998233

Claim:
A method comprising: a) providing a target having a reactive nucleophile at or near a site of interest; b) contacting the target with an extender thereby forming a target-extender complex wherein the extender comprises a first functionality that reacts with the nucleophile in the target to form a covalent bond and a second functionality that is capable of forming a disulfide bond, wherein the extender is of the formula: where R is unsubstituted C 1 –C 20 aliphatic, substituted C 1 –C 20 aliphatic, unsubstituted aryl, and substituted aryl; R′ is H, —SR 1 wherein R 1 is unsubstituted C 1 –C 10 aliphatic, substituted C 1 –C 10 aliphatic, unsubstituted aryl, and substituted aryl; X is a leaving group, and the boxes in each formula represent a binding determinant; c) contacting the target-extender complex with a candidate ligand that is capable of forming a disulfide bond with said target-extender complex; d) forming a disulfide bond between the target-extender complex and the candidate ligand thereby forming a target-extender-ligand conjugate; and, e) identifying the candidate ligand present in the target-extender-ligand conjugate.