Patent ID: 8748601

Claim:
A compound having the formula (IA): in which R 2 is hydrogen or a group having the formula —(CH 2 ) b R b wherein b is 0 or an integer from 1 to 3 and R b is an aromatic, heterocyclic or cyclical aliphatic group optionally substituted with one or more groups selected from lower alkyl, halogen, substituted alkyl, nitro, alkoxy, phenoxy, sulfonamido, carboxylic ester, a fluorescent label, an affinity tag, or carboxamide; R 4 is an aliphatic, aromatic, or heterocyclic group optionally substituted with a fluorescent label, an affinity tag, or one or more polar groups, which polar group may be protected or unprotected; R 5 is hydrogen, a fluorescent label, an affinity tag, or an alkyl- or aryl-substituted ether, thioether, or amine; and E is —(CH 2 ) m COR′, —CO(CH 2 ) n R′, —C(O)C(O)R′, or an olefin attached to an electron withdrawing group, wherein m and n are independently 0 or an integer from 1 to 6, wherein R′ is independently halogen, cyano, alkyl, substituted alkyl, aryl, substituted aryl, heterocyclic group or substituted heterocyclic group, and wherein the substituted alkyl, substituted aryl and substituted heterocyclic group are independently substituted with halo, hydroxyl, thiol, nitro, amino, amido, alkoxy, haloalkoxy, alkylenedioxy, alkyl, haloalkyl, or hydroxyalkyl.