Compositions and methods for modification of biomolecules

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—(CH2)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) —(CH2)n—W—(CH2)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) —(CH2)n—Z, wherein n is an integer from 1-4;
• and wherein Z is nitro, cyano, sulfonic acid, or a halogen;
• Y is H;
• and
• R1 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.