Patent ID: 7964729

Claim:
A compound of structure (I): wherein R 1 is hydroxy, amino, or thiol; R 2 and R 3 are each independently hydrogen, an electron-withdrawing group, or —SO 2 X; each R 4 is independently hydrogen, an electron-withdrawing group or —SO 2 X, wherein R 4 can substitute any open valence of any ring within structure (I); X is —OR′ or —NR′R″; Y is halogen, —SH, —NR′R′″, —CHO, or —CO 2 H; R′ and R″ are each independently hydrogen or C 1-6 alkyl; R′″ is hydrogen, unsubstituted C 1-6 alkyl, tBoc or Fmoc; n is 0, 1, 2 or 3; and m is 1, 2, or 3, and wherein at least one of R 2 , R 3 or R 4 is —SO 2 X and at least another one of R 2 , R 3 or R 4 is an electron-withdrawing group.