or biologically acceptable salts or pro-reporter molecules (such as methyl ester form of carboxyl-containing amino acid residues) thereof, wherein R1 is an N-terminal protecting group including t-butyloxycarbonyl, acetyl, benzyloxycarbonyl; each AA independently is a residue of any natural or non-natural ??-amino acid or ??-amino acid, or derivatives of an ??-amino acid or ??-amino acid; each n in