Multipurpose isothiocyanyl alanine/lysine: Use as solvatochromic IR probes and in site specific labeling/ligation of short peptides.

The solvatochromic IR responsivity of small side chain -NCS in two unexplored unnatural amino acids, isothiocyanyl alanine (NCS Ala = Ita) and lysine (NCS Lys = Itl), without perturbing the conformation is demonstrated in two designed short tripeptide (BocAla-NCS Ala-Ala-OMe) and hexapeptide (BocLeu-Val-Phe-Phe-NCS Lys-Gly-OMe). Demonstration of site specific fluorescent labeling in both the peptides and ligation type reaction in NCS Lys indicates the novelty of these two amino acids as alternative to the available canonical amino acids.