An Alkyne-functionalized Arginine for Solid-Phase Synthesis Enabling "Bioorthogonal" Peptide Conjugation.

Lately, amino-functionalized N ω-carbamoylated arginines were introduced as arginine surrogates enabling peptide labeling. However, this approach is hardly compatible with peptides also containing lysine or cysteine. Here, we present the synthesis of an alkyne-functionalized, N ω-carbamoylated arginine building block (7), which is compatible with Fmoc-strategy solid-phase peptide synthesis. The alkynylated arginine was incorporated into three biologically active linear hexapeptides and into a cyclic pentapeptide. Peptide conjugation to an azido-functionalized fluorescent dye via "click" chemistry was successfully demonstrated. In the case of a peptide also containing lysine besides the alkyne-functionalized arginine, this was feasible in a "bioorthogonal" manner.