Figure 2.

General schematic representation of the formation of the Cy5.5 analogs. In step 1, an Fmoc-L-propargylglycine residue with an alkyne moiety was attached at the N-terminus of the B-chain on solid phase and then cleaved from the resin. In step 2, the propargylglycine B-chain was combined with the A-chain, together with the formation of the interdisulfide bonds to give the alkyne product. In step 3, under a copper-catalyzed reaction, the formation of a stable triazole bond between an alkyne and azide group was able to proceed, leading to the formation of the Cy5.5 product of interest. Analytical RPLC was undertaken on a Vydac C18 column (250 × 4.6 mm, 300Å, 5 μm) with a buffer system of 0.1% trifluoroacetic acid in water (buffer A) and 0.1% trifluoroacetic acid in acetonitrile (buffer B). Elution was with a gradient of 20–50% B over 30 min.