STAMBP and melanoma: The MC1R was selected as a target for our investigations.MC1Ris overexpressed in melanoma cells7−12 and had previously been imaged with positron emission tomographyusing an 18F-labeled α-melanocyte stimulating hormone(MSH) analogue.11 To enable labeling withour biarsenical imaging probe, the α-MSH analogue NDP-α-MSH(2) with an 11-amino-acid sequence at the C-terminus(containing the CCPGCC fragment) was designed.11,13 The peptide was mildly and efficiently labeled with biarsenical 1 to afford the desired biarsenical-MSH peptide 3 (Scheme 2).