The present invention, among others, relates to a compound having a structure according to formula (I) or a pharmaceutically acceptable salt thereof, wherein Xaa 1 to Xaa 4 are independently of each other, an optionally N-alkylated natural or unnatural amino acid, R is H or methyl, L is a linker moiety, Ar is a spacer comprising an aromatic moiety, and D comprises, preferably is i) a combination of an organic complexation agent and a detectable label or ii) a detectable label, an organic complexation agent or an active substance, said active substance particularly being selected from cytotoxic agents, lipids, sugars, sugar conjugates, sugar derivatives, proteins and combinations thereof, with the proviso that -L-Ar-D does not comprise a 18 F-benzoyl residue.
