A compound of formula (I): wherein R 1 is selected from the group consisting of hydrogen, methyl and cyclopropylmethyl; AA-COOH is an amino acid selected from the group consisting of 2-amino-2-adamantane carboxylic acid, cyclohexylglycine and 9-amino-bicyclo[3.3.1]nonane-9-carboxylic acid; R 2 is selected from the group consisting of (C 1 -C 6 )alkyl, (C 3 -C 8 )cycloalkyl, (C 3 -C 8 )cycloalkylmethyl, halogen, nitro and trifluoromethyl; ALK is (C 2 -C 5 )alkylidene; R 3 , R 4 and R 5 are each and independently selected from the group consisting of hydrogen and (C 1 -C 4 )alkyl under the proviso that one of R 3 , R 4 and R 5 is of the following formula (II) wherein ALK' is (C 2 -C 5 )alkylidene; R 6 is selected from the group consisting of hydrogen and (C 1 -C 4 )alkyl; and R 7 is selected from the group consisting of H and an Effector moiety, wherein the Effector moiety is selected from the group consisting of Acceptor, -[Acceptor-Effector], - [Linker-Acceptor], and -[Linker-Acceptor-Effector], wherein - [Acceptor-Effector] is a moiety where the Effector is complexed or covalently bound to the Acceptor, - [Linker-Acceptor] is a moiety where the Linker is conjugated to the Acceptor, and - [Linker-Acceptor-Effector] is a moiety where the Linker is conjugated to the Acceptor, whereby the Effector is complexed or covalently bound to the Acceptor, wherein Effector is selected from the group consisting of a diagnostically active nuclide, a therapeutically active nuclide and a combination thereof, wherein Acceptor is a chelator or an aromate, and wherein Linker is a moiety which links the Acceptor to the N atom of formula (II) with the Acceptor, wherein the type of covalent linkage between the Linker and the N atom of the group of formula (II) is selected from the group consisting of amide, urea, thiourea and alkylamine; and the type of covalent linkage between the Linker and the Acceptor is selected from the group comprising amide, alkylamine, urea, ether, thioether, thiourea and carbamate; or a pharmacologically acceptable salt, solvate or hydrate thereof. R 1 is selected from the group consisting of hydrogen, methyl and cyclopropylmethyl; AA-COOH is an amino acid selected from the group consisting of 2-amino-2-adamantane carboxylic acid, cyclohexylglycine and 9-amino-bicyclo[3.3.1]nonane-9-carboxylic acid; R 2 is selected from the group consisting of (C 1 -C 6 )alkyl, (C 3 -C 8 )cycloalkyl, (C 3 -C 8 )cycloalkylmethyl, halogen, nitro and trifluoromethyl; ALK is (C 2 -C 5 )alkylidene; R 3 , R 4 and R 5 are each and independently selected from the group consisting of hydrogen and (C 1 -C 4 )alkyl under the proviso that one of R 3 , R 4 and R 5 is of the following formula (II) ALK' is (C 2 -C 5 )alkylidene; R 6 is selected from the group consisting of hydrogen and (C 1 -C 4 )alkyl; and R 7 is selected from the group consisting of H and an Effector moiety, wherein - [Acceptor-Effector] is a moiety where the Effector is complexed or covalently bound to the Acceptor, - [Linker-Acceptor] is a moiety where the Linker is conjugated to the Acceptor, and - [Linker-Acceptor-Effector] is a moiety where the Linker is conjugated to the Acceptor, whereby the Effector is complexed or covalently bound to the Acceptor, <EOS>