A compound of general formula wherein: the nitrogen atoms of the nitrogen-containing macrocycle are complexed with a metal ion Me, selected from the group consisting of Fe, Mn, Ru, in any permitted oxidation state; R1 is a group of general formula: wherein n = 2; A is selected from the group consisting of Ace-Asp, Ace-Asn and Ace-Pro; X1 is selected from the group consisting of Glu, Aada, Arg, hArg, and Leu; Y2 is Gln or Glu; Y3 is Gln or Glu; Y4 is Leu; X5 is selected from the group consisting of His, 4Taz and 5Taz; X6 is selected from the group consisting of Ser, Thr, Asn and aThr; Y7 is Gln or Glu; X8 is selected from the group consisting of Orn, Lys, Dap and Dab; X9 is selected from the group consisting of Glu, Aada, Arg, hArg, and Leu; Y10 is Lys or Orn; B is Ile-Thr-Leu-NH2; L is CO; R2 and R7 are CH3; R8 has formula Q- s- wherein s = 2 and Q is selected from the group consisting of NH2CO-, CH3CONH-, HOOC- and CH3OOC- or R8 has general formula: wherein m = 2; C is Ace-Asp, Ace-Asn or Ace-Pro; Z1 is selected from the group consisting of Glu, Aada, Arg and hArg; W2 is Gln or Glu; W3 is Gln or Glu; W4 is Leu; Z5 is selected from the group consisting of Ser, Gly, Ala and Aib; Z6 is selected from the group consisting of Gln, Glu and Ser; W7 is Gln or Glu; Z8 is selected from the group consisting of Orn, Lys, Dap and Dab; Z9 is an amino acid selected from the group consisting of Glu, Aada, Arg and hArg; D is NH2; P is CO; R3, R4, R5, R6, independently of one another are H or methyl. the nitrogen atoms of the nitrogen-containing macrocycle are complexed with a metal ion Me, selected from the group consisting of Fe, Mn, Ru, in any permitted oxidation state; R1 is a group of general formula: wherein n = 2; A is selected from the group consisting of Ace-Asp, Ace-Asn and Ace-Pro; X1 is selected from the group consisting of Glu, Aada, Arg, hArg, and Leu; Y2 is Gln or Glu; Y3 is Gln or Glu; Y4 is Leu; X5 is selected from the group consisting of His, 4Taz and 5Taz; X6 is selected from the group consisting of Ser, Thr, Asn and aThr; Y7 is Gln or Glu; X8 is selected from the group consisting of Orn, Lys, Dap and Dab; X9 is selected from the group consisting of Glu, Aada, Arg, hArg, and Leu; Y10 is Lys or Orn; B is Ile-Thr-Leu-NH2; L is CO; wherein n = 2; A is selected from the group consisting of Ace-Asp, Ace-Asn and Ace-Pro; X1 is selected from the group consisting of Glu, Aada, Arg, hArg, and Leu; Y2 is Gln or Glu; Y3 is Gln or Glu; Y4 is Leu; X5 is selected from the group consisting of His, 4Taz and 5Taz; X6 is selected from the group consisting of Ser, Thr, Asn and aThr; Y7 is Gln or Glu; X8 is selected from the group consisting of Orn, Lys, Dap and Dab; X9 is selected from the group consisting of Glu, Aada, Arg, hArg, and Leu; Y10 is Lys or Orn; B is Ile-Thr-Leu-NH2; L is CO; R2 and R7 are CH3; R8 has formula Q- s- wherein s = 2 and Q is selected from the group consisting of NH2CO-, CH3CONH-, HOOC- and CH3OOC- or R8 has general formula: wherein m = 2; C is Ace-Asp, Ace-Asn or Ace-Pro; Z1 is selected from the group consisting of Glu, Aada, Arg and hArg; W2 is Gln or Glu; W3 is Gln or Glu; W4 is Leu; Z5 is selected from the group consisting of Ser, Gly, Ala and Aib; Z6 is selected from the group consisting of Gln, Glu and Ser; W7 is Gln or Glu; Z8 is selected from the group consisting of Orn, Lys, Dap and Dab; Z9 is an amino acid selected from the group consisting of Glu, Aada, Arg and hArg; D is NH2; P is CO; wherein m = 2; C is Ace-Asp, Ace-Asn or Ace-Pro; Z1 is selected from the group consisting of Glu, Aada, Arg and hArg; W2 is Gln or Glu; W3 is Gln or Glu; W4 is Leu; Z5 is selected from the group consisting of Ser, Gly, Ala and Aib; Z6 is selected from the group consisting of Gln, Glu and Ser; W7 is Gln or Glu; Z8 is selected from the group consisting of Orn, Lys, Dap and Dab; Z9 is an amino acid selected from the group consisting of Glu, Aada, Arg and hArg; D is NH2; P is CO; R3, R4, R5, R6, independently of one another are H or methyl.