The organometallic precursor fac-[188Re (CO)3(H2O)3]+ is reacted with three novel tridentate ligands (L1NH2

L2H

L3NH2) and the properties of their 188Re complexes in vivo have been evaluated. The results of labeling condition experiments show that a radiochemical purity higher than 90% can be obtained within 60 min by the reaction of fac-[188Re (CO)3]+ core in the condition of pH=7.4 with a very small amount (10-5 mol/L) of these three new ligands. At the same time

three Re-tricarbonyl complexes of three ligands were also synthesized as reference samples

which were used to confirm the structures of 188 Re-tricarbonyl complexes of three ligands by HPLC. The stability experiments in vitro demonstrate that fac-[188Re(CO)3L1NH2]+

fac-[188Re(CO)3L2H] and fac-[188Re(CO)3L3NH2] do not decompose within 24 h (37 ℃

in new born small calf serum). Histidine and cysteine challenge experiments (37℃

PBS

pH=7.4) show that fac-[188Re(CO)3L1NH2]+ and fac-[188Re(CO)3L2H] have higher stabilities than fac-[188Re(CO)3L3NH2]

which indicates that the combination ability of –OH in –COOH with fac-[188Re(CO)3L2H] core was higher than that of –N in pyridine. It is also indicated that three novel tridentate ligands (L1NH2

L2H

L3NH2) are better bifunctional chelating agents for the labeling by the precursor fac-[188Re (CO)3(H2O)3]+.