Preparation of 99mTc-labelled conjugates of ouabagenin and their biological evaluation in animal models

BACKGROUNDOuabagenin and its 1,19-acetonide were conjugated with nitrilotriacetic acid (NTA) and diethylenetriaminepentaacetic acid (DTPA) through their respective anhydrides. METHODSThe reaction mixtures were exhaustively purified by silica gel column chromatography and preparative high-performance liquid chromatography to furnish the ligands in good purity and moderate yield. These ligands were labelled with Tc to produce four chelates in 90–95% yield. Of these chelates the Tc-oubagenin–NTA conjugate and the corresponding acetonide exhibited appreciable myocardial uptake with respect to that of other vicinal organs in a guinea-pig model. However, all these Tc chelates exhibited poor heart-to-blood ratios, which could be attributed to the absence of a 3β sugar residue in this molecule. CONCLUSIONThe result is in agreement with that previously reported in connection with radioiodinated digoxin and digoxigenin derivatives.