Novel Carbohydrate-Appended Metal Complexes for Potential Use in Molecular Imaging

Seven discrete sugar‐pendant diamines were complexed to the {M(CO)3}+ (99mTc/Re) core: 1,3‐diamino‐2‐propyl β‐D‐glucopyranoside (L1), 1,3‐diamino‐2‐propyl β‐D‐xylopyranoside (L2), 1,3‐diamino‐2‐propyl α‐D‐mannopyranoside (L3), 1,3‐diamino‐2‐propyl α‐D‐galactopyranoside (L4), 1,3‐diamino‐2‐propyl β‐D‐galactopyranoside (L5), 1,3‐diamino‐2‐propyl β‐(α‐D‐glucopyranosyl‐(1,4)‐D‐glucopyranoside) (L6), and bis(aminomethyl)bis[(β‐D‐glucopyranosyloxy)methyl]methane (L7). The Re complexes [Re(L1–L7)(Br)(CO)3] were characterized by 1H and 13C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L2)(CO)3Br] and [Re(L3)(CO)3Br], were characterized in the solid state by X‐ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H2O established that the complexes exist as [Re(L1–L7)(H2O)(CO)3]Br in aqueous conditions. Radiolabelling of L1–L7 with [99mTc(H2O)3(CO)3]+ afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period. Sugar‐pendant diamine ligands were complexed to the {M(CO)3}+ (99mTc/Re) core in an effort to develop new carbohydrate‐based pharmaceuticals. It was proven that the carbohydrate moieties remain pendant in solution and in the solid state (see X‐ray structure), thereby increasing the potential for interaction with hexose transport and metabolic pathways in vivo. The radiolabelled (99mTc) compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine.