Polymethylated DOTA ligands. 2. Synthesis of rigidified lanthanide chelates and studies on the effect of alkyl substitution on conformational mobility and relaxivity

  • Ranganathan R
  • Raju N
  • Fan H
 et al. 
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M4DOTA, [(2S,5S,8S,11S)-4,7,10-tris-carboxymethyl-2,5,8,11-tetramethyl-1,4,7,10-tetraazacyclododecan-1-yl]acetic acid (2e), and M4DOTMA, (R)-2-[(2S,5S,8S,11S)-4,7,10-tris-((R)-1-carboxyethyl)-2,5,8,11-tetramethyl-1,4,7,10-tetraazacyclododecan-1-yl]propionic acid (3e), are derivatives of ligand DOTA (1e) that form sterically crowded lanthanide chelates. M4DOTMA forms highly symmetric and totally rigid single Y3+ and Yb3+ species in which the ring substituents occupy corner positions in a square antiprismatic arrangement as shown by molecular mechanics calculations and by a quantitative interpretation of the relative magnitudes of the paramagnetic 1H NMR shifts of dipolar origin. The NMR spectrum of YbM4DOTMA- displays two intense methyl peaks outside the 0−10 ppm range whose shift difference is strongly temperature dependent. YbM4DOTMA- (3d) could be a useful probe in magnetic resonance thermometric imaging. With only four methyl substituents on the tetraaza ring, M4DOTA forms three Yb3+ species in solutio...

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  • Ramachandran S. Ranganathan

  • Natarajan Raju

  • Helen Fan

  • Xun Zhang

  • Michael F. Tweedle

  • Jean F. Desreux

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