Synthesis, isomerism and characterization of iopentol

The synthesis of iopentol is described, and the IR, NMR and FAB MS data of the compound are discussed. Iopentol exists as a mixture of several diastereomers and conformers. This topic is discussed in some detail. The kinetics of the isomerization from pure exo-iopentol to an equilibrium mixture of exo- and endo-iopentol is measured by HPLC and 1H NMR spectroscopy. At 40 degrees C the endo:exo ratio is calculated from the HPLC experiments to be 0.26. The time it takes endo-iopentol to reach half of its equilibrium concentration, and the equilibration time are calculated to be 0.8 h and 5.0 h, respectively. Iopentol may exist as exo/endo pairs of four racemates. Neither GC, HPLC, IR nor high field NMR spectroscopy were suited to reveal the diastereomeric composition of the product.