FerroCEST (Fe(II) Chemical Exchange Saturation Transfer) MRI contrast agents based on TACN (1,4,7-triazacyclononane) or CYCLEN (1,4,7,10-tetraazacyclododecane) macrocycles containing heterocyclic pendants will be presented.  Utilization of 6-methyl/6-amino-picolyl pendants on TACN or CYCLEN stabilizes a single diastereomeric form of the Fe(II) complex in aqueous solution as shown by the number of proton resonances which are highly dispersed from -80 to 280 ppm with 60-800 Hz line widths.  The Fe(II) CYCLEN-based complex bearing 6-amino-2-picolyl pendants demonstrates the most favorable CEST effect at -72 ppm.  Complexes with 6-methyl-2-picolyl pendants are not suitable for CEST, but may be useful in MRS thermometry because their proton resonances show temperature-dependent shifts with coefficients of up to -0.82 ppm/oC.  These Fe(II) complexes are stabilized in the +2 oxidation state and are kinetically inert over a wide range of pH values, as well as in the presence of physiologically relevant ions, making them promising for MRI/MRS applications in vivo.

FerroCEST agents for MRI and MRS applications

245th National Meeting (2013)

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