Scheme 2.

Synthesis of heMAMPa
aReagents and conditions: (a) K2CO3, CH3CN, reflux, 78%; (b) TFA/DCM, rt; (c) GdCl3, pH 5.5, rt, then 50 °C overnight; and (d) EDC.HCl, HOBt, NEt3, dimethyl sulfoxide (DMSO), 25%.

Synthesis of heMAMPa
aReagents and conditions: (a) K2CO3, CH3CN, reflux, 78%; (b) TFA/DCM, rt; (c) GdCl3, pH 5.5, rt, then 50 °C overnight; and (d) EDC.HCl, HOBt, NEt3, dimethyl sulfoxide (DMSO), 25%.