Scheme. (1) Reaction Conditions: a) microwave irradiation, 120ºC, 0.5 h, methanol; b) i. Diethylenetriamine, methanol, reflux, 2 h; ii) NaBH4, 2 h, water, overnight; c) t-butyl bromoacetate, N,N-diisopropylethylamine, microwave irradiation, 110ºC, 2 h; d) i) TFA, dichloromethane, room temperature; ii) diethyl ether; e) i) [Gd(NO3)00]·6H2O, pH = 7.5-8.0, reflux; ii) acetonitrile, reflux.