Synthesis of hexa aza cages, SarAr-NCS and AmBaSar and a study of their metal complexation, conjugation to nanomaterials and proteins for application in radioimaging and therapy

A novel hexa aza cage, N¹-(4-isothiocyanatobenzyl)-3,6,10,13,16, 19-hexaazabicyclo[6.6.6]icosane-1,8-diamine (SarAr-NCS) was synthesized in good yield and characterized by ¹H NMR and electrospray mass spectrometry. A new method for the synthesis of the related N¹-(4-carboxybenzyl)- 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine (AmBaSar) using the p-carboxybenzaldehyde is reported. The complexation of Cu²⁺, Co ²⁺ and Zn²⁺ by the two ligands over a range of pHs was found to be similar to the parent derivative SarAr. SarAr-NCS was conjugated to both silica particles (≈90 nm diam.) and the model B72.3 murine antibody. The SarAr-NCSN-silica particles were radiolabeled with Cu²⁺ doped ⁶⁴Cu and the number of ligands conjugated was calculated to be an average of 7020 ligands per particle. Conjugation of SarAr-NCS to the B72.3 antibody was optimized over a range of conditions. The SarAr-NCSN-B72.3 conjugate was stored in buffer and as a lyophilized powder at 4 °C over 38 days. Its radiolabeling efficiency, stability and immunoreactivity were maintained. The development of a high yielding synthesis of SarAr-NCS should provide an entry point for a wide range of Cu and Zn radiometal PET imaging agents and potentially radiotherapeutic agents with ⁶⁷Cu.