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Synthesis and characterisation of a dithiadiaza chelator NSNS2A, as well as copper complexes thereof are reported in this paper. Solution structures of copper(i/ii) complexes were calculated using density functional theory (DFT) and validated by both NMR and EPR spectroscopy. DFT calculations revealed a switch in the orientation of tetragonal distortion upon protonation, which might be responsible for poor stability of the Cu(II)NSNS2A complex in aqueous media, whilst the same switch in tetragonal distortion was experimentally observed by changing the solvent. The chelator was radiolabeled with 64Cu and evaluated using PET/MRI in rats. Despite a favorable redox potential to stabilize the cuprous state in vivo, the 64Cu(II)NSNS2A complex showed suboptimal stability compared to its tetraazamacrocyclic analogue, 64Cu(TE2A), with a significant 64Cu uptake in the liver.

Synthesis of 1,11-dithia-4,8-diazacyclotetradecane ( L1 ), a constitutional isomer of the macrocyclic [14]aneN 2 S 2 series, is accompanied with reaction and method optimization. Chelation of L1 with copper(II) provided assessment of lattice packing, ring contortion, and evidence of conformational fluxionality in solution through two unique crystal structures: L1Cu(ClO4) 2 and [(L1Cu) 2 μ-Cl](ClO 4 ) 3 . Multiple synthetic approaches are presented, supplemented with reaction methodology and reagent screening to access [14]aneN 2 S 2 L1 . Reductive alkylation of bis-tosyl-cystamine was integrated into the synthetic route, eliminating the use and isolation of volatile thiols and streamlining the synthetic scale-up. Late-stage cleavage of protecting sulfonamides was addressed using reductive N-S cleavage to furnish macrocyclic freebase L1 .

In this report, we present cyclohexylcyanine, a phthalocyanine analogue with two cyclohexane units incorporated into the backbone of the macrocycle; in the free base, the ionizable protons lie on the periphery of the ring, and when metalated with silver the macrocycle binds to the metal via these same meso nitrogen atoms.