Equilibrium, Kinetic and Structural Properties of Gallium(III) and Some Divalent Metal Complexes Formed with the New DATAm and DATA5m Ligands.

The development of 68 Ge/68 Ga generators has made the positron-emitting 68 Ga isotope widely accessible and raised interest in new chelate complexes of Ga3+ . The hexadentate 1,4-di(acetate)-6-methyl[amino(methyl)acetate]perhydro-1,4-diazepane (DATAm ) ligand and its bifunctional analogue, 1,4-di(acetate)-6-pentanoic acid[amino(methyl)acetate]perhydro-1,4-diazepane (DATA5m ), rapidly form complexes with 68 Ga in high radiochemical yield. The stability constants of DATAm and DATA5m complexes formed with Ga3+ , Zn2+ , Cu2+ , Mn2+ and Ca2+ have been determined by using pH potentiometry, spectrophotometry (Cu2+ ) and 1 H and 71 Ga NMR spectroscopy (Ga3+ ). The stability constants of Ga(DATAm ) and Ga(DATA5m ) complexes are slightly higher than those of Ga(AAZTA). The species distribution calculations indicated the predominance of Ga(L)OH mixed-hydroxo complexes at physiological pH. The 1 H and 71 Ga NMR spectroscopy studies provided information about the coordinated functional groups of ligands and on the kinetics of exchange between the Ga(L) and Ga(L)OH complexes. The transmetalation reactions between the Ga(L) complexes and Cu2+ citrate (6

Conformational analysis and synthetic approaches to polydentate perhydro-diazepine ligands for the complexation of gallium(III).

Synthetic approaches are reported to polydentate ligands based on 6-phenyl-6-amino-perhydro-1,4-diazepine. The synthetic route devised averts ring-opening reactions, allowing the exocyclic N-substituent to be introduced separately and involves a nitro-Mannich condensation, prior to chemoselective RANEY® nickel reduction. Comparison of the solid-state structures of four synthetic intermediates reveals that the seven-membered ring adopts a preferred twist-chair conformer in the solid state. Solution state NMR experiments highlight a conformational preference for the bulky aryl groups to adopt an equatorial site, pre-disposing the ligand to metal binding, by adoption of a conformation that creates a facial array of the ligand nitrogen atoms. This ligand conformation averts the formation of less stable metal complexes with differing ligation modes, notably in the binding of Ga(3+) to related ligands, where a C-methyl substituent replaces the phenyl group at the quaternary centre.

Instant kit preparation of 68Ga-radiopharmaceuticals via the hybrid chelator DATA: clinical translation of [68Ga]Ga-DATA-TOC.

PURPOSE: The widespread use of 68Ga for positron emission tomography (PET) relies on the development of radiopharmaceutical precursors that can be radiolabelled and dispensed in a simple, quick, and convenient manner. The DATA (6-amino-1,4-diazapine-triacetate) scaffold represents a novel hybrid chelator architecture possessing both cyclic and acyclic character that may allow for facile access to 68Ga-labelled tracers in the clinic. We report the first bifunctional DATA chelator conjugated to [Tyr3]octreotide (TOC), a somatostatin subtype 2 receptor (SST2)-targeting vector for imaging and functional characterisation of SSTR2 expressing tumours. METHODS: The radiopharmaceutical precursor, DATA-TOC, was synthesised as previously described and used to complex natGa(III) and 68Ga(III). Competition binding assays of [natGa]Ga-DATA-TOC or [natGa]Ga-DOTA-TOC against [125I-Tyr25]LTT-SS28 were conducted in membranes of HEK293 cells transfected to stably express one of the hSST2,3,5 receptor subtypes (HEK293-hSST2/3/5 cells). First in vivo studies were performed in female NMRI-nude mice bearing SST2-positive mouse phaeochromocytoma mCherry (MPC-mCherry) tumours to compare the in vivo SST2-specific tumour-targeting of [68Ga]Ga-DATA-TOC and its overall pharmacokinetics versus the [68Ga]Ga-DOTA-TOC reference. A direct comparison of [68Ga]Ga-DATA-TOC with the well-established PET radiotracer [68Ga]Ga-DOTA-TOC was additionally performed in a 46-year-old male patient with a well-differentiated NET (neuroendocrine tumour), representing the first in human administration of [68Ga]Ga-DATA-TOC. RESULTS: DATA-TOC was labelled with 68Ga with a radiolabelling efficiency of > 95% in less than 10 min at ambient temperature. A molar activity up to 35 MBq/nmol was achieved. The hSST2-affinities of [natGa]Ga-DATA-TOC and [natGa]Ga-DOTA-TOC were found similar with only sub-nanomolar differences in the respective IC50 values. In mice, [68Ga]Ga-DATA-TOC was able to visualise the tumour lesions, showing standardised uptake values (SUVs) similar to [68Ga]Ga-DOTA-TOC. Direct comparison of the two PET tracers in a NET patient revealed very similar tumour uptake for the two 68Ga-radiotracers, but with a higher tumour-to-liver contrast for [68Ga]Ga-DATA-TOC. CONCLUSION: [68Ga]Ga-DATA-TOC was prepared, to a quality appropriate for in vivo use, following a highly efficient kit type process. Furthermore, the novel radiopharmaceutical was comparable or better than [68Ga]Ga-DOTA-TOC in all preclinical tests, achieving a higher tumour-to-liver contrast in a NET-patient. The results illustrate the potential of the DATA-chelator to facilitate the access to and preparation of 68Ga-radiotracers in a routine clinical radiopharmacy setting.

Approaching 'Kit-Type' Labelling with (68)Ga: The DATA Chelators.

The DATA chelators are a novel class of tri-anionic ligands based on 6-amino-1,4-diazepine-triacetic acid, which have been introduced recently for the chelation of (68)Ga. Compared with macrocyclic chelators based on the cyclen scaffold (i.e., DOTA, DO3A, and DO2A derivatives), DATA chelators undergo quantitative radiolabelling more rapidly and under milder conditions. In this study, a systematic evaluation of the labelling of four DATA chelators--DATA(M), DATA(P), DATA(Ph), and DATA(PPh)--with (68)Ga is presented. The results highlight the extraordinary potential of this new class of chelators for application in molecular imaging using (68)Ga positron emission tomography (PET).

Cation exchange-based post-processing of (68)Ga-eluate: a comparison of three solvent systems for labelling of DOTATOC, NO2AP(BP) and DATA(m.).

Interest in (68)Ga has led to a number of innovations for its provision suitable for clinical application. Several post-processing methods are available to reduce eluate volume and remove metal trace impurities. In this work three cation exchange resin based post-processing methods (acetone, ethanol and NaCl) have been compared, using three model precursors (DOTATOC, NO2AP(BP) and DATA(m)), in terms of labelling yield and reproducibility. The acetone and ethanol based methods provided greater reproducibility and yields that makes subsequent purification unnecessary.

Crystallographic and solution NMR structural analyses of four hexacoordinated gallium(III) complexes based on ligands derived from 6-amino-perhydro-1,4-diazepine.

The crystal structures are reported of four gallium(III) complexes based on two pairs of 6-substituted-6-amino-perhydro-1,4-diazepine ligands, together with a study of their solution structures examined by (1)H and (71)Ga NMR spectroscopy. In each case, the ligand adopts a twisted chair conformation that creates a facial array of the three ligand nitrogen atoms. The coordination geometry about each gallium(III) ion is a slightly distorted octahedron, with the 6-phenyl series being slightly more distorted than the 6-methyl analogues. Pulsed NMR experiments allow solution NMR structures to be assessed, revealing good agreement with the solid-state structures.

Structure and stability of hexadentate complexes of ligands based on AAZTA for efficient PET labelling with gallium-68.

Pre-organised tricarboxylate ligands based on 6-amino-perhydro-1,4-diazepine bind (68)Ga rapidly and selectively in acetate buffer at pH 4 to 7, forming kinetically stable complexes suitable for use in PET imaging.

Sorption of small molecule vapours by single crystals of [Pt{4'-(Ph)trpy}(NCS)]SbF6 where trpy = 2,2':6',2''-terpyridine: a porous material with a structure stabilised by extended π-π interactions.

Treatment of [Pt{4'-(Ph)trpy}Cl]SbF(6) with AgSCN in a metathesis reaction in refluxing acetonitrile affords, after work-up, single crystals of [Pt{4'-(Ph)trpy}(NCS)]SbF(6)·CH(3)CN, where trpy is 2,2':6',2''-terpyridine. These crystals lose solvent to give single crystals of [Pt{4'-(Ph)trpy}(NCS)]SbF(6) (1). An X-ray crystal structure determination of 1 shows that the SCN(-) ion is N-bound and that the cation as a whole is approximately planar. Compound 1 is porous with "empty" channels that corkscrew through the crystal: this crystal structure is stabilised by extended π-π interactions between the planar cations. When a single crystal of 1 is exposed to vapours of acetonitrile the vapours are sorbed without loss of single crystallinity, as confirmed by crystal structure determinations of 1 and 1·CH(3)CN using the same single crystal. Similarly, single crystals of 1 sorb vapours of methanol without loss of single crystallinity, as confirmed by a crystal structure determination of 1·CH(3)OH. We also report the crystal structure of 1·(CH(3))(2)CO; however, in this case the single crystal was grown directly from acetone. Compound 1 and its solvates are all yellow. Nevertheless, there are differences between the emission spectra recorded for 1 and its solvates in the solid state. Thus, whereas 1 exhibits very weak multiple emission from (3)MLCT (MLCT = metal-to-ligand charge transfer) and excimeric (3)π-π* excited states, 1·CH(3)CN and 1·(CH(3))(2)CO both exhibit more intense (3)MLCT emission; and the emission by 1·CH(3)OH is complicated by the presence of metallophilic interactions in the crystal. We discuss the role of the solvent in causing these differences.

Speciation in solution, solid state spectroscopy and vapochromism of [Pt(trpy)(NCS)]SbF(6) where trpy = 2,2':6',2''-terpyridine.

Treatment of [Pt(trpy)Cl]SbF(6) with AgSCN in a metathesis reaction affords after work-up yellow crystals of [Pt(trpy)(NCS)]SbF(6).CH(3)CN where trpy is 2,2':6',2''-terpyridine. A single crystal structure determination of the solvate shows that the SCN(-) ion is N-bound to the Pt atom, and that the planar cations stack as Pt(2) dimers with a PtPt separation of 3.293(1) A. The crystals rapidly de-solvate under ambient conditions to give a polycrystalline maroon material characterised as [Pt(trpy)(NCS)]SbF(6) (). A (15)N NMR spectroscopic study of a solution of isotopically labeled [Pt(trpy)((15)N(13)CS)]SbF(6) in CD(3)CN shows that both linkage isomers of the SCN(-) ion co-exist in solution with the N-bound isomer dominant, and the S-bound isomer present at a much lower concentration. Compound exhibits temperature dependent (3)MMLCT emission in the solid state; at 280 K the emission maximises at 692 nm, but red-shifts systematically on cooling to reach 762 nm at 80 K. Compound shows vapochromic behaviour that is selective and reversible for vapours of acetonitrile, DMF and pyridine. The colour change is from maroon for to yellow for all three solvates. The emission spectra recorded for the solvates maximise at wavelengths that are all significantly blue-shifted compared to lambda(em)(max) recorded for : the blue-shifts measured at 77 K are 90, 115 and 155 nm for the acetonitrile, DMF and pyridine solvates respectively. The origin of the vapochromic properties of compound is likely to do with the breaking and making of metallophilic PtPt interactions in the solid state.