Kryptofix 222

All radiochemical reactions were carried out in anhydrous solvents in closed clear V-vials under air unless stated otherwise. All commercially available reagents were used without further purification unless stated otherwise. [¹⁸F]fluoride was produced via the ¹⁸O(p,n)¹⁸F reaction using a GE PETrace 800 series cyclotron at the Clinical Imaging Research Center (CIRC) and delivered as [¹⁸F]fluoride in enriched [¹⁸O]water. Acetonitrile, ethanol, potassium carbonate and Kryptofix 222 were of analytical grade and bought from Sigma-Aldrich. Water was obtained from an ELGA water purification system (model PF3XXXXM1). Tosyl-Fallypride TFA salt was bought from Bioduro LLC. MBCTT was bought from ABX. V-vials were bought from Fisher Scientific. Accell™ Plus QMA carbonate (46 mg) cartridges, Oasis® HLB light (30 mg) cartridges and ^tC18 light cartridges were bought from Waters. Gibco™ phosphate-buffered saline (PBS) solution 1× pH 7.4 was bought from Fisher Scientific. Detailed accounts for the radiosynthesis of [¹⁸F]FBCTT, [¹⁸F]fallypride and [¹⁸F]fluoro-l-thymidine can be found in the Supplementary Materials.

All reactions were carried out under a dry, argon atmosphere using a standard Schlenk line or glove box techniques. Solvents were purified as appropriate: en (Aldrich, 99.8%) was refluxed over CaH₂ for 24 hours, distilled and stored on 4 Å molecular sieves; DMF (Aldrich, 99.8%) and DMF-d₇ (Sigma-Aldrich, 99.5%) were stored over 3 Å molecular sieves for five days, distilled under vacuum (~50 mbar) and stored on 4 Å molecular sieves; acetonitrile (VWR Chemicals, >99%) was stored over 3 Å molecular sieves for five days, distilled and stored on 3 Å molecular sieves; and n-hexane (Sigma-Aldrich, >95%) and toluene (Acros Organics) were refluxed over Na for 24 hours, distilled and stored on 4 Å molecular sieves. The crypt-222 (Kryptofix 222, Sigma-Aldrich) was dried under vacuum. The A was prepared by the published procedure on a larger scale (0.50 mmol)^{44 (link)}. All other reagents were used as received: K (Acros Organics, 98%), Bi powder (ChemPur, 99.5%), [(cod)IrCl]₂ (ChemPur) and [CpRu(MeCN)₃][PF₆] (Sigma-Aldrich). K₅Bi₄ was synthesized by combining K and Bi in stoichiometric amounts in a niobium ampoule. The ampoule was sealed by arc-welding, sealed in a quartz tube under vacuum, placed in an oven and kept at 700 °C for 7 days.

All manipulations and reactions were performed under dry Ar atmosphere using standard Schlenk or glovebox techniques, as all Zintl compounds are sensitive to air and moisture. Elements were used as received: K lumps, Acros Organics, 98%; Ga pellets, Alfa Aesar, 99,9999% (metals basis); Bi powder, ChemPur Karlsruhe, 99%. Diphenyl zinc (ZnPh₂) was prepared according to a modified literature procedure^{54 (link)}: a 1:2 mixture of ZnCl₂ (0.2 mol/l in THF) and PhMgBr (1.3 mol/l in THF) in dry THF was stirred for 3 h at ambient temperature, before the solvent volume was doubled by addition of dioxane for precipitation of ZnPh₂ as colorless crystalline powder. The en and N,N-dimethylformamide (DMF; Aldrich, 99.8%) were distilled from CaH₂ and stored over 3 Å molecular sieves. Toluene (Acros Organics, 99%) was distilled from sodium–potassium alloy and stored over 4 Å molecular sieves. Kryptofix® 222 (crypt-222, Merck) was dried under vacuum overnight. A solid with the nominal composition K₅Ga₂Bi₄ was prepared by stoichiometric fusion of the elements in a homogeneous temperature chamber oven. The elements were weighed into a niobium tube that was sealed within an evacuated silica ampule. The mixture was heated to 550 °C, kept at this temperature for 24 h, and then cooled down to room temperature at a cooling rate of 5 K/h, and grinded prior to use.

For synthesis of FEC for human application, the method of Hara et al. [6 (link)] was improved and adopted to a TRACERlab FX_F-N automated system (GE Healthcare, Münster, Germany) in a certified GMP environment. Briefly, [¹⁸F]fluoride was produced at a PETtrace cyclotron (GE Healthcare, Uppsala, Sweden) and trapped on an anion exchange cartridge (Waters, Milford, MA, USA). Subsequently, radioactivity was eluted and azeotropically dried in presence of Kryptofix 2.2.2 (Merck, Darmstadt, Germany). In a first step, labelling of 1.2-bis(tosyloxy)ethane (Aldrich, Taufkirchen, Germany) with [¹⁸F]fluoride/[K/2.2.2] in acetonitrile yielded 2-[¹⁸F]fluoro-ethyltosylate, which was purified by HPLC and reversed phase solid phase extraction (RP SPE, Waters, Milford, MA, USA). In a second step, by reaction of the labelled tosylate with N,N-dimethylaminoethanol (DMAE) and subsequent cation exchange SPE (Waters, Milford, MA, USA) purification, FEC was obtained within 55 min, overall. After sterile filtration product volume was ca. 10 mL in buffered saline. Radiopharmaceutical quality control was performed following European Pharmacopoeia (Ph. Eur.) rules. Purity, pH, endotoxin content and sterility met the requirements for parenteralia.

DMSO (anhydrous, ≥99.9%), Kryptofix® 222 (for synthesis), oxalic acid (purified grade, 99.999% trace metals basis) and potassium hydroxide (semiconductor grade, pellets, 99.99% trace metals basis) were purchased from Merck KGaA (Darmstadt, Germany) or Sigma-Aldrich Chemie GmbH (Steinheim, Germany). Acetonitrile (for DNA synthesis, max. 10 ppm H₂O) was obtained from VWR International GmbH (Darmstadt, Germany). All other solvents were purchased from Merck KGaA (Darmstadt, Germany). The filters for sterile filtration (Cathivex-GV 25 mm PVDF 0,22 μm sterile) and venting (Millex-GS 0,22 μm Mixed Cellulose Esters) were obtained from Merck Chemicals GmbH (Darmstadt, Germany). Cartridges were purchased from Waters GmbH (Eschborn, Germany) and consumables from B. Braun Melsungen AG (Melsungen, Germany).

All manipulations and reactions were performed under dry Ar atmosphere by using standard Schlenk or glovebox techniques. All solvents were dried and freshly distilled prior to use. [2.2.2]crypt (4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, purchased as Kryptofix 222 from Merck) was dried in vacuo for at least 18 h. The synthesis of ternary phases K₁Ge₁As_x (x=0.5, 1) were approached by fusing K, Ge and As in the respective stoichiometric ratios in a silica glass ampoule with an oxygen torch or in a tantalum ampoule within an oven at 950 °C, respectively.