18 F-labeled 1,2,3-triazole-linked Glu-urea-Lys-based PSMA ligands have good pharmacokinetic properties for positron emission tomography imaging of prostate cancer.

BACKGROUND: Prostate-specific membrane antigen (PSMA) is increasingly recognized as an excellent target for prostate cancer imaging and therapy. Finding compounds with a high target-to-nontarget ratio are an important challenge in the development of positron emission tomography (PET) imaging agents. In this study, we attempted to find a suitable compound from a simply-synthesized compound library. METHOD: 18 F-labeling was achieved in a two-step synthesis consisting of [18 F]fluorination of azido sulfonates followed by copper(I)-catalyzed click ligation. In vitro binding experiment and in vivo studies were carried out using isogenic PSMA+ PC3-PIP and PSMA- PC3-flu cells and 22RV1 cells. [125 I]MIP-1095 was used to measure the binding affinities of compounds through a competitive binding assay, and [18 F]DCFPyL was used for a comparative assessment of compounds. Radiation dosimetry data were obtained using OLINDA/EXM software. RESULTS: Nine novel PSMA ligands were synthesized by the combination of three azido compounds and three terminal acetylene-containing Glu-urea-Lys compounds. Among them, compound 6f having a pyridine moiety showed a high binding affinity of 6.51 ± 0.19 nM (Ki ). 18 F-labeled compounds were obtained at moderate yields within 70 to 75 minutes (including high-performance liquid chromatography purification). Compound [18 F]6c had the lowest log P of -2.693. MicroPET/computed tomography (CT) images were acquired from 22RV1 cell xenograft mice after injecting [18 F]6c, [18 F]6f, and [18 F]6i. Additional microPET/CT experiments of [18 F]6c and [18 F]6f were performed using PSMA+ PC3-PIP and PSMA- PC3-flu cell-bearing mice. [18 F]6c was selected for further studies because it was found to have high uptake in tumors and rapid renal clearance, resulting in great tumor-to-nontumor ratios and distinct tumor images with very low background activity. Human dosimetry estimation of [18 F]6c using OLINDA/EXM software was calculated, resulting in an effective dose of 4.35 × 10-3 mSv/MBq. CONCLUSIONS: [18 F]6c showed significant tumor uptake, a high tumor-to-nontumor ratio, and good radiation dosimetry results, suggesting further development as a potential diagnostic PET agent for prostate cancer.

Synthesis and evaluation of 6-(3-[(18)F]fluoro-2-hydroxypropyl)-substituted 2-pyridylbenzothiophenes and 2-pyridylbenzothiazoles as potential PET tracers for imaging Aß plaques.

3-[(18)F]Fluoro-2-hydroxypropyl substituted compounds were synthesized and evaluated as novel (18)F-labeled PET tracers for imaging Aß plaque in a living brain. All compounds exhibited high binding affinities toward the synthetic Aß1-42 aggregate and/or Alzheimer's disease brain homogenate. In the microPET study with normal mice, the 3-[(18)F]fluoro-2-hydroxypropyl substituted compounds resulted in fast brain washout by reducing the lipophilicities of the compounds. Intriguingly, (S)-configured PET tracers, (S)-[(18)F]1b and (S)-[(18)F]1c, exhibited a 2.8 and 4.0-fold faster brain washout rate at a peak/30 min in the mouse brain than the corresponding (R)-configured PET tracers despite there being no meaningful difference in binding affinities toward Aß plaque. A further evaluation of (S)-[(18)F]1c with healthy rhesus monkeys also revealed excellent clearance from the frontal cortex with ratios of 7.0, 16.0, 30.0 and 49.0 at a peak/30, 60, 90, and 120 min, respectively. These results suggest that (S)-[(18)F]1c may be a potential PET tracer for imaging Aß plaque in a living brain.

Improving Theranostic Gallium-68/Lutetium-177-Labeled PSMA Inhibitors with an Albumin Binder for Prostate Cancer.

We developed a novel therapeutic radioligand, [177Lu]1h, with an albumin binding motif and evaluated it in a prostate-specific membrane antigen (PSMA)-expressing tumor xenograft mouse model. Fourteen PSMA target candidates were synthesized, and binding affinity was evaluated with an in vitro competitive binding assay. First, four compound candidates were selected depending on binding affinity results. Next, we selected four compounds ([68Ga]1e, [68Ga]1g, [68Ga]1h, and [68Ga]1k) were screened for tumor targeting efficiency by micro-positron emission tomography/computed tomography (micro-PET/CT) imaging. Finally, [177Lu]1h compound was evaluated the tumor targeting efficiency and therapeutic efficiency by micro-single-photon emission computed tomography/computed tomography (micro-SPECT/CT), biodistribution, and radiotherapy studies. Estimated human effective dose was calculated by biodistribution data. Compound 1h showed a high binding affinity (Ki value = 4.08 ± 0.08 nmol/L), and [177Lu]1h showed extended blood circulation (1 hour = 10.32 ± 0.31, 6 hours = 2.68 ± 1.07%ID/g) compared to [177Lu]PSMA-617 (1 h = 0.17 ± 0.10%ID/g). [177Lu]1h was excreted via the renal pathway and showed high tumor uptake (24.43 ± 3.36%ID/g) after 1 hour, which increased over 72 hours (72 hours = 51.39 ± 9.26%ID/g). Mice treated with 4 and 6 MBq of [177Lu]1h showed a median survival rate of >61 days. In particular, all mice treated with 6 MBq of [177Lu]1h survived for the entire monitoring period. The estimated human effective dose of [177Lu]1h was 0.07 ± 0.01 and 0.03 ± 0.00 mSv/MBq in total body and kidney, respectively. The current study indicates that [177Lu]1h has the potential for further investigation of metastatic castration-resistant prostate cancer (mCRPC) therapy in clinical trials.

Synergistic effect of two solvents, tert-alcohol and ionic liquid, in one molecule in nucleophilic fluorination.

We have demonstrated the synergistic effect in nucleophilic fluorination when we combined two solvents--ionic liquid (IL) and tert-alcohol--into one molecule. Consequently, these functionalized ILs not only increase the nucleophilic reactivities of the fluoride anion but also remarkably reduce the olefin byproduct. Although the mechanism of this synergistic effect remains to be elucidated, we have illustrated the possibility of solvent engineering for a specific reaction.

Efficiency of bulky protic solvent for SN2 reaction.

We calculate and compare the effects of aprotic vs protic solvent on the rate of SN2 reaction [F- + C3H7OMs--> C3H7F + OMs-]. We find that aprotic solvent acetonitrile is more efficient than a small protic solvent such as methanol. Bulky protic solvent (tert-butyl alcohol) is predicted to be quite efficient, giving the rate constant that is similar to that in CH3CN. Our calculated relative activation barriers of the SN2 reaction in methanol, tert-butyl alcohol, and CH3CN are in good agreement with experimental observations.

High efficiency synthesis of F-18 fluoromethyl ethers: an attractive alternative for C-11 methyl groups in positron emission tomography radiopharmaceuticals.

A rapid and efficient method for the synthesis of O-fluoromethyl aliphatic and aromatic ethers is presented. This method is so mild that it can be used for the preparation of positron emission tomography (PET) radiopharmaceuticals bearing O-[(18)F]fluoromethyl groups.

Highly efficient production of [(18)F]fallypride using small amounts of base concentration.

To minimize the base concentration of a phase-transfer catalyst, [(18)F]fluoride was extracted from (18)O-enriched water trapped on an activated ion exchange cartridge (Chromafix PS-HCO(3)) using different concentrations of tetrabutylammonium bicarbonate (TBAHCO(3)) or Kryptofix 2.2.2./K(2)CO(3) in organic solvents such as CH(3)CN/H(2)O or MeOH/H(2)O. The optimal labeling condition for [(18)F]fallypride with automated synthesis was that 2 mg of tosyl-fallypride in acetonitrile (1 mL) was heated at 100 degrees C for 10 min using 40% TBAHCO(3) (10 microL). [(18)F]Fallypride was obtained with a high radiochemical yield of approximately 68+/-1.6% (decay-corrected, n=42) with a total synthesis time of 51+/-1.2 min, including HPLC purification and solid-phase purification for the final formulation.

Copper nitride nanoparticles supported on a superparamagnetic mesoporous microsphere for toxic-free click chemistry.

Copper nitride nanoparticles supported on a mesoporous superparamagnetic silica microsphere exhibit superior activity toward the Huisgen cycloaddition of azides and alkynes. The nitride catalyst offers significant advantages over homogeneous Cu catalysts.

Convenient one-pot synthesis of 2,2-bis-(4-hydroxyphenyl)-cyclopentanone.

2,2-Bis-(4-hydroxyphenyl)-cyclopentanone (3a) was unexpectedly obtained in 76% yield from a reductive coupling reaction of 4,4'-dihydroxybenzophenone (1a) and cyclobutanone with TiCl4 and Zn. Further optimization showed that catechol as an external ligand and a hydroxy group on benzophenone facilitated the generation of a quinonemethide (intermediate II) that is involved in the pinacol-type rearrangement of intermediate I to give the rearranged product.

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter. Part 5: 2'-Substituted 6-nitroquipazines.

Five C2'-substituted 6-nitroquipazine (6-NQ) derivatives were prepared and evaluated in terms of their biological abilities (K(i)) to displace [(3)H]citalopram binding to serotonin transporter. The relationship between their structure and biological activities revealed that shorter alkyl groups tend to possess higher binding affinity. Both compounds 12a and 12c were found to have the equally highest binding affinity (K(i)=0.43+/-0.02 nM).

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter. Part 4: 3-Alkyl-4-halo-6-nitroquipazines.

On the basis of the structure-activity relationship (SAR) of 4-chloro-6-nitroquipazine (Ki = 0.03 nM) and 3-fluoropropyl-6-nitroquipazine (Ki = 0.32 nM), 3-alkyl-4-halo-6-nitroquipazines were synthesized and tested for their potential abilities in vitro to displace [3H]citalopram binding to the rat cortical membranes. Binding affinities of 3b and 4d were Ki = 2.70+/-0.32 and 2.23+/-0.46 nM, respectively. The syntheses of 3-alkyl-4-halo-6-nitroquipazine, their in vitro binding affinities, and the SAR of C3, C4 position in 6-nitroquipazine are described.

Novel synthesis of 2-chloroquinolines from 2-vinylanilines in nitrile solvent.

2-Vinyl- or heteroaryl-substituted anilines were reacted with diphosgene in acetonitrile solution via a reactive imidoyl moiety to afford the corresponding 2-chloroquinolines. Facile syntheses of nine 2-chloroquinoline derivatives from several anilines and their postulate mechanism is described. The postulate mechanism of 2-chloroquinoline formation via imidoyl moiety as a good leaving group shows that the reaction consists of the following three steps: (1) generation of phenylisocyanate, (2) quinoline ring formation, and (3) chlorination on C2 position of quinoline.

Suspension ring-opening metathesis polymerization: the preparation of norbornene-based resins for application in organic synthesis.

A series of norbornene-based resin beads were obtained by aqueous suspension ring-opening metathesis polymerization (ROMP) and used as polymeric supports for organic synthesis. These resins were prepared from norbornene, norborn-2-ene-5-methanol, and cross-linkers such as bis(norborn-2-ene-5-methoxy)alkanes, di(norborn-2-ene-5-methyl)ether, and 1,3-di(norborn-2-ene-5-methoxy)benzene. The resulting unsaturated ROMP (U-ROMP) resins containing olefin repeat units were chemically modified using hydrogenation, hydrofluorination, chlorination, and bromination reactions to produce saturated ROMP resins with different chemical and physical properties. The hydrogenated ROMP (H-ROMP) resin was found to be highly resistant to acidic, basic, Lewis acid, and Birch reduction conditions and was assessed as a polymeric support in a series of solid-phase synthetic applications. The H-ROMP resin was found to have superior performance compared to polystyrene-divinylbenzene (PS-DVB) copolymers in aromatic nitration and acylation reactions. In a conventional five-step solid-phase synthesis of a hydantoin, similar results were obtained for both the H-ROMP and PS-DVB resins. The U-ROMP resin was also shown to be effective in the solid-phase syntheses of benzimidazoles and benzimidazolones.

Syntheses and binding affinities of 6-nitroquipazine analogues for serotonin transporter: Part 3. A potential 5-HT transporter imaging agent, 3-(3-[18F]fluoropropyl)-6-nitroquipazine.

3-(3-[18F]Fluoropropyl)-6-nitroquipazine ([18F]FPNQ) as a 5-HT transporter imaging agents was designed, synthesized, and evaluated. FPNQ was selected due to its potent in vitro biological activity (K(i)=0.32 nM) in rat brain cortical membranes. The 18F-labeled FPNQ was prepared by reaction of the propyl mesylate as a precursor with tetra-n-butylammonium [18F]fluoride generated under NCA conditions. The precursor mesylate was synthesized from commercially available hydrocarbostyril in nine steps in 21% overall yield. The specific activity of the [18F]FPNQ determined by radioreceptor assay was 27.0 GBq/micromol. Tissue distribution studies in mice showed the highest uptake in the frontal cortex (5.79 %ID/g) at 60 min post-injection.