Design,synthesis and biological evaluation of novel substituted benzoylguanidine derivatives as potent Na+/H+ exchanger inhibitors

A novel series of substituted benzoylguanidine derivatives were designed and synthesized as potent NHE1 inhibitors. Most compounds can significantly inhibit NHE1-mediated platelet swelling in a concentration-dependent manner, among which compound 5f (IC₅₀ = 3.60 nM) and 5l (IC₅₀ = 4.48 nM) are 18 and 14 times respectively more potent than cariporide (IC₅₀ = 65.0 nM). Furthermore, when tested in vivo and in vitro, compound 5f showed superior cardioprotective effects against SD rat myocardial ischemic-reperfusion injury over cariporide, representing a promising lead compound for further exploration.     

Furo[3′,2′:3,4]naphtho[1,2-d]imidazole derivatives as potential inhibitors of inflammatory factors in sepsis

Synthesis and anti-inflammatory effects of certain furo[3′,2′:3,4]naphtho[1,2-d]imidazole derivatives 12–18 were studied. These compounds were synthesized from naphtho[1,2-b]furan-4,5-dione (10) which in turn was prepared from the known 2-hydoxy-1,4-naphthoquinone (7) in a one pot reaction. Furo[3′,2′:3,4]naphtho[1,2-d]imidazole (12) was inactive (IC₅₀ value of >30 μM) while its 5-phenyl derivative 13, with an IC₅₀ value of 16.3 and 11.4 μM against lysozyme and β-glucuronidase release, respectively, was comparable to the positive trifluoperazine. The same potency was observed for 5-furan derivative 16 with an IC₅₀ value of 19.5 and 11.3 μM against lysozyme and β-glucuronidase release, respectively. An electron-withdrawing NO₂ substituted on 5-phenyl or 5-furanyl group led to the devoid of activity as in the cases of 14 and 17. Among them, compound 15 exhibited significant inhibitory effects, with an IC₅₀ value of 7.4 and 5.0 μM against lysozyme and β-glucuronidase release, respectively.For the LPS-induced NO production, the phenyl derivatives 12–15 were inactive while the nitrofuran counterparts 17 and 18 suppress LPS-induced NO production significantly, with an IC₅₀ value of 1.5 and 1.3 μM, respectively, which are more active than that of the positive 1400 W. Compounds 16–18 were capable of inhibiting LPS-induced iNOS protein expression at a dose-dependent manner in which compound 18, with an IC₅₀ of 0.52 μM in the inhibition of iNOS expression, is approximately fivefold more potent than that of the positive 1400 W. In the CLP rat animal model, compound 18 was found to be more active than the positive hydrocortisone in the inhibition of the iNOS mRNA expression in rat lung tissue. The sepsis-induced PGE2 production in rat serum decreased 150% by the pretreatment of 18 in a dose of 10 mg/kg.     

Synthesis and biological evaluation of novel propargyl amines as potential fluorine-18 labeled radioligands for detection of MAO-B activity

The aim of this project was to synthesize and evaluate three novel fluorine-18 labeled derivatives of propargyl amine as potential PET radioligands to visualize monoamine oxidase B (MAO-B) activity.The three fluorinated derivatives of propargyl amine ((S)-1-fluoro-N,4-dimethyl-N-(prop-2-ynyl)-pent-4-en-2-amine (5), (S)-N-(1-fluoro-3-(furan-2-yl)propan-2-yl)-N-methylprop-2-yn-1-amine (10) and (S)-1-fluoro-N,4-dimethyl-N-(prop-2-ynyl)pentan-2-amine (15)) were synthesized in multi-step organic syntheses. IC₅₀ values for inhibition were determined for compounds 5, 10 and 15 in order to determine their specificity for binding to MAO-B. Compound 5 inhibited MAO-B with an IC₅₀ of 664 ± 48.08 nM. No further investigation was carried out with this compound. Compound 10 inhibited MAO-B with an IC₅₀ of 208.5 ± 13.44 nM and compound 15 featured an IC₅₀ of 131.5 ± 0.71 nM for its MAO-B inhibitory activity. None of the compounds inhibited MAO-A activity (IC₅₀ > 2 μM).The fluorine-18 labeled analogues of the two higher binding affinity compounds (10 and 15) (S)-N-(1-[¹⁸F]fluoro-3-(furan-2-yl)propan-2-yl)-N-methylprop-2-yn-1-amine (16) and (S)-1-[¹⁸F]fluoro-N,4-dimethyl-N-(prop-2-ynyl)pentan-2-amine (18) were both prepared from the corresponding precursors 9A, 9B and 14A, 14B by a one-step fluorine-18 nucleophilic substitution reaction. Autoradiography experiments on human postmortem brain tissue sections were performed with 16 and 18. Only compound 18 demonstrated a high selectivity for MAO-B over MAO-A and was, therefore, chosen for further examination by PET in a cynomolgus monkey.The initial uptake of 18 in the monkey brain was 250% SUV at 4 min post injection. The highest uptake of radioactivity was observed in the striatum and thalamus, regions with high MAO-B activity, whereas lower levels of radioactivity were detected in the cortex and cerebellum. The percentage of unchanged radioligand 18 was 30% in plasma at 90 min post injection.In conclusion, compound 18 is a selective inhibitor of MAO-B in vitro and demonstrated a MAO-B specific binding pattern in vivo by PET in monkey. It can, therefore, be considered as a candidate for further investigation in human by PET.     

Evaluation of pyrrolin-2-one derivatives synthesized by a new practical method as inhibitors of plasminogen activator inhibitor-1 (PAI-1)

We describe in this Letter a new synthetic method for pyrrolin-2-ones as potent plasminogen activator inhibitor-1 (PAI-1) inhibitors. Pyrrolin-2-one derivatives synthesized from N-2-oxoethylamides and aldehydes in aqueous NaOH by one-pot were evaluated for their PAI-1 inhibitory activity. Among these derivatives, compounds 16 and 18 were found to possess potent PAI-1 inhibitory activity (compound 16: IC₅₀: 0.69 μM, compound 18: IC₅₀: 0.65 μM).     

The immunomodulation potential of the synthetic derivatives of benzothiazoles: Implications in immune system disorders through in vitro and in silico studies

Benzothiazole and its natural or synthetic derivatives have been used as precursors for several pharmacological agents for neuroprotective, anti-bacterial, and anti-allergic activities. The objecctive of the present study was to evaluate effects of benzothiazole analogs (compounds 1–26) for their immunomodulatory activities. Eight compounds (2, 4, 5, 8–10, 12, and 18) showed potent inhibitory activity on PHA-activated peripheral blood mononuclear cells (PBMCs) with IC₅₀ ranging from 3.7 to 11.9 μM compared to that of the standard drug, prednisolone <1.5 μM. Some compounds (2, 4, 8, and 18) were also found to have potent inhibitory activities on the production of IL-2 on PHA/PMA-stimulated PBMCs with IC₅₀ values ranging between <4.0 and 12.8 μM. The binding interaction of these compounds was performed through silico molecular docking. Compounds 2, 8, 9, and 10 significantly suppressed oxidative burst ROS production in phagocytes with IC₅₀ values between <4.0 and 15.2 μM. The lipopolysaccharide (LPS)-induced nitrites in murine macrophages cell line J774 were found to be inhibited by compounds 4, 8, 9, and 18 at a concentration of 25 μg/mL by 56%, 91%, 58%, and 78%, respectively. Furthermore, compounds 5, 8, 12, and 18 showed significant (P < 0.05) suppressive activity on Th-2 cytokine, interleukin 4 (IL-4) with an IC₅₀ range of <4.0 to 40.3 μM. Interestingly compound 4 has shown a selective inhibitory activity on IL-2 and T cell proliferation (naïve T cell proliferation stage) rather than on IL-4 cytokine, while compound 12 displayed an interference with T-cell proliferation and IL-4 generation. Moreover compound 8 and 18 exert non-selective inhibition on both IL-2 and IL-4 cytokines, indicating a better interference with stage leading to humoral immune response and hence possible application in autoimmune diseases.     

Development of a novel fluorine-18 labeled deuterated fluororasagiline ([18F]fluororasagiline-D2) radioligand for PET studies of monoamino oxidase B (MAO-B)

The objective of this study was to synthesize and evaluate a novel fluorine-18 labeled deuterium substituted analogue of rasagiline (9, [¹⁸F]fluororasagiline-D₂) as a potential PET radioligand for studies of monoamine oxidase B (MAO-B).The precursor compound (6) and reference standard (7) were synthesized in multi-step syntheses. Radiolabeling of 9 was accomplished by a two-step synthesis, compromising a nucleophilic substitution followed by hydrolysis of the sulfamidate group. The incorporation radiochemical yield from fluorine-18 fluoride was higher than 30%, the radiochemical purity was >99% and the specific radioactivity was >160 GBq/μmol at the time of administration.In vitro compound 7 inhibited the MAO-B activity with an IC₅₀ of 173.0 ± 13.6 nM. The MAO-A activity was inhibited with an IC₅₀ of 9.9 ± 1.1 μM. The fluorine-18 version 9 was characterized in the cynomolgus monkey brain where a high brain uptake was found (275% SUV at 4 min). There was a higher uptake in the striatum and thalamus compared to the cortex and cerebellum. A pronounced blocking effect (50% decrease) was observed in the specific brain regions after administration of l-deprenyl (0.5 mg/kg) 30 min prior to the administration of 9. Radiometabolite studies demonstrated 40% of unchanged radioligand at 90 min post injection.An efficient radiolabeling of 9 was successfully established and in the monkey brain 9 binds to MAO-B rich regions and its binding is blocked by the selective MAO-B compound l-deprenyl. The radioligand 9 is a potential candidate for human PET studies.     

Synthesis and structure–activity relationships of N-benzyl-N-(X-2-hydroxybenzyl)-N′-phenylureas and thioureas as antitumor agents

Two series of novel N-benzyl-N-(X-2-hydroxybenzyl)-N′-phenylureas and thioureas (1a–18a; 1b–18b) as potential EGFR and HER-2 kinase inhibitors have been discovered. These compounds displayed good EGFR and HER-2 inhibitory activity and the SARs are also been studied. Especially compound 7b demonstrated significant EGFR and HER-2 inhibitory activity (IC₅₀ = 0.08 μM for EGFR and IC₅₀ = 0.35 μM for HER-2). Docking simulation was performed to position compound 7b into the EGFR active site to determine the probable binding conformation and antiproliferative assay results indicating that these series of urea and thioureas own high antiproliferative activity against MCF-7. Above all, thiourea 7b would be a potential anticancer agent deserves further research.     

A benzenesulfonamide derivative as a novel PET radioligand for CXCR4

CXCR4 is involved in various diseases such as inflammation, tumor growth, and cancer metastasis through the interaction with its natural endogenous ligand, chemokine CXCL12. In an effort to develop imaging probes for CXCR4, we developed a novel small molecule CXCR4-targeted PET agent (compound 5) by combining our established benzenesulfonamide scaffold with a labeling component by virtue of click chemistry. 5 shows nanomolar affinity (IC₅₀ = 6.9 nM) against a known CXCR4 antagonist (TN14003) and inhibits more than 65% chemotaxis at 10 nM in vitro assays. Radiofluorinated compound 5 ([¹⁸F]5) demonstrates a competitive cellular uptake against CXCL12 in a dose-dependent manner. Further, microPET images of [¹⁸F]5 exhibits preferential accumulation of radioactivity in the lesions of λ-carrageenan-induced paw edema, human head and neck cancer orthotopic xenograft, and metastatic lung cancer of each mouse model.     

Synthesis of structurally diverse benzosuberene analogues and their biological evaluation as anti-cancer agents

Diversely functionalized, fused aryl–alkyl ring systems hold a prominent position as well-established molecular frameworks for a variety of anti-cancer agents. The benzosuberene (6,7 fused, also referred to as dihydro-5H-benzo[7]annulene and benzocycloheptene) ring system has emerged as a valuable molecular core component for the development of inhibitors of tubulin assembly, which function as antiproliferative anti-cancer agents and, in certain cases, as vascular disrupting agents (VDAs). Both a phenolic-based analogue (known as KGP18, compound 39) and its corresponding amine-based congener (referred to as KGP156, compound 45), which demonstrate strong inhibition of tubulin assembly (low micromolar range) and potent cytotoxicity (picomolar range for KGP18 and nanomolar range for KGP156) are noteworthy examples of such benzosuberene-based compounds. In order to extend the structure–activity relationship (SAR) knowledge base related to benzosuberene anti-cancer agents, a series of eleven analogues (including KGP18) were prepared in which the methoxylation pattern on the pendant aryl ring as well as functional group incorporation on the fused aryl ring were varied. The synthetic approach to these compounds featured a sequential Wittig olefination, reduction, Eaton’s reagent-mediated cyclization strategy to achieve the core benzosuberone intermediate, and represented a higher-yielding synthesis of KGP18 (which we prepared previously through a ring-expansion strategy). Incorporation of a fluorine or chlorine atom at the 1-position of the fused aryl ring or replacement of one of the methoxy groups with hydrogen (on the pendant aryl ring of KGP18) led to benzosuberene analogues that were both strongly inhibitory against tubulin assembly (IC₅₀ approximately 1.0 μM) and strongly cytotoxic against selected human cancer cell lines (for example, GI₅₀ = 5.47 nM against NCI-H460 cells with fluoro-benzosuberene analogue 37). A water-soluble phosphate prodrug salt of KGP18 (referred to as KGP265, compound 44) and a water-soluble serinamide salt (compound 48) of KGP156 were also synthesized and evaluated in this study.     

Synthesis and topoisomerases inhibitory activity of heteroaromatic chalcones

The critical role of nuclear topoisomerase enzymes during cell proliferation process guided topoisomerases to be one of the major targets for anticancer drug development. We have designed and synthesized 22 heteroaromatic ring incorporated chalcone derivatives substituted with epoxide or thioepoxide. Topoisomerase enzyme inhibitory activity and cytotoxic tests were also conducted to evaluate compounds’ pharmacological efficacy. In the topoisomerase I inhibitory test, compound 1 was most active one, 24% of inhibition at 20 μM, among all the compounds but it was lower than camptothecin. Compounds 9, 11, and 13 inhibited the function of topoisomerase II more strongly than etoposide with almost same magnitude (around 90% and 30% inhibition at 100 and 20 μM, respectively) which were higher than those of etoposide (72% and 18% inhibition). In the cytotoxicity test, compound 9 inhibited T47D cancer cell growth with the IC₅₀ value of 6.61 ± 0.21 μM. On the other hand, compound 13 (IC₅₀: 4.32 ± 0.18 μM) effectively suppressed MDA-MB468 cancer cell growth.     

Discovery of novel 2,4-disubstituted pyrimidines as Aurora kinase inhibitors

In order to explore novel Aurora kinase inhibitors, a series of novel 2,4-disubstituted pyrimidines were designed, synthesized and evaluated their in vitro anti-proliferative activities against a panel of cancerous cell lines (A549, HCT-116 and MCF-7). Among them, compound 12a showed the moderate to high anti-proliferative activities against A549 (IC₅₀ = 12.05 ± 0.45 μM), HCT-116 (IC₅₀ = 1.31 ± 0.41 μM) and MCF-7 (IC₅₀ = 20.53 ± 6.13 μM) cells, as well as the Aurora A and Aurora B inhibitory activities with the IC₅₀ values of 309 nM and 293 nM, respectively. Furthermore, compound 12a induced apoptosis by upregulated the pro-apoptotic proteins Bax and decreased the anti-apoptotic protein Bcl-xl in HCT-116 cells. Moreover, the molecular docking study showed that compound 12a had good binding modes with Aurora A and Aurora B and the bioinformatics prediction discovered that compound 12a exhibited good drug likeness using SwissADME. Taken together, these results indicated that 12a may be a potential anticancer compound that was worthy of further development as Aurora kinase inhibitor.     

Synthesis and evaluation of Al18F-NODA complex conjugated 2-(4-aminophenyl)benzothiazole as a potential tumor imaging agent

The objective of the study was to prepare and evaluate a ¹⁸F-radiolabled tracer (Al¹⁸F-5), derivated from the antitumor agent 2-(4-aminophenyl)benzothiazole, as a PET probe for tumor imaging. Al¹⁸F-5 was successfully prepared with approx. 40% radiochemical yield in aqueous phase. In in vitro cell uptake experiments and competition assay, Al¹⁸F-5 displayed good tumor-binding ability and specificity in HeLa cells (24.7 ± 0.9% ID/10⁶ cells, IC₅₀ = 63.8 ± 13.6 nM) and MCF-7 cells (6.8 ± 0.3% ID/10⁶ cells, IC₅₀ = 331.1 ± 33.7 nM). The nonradioactive compound, Al¹⁹F-5, visibly marked HeLa cells and MCF-7 cells but did not stain HEB cells in florescent staining, which further indicated the tumor-binding ability of Al¹⁸F-5. In in vivo PET imaging, HeLa and MCF-7 tumors were clearly delineated by specific accumulation of Al¹⁸F-5 in model mice. In biodistribution study, Al¹⁸F-5 exhibited good tumor uptake (4.66 ± 0.13% ID/g and 3.69 ± 0.56% ID/g, respectively), moderate tumor-to-muscle ratio (3.38 and 2.48, respectively) at 1 h post injection, which were in a good consistency with the results of PET imaging. In conclusion, Al¹⁸F-5 might be developed as a candidate PET probe for tumor imaging, though additional optimizations are still needed to improve pharmacokinetics in vivo.     

Synthesis and anti-tumor evaluation of B-ring substituted steroidal pyrazoline derivatives

The synthesis and anti-tumor activity screening of new steroidal derivatives (4–18) containing pharmacologically attractive pyrazoline moieties are performed. During in vitro anticancer evaluation, the newly synthesized compounds displayed moderate to good cytotoxicity on cervical and leukemia cancer cell lines. In addition these compounds were found to be nontoxic to normal cell (PBMCs) (IC₅₀ > 50 μM). The structure–activity relationship is also discussed. The most effective anticancer compound 9 was found to be active with IC₅₀ value of 10.6 μM. It demonstrated significant antiproliferative influence on Jurkat cell lines. The morphological changes and growth characteristics of HeLa cells treated with compound 4 were analyzed by means of SEM.     

Synthesis and SAR of derivatives based on 2-biarylethylimidazole as bombesin receptor subtype-3 (BRS-3) agonists for the treatment of obesity

This Letter describes a series of potent and selective BRS-3 agonists containing a biarylethylimidazole pharmacophore. Extensive SAR studies were carried out with different aryl substitutions. This work led to the identification of a compound 2-{2-[4-(pyridin-2-yl)phenyl]ethyl}-5-(2,2-dimethylbutyl)-1H-imidazole 9 with excellent binding affinity (IC₅₀ = 18 nM, hBRS-3) and functional agonist activity (EC₅₀ = 47 nM, 99% activation). After oral administration, compound 9 had sufficient exposure in diet induced obese mice to demonstrate efficacy in lowering food intake and body weight via BRS-3 activation.     

Triazoxins: Novel nucleosides with anti-Giardia activity

Novel nucleoside analogues named “triazoxins” were synthesized. Of these, two analogues were found to be highly effective against Giardia lamblia, an intestinal parasite and a major cause of waterborne infection, worldwide. While compound 7 reduced the growth of trophozoites in culture (IC₅₀, ~5 μM), compound 21 blocked the in vitro cyst production (IC₅₀ ~5 μM). Compound 21 was also effective against trophozoites (IC₅₀, ~36 μM). A third analogue (compound 8) was effective against both trophozoites (IC₅₀, ~36 μM) and cysts (IC₅₀, ~20 μM) although at higher concentration. Thus triazoxin analogues are unique and exhibit morphology (i.e., trohozoites or cysts) -specific effects against Giardia.     

Application of natural products as insecticide candidates: Semisynthesis and biological evaluation of some novel osthole-based esters

Natural products are very important sources for the development of new pesticides. Osthole, derived from many medical plants such as Cnidium, Angelica and Citrus plants, is a naturally occurring coumarin compound. To discover the new natural products-based insecticides, thirty-one osthole-based esters containing O-acyl-hydroxylamine groups were prepared, and their structures were identified by different spectral analysis methods. Derivatives A7, A17, A20 and A25 displayed more potent growth inhibitory (GI) activity than the botanical insecticide, toosendanin. Over half of target osthole derivatives had more effective larvicidal effect on P. xylostella than toosendanin. Among all title derivatives, compound A18 displayed more pronounced larvicidal activity (LC₅₀ = 0.64 μmol mL⁻¹) when compared with toosendanin (LC₅₀ = 0.94 μmol mL⁻¹). Some interesting results of structure–activity relationships (SARs) of these osthole derivatives were also discussed. In addition, the hemolysis and cytotoxicity assays indicated that these osthole derivatives showed very low toxicity toward normal mammalian cells.     

Design,synthesis and biological evaluation of 4-aminopyrimidine-5-cabaldehyde oximes as dual inhibitors of c-Met and VEGFR-2

The synergistically collaboration of c-Met/HGF and VEGFR-2/VEGF leads to development of tumor angiogenesis and progression of various human cancers. Therefore, inhibiting both HGF/c-Met and VEGF/VEGFR signaling may provide a novel and effective therapeutic approach for treating patients with abroad spectrum of tumors. Toward this goal, we designed and synthesized a series of derivatives bearing 4-aminopyrimidine-5-cabaldehyde oxime scaffold as potent dual inhibitors of c-Met and VEGFR-2. The cell proliferation assay in vitro demonstrated most target compounds have inhibition potency both on c-Met and VEGFR-2 with IC₅₀ values in nanomolar range, especially compound 14i, 18a and 18b. Based on the further enzyme assay in vitro, compound 18a was considered as the most potent one, the IC₅₀s of which were 210 nM and 170 nM for c-Met and VEGFR-2, respectively. Following that, we docked the compound 10 and 18a with the proteins c-Met and VEGFR-2, and interpreted the SAR of these analogs. All the results indicate that 18a is a dual inhibitors of c-Met and VEGFR-2 that holds promising potential.     

Discovery of potent dipeptidyl peptidase IV inhibitors through pharmacophore hybridization and hit-to-lead optimization

A novel dipeptidyl peptidase IV inhibitor hit (5, IC₅₀ = 0.86 μM) was structurally derived from our recently disclosed preclinical candidate 4 by replacing the cyanobenzyl with a butynyl based on pharmacophore hybridization. A hit-to-lead optimization effort was then initiated to improve its potency. Most N-substituted analogs exhibited good in vitro activity, and compound 18o (IC₅₀ = 1.55 nM) was identified to be a potent dipeptidyl peptidase IV inhibitor with a significantly improved pharmacokinetic properties (bioavailablity: 41% vs 82.9%; T_1/2: 2 h vs 4.9 h).     

Identification of 2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-derived ureas as potent inhibitors of human nicotinamide phosphoribosyltransferase (NAMPT)

Potent nicotinamide phosphoribosyltransferase (NAMPT) inhibitors containing 2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-derived ureas were identified using structure-based design techniques. The new compounds displayed improved aqueous solubilities, determined using a high-throughput solubility assessment, relative to previously disclosed urea and amide-containing NAMPT inhibitors. An optimized 2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-derived compound exhibited potent anti-NAMPT activity (18; BC NAMPT IC₅₀ = 11 nM; PC-3 antiproliferative IC₅₀ = 36 nM), satisfactory mouse PK properties, and was efficacious in a PC-3 mouse xenograft model. The crystal structure of another optimized compound (29; NAMPT IC₅₀ = 10 nM; A2780 antiproliferative IC₅₀ = 7 nM) in complex with the NAMPT protein was also determined.     

Synthesis and evaluation of new 1-oxa-8-azaspiro[4.5]decane derivatives as candidate radioligands for sigma-1 receptors

We report the design, synthesis, and evaluation of a series of 1-oxa-8-azaspiro[4.5]decane and 1,5-dioxa-9-azaspiro[5.5]undecane derivatives as selective σ₁ receptor ligands. All seven ligands exhibited nanomolar affinity for σ₁ receptors (K_i(σ₁) = 0.47 – 12.1 nM) and moderate selectivity over σ₂ receptors (K_i(σ₂)/ K_i(σ₁) = 2 – 44). Compound 8, with the best selectivity among these ligands, was selected for radiolabeling and further evaluation. Radioligand [¹⁸F]8 was prepared via nucleophilic ¹⁸F-substitution of the corresponding tosylate precursor, with an overall isolated radiochemical yield of 12–35%, a radiochemical purity of greater than 99%, and molar activity of 94 – 121 GBq/μmol. Biodistribution studies of [¹⁸F]8 in mice demonstrated high initial brain uptake at 2 min. Pretreatment with SA4503 resulted in significantly reduced brain-to-blood ratio (70% − 75% at 30 min). Ex vivo autoradiography in ICR mice demonstrated high accumulation of the radiotracer in σ₁ receptor-rich brain areas. These findings suggest that [¹⁸F]8 could be a lead compound for further structural modifications to develop potential brain imaging agents for σ₁ receptors.