The first radiosynthesis of [11C]AZD8931 as a new potential PET agent for imaging of EGFR,HER2 and HER3 signaling

The reference standard AZD8931{2-(4-((4-((3-chloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)piperidin-1-yl)-N-methylacetamide} (11a) was synthesized from methyl 4,5-dimethoxy-2-nitrobenzoate or ethyl 4,5-dimethoxy-2-nitrobenzoate and 2-chloro-N-methylacetamide in 11 steps with 2–5% overall chemical yield. The precursor N-desmethyl-AZD8931{2-(4-((4-((3-chloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)piperidin-1-yl)acetamide} (11b) was synthesized from methyl 4,5-dimethoxy-2-nitrobenzoate or ethyl 4,5-dimethoxy-2-nitrobenzoate and 2-bromoacetamide in 11 steps with 2–4% overall chemical yield. The target tracer [¹¹C]AZD8931 {2-(4-((4-((3-chloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)piperidin-1-yl)-N-[¹¹C]methylacetamide} ([¹¹C]11a) was prepared from N-desmethyl-AZD8931 (11b) with [¹¹C]CH₃OTf under basic condition (NaH) through N-[¹¹C]methylation and isolated by HPLC combined with solid-phase extraction (SPE) in 40–50% radiochemical yield based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB) with 370–1110 GBq/μmol specific activity at EOB.     

Synthesis of carbon-11-labeled aminoalkylindole derivatives as new candidates of cannabinoid receptor radioligands for PET imaging of alcohol abuse

Carbon-11-labeled aminoalkylindole derivatives (1-butyl-7-[¹¹C]methoxy-1H-indol-3-yl)(naphthalene-1-yl)methanone ([¹¹C]3), 1-butyl-7-[¹¹C]methoxy-3-(naphthalene-1-ylmethyl)-1H-indole ([¹¹C]5), and 1-butyl-7-[¹¹C]methoxy-3-(naphthalene-2-yl)-1H-indole ([¹¹C]8) were prepared by O-[¹¹C]methylation of their corresponding precursors with [¹¹C]CH₃OTf under basic condition (2 N NaOH) and isolated by a simplified solid-phase extraction (SPE) method in 50–60% radiochemical yields based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 23 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 185–555 GBq/μmol.     

Synthesis of carbon-11-labeled 5-HT6R antagonists as new candidate PET radioligands for imaging of Alzheimer’s disease

Carbon-11-labeled serotonin (5-hydroxytryptamine) 6 receptor (5-HT₆R) antagonists, 1-[(2-bromophenyl)sulfonyl]-5-[¹¹C]methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole (O-[¹¹C]2a) and 1-[(2-bromophenyl)sulfonyl]-5-methoxy-3-[(4-[¹¹C]methyl-1-piperazinyl)methyl]-1H-indole (N-[¹¹C]2a), 5-[¹¹C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-indole (O-[¹¹C]2b) and 5-methoxy-3-((4-[¹¹C]methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-indole (N-[¹¹C]2b), 1-((4-isopropylphenyl)sulfonyl)-5-[¹¹C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole (O-[¹¹C]2c) and 1-((4-isopropylphenyl)sulfonyl)-5-methoxy-3-((4-[¹¹C]methylpiperazin-1-yl)methyl)-1H-indole (N-[¹¹C]2c), 1-((4-fluorophenyl)sulfonyl)-5-[¹¹C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole (O-[¹¹C]2d) and 1-((4-fluorophenyl)sulfonyl)-5-methoxy-3-((4-[¹¹C]methylpiperazin-1-yl)methyl)-1H-indole (N-[¹¹C]2d), were prepared from their O- or N-desmethylated precursors with [¹¹C]CH₃OTf through O- or N-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–50% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ～40-min from EOB.     

Synthesis of carbon-11-labeled casimiroin analogues as new potential PET agents for imaging of quinone reductase 2 and aromatase expression in breast cancer

Carbon-11-labeled casimiroin analogues were first designed and synthesized as new potential PET agents for imaging of quinone reductase (QR) 2 and aromatase expression in breast cancer. [¹¹C]casimiroin (6-[¹¹C]methoxy-9-methyl-[1,3]dioxolo[4,5-h]quinolin-8(9H)-one, [¹¹C]11) and its carbon-11-labeled analogues 5,6,8-trimethoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]17), 8-methoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]21a), 6,8-dimethoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]21b), and 5,8-dimethoxy-1-[¹¹C]methyl-4-methylquinolin-2(1H)-one ([¹¹C]21c), were prepared from their corresponding precursors with [¹¹C]methyl triflate ([¹¹C]CH₃OTf) under basic conditions (NaH) through either O- or N-[¹¹C]methylation and isolated by semi-preparative HPLC method in 40-50% radiochemical yields decay corrected to end of bombardment (EOB), based on [¹¹C]CO₂, and 111-185 GBq/μmol specific activity at the end of synthesis (EOS).     

Synthesis of (Z)-2-((1H-indazol-3-yl)methylene)-6-[11C]methoxy-7-(piperazin-1-ylmethyl)benzofuran-3(2H)-one as a new potential PET probe for imaging of the enzyme PIM1

(Z)-2-((1H-Indazol-3-yl)methylene)-6-methoxy-7-(piperazin-1-ylmethyl)benzofuran-3(2H)-one is a potent and selective proviral integration site in moloney murine leukemia virus kinase 1 (PIM1) inhibitor with an IC₅₀ value of 3 nM. (Z)-2-((1H-Indazol-3-yl)methylene)-6-[¹¹C]methoxy-7-(piperazin-1-ylmethyl)benzofuran-3(2H)-one, a new potential PET probe for imaging of the enzyme PIM1, was first designed and synthesized in 20–30% decay corrected radiochemical yield and 370–740 GBq/μmol specific activity at end of bombardment (EOB). The synthetic strategy was to prepare a carbon-11-labeled Boc-protected intermediate followed by a quick acidic de-protection.     

Concise and high-yield synthesis of T808 and T808P for radiosynthesis of [18F]-T808, a PET tau tracer for Alzheimer’s disease

The authentic standard T808 and its corresponding mesylate precursor T808P were synthesized in six steps using ethyl vinyl ether and trichlorocetyl chloride as starting materials. The overall chemical yields of T808 and T808P were 35% and 52%, respectively. [¹⁸F]-T808 was synthesized from T808P by the nucleophilic substitution with K[¹⁸F]F/Kryptofix 2.2.2 and isolated by HPLC combined with solid-phase extraction (SPE) purification in 35–45% radiochemical yield with 37–370 GBq/μmol specific activity at end of bombardment (EOB).     

Radiosynthesis and preclinical evaluation of [18F]FEM as a potential novel PET probe for tumor imaging

In the 21st century, the incidence and mortality of cancer, one of the most challenging diseases in the world, have rapidly increased. The purpose of this study was to develop 2-(2-[¹⁸F]fluoroethoxy)ethyl 4-methylbenzenesulfonate ([¹⁸F]FEM) as a positron emission tomography (PET) agent for tumor imaging. In this study, [¹⁸F]FEM was synthesized with a good radiochemical yield (45.4 ± 5.8%), high specific radioactivity (over 25 GBq/μmol), and commendable radiochemical purity (over 99%). The octanol/water partition coefficient of [¹⁸F]FEM was 1.44 ± 0.04. The probe demonstrated good stability in vitro (phosphate-buffered saline (PBS) and mouse serum (MS)), and binding specificity to five different tumor cell lines (A549, PC-3, HCC827, U87, and MDA-MB-231). PET imaging of tumor-bearing mice showed that [¹⁸F]FEM specifically accumulated at the tumor site of the five different tumor cell lines. The average tumor-to-muscle (T/M) ratio was over 2, and the maximum T/M values reached about 3.5. The biodistribution and dynamic PET imaging showed that most probes were metabolized by the liver, whereas a small part was metabolized by the kidney. Moreover, dynamic brain images and quantitative data showed [¹⁸F]FEM can quickly cross the blood brain barrier (BBB) and quickly fade out, thereby suggesting it may be a promising candidate probe for the imaging of brain tumors. The presented results demonstrated that [¹⁸F]FEM is a promising probe for tumor PET imaging.     

Facile radiosynthesis of new carbon-11-labeled propanamide derivatives as selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging

The androgen receptor (AR) is an attractive target for the treatment and molecular imaging of prostate cancer. New carbon-11-labeled propanamide derivatives were first designed and synthesized as selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging using the biomedical imaging technique positron emission tomography (PET). The target tracers, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-[¹¹C]methoxyphenoxy)-2-methylpropanamide ([¹¹C]8a), (S)-2-hydroxy-3-(2-[¹¹C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide ([¹¹C]8e), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-[¹¹C]methoxyphenoxy)-2-methylpropanamide ([¹¹C]8c) and (S)-2-hydroxy-3-(4-[¹¹C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide ([¹¹C]8g), were prepared by O-[¹¹C]methylation of their corresponding precursors, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-hydroxyphenoxy)-2-methylpropanamide (9a), (S)-2-hydroxy-3-(2-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide (9b), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methylpropanamide (9c) and (S)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide (9d), with [¹¹C]CH₃OTf under basic conditions and isolated by a simplified C-18 solid-phase extraction (SPE) method in 55 ± 5% (n = 5) radiochemical yields based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 23 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 277.5 ± 92.5 GBq/μmol (n = 5).     

Synthesis and evaluation of 18F labeled crizotinib derivative [18F]FPC as a novel PET probe for imaging c-MET-positive NSCLC tumor

c-MET-positive NSCLC is an important subtype accounting for about 5%~22% of lung cancer. NSCLC patients with activating c-MET are intensively sensitive to c-MET selective receptor tyrosine kinase (RTK) inhibitors, so we aimed to develop a specific PET probe targeting to c-MET-positive NSCLC for potential patients screened by PET/CT. Herein, PET tracer ¹⁸F-radiolabeled crizotinib derivative ([¹⁸F]FPC) was successfully achieved through a simple one-step ¹⁸F-labeling method. [¹⁸F]FPC PET imaging on c-MET-positive (as well as blocking group) and negative NSCLC models were further evaluated, and results showed that [¹⁸F]FPC was effective as a PET imaging probe that targeted c-MET-positive tumor. Therefore, [¹⁸F]FPC could be a potential PET imaging probe for NSCLC tumor which was sensitive to c-MET-TKIs. By virtue of this property, it will benefit NSCLC patients for c-MET-TKI treatment.     

Synthesis and in vitro evaluation of small-molecule [18F] labeled gonadotropin-releasing hormone (GnRH) receptor antagonists as potential PET imaging agents for GnRH receptor expression

Two novel small molecule gonadotropin-releasing hormone (GnRH) receptor antagonists (12 and 13) of the furamide-class were synthesized and evaluated in vitro for their receptor binding affinities for the rat GnRH receptor. Radiolabeling with no carrier added fluorine-18 of the appropriate precursors was investigated in a one-step reaction. Log P (Octanol/PBS pH 7.4) and serum stability of the compounds were investigated. The antagonists showed low nM affinity for the rat GnRH receptor. ¹⁸F-radiolabled compounds were obtained in high radiochemical purity (>95%) and specific activity (>75 GBq/μmol). These findings suggest this class of compounds holds promise as potential probes for PET targeting of GnRH-receptor expression.     

Development of a tightly regulated and highly inducible ecdysone receptor gene switch for plants through the use of retinoid X receptor chimeras

Chemical inducible gene regulation systems provide essential tools for the precise regulation of transgene expression in plants and animals. Recent development of a two-hybrid ecdysone receptor (EcR) gene regulation system has solved some of the drawbacks that were associated with the monopartate gene switch. To further improve the versatility of the two-hybrid EcR gene switch for wide spread use in plants, chimeras between Homo sapiens retinoid X receptor (HsRXR) and insect, Locusta migratoria RXR (LmRXR) were tested in tobacco protoplasts as partners with Choristoneura fumiferana EcR (CfEcR) in inducing expression of the luciferase reporter gene. The RXR chimera 9 (CH9) along with CfEcR, in a two-hybrid format gave the best results in terms of low-background expression levels in the absence of ligand and high-induced expression levels of the reporter gene in the presence of nanomolar concentrations of the methoxyfenozide ligand. The performance of CH9 was further tested in corn and soybean protoplasts and the data obtained was compared with the other EcR switches that contained the wild-type LmRXR or HsRXR as EcR partners. In both transient expression studies and stable transformation experiments, the fold induction values obtained with the CH9 switch were several times higher than the values obtained with the other EcR switches containing LmRXR or HsRXR. The new CfEcR two-hybrid gene switch that uses the RXR CH9 as a partner in inducing reporter gene expression provides an efficient, ligand-sensitive and tightly regulated gene switch for plants.     

Synthesis and preliminary biological evaluation of a novel P2X7R radioligand [18F]IUR-1601

The reference standard IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from tert-butyl (S)-5-oxopyrrolidine-2-carboxylate, fluoroethylbromide, and 2-chloro-3-(trifluoromethyl)benzylamine with overall chemical yield 12% in three steps. The target tracer [¹⁸F]IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-[¹⁸F]fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from desmethyl-GSK1482160 with 2-[¹⁸F]fluoroethyl tosylate, prepared from 1,2-ethylene glycol-bis-tosylate and K[¹⁸F]F/Kryptofix2.2.2, in two steps and isolated by HPLC combined with SPE in 1–3% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity at end of bombardment (EOB) was 74–370?GBq/μmol. The potency of IUR-1601 in comparison with GSK1482160 was determined by a radioligand competitive binding assay using [¹¹C]GSK1482160, and the binding affinity K_i values for IUR-1601 and GSK1482160 are 4.31 and 5.14?nM, respectively.     

Synthesis and biological evaluation of novel radioiodinated imidazopyridine derivatives for amyloid-β imaging in Alzheimer’s disease

Non-invasive detection for amyloid-β peptide (Aβ) deposition has important significance for the early diagnosis and medical intervention for Alzheimer’s disease (AD). In this study, we developed a series of imidazopyridine derivatives as potential imaging agents for single-photon emission computed tomography (SPECT). Two of them, compounds DRK092 and DRM106, showed higher affinity for synthetic human Aβ 1–40 fibrils than did the well-known amyloid-imaging agent IMPY. A metabolite analysis revealed brain-permeable radioactive metabolites of ¹²⁵I-labeled DRK092 and IMPY; no radioactive metabolites from ¹²⁵I-labeled DRM106 ([¹²⁵I]DRM106) were detected. In addition, in vitro autoradiography clearly demonstrated specific binding of [¹²⁵I]DRM106 in the hippocampal region of AD enriched with Aβ plaques. Thus, our results strongly suggested that compound DRM106 can be used as an imaging agent for SPECT to detect Aβ deposition in AD brain.     

Synthesis of carbon-11 labeled fluorinated 2-arylbenzothiazoles as novel potential PET cancer imaging agents

Fluorinated 2-arylbenzothiazoles are new potential antitumor drugs, which show potent and selective inhibitory activity against breast, lung, and colon cancer cell lines. Carbon-11 labeled fluorinated 2-arylbenzothiazoles may serve as novel probes for positron emission tomography (PET) to image tyrosine kinase in cancers. The preparation of 4-fluorinated 2-arylbenzothiazoles 4-fluoro-2-(3-benzloxy-4-methoxyphenyl)benzothiazole (6a) and 4-fluoro-2-(3,4-dimethoxyphenyl)benzothiazole (6b) was achieved by a modification of Jacobson thioanilide radical cyclization chemistry. Hydrogenolytic cleavage of the benzyl ether group of compound 6a using H₂/Pd–C provided the precursor 4-fluoro-2-(3-hydroxy-4-methoxyphenyl)benzothiazole (7) for radiolabeling. Synthesis of radiolabeling precursors and the reference standards 5- and 6-fluorinated arylbenzothiazoles (11c–n) was achieved via the reaction of o-aminothiophenol disulfides with substituted benzaldehydes under reducing conditions. The target radiotracers carbon-11 labeled 4-, 5-, and 6-fluorinated arylbenzothiazoles (3-[¹¹C]6b, 4-[¹¹C]11c, 3-[¹¹C]11c, 5-[¹¹C]11f, 4-[¹¹C]11f, 4-[¹¹C]11i, 3-[¹¹C]11i, 5-[¹¹C]11l, and 4-[¹¹C]11l) were prepared by O-[¹¹C]methylation of the phenolic hydroxyl precursors (7, 11d, 11e, 11g, 11h, 11j, 11k, 11m, and 11n) with [¹¹C]methyl triflate and isolated by solid-phase extraction (SPE) purification in 30–55% radiochemical yields.     

Radioligands targeting purinergic P2X7 receptor

The purinergic P2X7 receptor (P2X7R) is an adenosine triphosphate (ATP) ligand-gated cationic channel receptor. P2X7R is closely associated with various inflammatory, immune, cancer, neurological, musculoskeletal and cardiovascular disorders. P2X7R is an interesting therapeutic target as well as molecular imaging target. This brief digest highlights the radioligands targeting P2X7R recently developed in drug discovery and molecular imaging agent development.     

Synthesis and evaluation of a 18F-curcumin derivate for β-amyloid plaque imaging

IntroductionCurcumin is a neuroprotective compound that inhibits the formation of amyloid oligomers and fibrils and binds to β-amyloid plaques in Alzheimer’s disease (AD). We aimed to synthesize an ¹⁸F-labeled curcumin derivate ([¹⁸F]4) and to characterize its positron emission tomography (PET) tracer-binding properties to β-amyloid plaques in a transgenic APP23 mouse model of AD.MethodsWe utilized facile one-pot synthesis of [¹⁸F]4 using nucleophilic ¹⁸F-fluorination and click chemistry. Binding of [¹⁸F]4 to β-amyloid plaques in the transgenic APP23 mouse brain cryosections was studied in vitro using heterologous competitive binding against PIB. [¹⁸F]4 uptake was studied ex vivo in rodents and in vivo using PET/computed tomography of transgenic APP23 and wild-type control mice.ResultsThe radiochemical yield of [¹⁸F]4 was 21 ± 11%, the specific activity exceeded 1 TBq/μmol, and the radiochemical purity exceeded 99.3% at the end of synthesis. In vitro studies of [¹⁸F]4 with the transgenic APP23 mouse revealed high β-amyloid plaque binding. In vivo and ex vivo studies demonstrated that [¹⁸F]4 has fast clearance from the blood, moderate metabolism but low blood–brain barrier (BBB) penetration.Conclusions[¹⁸F]4 was synthesized in high yield and excellent quality. In vitro studies, metabolite profile, and fast clearance from the blood indicated a promising tracer for Aβ imaging. However, [¹⁸F]4 has low in vivo BBB penetration and thus further studies are needed to reveal the reason for this and to possibly overcome this issue.     

11C]enzastaurin, the first design and radiosynthesis of a new potential PET agent for imaging of protein kinase C

Enzastaurin (LY317615) is a potent and selective protein kinase C (PKC) inhibitor with an IC₅₀ value of ∼6 nM. [¹¹C]Enzastaurin (3-(1-[¹¹C]methyl-1H-indol-3-yl)-4-[1-[1-(2-pyridinylmethyl)-4-piperidinyl]-1H-indol-3-yl]-1H-pyrrole-2,5-dione), a new potential PET agent for imaging of PKC, was first designed and synthesized in 20-25% decay corrected radiochemical yield and 370-555 GBq/μmol specific activity at end of bombardment (EOB). The synthetic strategy was to prepare a carbon-11-labeled maleic anhydride intermediate followed by the conversion to maleimide.     

Synthesis and preliminary evaluation of a new fluorine-18 labelled triazine derivative for PET imaging of cannabinoid CB2 receptor

Cannabinoid CB2 PET tracers are considered as a promising alternative to PBR/TSPO tracers for the in-vivo imaging of neuroinflammation. We describe here the synthesis and characterization of compound 3, a new potent and brain penetrating CB2 ligand based on an original triazine template. The PET tracer [¹⁸F]-dideutero-3 was prepared in a three steps radiosynthesis, and demonstrated significant uptake in rhesus macaque and baboon brain with a maximum SUV of about 0.7–0.9 g/mL, followed by a moderate washout over time.     

Synthesis of carbon-11-labeled isonicotinamides as new potential PET agents for imaging of GSK-3 enzyme in Alzheimer’s disease

The authentic standards 2-(cyclopropanecarboxamido)-N-(4-methoxypyridin-3-yl)isonicotinamide (4a) and 2-(cyclopropanecarboxamido)-N-(4-(4-methoxyphenyl)pyridin-3-yl)isonicotinamide (7a), and their corresponding precursors 2-(cyclopropanecarboxamido)-N-(4-hydroxypyridin-3-yl)isonicotinamide (4b) and 2-(cyclopropanecarboxamido)-N-(4-(4-hydroxyphenyl)pyridin-3-yl)isonicotinamide (7b) were synthesized from methyl 2-aminoisonicotinate and cyclopropanecarbonyl chloride with overall chemical yield 47% in three steps, 22% in four steps, 40% in three steps, and 17% in four steps, respectively. The target tracers 2-(cyclopropanecarboxamido)-N-(4-[¹¹C]methoxypyridin-3-yl)isonicotinamide ([¹¹C]4a) and 2-(cyclopropanecarboxamido)-N-(4-(4-[¹¹C]methoxyphenyl)pyridin-3-yl)isonicotinamide ([¹¹C]7a) were prepared from the precursors (4b and 7b) with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–50% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the specific activity (SA) at EOB was 370–1110 GBq/μmol with a total synthesis time of ～40-min from EOB.     

Synthesis of carbon-11-labeled CK1 inhibitors as new potential PET radiotracers for imaging of Alzheimer’s disease

The reference standards methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate (5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-methoxybenzamide (5c), and their corresponding desmethylated precursors 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoic acid (6a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-hydroxybenzamide (6b), were synthesized from 5-amino-2,2-difluoro-1,3-benzodioxole and 3-substituted benzoic acids in 5 and 6 steps with 33% and 11%, 30% and 7% overall chemical yield, respectively. Carbon-11-labeled casein kinase 1 (CK1) inhibitors, [¹¹C]methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate ([¹¹C]5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-[¹¹C]methoxybenzamide ([¹¹C]5c), were prepared from their O-desmethylated precursor 6a or 6b with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–45% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ～40-min from EOB.