Synthesis of carbon-11-labeled tricyclic necroptosis inhibitors as new potential PET agents for imaging of tumor necrosis factor alpha (TNF-alpha)

Carbon-11-labeled tricyclic necroptosis inhibitors were first designed and synthesized as new potential PET agents for imaging of tumor necrosis factor alpha (TNF-alpha). The target tracers were prepared by O-[(11)C]methylation of their corresponding precursors using [(11)C]CH(3)OTf under basic conditions and isolated by a simplified SPE method in 50-60% radiochemical yields based on [(11)C]CO(2) and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 15-20 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 111-185 GBq/micromol.

Synthesis of carbon-11-labeled tariquidar derivatives as new PET agents for imaging of breast cancer resistance protein (ABCG2)

Carbon-11-labeled tariquidar derivatives were first designed and synthesized as new PET agents for imaging of breast cancer resistance protein. The target tracers were prepared by O-[(11)C]methylation of their corresponding acid precursors using [(11)C]CH3OTf under basic conditions and isolated by a simplified solid-phase extraction (SPE) method in 50-60% radiochemical yields based on [(11)C]CO(2) and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 15-20 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 111-185 GBq/micromol.

Design and synthesis of carbon-11-labeled dual aromatase-steroid sulfatase inhibitors as new potential PET agents for imaging of aromatase and steroid sulfatase expression in breast cancer

Aromatase and steroid sulfatase (STS) are particularly attractive targets in the treatment of estrogen-receptor-positive breast cancer and the development of enzyme-based cancer imaging agents for the biomedical imaging technique positron emission tomography (PET). New carbon-11-labeled sulfamate derivatives were first designed and synthesized as potential PET dual aromatase-steroid sulfatase inhibitor (DASSI) radiotracers for imaging of aromatase and STS expression in breast cancer. The target tracers 5-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-[(11)C]methoxyphenyl sulfamate ([(11)C]8a) and 4-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-[(11)C]methoxyphenyl sulfamate ([(11)C]8b) were prepared from their corresponding precursors 5-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-hydroxyphenyl sulfamate (16) and 4-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-hydroxyphenyl sulfamate (21) with [(11)C]CH(3)OTf under basic conditions through the O-[(11)C]methylation and isolated by the reversed-phase high pressure liquid chromatography (HPLC) method in 30-45% radiochemical yields based on [(11)C]CO(2) and decay corrected to end of bombardment (EOB). The specific activity at end of synthesis (EOS) was 111-185GBq/micromol.

Synthesis of carbon-11-labeled 4-aryl-4H-chromens as new PET agents for imaging of apoptosis in cancer

Carbon-11-labeled 4-aryl-4H-chromenes, 2-amino-7-(dimethylamino)-4-(3-[(11)C]methoxy-5-methoxyphenyl)-4H-chromene-3-carbonitrile ([(11)C]6a), 2-amino-4-(3-bromo-4-[(11)C]methoxy-5-methoxyphenyl)-7-(dimethylamino)-4H-chromene-3-carbonitrile ([(11)C]6c), 2-amino-4-(3-[(11)C]methoxy-5-methoxyphenyl)-4,7-dihydropyrano[2,3-e]indole-3-carbonitrile ([(11)C]6d), 2-amino-4-(3-bromo-4-[(11)C]methoxy-5-methoxyphenyl)-4,7-dihydropyrano[2,3-e]indole-3-carbonitrile ([(11)C]6f), 2-amino-4-(3-[(11)C]methoxy-5-methoxyphenyl)-4,9-dihydropyrano[3,2-g]indole-3-carbonitrile ([(11)C]6g), 2-amino-4-(3-bromo-4-[(11)C]methoxy-5-methoxyphenyl)-4,9-dihydropyrano[3,2-g]indole-3-carbonitrile ([(11)C]6i), 2-amino-4-(3-[(11)C]methoxy-5-methoxyphenyl)-7-methyl-4,7-dihydropyrano[2,3-e]indole-3-carbonitrile ([(11)C]6j) and 2-amino-4-(3-bromo-4-[(11)C]methoxy-5-methoxyphenyl)-7-methyl-4,7-dihydropyrano[2,3-e]indole-3-carbonitrile ([(11)C]6l), were prepared by O-[(11)C]methylation of their corresponding precursors using [(11)C]CH(3)OTf under basic conditions and isolated by a simplified solid-phase extraction (SPE) method in 30-50% radiochemical yields based on [(11)C]CO(2) and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 15-20min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 111-185GBq/micromol.

Fully automated synthesis and initial PET evaluation of [11C]PBR28

Fully automated synthesis and initial PET evaluation of a TSPO radioligand, [11C]PBR28 (N-(2-[11C]methoxybenzyl)-N-(4-phenoxypyridin-3-yl)acetamide), are reported. These results facilitate the potential preclinical and clinical PET studies of [11C]PBR28 in animals and humans.

Synthesis of [11C]FEDAA1106 as a new PET imaging probe of peripheral benzodiazepine receptor expression

Peripheral benzodiazepine receptor (PBR) is associated with neuroinflammation and tumor progression. [(11)C]DAA1106 and [(18)F]FEDAA1106 are two promising radioligands for positron emission tomography (PET) imaging of PBR. This study was designed to develop a new radiolabeled analog of [(11)C]DAA1106 and [(18)F]FEDAA1106, [(11)C]FEDAA1106, for PET imaging of PBR expression in brain and cancer. Precursor N-(5-fluoro-2-phenoxyphenyl)-N-(2-(2-fluoroethoxy)-5-hydroxybenzyl)acetamide (9) was synthesized in multiple steps with moderate to high chemical yields. Precursor 9 was labeled by [(11)C]CH(3)OTf and isolated by high pressure liquid chromatography (HPLC) purification to provide target radioligand N-(5-fluoro-2-phenoxyphenyl)-N-(2-(2-fluoroethoxy)-5-[(11)C]methoxybenzyl)acetamide ([(11)C]FEDAA1106, [(11)C]10) in 60-70% radiochemical yields, decay corrected to end of bombardment (EOB), based on [(11)C]CO(2). The specific activity of the target radiotracer [(11)C]10 was in a range of 111-185GBq/micromol at the end of synthesis (EOS).

Synthesis of new carbon-11-labeled carboxamide derivatives as potential PET dopamine D3 receptor radioligands

Carbon-11-labeled carboxamide derivatives, (E)-4-fluoro-N-(4-(4-(2-[(11)C]methoxyphenyl)piperazin-1-yl)butyl)cinnamoylamide, ([(11)C]3a), (E)-4-chloro-N-(4-(4-(2-[(11)C]methoxyphenyl)piperazin-1-yl)butyl)cinnamoylamide ([(11)C]3b), (E)-4-bromo-N-(4-(4-(2-[(11)C]methoxyphenyl)piperazin-1-yl)butyl)cinnamoylamide, ([(11)C]3c), (E)-4-methoxy-N-(4-(4-(2-[(11)C]methoxyphenyl)piperazin-1-yl)butyl)cinnamoylamide ([(11)C]3d), N-(4-(4-(2-[(11)C]methoxyphenyl)piperazin-1-yl)butyl)naphthyl-2-carboxamide ([(11)C]BP897, [(11)C]3e), and N-(4-(4-(2-[(11)C]methoxyphenyl)piperazin-1-yl)butyl)biphenyl-4-carboxamide ([(11)C]3f), have been synthesized as new potential PET radioligands for imaging of dopamine D(3) receptors. The target tracers were prepared by O-[(11)C]methylation of their corresponding precursors using [(11)C]CH(3)OTf and isolated by a simplified solid-phase extraction (SPE) purification procedure in 50-65% radiochemical yields decay corrected to end of bombardment (EOB), 20 min overall synthesis time, and 111-148GBq/micromol specific activity at end of synthesis (EOS).

Synthesis of carbon-11 labeled 1-(3,4-dimethoxybenzyl)-2,2-dimethyl-1,2,3,4-tetrahydroisoquinolinium derivatives as new potential PET SKCa channel imaging agents

Small conductance Ca2+-activated K+ (SKCa) channels play an important role in many functions such as neuronal communication and behavioral plasticity, secretion, and cell proliferation. SKCa channel modulation is associated with various brain, heart, and cancer diseases. N-methyl-laudanosine and its structurally related derivatives, substituted 1-(3,4-dimethoxybenzyl)-2,2-dimethyl-1,2,3,4-tetrahydroisoquinoliniums, are reversible and selective SKCa channel blockers. Carbon-11 labeled N-methyl-laudanosine and its tetrahydroisoquinolinium derivatives may serve as new probes for positron emission tomography (PET) to image SKCa channels in the brain, heart, and cancer. The key intermediates, substituted isoquinolines (3a-c), were synthesized using a modification of the Pomeranz-Fritsch procedure. The precursors, substituted 1-(3,4-dimethoxybenzyl)-2-methyl-1,2,3,4-tetrahydroisoquinolines (8a-c), and their corresponding reference standards, substituted 1-(3,4-dimethoxybenzyl)-2,2-dimethyl-1,2,3,4-tetrahydroisoquinoliniums (9a-c), were synthesized from compounds 3a-c with 3,4-dimethoxybenzyl chloride (2) in multiple steps with moderate to excellent chemical yields. The precursor 6,7-dimethoxy-1-(3,4-dimethoxybenzyl)-2-methyl-1,2,3,4-tetrahydroisoquinoline (10) was commercially available, and the methylation of compound 10 with methyl iodide provided N-methyl-laudanosine (11). The target quaternary ammonium tracers, carbon-11 labeled 1-(3,4-dimethoxybenzyl)-2,2-dimethyl-1,2,3,4-tetrahydroisoquinoliniums ([11C]9a-c and [11C]11), were prepared by N-[11C]methylation of the tertiary amine precursors (8a-c and 10) with [11C]methyl triflate and isolated by a simplified solid-phase extraction (SPE) purification using a SiO2 or cation-exchange CM Sep-Pak cartridge in 40-65% radiochemical yields.

Synthesis and preliminary biological evaluation of new carbon-11 labeled tetrahydroisoquinoline derivatives as SERM radioligands for PET imaging of ER expression in breast cancer

The estrogen receptors (ERs) are attractive targets in the treatment of breast cancer and the development of receptor-based breast cancer imaging agents for diagnostic use in biomedical imaging technique positron emission tomography (PET). Tetrahydroisoquinoline derivatives are a class of selective estrogen receptor modulators (SERMs) with high binding affinity and specificity exhibiting up to 50 folds for ERalpha over ERbeta. New carbon-11 labeled tetrahydroisoquinoline derivatives, [11C]methyl 1-(2-(4-(2-(4-fluorophenyl)-6-hydroxy-1-methyl-1,2,3,4-tetrahydroisoquinolin-1-yl)phenoxy)ethyl)piperidine-4-carboxylate ([11C]10a) and [11C]methyl 1-(2-(4-(2-(4-chlorophenyl)-6-hydroxy-1-methyl-1,2,3,4-tetrahydroisoquinolin-1-yl)phenoxy)ethyl)piperidine-4-carboxylate ([11C]10b), have been first designed, synthesized and evaluated. The target tracers were prepared by O-[11C]methylation of their corresponding precursors using [11C]CH3OTf and isolated by solid-phase extraction (SPE) purification procedure in 40-60% radiochemical yields, which were decay corrected to the end of bombardment (EOB), based on [11C]CO2. The overall synthesis time was 15-20 min from EOB. The radiochemical purity was >99%, and specific activity was in a range of 74-111GBq/micromol at the end of synthesis (EOS). Preliminary findings from in vitro biological assay indicate that the synthesized derivatives displayed similar potencies in the MCF-7 human breast cancer cell line in comparison with 4-hydroxytamoxifen, a well-known potent SERM. These results encourage further in vivo evaluation of carbon-11 labeled tetrahydroisoquinoline derivatives as new potential SERM radioligands for PET imaging of ER expression in breast cancer.

Synthesis of carbon-11 labeled biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues as new potential PET glioma tumor imaging agents

Carbon-11 labeled biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues, 2-(2-(biphenyl-4-yl)ethyl)-6-[(11)C]methoxy-7-methoxy-1,2,3,4-tetrahydroisoquinoline ([(11)C]3); 1-(biphenyl-4-yl)methyl-6,7-dimethoxy-2-[(11)C]methyl-1,2,3,4-tetrahydroisoquinoline (N-[(11)C]7) and 1-(biphenyl-4-yl)methyl-6-[(11)C]methoxy-7-methoxy-2-methyl-1,2,3,4-tetrahydroisoquinoline (O-[(11)C]7); and 2-(biphenyl-4-yl)-N-(3,4-dimethoxy-phenethyl)-N-[(11)C]methyl-ethanamine (N-[(11)C]10) and 2-(biphenyl-4-yl)-N-(3-methoxy-4-[(11)C]methoxy-phenethyl)-N-methyl-ethanamine (O-[(11)C]10), have been synthesized as new potential positron emission tomography (PET) glioma tumor imaging agents, either by O-[(11)C]methylation or by N-[(11)C]methylation of the appropriate precursors using [(11)C]CH(3)OTf and isolated either by a simplified solid-phase extraction (SPE) purification procedure or by HPLC method in 30-55% radiochemical yields decay corrected to EOB, 15-25 min overall synthesis time, and 4.0-6.0 Ci/mumol specific activity at EOB.

Synthesis and biodistribution of new radiolabeled high-affinity choline transporter inhibitors [11C]hemicholinium-3 and [18F]hemicholinium-3

The high-affinity choline transporter (CHT1) system is an attractive target for the development of positron emission tomography (PET) biomarkers to probe brain, cardiac, and cancer diseases. An efficient and convenient synthesis of new radiolabeled CHT1 inhibitors [(11)C]hemicholinium-3 and [(18)F]hemicholinium-3 by solid-phase extraction (SPE) technique using a cation-exchange CM Sep-Pak cartridge has been well developed. The preliminary evaluation of both tracers through biodistribution studies in 9L-glioma rats has been performed, and the uptakes in the heart and tumor were observed, while very low brain uptake was seen.

Evaluation of [11C]hemicholinium-15 and [18F]hemicholinium-15 as new potential PET tracers for the high-affinity choline uptake system in the heart

[(11)C]Hemicholinium-15 ([(11)C]HC-15) and [(18)F]hemicholinium-15 ([(18)F]HC-15) have been synthesized as new potential PET tracers for the heart high-affinity choline uptake (HACU) system. [(11)C]HC-15 was prepared by N-[(11)C]methylation of the appropriate precursor, 4-methyl-2-phenyl-morpholin-2-ol, using [(11)C]CH(3)OTf in 55-70% radiochemical yield decay corrected to end of bombardment (EOB) and 2-3Ci/mumol specific activity at end of synthesis (EOS). [(18)F]HC-15 was prepared by N-[(18)F]fluoromethylation of the precursor using [(18)F]FCH(2)OTf in 20-30% radiochemical yield decay corrected to EOB and >1.0Ci/mumol specific activity at EOS. The biodistribution of both compounds was determined in rats at 20min post-intravenous injection, and the results show the heart region uptakes 1.32+/-0.75%ID/g in R-ventricle for [(11)C]HC-15 and 1.28+/-0.81%ID/g in L-ventricle for [(18)F]HC-15, respectively. The dynamic PET imaging studies of [(11)C]HC-15 in rats were acquired 60min post-intravenous injection of the tracer using the IndyPET-II scanner. For the blocking experiments, the rats were intravenously pretreated with 3.0mg/kg of unlabeled HC-15 prior to [(11)C]HC-15 injection. [(11)C]HC-15 rat heart PET studies show rapid heart uptake to give clear heart images. The rat heart PET blocking studies found no significant blocking effect. The dynamic PET studies in normal and ablated dogs were performed using Siemens PET scanner with [(13)N]NH(3), [(11)C]HC-15, and [(18)F]HC-15. PET studies in dogs of both [(11)C]HC-15 and [(18)F]HC-15 also show significant heart uptake and give images of the heart. However, there is no significant change in [(11)C]HC-15 L-ventricle uptake following radiofrequency ablation in the dog. These results suggest that the localization of HC-15 tracers in the heart is mediated by non-specific processes, and the visualization of HC-15 tracers on the heart is related to non-specific binding of HACU.

Synthesis of carbon-11 labeled sulfonanilide analogues as new potential PET agents for imaging of aromatase in breast cancer

Aromatase is a particularly good target in the treatment of estrogen receptor positive breast cancer. Novel carbon-11 labeled sulfonanilide analogues, N-[11C]methyl-N-(2-alkyloxy-4-nitrophenyl)-methanesulfonamides ([11C]3a-f, alkyl=propyl, isopropyl, 1-ethyl-propyl, cyclopentyl, cyclohexyl, and cyclohexylethyl), were designed and synthesized as potential PET agents for imaging of aromatase in breast cancer.

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 H(2)/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-[(11)C]6b, 4-[(11)C]11c, 3-[(11)C]11c, 5-[(11)C]11f, 4-[(11)C]11f, 4-[(11)C]11i, 3-[(11)C]11i, 5-[(11)C]11l, and 4-[(11)C]11l) were prepared by O-[(11)C]methylation of the phenolic hydroxyl precursors (7, 11d, 11e, 11g, 11h, 11j, 11k, 11m, and 11n) with [(11)C]methyl triflate and isolated by solid-phase extraction (SPE) purification in 30-55% radiochemical yields.

Synthesis of radiolabeled stilbene derivatives as new potential PET probes for aryl hydrocarbon receptor in cancers

New carbon-11 and fluorine-18 labeled stilbene derivatives, cis-3,5-dimethoxy-4'-[11C]methoxystilbene (4'-[11C]8a), cis-3,4',5-trimethoxy-3'-[11C]methoxystilbene (3'-[11C]8b), trans-3,5-dimethoxy-4'-[11C]methoxystilbene (4'-[11C]10a), trans-3,4',5-trimethoxy-3'-[11C]methoxystilbene (3'-[11C]10b), cis-3,5-dimethoxy-4'-[18F]fluorostilbene (4'-[18F]12a), and trans-3,5-dimethoxy-4'-[18F]fluorostilbene (4'-[18F]13a), were designed and synthesized as potential PET probes for aryl hydrocarbon receptor (AhR) in cancers.