Synthesis of tritium and carbon‐14 labelled NNC 61‐4655: a potent dual‐acting PPARα and PPARγ agonist

The synthesis of the potent dual‐acting PPARα and PPARγ agonist NNC 61‐4655 labelled with tritium and carbon‐14 is reported. Tritium labelled NNC 61‐4655 was obtained in three steps with introduction of tritium through catalytic tritium‐halogen exchange of an aryl bromide precursor. This provided [³H]NNC 61‐4655 in 39% overall radiochemical yield with a specific activity of 49 Ci/mmol. Carbon‐14 labelled NNC 61‐4655 was obtained in five steps starting from bromo[1‐¹⁴C]acetic acid. The synthetic sequence, which included a Horner–Wadsworth–Emmons olefination and a Mitsunobu alkylation, provided [¹⁴C]NNC 61‐4655 in 33% overall radiochemical yield with a specific activity of 57.4 mCi/mmol. Copyright © 2003 John Wiley & Sons, Ltd.     

Carbon‐14 labelling of selective H3 receptor antagonists

The fast and efficient carbon‐14 labelling of the three potent H₃ antagonists NNC 38‐1202, NNC 38‐1384, and NNC 38‐1401 is reported. The two‐step synthetic sequence, which included a Knoevenagel reaction, provided the carbon‐14‐labelled compounds in 38–55% overall yield starting from [2‐¹⁴C]malonic acid. The compounds were all obtained in high radiochemical purity ( > 99%) and with high specific activity (55.8 mCi/mmol). Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of [14C]‐radiolabelled entecavir

Radiolabelled [¹⁴C]entecavir, ( 1 ), was prepared in 12 steps from (1S,2R,3S,5R)‐3‐(benzyloxy)‐2‐(benzyloxymethyl)‐6‐oxa‐bicyclo[3.1.0]hexane 2 . The chemical yield of [¹⁴C]entecavir was 14% from the epoxide 2 . Introduction of [¹⁴C] radiolabel was achieved by elaboration of 4,5‐diaminopyrimidine 8 with triethyl[¹⁴C]orthoformate to purine derivative 9 . The radiochemical yield of [¹⁴C]entecavir from triethyl[¹⁴C]orthoformate was 11.3%. Radiochemical purity of [¹⁴C]entecavir determined by HPLC was 99.8%. The specific activity of [¹⁴C]entecavir was 108 µCi/mg (29.9 mCi/mmol). Copyright © 2005 John Wiley & Sons, Ltd.     

A novel synthesis of [2‐14C]2,5‐dichloropyrimidine

[2‐¹⁴ C]2,5‐dichloropyrimidine is a useful reagent for labeling biologically active compounds for use in hepatocyte transport studies, protein covalent binding, and metabolic profiling. This paper describes a novel five‐step synthesis of [2‐¹⁴ C]2,5‐dichloropyrimidine from readily available [¹⁴C]urea by way of a boronic acid intermediate. A total of 4.34 mCi of [2‐¹⁴ C]2,5‐dichloropyrimidine was obtained with a specific activity of 226.0 μCi/mg (33.7 mCi/mmol). The radiochemical purity was 95.8%, and the overall radiochemical yield was 22% based on 20 mCi of [¹⁴C]urea starting material. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of carbon‐14 labelled midazolam

Cytochrome P450 (CYP) enzymes are responsible for much of the phase I oxidative metabolism observed in vivo. Many important pharmaceutical compounds are metabolized by CYP. Co‐administration of a drug with another agent can alter the efficacy or the toxicity, especially in cases where drug clearance depends primarily on the CYP metabolism. Compounds that induce or inhibit the CYP activity are often used in drug–drug interaction studies. Midazolam is one such compound that is routinely used in drug–drug interaction studies because it is a known substrate for CYP3A enzymes. The synthesis of this important tool molecule has been documented, but unfortunately a detailed preparation of carbon‐14‐labelled midazolam has not been reported in the literature. This paper describes a two‐step synthesis leading to [¹⁴C]midazolam. A total of 4.5 mCi of [¹⁴C]midazolam was obtained having a specific activity of 120.1 µCi/mg (39.12 mCi/mmol). The radiochemical purity as determined by HPLC was 99.8% and the overall radiochemical yield was 9%. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of 3H and 14C labeled (S)‐3‐(5‐chloro‐2‐methoxyphenyl)‐1,3‐dihydro‐3‐fluoro‐6‐(trifluoromethyl)‐2H‐indol‐2‐one,maxipost™. An agent for post‐stroke neuroprotection

The syntheses of tritium labeled (S)‐3‐(5‐chloro‐2‐[OC³H₃]methoxyphenyl‐1,3‐dihydro‐3‐fluoro‐6‐(trifluoromethyl)‐1H‐indol‐2‐one, and carbon‐14 (S)‐3‐(5‐chloro‐2‐methoxyphenyl)‐1,3‐dihydro‐3‐fluoro‐6‐(trifluoromethyl)‐2H‐[2,3‐¹⁴C₂] indol‐2‐one are reported. The ³H‐labeled compound was prepared in a two‐step synthesis from C³H₃I. The final product was purified via chiral HPLC to yield the desired enantiomer in a 4% radiochemical yield and a specific activity of 60 Ci/mmol. The ¹⁴C‐labeled compound was prepared in a four‐step synthesis from diethyl [carboxylate‐¹⁴C₁,₂] oxalate. The final product was purified via chiral HPLC to yield the desired enantiomer in a 20% radiochemical yield and a specific activity of 28.4 μCi/mg. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of 3H, 14C and 2H4 labelled SCH 211803

[³H]SCH 211803, at a specific activity of 1.56 Ci/mmol, was prepared by direct exchange with tritiated water and platinum metal. [²H₄]SCH 211803 was prepared from [²H]formaldehyde in a seven step synthesis in 10% yield. [¹⁴C]SCH 211803 was prepared from N‐benzyl‐4‐hydroxy[2‐¹⁴C]piperidine in a four‐step synthesis in 35% radiochemical yield. Additionally a high specific activity batch of [³H]SCH 211803 was prepared by Ru(Ph₃P)₃Cl₂ catalysed exchange with 90 at% tritiated water to a specific activity of 35 Ci/mmol. Copyright © 2007 John Wiley & Sons, Ltd.     

M+4 stable isotope labeling of levovirin and M+7 and carbon‐14 labeling of levovirin valinate pro‐drug

[M+4]‐labeled levovirin 5 (231 mg) was synthesized as an MS reference compound from [M+4] triazole ester 2 . [M+7]‐labeled levovirin valinate 6 (127 mg) was synthesized as a comparison MS reference compound from [M+6] triazole ester 3 . [¹⁴C]‐Levovirin 7 and [¹⁴C]‐levovirin valinate 8 were synthesized to support metabolism studies. The synthesis of 7 was accomplished in 33% overall yield (35.4 mCi, 57 mCi/mmol) from Ba¹⁴CO₃ and 8 was synthesized in 41% yield (12.5 mCi, 57 mCi/mmol) from 7 . An efficient metallation/carbonation reaction was developed to synthesize [¹⁴C]‐triazole ester 4 . Copyright © 2006 John Wiley & Sons, Ltd.     

The syntheses of [13C6] and [phenyl‐14C(U)]BMS‐816336, an inhibitor of 11β‐hydroxysteroid dehydrogenase type 1, for type 2 diabetes

Type 2 diabetes is a significant worldwide health problem. To support the development of BMS‐816336 as an inhibitor of 11β‐hydroxysteroid dehydrogenase type 1 for type 2 diabetes, the synthesis of carbon‐14 labeled material was required for use in metabolic profiling. [Phenyl‐¹⁴C(U)]BMS‐816336 was synthesized in 8 steps and 22% radiochemical yield from commercially available [¹⁴C(U)]bromobenzene. The radiochemical purity of [phenyl‐¹⁴C(U)]BMS‐816336 was 100% having a specific activity of 84.4 μCi/mg or 28.8 mCi/mmol for a total of 8.9 mCi. It was also necessary to synthesize [¹³C₆]BMS‐816336 for use as a liquid chromatography/mass spectrometry standard. [¹³C₆]BMS‐816336 was also prepared in 8 labeled steps in 26% yield from [¹³C₆]bromobenzene.     

Convenient synthesis of D‐threo‐[dichloroacetyl 1–14C] chloramphenicol

A convenient synthesis of chloramphenicol labelled with carbon‐14 in the dichloroacetyl group at the 1 position is described. It was prepared as part of a 4‐step sequence from [1 ‐ ¹⁴C] glycine and the product was purified by preparative HPLC. A radiochemical yield of 47% was obtained based on [1 ‐ ¹⁴C] glycine and the product had a specific activity of 0.47 mCi/mmol. The procedure can be employed for the synthesis of high specific activity [¹⁴C] chloramphenicol, labelled at 1, 2 or both the positions of dichloroacetyl group. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of 14C‐labelled myosmine, [2′‐14C] ‐3‐(1‐pyrrolin‐2‐yl)pyridine

¹⁴C‐Labelled myosmine ([2′‐¹⁴C]‐3‐(1‐pyrrolin‐2‐yl)pyridine) was synthesized for autoradiography studies starting from [carboxyl‐¹⁴C]‐nicotinic acid by initial esterification of the latter in the presence of 1,1,1‐triethoxyethane. Without any purification the ethyl nicotinate formed was directly reacted with N‐vinyl‐2‐pyrrolidinone in the presence of sodium hydride, yielding ¹⁴C‐labelled myosmine. The product was purified by silica gel column chromatography. The radiochemical yield was 15% and the specific activity 55.2 mCi/mmol. Copyright © 2003 John Wiley & Sons, Ltd.     

The synthesis of 14C‐labeled, 13CD2‐labeled saxagliptin,and its 13CD2‐labeled 5‐hydroxy metabolite

¹⁴C‐labeled saxagliptin, ¹³CD₂‐labeled saxagliptin, and its ¹³CD₂‐labeled 5‐hydroxy metabolite were synthesized to further support development of the compound for biological studies. This paper describes new syntheses leading to the desired compounds. A total of 3.0 mCi of ¹⁴C‐labeled saxagliptin was obtained with a specific activity of 53.98 μCi/mg (17.13 mCi/mmol). The radiochemical purity determined by HPLC was 99.29%, and the overall radiochemical yield was 3.0% based upon 100 mCi of [¹⁴C]CH₂I₂ starting material. By following similar synthetic routes, 580.0 mg of ¹³CD₂‐labeled saxagliptin and 153.1 mg of ¹³CD₂‐labeled 5‐hydroxysaxagliptin metabolite were prepared. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of deuterium,tritium, and carbon‐14 labeled BIRB 796, a p38 MAP kinase inhibitor

1‐(5‐tert‐Butyl‐2‐p‐tolyl‐2H‐pyrazol‐3‐yl)‐3‐[4‐(2‐morpholin‐4‐yl‐ethoxy)naphthalen‐1‐yl]urea (BIRB 796), currently in clinical trials for the treatment of inflammatory diseases, is a potent inhibitor of p38 MAP kinase. Labeled BIRB 796 with stable and radioactive isotopes was required for metabolism, distribution, and absorption studies. We first report the synthesis of carbon‐14 labeled BIRB 796 with a specific activity of 2 GBq/mmol (54.2 mCi/mmol), using [¹⁴C]‐phosgene under modified Schotten–Baumann conditions; second the preparation of tritium‐labeled BIRB 796 with a specific activity of 659 GBq/mmol (17.81 Ci/mmol) by reductive dehalogenation of iodo‐BIRB 796 with tritium gas; and finally, the synthesis of ²H₈‐BIRB 796 using morpholine‐2,2,3,3,5,5,6,6‐²H₈ with isotopic enrichment of 98.9 at% ²H. Copyright © 2004 John Wiley & Sons, Ltd.     

Syntheses of a radiolabelled CXCR2 antagonist AZD5069 and its major human metabolite

The CXCR2 antagonist AZD5069 has been synthesized in tritium and carbon‐14‐labelled forms. [³H]AZD5069 was prepared via reductive dehalogenation of an iodinated precursor with tritium gas to provide material with a specific activity of 25.1 Ci/mmol. [¹⁴C]AZD5069 was labelled in the pyrimidine ring from [¹⁴C]thiourea in an overall radiochemical yield of 18%. In addition, a synthetic route to the major metabolite of AZD5069 was developed. The synthesis of this metabolite was achieved from AZD5069 using a chemoselective Lindgren–Pinnick reaction in order to minimize oxidation of the sulphide group.     

Radiosynthesis of N‐[4‐(4‐fluorobenzyl)piperidin‐1‐yl]‐N′‐(2‐[11C]oxo‐1,3‐dihydrobenzimidazol‐5‐yl)oxamide,a NR2B‐selective NMDA receptor antagonist

In order to perform in vivo imaging of the NR2B NMDA receptor system by positron emission tomography, a NR2B selective NMDA receptor antagonist has been labelled with carbon‐11 (half‐life: 20 min). N‐[4‐(4‐fluorobenzyl)piperidin‐1‐yl]‐N′‐(2‐oxo‐1,3‐dihydrobenzimidazol‐5‐yl)oxamide has been described demonstrating high affinity and selectivity for the NR2B receptors (IC₅₀ of 5 nM in [³H]Ro‐25,6981 binding assay). The labelling precursor and the reference compound were synthesized by coupling the 4‐(4‐fluorobenzyl)piperidine with the corresponding oxalamic acid. The reaction of [¹¹C]phosgene with phenylenediamine precursor led the formation of the [¹¹C]benzimidazolone ring present on the ligand. The labelling occurred in THF or acetonitrile and the decay corrected radiochemical yield was 30–40% from the produced [¹¹C]methane. HPLC purification and formulation led to 2.6–3.7 GBq (70–100 mCi) of radioligand within 30–35 min. The specific radioactivity was 72–127 GBq/µmol (2–3.4 Ci/µmol) at the end of synthesis. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of [14C] ‐ and [13C6]‐labeled tipranavir and its potential hydroxyl metabolite and the glucuronide conjugate

Tipranavir or Aptivus^® is a non‐peptidic protease inhibitor approved for the combination treatment with ritonavir of HIV infection. Tipranavir labeled with radioactive and stable isotopes of carbon was required for drug metabolism (excretion, distribution, and absorption) studies and to develop bioanalytical methods needed for the support of clinical studies. [7‐¹⁴C]‐Benzoic acid and uniformly labeled benzoic acid (ring‐¹³C₆ 99 at% ¹³C) were used to prepare [¹⁴C]‐ and [¹³C₆]‐labeled tipranavir, respectively. Radioactively labeled tipranavir was prepared with a specific activity of 54 mCi/mmol (2GBq/mmol); it was necessary to dilute its specific activity with unlabeled tipranavir to 28 mCi/mmol (46.45 µCi/mg) because of its instability. The N‐hydroxyl metabolite (12) and the glucuronide conjugate (13), the most abundant metabolites of tipranavir (when administered in conjunction with ritonavir) were also synthesized. Copyright © 2008 John Wiley & Sons, Ltd.     

A facile synthesis of high specific activity sodium [1‐14C] lauryl sulphate under microwave irradiation

A highly efficient and optimized synthesis of sodium[1‐¹⁴C] lauryl sulphate having high specific activity (50 mCi/mmol) is described. Lauric acid was converted to undecyl bromide using a modified Hunsdiecker reaction. This was treated with potassium ¹⁴C cyanide (specific activity 50 mCi/mmol) using phase transfer catalysis to yield [1‐¹⁴C]lauronitrile, which was subsequently hydrolysed with a mixture of concentrated hydrochloric acid:propionic acid (1:2 v/v) under microwave irradiation for 2 min to obtain [1‐¹⁴C] lauric acid in quantitative yield. The latter on reaction with chlorosulphonic acid and subsequent neutralization with sodium bicarbonate yielded the title compound. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of [3′‐14C] coenzyme Q10

Radio‐labelled coenzyme Q₁₀, labelled at the 3′‐position with ¹⁴C, was synthesized starting from natural solanesol and ethyl [3‐¹⁴C] acetoacetate. The radiochemical yield was 8.0% from ethyl [3‐¹⁴C] acetoacetate. The specific radioactivity of the product was 44.8 μCi, 1.66 MBq/mg. The specific radioactivity and radiochemical purity are sufficiently high to enable us to use this labelled form of coenzyme Q₁₀ in metabolic studies. Copyright © 2002 John Wiley & Sons, Ltd.     

Methylation of the thiophene ring using Carbon‐11‐labelled methyl iodide: formation of 3‐[11C]methylthiophene

This paper describes the radiosynthesis of 3‐[¹¹C]methylthiophene, chosen as a model reaction for the preparation of heteroaromatic methylthienyl compounds. Labelling was performed from the corresponding lithiothiophene derivative and [¹¹C]methyl iodide as the alkylating agent in THF at ?78°C. The conditions used were the following: (1) trapping for 2–3 min at ?78°C of the [¹¹C]methyl iodide in the THF solution containing the freshly prepared 3‐lithiothiophene; (2) Hydrolysis of the reaction mixture by adding 0.5 ml of the HPLC mobile phase and (3) HPLC purification. 3‐[¹¹C]Methylthiophene ([¹¹C]‐ 1 ) was collected in high yield as the unique peak of the HPLC radiochromatogram. Non‐reacted [¹¹C]methyl iodide was not present. Typically, 50–60 mCi (1.85–2.22 GBq) of 3‐[¹¹C]methylthiophene ([¹¹C]‐ 1 ) were obtained within 20 min of radiosynthesis (including HPLC purification) with specific radioactivities ranging from 0.6 to 1.0 Ci/μmol (22.2–37.0 GBq/μmol) starting from 180 to 200 mCi (6.66–7.40 GBq) of [¹¹C]CO₂ (10 μA, 10 min (6000 μC) irradiation). Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of [14C]‐imexon

A four‐step synthesis of [¹⁴C]‐imexon is described, starting from [¹⁴C]‐phosgene. The overall yield is 27% and the specific activity is 55 mCi/mmol. Copyright © 2005 John Wiley & Sons, Ltd.