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.     

Syntheses of [14C]‐labeled 2‐(3‐chlorophenyloxy)‐3‐[3‐(3‐hydroxy) pyridin‐4‐yl propoxy]pyridine,a phosphodiesterase 4 inhibitor and its metabolites

We describe here the synthesis of [¹⁴C]‐2‐(3‐chlorophenyloxy)‐3‐[3‐(3‐hydroxy)pyridin‐4‐yl propoxy]pyridine (1), a phosphodiesterase 4 inhibitor. [¹⁴C]‐Labeled 1 was prepared in three steps from [¹⁴C]‐2‐bromopyridin‐3‐ol in an overall yield of 32%. Preparation of [¹⁴C]‐labeled 2 and 3, two metabolites of 1, is also described. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of isotope‐labeled HSP90 inhibitor: [13CD3] and [14C]‐TAK‐459

[¹³CD₃]‐TAK‐459 (1A), an HSP90 inhibitor, was synthesized from [¹³CD₃]‐sodium methoxide in three steps in an overall yield of 29%. The key intermediate [¹³CD₃]‐2‐methoxy‐6‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)pyridine was synthesized in two steps from 2,6‐dibromopyridine and stable isotope‐labeled sodium methoxide. [¹⁴C]‐TAK‐459 (1B) was synthesized from [¹⁴C(U)]‐guanidine hydrochloride in five steps in an overall radiochemical yield of 5.4%. The key intermediate, [¹⁴C]‐(R)‐2‐amino‐7‐(2‐bromo‐4‐fluorophenyl)‐4‐methyl‐7,8‐dihydropyrido[4,3‐d]pyrimidin‐5(6H)‐one, was prepared by microwave‐assisted condensation.     

Synthesis of [4‐14C]‐pelargonidin chloride and [4‐14C]‐delphinidin chloride

The synthesis of [4‐¹⁴C]‐pelargonidin chloride and [4‐¹⁴C]‐delphinidin chloride via [formyl‐¹⁴C]‐2‐(benzoyloxy)‐4,6‐dihydroxybenzaldehyde, ω,4‐diacetoxyacetophenone and ω,3,4,5‐tetraacetoxyacetophenone is described. The first step comprised labelling of the carbonyl group of 2‐(benzoyloxy)‐4,6‐dihydroxybenzaldehyde, verifying that the coupling with ω,4‐diacetoxyacetophenone or ω,3,4,5‐tetraacetoxyacetophenone under hydrogen chloride atmosphere resulted in the formation of [4‐¹⁴C] labelled anthocyanidins. Copyright © 2006 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.     

Synthesis of [14C]‐ and [13C6]‐labeled potent HIV non‐nucleoside reverse transcriptase inhibitor

5,11‐Dihydro‐11‐ethyl‐5‐methyl‐8‐{2‐{(1‐oxido‐4‐quinolinyl)oxy}ethyl}‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one, (1), labeled with carbon‐14 in the quinoline–benzene ring, in one of the pyridine rings of the dipyridodiazepinone tricyclic moiety, and in the side chain, was prepared in three different syntheses with specific activities ranging from 44 to 47 mCi/mmol (1.63–1.75 GBq/mmol). In the first synthesis, 5,11‐dihydro‐11‐ethyl‐8‐(2‐hydroxyethyl)‐5‐methyl‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one (2) was coupled to 4‐hydroxyquinoline, [benzene‐¹⁴C(U)]‐, using Mitsunobu's reaction conditions, followed by the oxidation of the quinoline nitrogen with 3‐chloroperoxybenzoic acid to give ([¹⁴C]‐(1a)) in 43% radiochemical yield. Second, 3‐amino‐2‐chloropyridine, [2,6‐¹⁴C]‐, was used to prepare 8‐bromo‐5,11‐dihydro‐11‐ethyl‐5‐methyl‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one (8), and then Stille coupled to allyl(tributyl)tin followed by ozonolysis of the terminal double bond and in situ reduction of the resulting aldehyde to alcohol (10). Mitsunobu etherification and oxidation as seen before gave ([¹⁴C]‐(1b)) in eight steps and in 11% radiochemical yield. Finally, carbon‐14 potassium cyanide was used to prepare isopropyl cyanoacetate (12), which was used to transform bromide (8) to labeled aryl acetic acid (13) under palladium catalysis. Trihydroborane reduction of the acid gave alcohol (14) labeled in the side chain, which was used as described above to prepare ([¹⁴C]‐(1c)) in 4.3% radiochemical yield. The radiochemical purities of these compounds were determined by radio‐HPLC and radio‐TLC to be more than 98%. To prepare [¹³C₆]‐(1), [¹³C₆]‐4‐hydroxyquinoline was prepared from [¹³C₆]‐aniline and then coupled to (2) and oxidized as seen before. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of [1‐13C]‐para‐xylene and [2‐13C]‐para‐xylene

An efficient synthesis of [1‐¹³C]‐para‐xylene ( 1a ) and [2‐¹³C]‐para‐xylene ( 1b ) is described. The incorporation of the label has been achieved by cyclocondensation of suitable 1,5‐bis(bromomagnesio)alkanes with either ethyl [1‐¹³C]acetate or ethyl [¹³C]formate which gave [ring‐¹³C]‐labelled dimethylcyclohexanols. Dehydration of these alcohols followed by dehydrogenation of the intermediate dimethylcyclohexenes furnished the title compounds in 32 and 40% overall yield, respectively. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of [uniformly ring‐14C]‐labelled 4‐hydroxybenzaldehyde,vanillin, and protocatechualdehyde

[Uniformly ring‐¹⁴C]‐labelled 4‐hydroxybenzaldehyde, vanillin, and protocatechualdehyde were synthesized from [¹⁴C]‐labelled phenol, guaiacol, and catechol with methyl dichloromethyl sulfide (CH₃SCHCl₂) under Friedel–Crafts alkylation conditions in dichloromethane at ?78°C for 5 min (in the case of phenol and guaiacol) or at ?20°C for 1 min (in the case of catechol), by rapid addition of SnCl₄ to mixtures of the phenolic compound and CH₃SCHCl₂, followed by hydrolysis with HCl. Regioselective formylation (para to the –OH group) was achieved. The conversion rates were 96, 81, and 88% for 4‐hydroxybenzaldehyde, vanillin, and protocatechualdehyde, respectively, and the yields of the recovered products after work‐up amounted to 88, 75, and 83%, respectively. In the case of guaiacol, 17% of isovanillin was obtained as by‐product. It was found that the presence of water or ethyl acetate in the reaction mixture, at a molar ratio of 60:1 (water:guaiacol) or 120:1 (ethyl acetate:guaiacol), had little influence on the yields under the reaction conditions. Factors influencing the yields are discussed in the study. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of C‐14 and C‐13, H‐2‐labeled IKK inhibitor: [14C] and [13C4,D3]‐N‐(6‐chloro‐7‐methoxy‐9H‐pyrido[3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide

[¹⁴C]‐N‐(6‐Chloro‐7‐methoxy‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide (5B ), an IKK inhibitor, was synthesized from [¹⁴C]‐barium carbonate in two steps in an overall radiochemical yield of 41%. The intermediate, [carboxyl‐¹⁴C]‐2‐methylnicotinic acid, was prepared by the lithiation and carbonation of 3‐bromo‐2‐methylpyridine. [¹³C₄,D₃]‐N‐(6‐chloro‐7‐methoxy‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide (5C ) was synthesized from [1,2,3,4‐¹³C₄]‐ethyl acetoacetate and [D₄]‐methanol in six steps in an overall yield of 2%. [¹³C₄]‐2‐methylnicotic acid, was prepared by condensation of [¹³C₄]‐ethyl 3‐aminocrotonate and acrolein, followed by hydrolysis with lithium hydroxide. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of [14C]‐labelled repinotan hydrochloride and its major metabolite M‐6

For studies of pharmacokinetics and drug metabolism of the new 5‐HT_1A agonist repinotan, the ¹⁴C‐labelled version was synthesized. Starting from [U‐¹⁴C]phenol, a 10‐step synthesis led to 457 mg (1.58 GBq) of [U‐¹⁴C]repinotan hydrochloride, labelled uniformly in the aromatic ring of the chromane moiety. For a study in man, a mono‐carbon‐14 labelled substance was required. Therefore a 7‐step synthesis was performed starting from [carbonyl‐¹⁴C]2‐hydroxy‐acetophenone. The yield was 106 mg (0.396 GBq) of [4‐chromane‐¹⁴C]repinotan hydrochloride. The carbon‐14 labelled major metabolite, hydroxylated in the 6‐position of the chromane moiety, was synthesised as reference compound. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of [quinoline‐3‐14C]‐SSR97193 (ferroquine) from [2‐14C]‐malonic acid

The antimalarial [quinoline‐3‐¹⁴C]‐SSR97193 (ferroquine) ( 8 ), an analogue of chloroquine (CQ) ( 1 ), was synthesized from [2‐¹⁴C]‐malonic acid with an overall radiochemical yield of 15%. The synthetic route via [¹⁴C]‐Meldrum's acid ( 9 ) was designed to minimize the intermediacy of radiolabelled volatiles. This synthesis involves a four‐step route to labelled 4,7‐dichloroquinoline, which is the key intermediate for the synthesis of many analogues of CQ. Copyright © 2004 John Wiley & Sons, Ltd.     

Alternative methods for labeling the 5‐HT1A receptor agonist, 1‐[2‐(4‐fluorobenzoylamino)ethyl]‐4‐(7‐methoxynaphthyl)piperazine (S14506), with carbon‐11 or fluorine‐18

1‐[2‐(4‐Fluorobenzoylamino)ethyl]‐4‐(7‐methoxynaphthyl)piperazine (S14506) is one of the most potent and selective agonists at 5‐HT_1A receptors. For the purpose of prospective 5‐HT_1A receptor imaging with positron emission tomography and the investigation of radioligand metabolic pathways, S14506 was labeled with a positron emitter, either carbon‐11 (t_1/2=20.4 min) or fluorine‐18 (t_1/2=109.7 min), at different positions. Thus, [O‐methyl‐¹¹C]S14506 was obtained in a radiosynthesis time of 35 min by treating O‐desmethyl‐S14506 with [¹¹C]iodomethane and tetrabutylammonium hydroxide in N,N–dimethylformamide. The overall decay‐corrected radiochemical yield (RCY) of [O‐methyl‐¹¹C]S14506 ranged between 6 and 24% and the specific activity (SA) between 1343 and 3101 Ci/mmol (mean 2390; n=30). [carbonyl‐¹¹C]S14506 was synthesized through a microwave‐enhanced direct coupling of in situ generated [¹¹C]organocarboxymagnesium bromide with amine precursor. RCYs ranged from 10 to 18%. [¹⁸F]S14506 was prepared via nucleophilic aromatic fluoridation of the 4‐nitro analog in 14–35% RCY and with SA ranging from 1063 to 2302 Ci/mmol (mean 1617; n=14) in a radiosynthesis time of 115 min. Heating the radiofluoridation mixture for 5 min at 180°C in a single mode microwave cavity gave similar RCY and SA to heating for 30 min in an oil bath at the same temperature. 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.     

Synthesis of morphine‐[N‐methyl‐14C]‐6‐β‐D‐glucuronide

Protected morphine‐6‐glucuronide was converted into morphine‐[N‐methyl‐¹⁴C]‐6‐glucuronide by a three‐step procedure. Methyl (3‐pivaloylmorphin‐6‐yl 2,3,4‐tri‐O‐isobutyryl‐β‐D‐glucopyranosid)uronate was N‐demethylated by treatment with 1‐chloroethyl chloroformate to afford protected normorphine‐6‐glucuronide as its hydrochloride salt. The normorphine‐6‐glucuronide derivative was alkylated with iodomethane‐[¹⁴C] in the presence of potassium carbonate to produce C‐14 labelled protected morphine‐6‐glucuronide. Finally, hydrolysis of the protecting groups using 5% sodium hydroxide solution gave morphine‐[N‐methyl‐¹⁴C]‐6‐β‐D‐glucuronide with a specific activity of 41.8 mCi mmol^?1 and radiochemical purity of 99.2% (HPLC). Copyright © 2002 John Wiley & Sons, Ltd.     

[5‐14C]‐4‐methyltriazolepyridines via facile preparation of methyl‐[14C]‐isothiocyanate

A fast and convenient microwave assisted one‐pot synthesis of methyl‐[¹⁴C]‐isothiocyanate 4 was shown. The continued one‐pot synthesis with 4 to a highly refined material like [5‐¹⁴C]‐dimethylsulfanyltriazolepyridines 8 and 13 without any intermediate purification, six steps in the same pot from [¹⁴C]KCN. Oxidation of the sulfur provided access to triazole‐ethers upon reaction with alcohols. The triazole‐ethers, 15, were obtained at fair to good yields and specific activities above 2 GBq/mmol. Copyright © 2008 John Wiley & Sons, Ltd.     

The synthesis of [3,4,1′‐13C3]genistein

A facile synthesis is described for [3,4,1′‐¹³C₃]genistein for use as an internal standard in isoflavone analysis by mass spectrometric methods. Ethyl 4‐hydroxy[1‐¹³C]benzoate was first prepared from the reaction of diethyl [2‐¹³C]malonate and 4H‐pyran‐4‐one. Two further ¹³C atoms were incorporated using potassium [¹³C]cyanide as the source to give 4′‐benzyloxy‐[1,2,1′‐¹³C₃]phenylacetonitrile. [3,4,1′‐¹³C₃]Genistein was then constructed through coupling of the isotopically labelled phenylacetonitrile with phloroglucinol under Hoesch conditions, followed by formylation and cyclization. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of isotopically labelled [14C]ZT‐1 (Debio‐9902), [d3]ZT‐1 and (−)‐[d3]huperzine A,a new generation of acetylcholinesterase inhibitors

A method has been developed for the synthesis of two isotopically labelled forms of a pro‐drug of the acetylcholinesterase inhibitor (?)‐huperzine A. These labelled compounds,[¹⁴C]ZT‐1 (Debio‐9902) and [d₃]ZT‐1, were used in clinical studies to evaluate a potential treatment for Alzheimer's disease. The pro‐drug [¹⁴C]ZT‐1 was isolated with a radiochemical purity of >98% and a gravimetric specific activity of 129 μCi/mg in a seven‐step synthesis starting from [U‐¹⁴C]phenol in 7% yield. Subsequently, the deuterium labelled target (?)‐[d₃]huperzine A was achieved in six steps with an overall yield of 15% and gave an isotopic distribution of d₂ (1.65% huperzine A) and d₃ (97.93% huperzine A) with a chemical purity of 98.5%. Condensation of the substrate (?)‐[d₃]huperzine A with 5‐chloro‐o‐vanillin gave the Schiff base [d₃]ZT‐1 in a chemical yield of 80%. Reduction of the Schiff base gave reduced‐[d₃]ZT‐1, which was converted into the hydrochloride salt with an isotopic distribution of d₂ (1.60%) and d₃ (98.02%). Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of 3‐[[4‐(4‐[18F] fluorophenyl)piperazin‐1‐yl]methyl]‐1H‐pyrrolo[2,3‐b]pyridine

3‐[[4hyphen;(4‐[¹⁸F]fluorophenyl)piperazin‐1‐yl] methyl] ‐1H‐pyrrolo[2,3‐b]pyridine, acandidate to image dopamine D₄ receptors, was synthesised via electrophilic fluorination of a trimethylstannyl precursor with high specific radioactivity [¹⁸F]F₂. The precursor was obtained by a facile four‐step synthetic approach; the trimethylstannyl leaving group was introduced by displacement of iodine utilising palladium catalysis and hexamethyldistannane in an inert solvent. The total radiosynthesis time was 50 min, including purification and formulation for injection. Decay corrected radiochemical yield was <1% as calculated from the amount of [¹⁸F]F^? produced. Specific radioactivity at the end of synthesis was 12.8–16.4 GBq/μmol. Radiochemical purity was 88–92%. Ex vivo studies in rats showed homogeneous distribution of radioactivity within rat brain. Copyright © 2002 John Wiley & Sons, Ltd.     

Regioselective syntheses of [13C]4‐labelled sodium 1‐carboxy‐2‐(2‐ethylhexyloxycarbonyl)ethanesulfonate and sodium 2‐carboxy‐1‐(2‐ethylhexyloxycarbonyl)ethanesulfonate from [13C]4‐maleic anhydride

The entitled monohydrolysis products, also known as α‐ethylhexyl and β‐ethylhexyl sulfosuccinate (EHSS), of the surfactant diisooctyl sulfosuccinate (DOSS) were synthesized in stable isotope‐labelled form from [¹³C]₄‐maleic anhydride. Sodium [¹³C]₄‐1‐carboxy‐2‐(2‐ethylhexyloxycarbonyl)ethanesulfonate (α‐EHSS) was prepared by the method of Larpent by reaction of 2‐ethylhexan‐1‐ol with [¹³C]₄‐maleic anhydride followed by regioselective conjugate addition of sodium bisulfite to the resulting monoester (38% overall yield). The regiochemical outcome of bisulfite addition was confirmed by a combination of ¹³C/¹³C (incredible natural abundance double quantum transfer) and ¹H/¹³C (heteronuclear multiple‐bond correlation (HMBC)) NMR spectral correlation experiments. Sodium [¹³C]₄‐2‐carboxy‐1‐(2‐ethylhexyloxycarbonyl)ethanesulfonate (β‐EHSS) was prepared in four steps by reaction of 4‐methoxybenzyl alcohol with [¹³C]₄‐maleic anhydride, regioselective sodium bisulfite addition, N,N′‐dicyclohexylcarbodiimide‐mediated esterification with 2‐ethylhexan‐1‐ol, and p‐methoxybenzyl ester deprotection with trifluoroacetic acid (13% overall yield). The regiochemical outcome of the second synthesis was confirmed by a combination of ¹J_CC scalar coupling constant analysis and ¹H/¹³C (HMBC) NMR spectral correlation. The materials prepared are required as internal standards for the liquid chromatography–mass spectrometry (LC‐MS)/MS trace analysis of the degradation products of DOSS, the anionic surfactant found in Corexit, the oil dispersant used during emergency response efforts connected to the Deepwater Horizon oil spill of April 2010. Copyright © 2014 John Wiley & Sons, Ltd.     

[125I], [127I]‐and [14C]‐Labelling of the GLP‐1‐(7‐37) derivative NN2211

Arg³⁴Lys²⁶(N^ε‐(γ‐L ‐glutamyl(N^α‐palmitoyl)))‐GLP‐1(7‐37) (NN2211) is currently in development as a diabetes type 2 drug. The fatty acid attached to the GLP‐1(7‐37) ensures a long and controlled duration of action. The synthesis of [¹²⁵I]NN2211, [¹²⁷I]NN2211 and [¹⁴C]NN2211 used for preclinical ADME studies are described. NN2211 was iodinated using the lactoperoxidase/hydrogen peroxide method, and [¹⁴C]NN2211 was synthesized in 4 steps by two routes both starting from an α‐protected [U‐¹⁴C]glutamic acid. Copyright © 2003 John Wiley & Sons, Ltd.