Synthesis of C‐14‐labeled novel IKK inhibitor: 2‐[14C]‐N‐(6‐chloro‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐3‐pyridinecarboxamide

2‐[¹⁴C]‐N‐(6‐Chloro‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐3‐pyridinecarboxamide (9A , also referred to as [¹⁴C]‐PS‐1145) was synthesized from [¹⁴C]‐paraformaldehyde in five steps in an overall radiochemical yield of 15%. The key intermediate 1‐[¹⁴C]‐6‐chloro‐1,2,3,4‐tetrahydro‐β‐carboline was obtained by Pictet–Spengler cyclization of chlorotryptamine with [¹⁴C]‐paraformaldehyde. Similar reactions were conducted with tryptamine to address the generality of the methodology. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of 5‐[4,5‐13C2]‐ and 5‐[1,5‐13C2]aminolevulinic acid

5‐[4,5‐¹³C₂]‐ and 5‐[1,5‐¹³C₂]Aminolevulinic acid (ALA) have been synthesized by the Gabriel condensation of potassium phthalimide with ethyl bromo[1,2‐¹³C₂]acetate (derived from [1,2‐¹³C₂]acetic acid) or ethyl bromo[2‐¹³C]‐acetate (derived from sodium [2‐¹³C]acetate), followed by conversion to the chloride, coupling reaction with 2‐ethoxycarbonylethylzinc iodide derived from ethyl 3‐iodopropionate or 2‐methoxy[¹³C]carbonylethylzinc iodide derived from methyl 3‐iodo[1‐¹³C]propionate (generated from potassium [¹³C]cyanide), and hydrolysis. Copyright © 2002 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.     

13C‐ and 14C‐labelling of N‐[1‐(4‐chlorophenyl)‐1H‐pyrrol‐2‐yl‐methyleneamino] guanidinium acetate

N‐[1‐(4‐chlorophenyl)‐1H‐pyrrol‐2‐yl‐¹³C₄‐methyleneamino]guanidinium acetate has been synthesized by a four‐step procedure. This involved reduction of the Weinreb amide N,N′‐dimethyl‐N,N′‐dimethyloxybutane‐1,4‐diamide‐1,2,3,4‐¹³C₄ by Dibal‐H to give the corresponding unstable dialdehyde which is reacted in situ with 4‐chloroaniline to form 1‐(4‐chlorophenyl)‐1H‐pyrrole‐¹³C₄. This pyrrole analogue underwent a Vilsmeyer acylation with POCl₃/DMF followed by final reaction with aminoguanidine bicarbonate to produce the desired labelled compound with 99% atom ¹³C. By using DMF [α‐¹⁴C] a radio‐labelled analogue was synthesized with a specific activity of 60 mCi/mmol. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of a delta opioid agonist in [2H6], [2H4], [11C], and [14C] labeled forms

In support of a program to develop a treatment for depression, four labeled forms of a delta opioid agonist were prepared. The [²H₄] labeled form was prepared using a relatively straightforward conversion of [²H₄]bromoethanol to [²H₄]N‐methyl‐2‐hydroxyethylamine. The key step in the synthesis of the [²H₆] labeled form involved the Pd‐catalyzed exchange in D₂O of 8‐quinolin‐8‐ol to give [²H₆] 8‐quinolin‐8‐ol. The C‐14 labeled form was synthesized in one step using [¹⁴C]carbonylation, and the C‐11 labeled form was prepared in two steps from ¹¹CH₃I. Copyright © 2011 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.     

Synthesis of [2‐13C, 4‐13C]‐(2R,3S)‐catechin and [2‐13C, 4‐13C]‐(2R,3R)‐epicatechin

The first synthesis of doubly labeled, [2‐¹³C, 4‐¹³C]‐(2R,3S)‐catechin 15 and [2‐¹³C, 4‐¹³C]‐(2R,3R)‐epicatechin 18 starting from labeled 2‐hydroxy‐4, 6‐bis(benzyloxy)acetophenone 3 and labeled 3, 4‐bis(benzyloxy)‐benzaldehyde 7 are described. Copyright © 2010 John Wiley & Sons, Ltd.     

A method for the preparation of [13C6]‐labelled 2‐substituted naphthalenes

A reliable route is described for the preparation of various 2‐substituted derivatives of [1,2,3,4,4a,8a‐¹³C₆]‐naphthalene via the bromide 10. The approach is used to prepare [naphthalene‐1,2,3,4,4a,8a‐¹³C₆]‐2‐(2‐bromoethyl)naphthalene (1), a key intermediate in the synthesis of labelled SR57746A, Xaliproden (2). Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of [13C6]‐labelled phenethylamine derivatives for drug quantification in biological samples

The availability of high‐quality ¹³C‐labelled internal standards will improve accurate quantification of narcotics and drugs in biological samples. Thus, the synthesis of 10 [¹³C₆]‐labelled phenethylamine derivatives, namely amphetamine, methamphetamine, 3,4‐methylenedioxyamphetamine, 3,4‐methylenedioxymethamphetamine, 3,4‐methylenedioxy‐N‐ethylamphetamine, 4‐methoxyamphetamine, 4‐methoxymethamphetamine, 3,5‐dimethoxyphenethylamine 4‐bromo‐2,5‐dimethoxyphenethylamine and 2,5‐dimethoxy‐4‐iodophenethylamine, have been undertaken. [¹³C₆]‐Phenol proved to be an excellent starting material for making ¹³C‐labelled narcotic substances in the phenethylamine class, and a developed Stille‐type coupling enabled an efficient synthesis of the 3,4‐methylenedioxy and 4‐methoxy derivatives. The pros and cons of alternative routes and transformations are also discussed. The [¹³C₆]‐labelled compounds are intended for use as internal standards in forensic analysis, health sciences and metabolomics studies by gas chromatography‐mass spectrometry and liquid chromatography‐tandem mass spectrometry. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of [thiazolium‐2,2′‐14C2]‐SAR97276A from [14C]‐thiourea

[thiazolium‐2,2′‐¹⁴C₂]‐SAR97276A, a bis(thiazolium) antimalarial development candidate, was synthesized from [¹⁴C]‐thiourea with an overall radiochemical yield of 15%. The synthetic route involves a modified procedure for the synthesis of [¹⁴C]‐sulfurol, also a key intermediate in thiamine synthesis, which was developed due to unlabelled chemistry proving irreproducible with the radiolabelled substrate. Copyright © 2010 John Wiley & Sons, Ltd.     

The synthesis of [1‐14C]2‐(1H‐tetrazol‐5‐yl)acetic acid

Tetrazoles are a common heterocyclic functionality in many biologically active molecules. [1‐¹⁴C]2‐(1H‐Tetrazol‐5‐yl)acetic acid was required as an intermediate in the synthesis of a development candidate as part of a discovery phase program to complete metabolic profiling studies. [1‐¹⁴C]2‐(1H‐Tetrazol‐5‐yl)acetic acid was prepared in 4 steps overall and in 3 radiochemical steps from K¹⁴CN in an overall 32% radiochemical yield.     

Synthesis of 13C and 15N labeled 2,4‐dinitroanisole

Syntheses of [¹³C₆]‐2,4‐dinitroanisole (ring‐¹³C₆) from [¹³C₆]‐anisole (ring‐¹³C₆) and [¹⁵N₂]‐2,4‐dinitroanisole from anisole using in situ generated acetyl nitrate and [¹⁵N]‐acetyl nitrate, respectively, are described. Treatment of [¹³C₆]‐anisole (ring‐¹³C₆) with acetyl nitrate generated in 100% HNO₃ gave [¹³C₆]‐2,4‐dinitroanisole (ring‐¹³C₆) in 83% yield. Treatment of anisole with [¹⁵N]‐acetyl nitrate generated in 10 N [¹⁵N]‐HNO₃ gave [¹⁵N₂]‐2,4‐dinitroanisole in 44% yield after two cycles of nitration. Byproducts in the latter reaction included [¹⁵N]‐2‐nitroanisole and [¹⁵N]‐4‐nitroanisole.     

Synthesis of carbon‐14‐labeled isotopomer of 6‐(4‐methanesulfonylphenyl)‐5‐[4‐(2‐piperidin‐1‐yl‐ethoxy)phenoxy]‐naphthalen‐2‐ol HCL salt (LY2066948‐[14C] HCL salt)

Carbon‐14‐labeled 6‐(4‐methanesulfonylphenyl)‐5‐[4‐(2‐piperidin‐1‐yl‐ethoxy)phenoxy]naphthalen‐2‐ol, a novel selective estrogen receptor modulator (SERM) was synthesized. The key component, 6‐methoxy‐1‐tetralone‐[carbonyl‐¹⁴C], was synthesized from 3‐(3‐methoxyphenyl)‐propionic acid via an intra‐molecular Friedel–Crafts acylation of 4‐(3‐methoxyphenyl)butanoic acid‐[carboxy‐¹⁴C]. A palladium catalyzed alpha‐keto arylation of 6‐methoxy‐1‐tetralone with 4‐methanesulfonyl‐phenyl bromide, followed by a sequence of bromination, DDQ dehydrogenation, aryl Ullmann reaction, and demethylation with BBr₃ gave the desired product LY2066948‐[¹⁴C]. Copyright © 2007 John Wiley & Sons, Ltd.     

Efficient syntheses of benzyl and n‐octyl [1,3‐13C2]acetoacetates,and their application to syntheses of 13C‐labelled pyrrole and 13C‐labelled hymecromone

Benzyl [1‐¹³C]acetate (2a) was prepared via esterification of sodium [1‐¹³C]acetate (1) with benzyl bromide in the presence of 18‐crown‐6‐ether in 97% yield. n‐Octyl [1‐¹³C]acetate (2b) was rapidly obtained by microwave irradiation of 1‐bromooctane and potassium [1‐¹³C]acetate (obtained by salt exchange of 1) absorbed on Al₂O₃ in 82% yield. Solvent‐free Claisen condensation of benzyl or n‐octyl [1‐¹³C]acetate (2a or 2b) in the presence of potassium tert‐butoxide efficiently gave benzyl or n‐octyl [1,3‐¹³C₂]acetoacetate (3a or 3b) in 51 or 68% yield, respectively. Dibenzyl 2,4‐dimethyl[2,4‐¹³C₂]pyrrole‐3,5‐di[¹³C]carboxylate (4) was synthesized from benzyl [1,3‐¹³C₂]acetoacetate (3a) in 54% yield. [2,4‐¹³C₂]Hymecromone (6) (7‐hydroxy‐4‐methyl[2,4‐¹³C₂]coumarin) was obtained from n‐octyl [1,3‐¹³C₂]acetoacetate (3b) and 1,3‐benzenediol (5) in 73% yield. Copyright © 2008 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.     

Synthesis of [13C2]nifedipine

[¹³C₂]Nifedipine (3 ) was synthesized from [¹³C]methanol (&1macr;) in two steps. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of [13C5] and [carbonyl‐14C]‐5‐chlorofuran‐2‐carboxylic acid

The inventory of labeled compounds and methods for their preparation are constantly growing, but still more building blocks of biologically relevant compounds need to be developed. Furans are frequently encountered in bioactive molecules, and a good synthesis of labeled furan is found in the literature. We required a relatively uncommon labeled furan, 5‐chloro‐2‐furoic acid, for investigative work labeled with C‐13 and C‐14. Carboxylation of the lithium anion of [¹³C₄]furan with ¹³CO₂ followed by chlorination using benzyltrimethylammonium dichloroiodate provided the target compound in modest yield and high purity. The same procedure was then repeated with unlabeled furan and ¹⁴CO₂ to give [carbonyl‐¹⁴C]‐5‐chlorofuran‐2‐carboxylic acid. Copyright © 2010 John Wiley & Sons, Ltd.     

Syntheses of [14C] and [2H4]PD0205520, an inhibitor of the tyrosine kinase activity of the epidermal growth factor receptor

5‐(4‐Methyl‐piperazin‐1‐yl)‐pent‐2‐ynoic acid [4‐(3‐chloro‐4‐fluoro‐phenylamino)‐pyrido[3,4‐d]pyrimidin‐6‐yl]‐amide, PD0205520, was under investigation as a potential inhibitor of the tyrosine kinase (TK) activity of the epidermal growth factor receptor (EGFR) for cancer treatment. Both radio‐ and stable‐isotope‐labeled compounds were required for drug absorption, distribution, metabolism and excretion (ADME) and quantitative mass spectrometry bio‐analytical studies. PD0205520 ^I4C‐labeled in the pyrimidine ring system was prepared in seven steps in an overall radiochemical yield of 26% from [¹⁴C]thiourea. PD0205520 ²H‐Iabeled in the piperazine ring was synthesized in four steps in a 32% overall yield. 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 [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.