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 deleobuvir,a potent hepatitis C virus polymerase inhibitor,and its major metabolites labeled with carbon‐13 and carbon‐14

Deleobuvir, (2E)‐3‐(2‐{1‐[2‐(5‐bromopyrimidin‐2‐yl)‐3‐cyclopentyl‐1‐methyl‐1H‐indole‐6‐carboxamido]cyclobutyl}‐1‐methyl‐1H‐benzimidazol‐6‐yl)prop‐2‐enoic acid (1), is a non‐nucleoside, potent, and selective inhibitor of hepatitis C virus NS5B polymerase. Herein, we describe the detailed synthesis of this compound labeled with carbon‐13 and carbon‐14. The synthesis of its three major metabolites, namely, the reduced double bond metabolite (2) and the acyl glucuronide derivatives of (1) and (2), is also reported. Aniline‐¹³C₆ was the starting material to prepare butyl (E)‐3‐(3‐methylamino‐4‐nitrophenyl‐¹³C₆)acrylate [¹³C₆]‐(11) in six steps. This intermediate was then used to obtain [¹³C₆]‐(1) and [¹³C₆]‐(2) in five and four more steps, respectively. For the radioactive synthesis, potassium cyanide‐¹⁴C was used to prepare 1‐cylobutylaminoacid [¹⁴C]‐(23) via Buchrer–Bergs reaction. The carbonyl chloride of this acid was then used to access both [¹⁴C]‐(1) and [¹⁴C]‐(2) in four steps. The acyl glucuronide derivatives [¹³C₆]‐(3), [¹³C₆]‐(4) and [¹⁴C]‐(3) were synthesized in three steps from the acids [¹³C₆]‐(1), [¹³C₆]‐(2) and [¹⁴C]‐(1) using known procedures.     

Synthesis of a highly potent leukocyte function‐associated antigen‐1 antagonist and its metabolite labeled with stable isotopes and carbon‐14, part 2

(S)‐2‐[(R)‐7‐(3,5‐Dichlorophenyl)‐5‐methyl‐6‐oxo‐5‐(4‐trifluoromethoxybenzyl)‐6,7‐dihydro‐5H‐imidazo[1,2‐a]imidazole‐3‐sulfonylamino]‐proprionamide (1), a potent lymphocyte function‐associated antigen‐1 antagonist and its sulfonamide metabolite (2) labeled with stable isotopes and carbon‐14 were prepared for Drug Metabolism and PharmacoKinetics and other studies. A long linear route was used to prepare [¹³C₂, ²H₃]‐(1) using [3,3,3‐²H]‐D‐alanine and [¹³C₂]‐glycine in 15 steps and 2.5% overall yield. With the availability of [¹³C₆]‐3,5‐dichloroaniline, the sulfonamide [¹³C₆]‐(2) was prepared in 12 steps and in 5.6% overall yield. For the carbon‐14 synthesis, a six‐step synthesis gave both compounds [¹⁴C]‐(1) and [¹⁴C]‐(2) from the common sulfonyl chloride intermediate [¹⁴C]‐(15) in 18% and 4% radiochemical yields and specific activities of 44 and 40.5 mCi/mmol, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of deuterium‐labelled (−)‐galanthamine

The synthesis of deuterium‐labelled galanthamine is reported. 6‐[²H₃]methoxy‐N‐[²H₃]methyl‐(?)‐galanthamine was obtained in seven steps from galanthamine. The synthesis was carried out by selective O‐ and N‐demethylations. The [²H₃]‐N‐methyl and [²H₃]‐O‐methyl‐groups were introduced by selective aminoreduction and O‐methylation. Copyright © 2008 John Wiley & Sons, Ltd.     

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 deuterium‐labeled 3‐O‐methyldopa and 4‐O‐methyldopa

Concise methods for the synthesis of 4‐hydroxy‐3‐[²H₃]‐methoxyphenylalanine (3‐O‐[²H₃]‐methydopa) and 3‐hydroxy‐4‐[²H₃]‐methoxyphenylalanine (4‐O‐[²H₃]‐methydopa) are described. The 3‐O‐[²H₃]‐methydopa is a valuable internal standard for the tandem MS quantification of 3‐O‐methyldopa, a metabolite of value in the diagnosis of aromatic l‐amino acid decarboxylase (AADC) deficiency. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of 14C‐labeled and 13C‐,15N‐labeled dasatinib and its piperazine N‐dealkyl metabolite

Dasatinib (SPRYCEL^®) is a multiple kinase inhibitor approved for the treatment of chronic myelogenous leukemia and Philadelphia chromosome‐positive acute lymphoblastic leukemia in patients with resistance to prior therapy, including imatinib mesylate (Gleevec^®). Radiolabeled dasatinib and its piperazine N‐dealkyl metabolite were synthesized to investigate absorption, distribution, metabolism, and elimination of the compounds in humans and animals. These compounds were prepared following a three‐step sequence, which included thiazole carboxamide formation via cyclization of labeled thiourea with a brominated oxyacrylamide precursor. In the final step a common intermediate was converted to either [¹⁴C]dasatinib or the radiolabeled piperazine N‐dealkyl metabolite with labeling in the aminothiazole ring. Syntheses of both compounds were achieved with radiochemical purities in excess of 98%. Stable‐labeled dasatinib and the piperazine N‐dealkyl metabolite were also needed for use as mass spectral internal standards in support of bioanalytical assays. By following the same route used for the carbon‐14 synthesis, [¹³C₄, ¹⁵N₂]dasatinib and the [¹³C₄, ¹⁵N₂]metabolite were prepared with labeling in both the dichloropyrimidine and thiazole ring systems. This convergent process introduced stable isotope labeling through (1, 2, 3‐¹³C₃) diethyl malonate and [¹³C,¹⁵N₂]thiourea. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 3H‐, 14C‐, and stable‐isotope‐labelled galantamine

Reminyl^® is a newly approved drug, used in the treatment of mild to moderate Alzheimer disease. The active compound, galantamine, was initially isolated from the bulbs of certain Narcissus species, but is at the moment also produced synthetically. In the process leading to the final approval, the synthesis of tritium‐, carbon‐14‐ and stable‐isotope‐labelled galantamine for pharmacokinetic studies was required. Racemic (±)‐1‐bromonarwedine, a compound available as intermediate from the commercial synthesis, was transformed to racemic 1‐bromo‐galantamine. Catalytic bromo‐tritium exchange, followed by HPLC purification and resolution afforded tritium‐labelled galantamine. The [¹⁴C]‐label was introduced on the nitrogen as well as on the oxygen‐methyl position. This was achieved by N‐ and O‐demethylation of galantamine and reaction of the thoroughly purified intermediate with [¹⁴C]‐methyl iodide. Stable‐isotope‐labelled galantamine was obtained likewise by ¹³CD₃OD‐methylation of O‐demethylated galantamine under Mitsunobu conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of stable isotope‐labeled metabolites of asenapine

The stable isotope‐labeled synthesis of four of the major metabolites of asenapine is described. The synthesis of [¹³CD₃]‐asenapine N‐oxide proceeded in two synthetic steps. Preparation of [¹³CD₃]‐asenapine 11‐hydroxysulfate and [¹³C₆]‐N‐desmethylasenapine paralleled established synthetic protocols with effective utilization of labeled precursors. The synthesis of [¹³CD₃]‐asenapine N⁺‐glucuronide was achieved in three chemical steps followed by purification.     

An overview of radio or stable isotope‐labeled cis‐neonicotinoid analogs

To support the metabolism and toxicology study of cis‐neonicotinoids, radio or stable isotope was introduced into different sites of the key intermediate 2‐chloro‐5‐((2‐(nitromethylene)imidazolidin‐1‐yl)methyl)pyridine (6‐Cl‐PMNI). [³H₂]‐ and [¹⁴C]‐label were successively prepared from initial materials NaB³H₄ and [¹⁴C]‐nitromethane, respectively. Similarly, [D₂]‐6‐Cl‐PMNI was prepared from NaBD₄ in four steps, with 52.6% overall isotopic yield, and dual‐labeled [D₂, ¹³C]‐target was obtained from NaBD₄ and [¹³C]‐nitromethane, affording overall isotopic yield of 42.5%. Moreover, [¹⁴C₂] was introduced from [U‐¹⁴C]‐ethylenediamine dihydrochloride in three steps, with a 58.3% overall chemical yield. Finally, typical labeled cis‐neonicotinoids paichongding and cycloxaprid were prepared and characterized. The methods were proved to have good generality in the synthesis of other cis‐neonicotinoids, and all results would be useful in metabolism studies of new cis‐neonicotinoids. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of highly potent lymphocyte function‐associated antigen‐1 antagonists labeled with carbon‐14 and with stable isotopes,part 3

The drug candidates ( 2 ) and ( 3 ) are highly potent LFA‐1 inhibitors. They were efficiently prepared labeled with carbon‐14 using a palladium‐catalyzed carboxylation of an iodo‐precursor ( 5 ) and sodium formate‐¹⁴C to afford acid [¹⁴C]‐( 6 ), which was coupled via an amide bond to chiral amines ( 7 ) and ( 8 ) in 52% and 48% overall yield, respectively, and with specific activities higher than 56 mCi/mmol and radiochemical purities of 99%. For stable isotopes synthesis, the amine [²H₈]‐( 7 ) was synthesized in three steps from 2‐cyanopyridine‐²H₄ using Kulinkovich‐Szymonik aminocyclopropanation, followed by coupling to L ‐alanine‐2,3,3,3‐²H₄‐N‐t‐BOC, and then removal of the BOC‐protecting group. Amide bond formation with acid ( 6 ) gave [²H₈]‐( 2 ) in 36% overall yield. The amine [¹³C₄,¹⁵N]‐( 8 ) was obtained in two steps using L‐threonine‐¹⁴C₄,¹⁵N and then coupled to acid [¹³C]‐( 6 ) to give [¹³C₅,¹⁵N]‐( 3 ) in 56% overall yield.     

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.     

Synthesis of deuterium and C‐13‐labelled ethyl glycolate and their subsequent use in the synthesis of labelled analogues of the DNA adduct O6‐carboxymethyl‐2′‐deoxyguanosine

The adduct O⁶‐carboxymethyl‐2′‐deoxyguanosine (O⁶CMdG) is of importance as it has been previously linked to high red meat diet in humans, and as yet, a liquid chromatography‐mass spectrometry (LC‐MS) method has not been developed due to lack of appropriate standards. The synthesis of the deuterated and C‐13 analogues required the use of [²H₂]‐ and [¹³C₂]ethyl glycolate to label the carboxymethyl moiety of O⁶CMdG. [²H₂]Ethyl glycolate was synthesised via acid hydrolysis of ethyl diazoacetate using deuterated solvents (59% yield), whilst [¹³C₂]ethyl glycolate was synthesised from [¹³C₂]glycine in a three‐step procedure (35% yield). The labelled ethyl glycolates were then used to synthesise [²H₂]‐ and [¹³C₂]O⁶CMdG for future use as internal standards in the LC‐MS analysis of biological samples. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of [18O2]‐curcumin

Curcumin, a pigment isolated from rhizomes of Curcuma longa, is a potent cancer chemopreventive and chemotherapeutic agent and is now evaluated in phase III human clinical trials. This report describes an efficient synthesis of [¹⁸O₂]‐curcumin. [¹⁸O₂]‐Curcumin was prepared in three steps from 1‐iodo‐2‐methoxy‐4‐methylbenzene in an overall yield of 53%.     

Synthesis of JTT‐501 and its metabolite JTP‐20604 labelled with 13C

JTT‐501 specifically labelled with ¹³C was obtained via a four‐step synthesis at an isotopic enrichment level of 99% and in 14% overall chemical yield starting from 4‐hydroxy‐[ring‐U‐¹³C₆]benzaldehyde (3) . The hydrogenation of [¹³C₆]JTT‐501 over Pd/C gave [¹³C₆]JTP‐20604 in 90% chemical yield. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of labelled N‐(4‐hydroxy‐[14C(U)]phenyl)‐2‐[2,3‐dihydro‐3‐oxo‐l,2‐benzisothiazol‐2‐yl‐1,1‐dioxide]acetamide

The amidation of 2‐[1,1‐dioxide‐3‐oxo‐1,2‐benzisothiazole‐2(3H)‐yl] acetyl chloride with carbon‐14‐labelled 4‐amino‐[¹⁴C(U)]phenol in NaOAc‐HOAc buffer solution at ?10°C gave N‐(4‐hydroxy‐[¹⁴C(U)]phenyl)‐2‐[2,3‐dihydro‐3‐oxo‐1,2‐benziso‐thiazol‐2‐yl‐1,1‐dioxide]acetamide in 82% yield. Subsequent hydrolysis with aqueous 0.5 N NaOH solution afforded the ring opened product N‐(4‐hydroxy‐[¹⁴C(U)]‐phenyl)‐2‐[2‐carboxy‐phenylsulfonamido]acetamide in 80% yield. Copyright © 2005 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 N‐(2‐chloro‐3,4‐dimethoxybenzylideneamino)guanidinium acetate [α‐14C]

¹⁴C‐Labelled N‐(2‐chloro‐3,4‐dimethoxybenzylideneamino)guanidinium acetate has been synthesized as a part of a four‐step procedure which involved decarboxylation of 2‐chloro‐3,4‐dimethoxybenzoic acid by Pb(OAc)₄ to give 2‐chloro‐3,4‐dimethoxy‐1‐iodobenzene, followed by a selective lithiation at the iodine position and electrophilic substitution with N,N‐dimethylformamide [α‐¹⁴C] and final reaction with aminoguanidine bicarbonate. The specific activity was 59 mCi/mmol and the overall yield 49%. Copyright © 2002 John Wiley & Sons, Ltd.     

Fluorine‐18‐ and iodine‐125‐labelling of spiegelmers

Spiegelmers are high‐affinity l‐enantiomeric oligonucleotide ligands (aptamers) that display high resistance to enzymatic degradation compared to d‐oligonucleotides. Spiegelmers belong to the third generation of aptamers, and are currently extensively investigated as potential therapeutic agents. We have previously developed an original method to label natural oligonucleotides with radiohalogens and particularly with fluorine‐18, the most widely used positron‐emitter, t_1/2: 109.8 min. Using the same strategy, we herein report the labelling of Spiegelmers, both with fluorine‐18 for positron emission tomography imaging and iodine‐125 for high resolution autoradiography. Three 25‐mer l‐oligonucleotides have been used, differing (a) by the position of the terminal phosphorothioate monoester group (3′‐ or 5′‐end, and therefore differing by the position of the labelling on the macromolecule) and (b) by the nature of the backbone sugar moiety (2′‐OH or 2′‐H, therefore covering the RNA and DNA series, respectively). N‐(4‐[¹⁸F]fluorobenzyl)‐2‐bromoacetamide was synthesized in three radiochemical steps from 4‐cyano‐N,N,N‐trimethylanilinium trifluoromethanesulfonate and HPLC‐purified in 90 min (typical production: 2.2–2.4 GBq starting from a batch of 22–24 GBq of [¹⁸F]fluoride). N‐(4‐[¹²⁵I]iodobenzyl)‐2‐bromoacetamide was synthesized from the corresponding trimethylsilyl derivative (one pot, two radiochemical steps) and HPLC‐purified in 60 min (typical production: 24 MBq starting from 37 MBq of Na[¹²⁵I]I). Coupling of the Spiegelmers with the appropriate HPLC‐purified [radiolabelled]‐halobenzyl‐2‐bromoacetamide (MeOH/PBS (0.1 M, pH 8), 10 min, 120°C) gave the corresponding labelled conjugated Spiegelmers after RP‐HPLC purification. For fluorine‐18, the whole synthetic procedure yields up to 1.1 GBq of pure labelled Spiegelmers in 160 min with a specific radioactivity of 37–74 GBq/μmol at the end of synthesis starting from 22–24 GBq of [¹⁸F]fluoride. For iodine‐125, the whole synthetic procedure allows producing up to 7.4 MBq of pure labelled Spiegelmers in 100 min with a specific radioactivity of 11–37 GBq/μmol starting from 37 MBq of Na[¹²⁵I]I. Copyright © 2003 John Wiley & Sons, Ltd.     

N‐Arylation of indoles with 4‐[18F]fluoroiodobenzene: synthesis of 18F‐labelled σ2 receptor ligands for positron emission tomography (PET)

The palladium‐mediated N‐arylation of indoles with 4‐[¹⁸F]fluoroiodobenzene as a novel radiolabelling method has been developed. Optimized reaction conditions were elaborated by variation of different catalyst systems (CuI/1,2‐diamines and Pd₂(dba)₃/phosphine ligands), bases and solvents in the reaction of indole with 4‐[¹⁸F]fluoroiodobenzene. Optimized reaction conditions (Pd₂(dba)₃/(2‐(dicyclohexyl‐phosphino)‐2′‐(N,N‐dimethylamino)‐biphenyl, NaOBu^t, toluene, 100°C for 20 min) were applied for the synthesis of ¹⁸F‐labelled σ₂ receptor ligands [¹⁸F]‐11 and [¹⁸F]‐13 which were obtained in 91 and 84% radiochemical yields, respectively. Copyright © 2004 John Wiley & Sons, Ltd.