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 [13C4,15N2]pyrrolo[2,1‐f][1,2,4]triazinone

[¹³C₄,¹⁵N₂]Pyrrolotriazinone, 1 , was synthesized in six steps from ethyl (1,2,3,4‐¹³C₄)acetoacetate and (¹⁵N)ammonium hydroxide. A total of 1.3 g [¹³C₄,¹⁵N₂]pyrrolotriazinone was obtained in an overall yield of 17% based on isotopic ethyl acetoacetate. Chemical purity was determined by HPLC to be 99.5%. The percent [¹³C,¹⁵N]‐isotopic abundance in [¹³C₄,¹⁵N₂]pyrrolotriazinone was determined by mass spectral analysis to be 98.0%. The fully assigned ¹H and ¹³C NMR spectra of [¹³C₄,¹⁵N₂]pyrrolotriazinone were consistent with the desired structure. Copyright © 2006 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 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.     

Synthesis of 13C215N2‐labeled anti‐inflammatory and cytoprotective tricyclic bis(cyanoenone) ([13C215N2]‐TBE‐31) as an internal standard for quantification by stable isotope dilution LC‐MS method

Tricyclic bis(cyanoenone), TBE‐31, one of the most potent activators of the Keap1/Nrf2/antioxidant response element pathway, has been developed as a new anti‐inflammatory and cytoprotective agent. ¹³C₂¹⁵N₂‐labeled TBE‐31 ([¹³C₂¹⁵N₂]‐TBE‐31), which has two ¹³C and two ¹⁵N atoms in two cyano groups, was designed to develop a method for quantification of cell, tissue, and plasma levels of TBE‐31 that involves chromatography/mass spectrometry coupled with the use of a stable isotope‐labeled internal standard. [¹³C₂¹⁵N₂]‐TBE‐31 was successfully synthesized in four steps from a previously reported intermediate, which is prepared in 11 steps from cyclohexanone, by introduction of two ¹³C atoms with ethyl [¹³C]formate and two ¹⁵N atoms with hydroxyl[¹⁵N]amine. The stable isotope dilution liquid chromatography–mass spectrometry method for quantification of TBE‐31 was successfully developed using [¹³C₂¹⁵N₂]‐TBE‐31 to compensate for any variables encountered during sample processing and analysis.     

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 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.     

A gram‐scale synthesis of [3,4‐13C2,1α,7‐2H2]cortisone

A gram‐scale synthesis of [3,4‐¹³C₂,1α,7‐²H₂]cortisone from prednisone was developed. The deuterium atom at the C‐1 position was introduced through a regioselective and stereoselective deuteration of the 1,2‐double bond of the 1,4‐diene‐3‐one using Wilkinson's catalyst. After the oxidative cleavage of the A‐ring, two carbon‐13 atoms were introduced via acetylation of an A‐ring enol lactone with [1,2‐¹³C₂]acetyl chloride. The steroidal A‐ring was then reconstructed to incorporate the carbon‐13 atoms into the C‐3 and C‐4 positions. The deuterium atom at C‐7 was introduced through a regioselective deuteration of the 6,7‐double bond of a 4,6‐diene‐3‐one intermediate using palladium on strontium carbonate. The M + 4 stable isotope labeled cortisone was thus prepared in ca. 4% overall yield. In addition, [3,4‐¹³C₂,1α,7‐²H₂]‐11‐dehydrocorticosterone, [3,4‐¹³C₂,1α,7‐²H₂]cortisol, and [3,4‐¹³C₂,1α,7‐²H₂]corticosterone were also prepared. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of isotopically labelled glycyl‐L‐prolyl‐L‐glutamic acid (Glypromate®) and derivatives

The related tripeptides glycyl‐L ‐prolyl‐L ‐glutamic acid (GPE) and glycyl‐L ‐2‐methylprolyl‐L ‐glutamic acid (G‐2‐MePE) were labelled with commercially available [1,2,3,4,5‐¹³C₅, 2‐¹⁵N₁]‐L ‐glutamic acid in 3 steps in excellent overall yield with high isotope incorporation. A related cyclic dipeptide was labelled with [2,2‐²H₂, 2‐¹⁵N₁]glycine giving a mixture of compounds resulting from deuterium scrambling. Copyright © 2006 John Wiley & Sons, Ltd.     

Rapid and efficient synthesis of stable isotope labeled [13C4, D4]‐5‐(hydroxymethyl)thiazole: versatile building block for biologically interesting compounds

5‐(Hydroxymethyl)thiazole is a versatile building block for many biologically active compounds. A rapid and efficient four‐step synthesis of its stable isotope labeled counterpart with four ¹³C and four deuterium atoms in 32% total yield is reported. Condensation of [¹³C₂]‐chloro acetic acid with [¹³C]‐thiourea gave [¹³C₃]‐2,4‐thiazolidinedione. Reaction of [¹³C₃]‐2,4‐thiazolidinedione with phosphorus oxybromide and [¹³C, D]‐DMF (Me₂N¹³CDO) produced [¹³C₄, D]‐2,4‐dibromo‐thiazole‐5‐carboxaldehyde. The resultant aldehyde was then reduced by sodium borodeuteride to [¹³C₄, D₂]‐(2,4‐dibromo‐thiazol‐5‐yl)‐methanol. Catalytic deuteration of [¹³C₄, D₂]‐(2,4‐dibromo‐thiazol‐5‐yl)‐methanol by palladium black with deuterium gas at 1 atm pressure and room temperature produced completely de‐brominated [¹³C₄, D₄]‐5‐(hydroxymethyl)thiazole. De‐bromination of the 2,4‐dibromothiazole by the catalysis of palladium black provides a simple and convenient synthetic method for the stable isotope labeled and potentially radioactive isotope labeled thiazole compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of two D2 partial agonists in C‐14 and stable isotope labeled forms

In support of a program to develop a treatment for diseases resulting from an imbalance in dopamine levels, two drug candidates, 1 and 2, were prepared in stable isotope and C‐14 labeled forms. Both compounds contained an aminothiazole ring, and the C‐14 label was introduced into the ring using KS¹⁴CN. However, the use of KS¹⁴CN to form [¹⁴C]‐2 gave poor results; therefore, benzoyl [¹⁴C]isothiocyanate was used instead, which led to a much improved yield. The stable isotope labeled forms were prepared with the label in the side chain from [²H₅]ethyl iodide for [²H₅]‐1 and from 1‐[¹³C]methyl [¹⁵N₂]pyrazole[¹³C]carboxaldehyde, which was prepared in turn from [carbonyl‐¹³C]DMF, [¹⁵N₂]hydrazine sulfate, and [¹³C]methyliodide for [¹³C₂, ¹⁵N₂]‐2. Copyright © 2012 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.     

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 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.     

An innovative and efficient synthesis of stable isotope labelled 1‐methyl‐5‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐1H‐pyrazole via [13C42H3] N‐methylpyrazole

In support of a programme to develop a treatment for cancer, a stable isotope labelled version of the drug candidate was required. The key labelled intermediate was [¹³C₄²H₃] N‐methylpyrazole prepared by a novel bisacetal cyclisation. This was prepared from commercially available diethyl [¹³C₃] malonate and [¹³C²H₃] iodomethane. Copyright © 2012 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.     

Expeditious syntheses of stable and radioactive isotope‐labeled anticonvulsant agent,JNJ‐26990990, and its metabolites

Syntheses of stable and radioactive isotope‐labeled anticonvulsant agent, JNJ‐26990990, that is, N‐(benzo[b]thien‐3‐ylmethyl)‐sulfamide and its metabolites are described. [¹³C¹⁵N]Benzo[b]thiophene‐3‐carbonitrile was first prepared by coupling of 3‐bromo‐benzo[b]thiophene with [¹³C¹⁵N]‐copper cyanide. The resultant [¹³C¹⁵N]benzo[b]thiophene‐3‐carbonitrile was reduced with lithium aluminum deuteride to give [¹³CD₂¹⁵N]benzo[b]thiophen‐3‐yl‐methylamine; which was then coupled with sulfamide to afford [¹³CD₂¹⁵N]‐N‐(benzo[b]thien‐3‐ylmethyl)‐sulfamide, the stable isotope‐labeled compound with four stable isotope atoms. Direct oxidation of [¹³CD₂¹⁵N]‐N‐(benzo[b]thien‐3‐ylmethyl)‐sulfamide with hydrogen peroxide and peracetic acid gave the stable isotope‐labeled sulfoxide and sulfone metabolites. On the other hand, radioactive ¹⁴C‐labeled N‐(benzo[b]thien‐3‐ylmethyl)‐sulfamide was prepared conveniently by sequential coupling of 3‐bromo‐benzo[b]thiophene with [¹⁴C]‐copper cyanide, reduction of the carbonitrile to carboxaldehyde, and reductive amination with sulfamide.     

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.     

Syntheses of [2H3, 15N], [14C]Nexavar™ and its labeled metabolites

Nexavar?, Sorafenib tosylate (BAY 43‐9006 tosylate) is a potent small molecule Raf kinase inhibitor for the treatment of hyperproliferative disorders such as cancer. Both radiolabeled and stable isotope labeled compounds were required for drug absorption, distribution, metabolism and excretion (ADME) and quantitative mass spectrometry bio‐analytical studies. Nexavar? labeled with carbon‐14 in the carboxamide group was prepared in two steps in an overall radiochemical yield of 42% starting from 4‐chloro‐N‐methyl‐2‐pyridine‐[¹⁴C]carboxamide. The [²H₃,¹⁵N] version of Nexavar? was prepared in 75% yield based on 4‐chloro‐N‐[²H₃]methyl‐2‐pyridine‐[¹⁵N]carboxamide. The pyridine N‐oxide metabolite labeled with carbon‐14 as well as with deuterium and nitrogen‐15 and was synthesized by oxidation in yields of 59% and 87%, respectively. Starting from [²H₂, ¹³C]formaldehyde the N‐hydroxymethyl metabolite was labeled with carbon‐13 and deuterium in one step in a 45% overall yield. Copyright © 2006 John Wiley & Sons, Ltd.     

Facile synthesis of stable isotope‐labeled antibacterial agent RWJ‐416457 and its metabolite

Synthesis of multiple stable isotope‐labeled antibacterial agent RWJ‐416457, (N‐{3‐[3‐fluoro‐4‐(2‐methyl‐2,6‐dihydro‐4H‐pyrrolo[3,4‐c]pyrazol‐5‐yl)‐phenyl]‐2‐oxo‐oxazolidin‐5‐ylmethyl}‐acetamide), and its major metabolite, N‐{3‐[4‐(2,6‐dihydro‐4H‐pyrrolo[3,4‐c]pyrazol‐5‐yl)‐3‐fluoro‐phenyl]‐2‐oxo‐oxazolidin‐5‐ylmethyl}‐acetamide, is described. The stable isotope‐labeled [¹³CD₃]RWJ‐416457 was prepared readily by acetylation of the precursor amine, 5‐aminomethyl‐3‐[3‐fluoro‐4‐(2‐methyl‐2,6‐dihydro‐4H‐pyrrolo[3,4‐c]pyrazol‐5‐yl)‐phenyl]‐oxazolidin‐2‐one with CD₃¹³COCl in pyridine. Synthesis of the stable isotope‐labeled metabolite involved a construction of multiple isotope‐labeled pyrazole ring. N,N‐dimethyl(formyl‐¹³C,D)amide dimethyl acetal was first prepared by treating N,N‐dimethyl(formyl‐¹³C,D)amide with dimethyl sulfate, followed by sodium methoxide. Then, N‐{3‐[3‐fluoro‐4‐(3‐oxo‐pyrrolidin‐1‐yl)‐phenyl]‐2‐oxo‐oxazolidin‐5‐ylmethyl}‐acetamide was condensed with N,N‐dimethyl(formyl‐¹³C,D)amide dimethyl acetal, and the resultant β‐ketoenamine intermediate underwent pyrazole ring formation with hydrazine‐¹⁵N₂, to give the [¹³C¹⁵N₂D]‐labeled metabolite. Copyright © 2012 John Wiley & Sons, Ltd.