A potent IκB kinase‐β inhibitor labeled with carbon‐14 and deuterium

3‐Amino‐4‐(1,1‐difluoro‐propyl)‐6‐(4‐methanesulfonyl‐piperidin‐1‐yl)‐thieno[2,3‐b]pyridine‐2‐carboxylic acid amide (1) is a potent IκB Kinase‐β (IKK‐β) inhibitor. The efficient preparations of this compound labeled with carbon‐14 and deuterium are described. The carbon‐14 synthesis was accomplished in six radiochemical steps in 25% overall yield. The key transformations were the modified Guareschi–Thorpe condensation of 2‐cyano‐¹⁴C‐acetamide and a keto‐ester followed by chlorination to 2,6‐dichloropyridine derivative in one pot. The isolated dichloropyridine was then converted in three steps in one pot to [¹⁴C]‐ (1) . The carbon‐14 labeled (1) was isolated with a specific activity of 54.3 mCi/mmol and radiochemical purity of 99.8%. The deuterium labeled (1) was obtained in eight steps and in 57% overall chemical yield using 4‐hydroxypiperidine‐2,2,3,3,4,5,5,6,6‐²H₉. The final three steps of this synthesis were run in one pot.     

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 three isotopically labeled versions and a metabolite of Aurora A kinase inhibitor

Sodium ring‐[¹⁴C]‐4‐[[9‐chloro‐7‐(2,6‐difluorophenyl)‐5H‐pyrimido[5,4‐d][2]benzazepin‐2‐yl]amino]‐benzoate (1A, MLN8054), an Aurora A kinase inhibitor, was synthesized from [¹⁴C]‐cyanamide in two steps in an overall radiochemical yield of 7%. The intermediate, [¹⁴C]‐4‐guanidinobenzoic acid, was prepared by coupling [¹⁴C]‐cyanamide with 4‐aminobenzoic acid. Sodium carboxyl‐[¹⁴C]‐4‐[[9‐chloro‐7‐(2,6‐difluorophenyl)‐5H‐pyrimido[5,4‐d][2]benzazepin‐2‐yl]amino]‐benzoate (1B) was synthesized from carboxyl‐[¹⁴C]‐4‐guanidinobenzoic acid in one step in a radiochemical yield of 35%. [D₄,¹⁵N]‐4‐[[9‐chloro‐7‐(2,6‐difluorophenyl)‐5H‐pyrimido[5,4‐d][2]benzazepin‐2‐yl]amino]‐benzoic acid (1C) was synthesized from [¹⁵N₂]‐cyanamide and [D₄]‐4‐aminobenzoic acid in two steps in an overall yield of 37%. The major metabolite, β‐acyl glucuronide of 4‐[[9‐chloro‐7‐(2,6‐difluorophenyl)‐5H‐pyrimido[5,4‐d][2]benzazepin‐2‐yl]amino]‐benzoic acid (14), was synthesized from D‐glucuronic acid in three steps in an overall yield of 1%. The key intermediate for synthesis of glucuronide was prepared by HATU catalyzed coupling of 4‐[[9‐chloro‐7‐(2,6‐difluorophenyl)‐5H‐pyrimido[5,4‐d][2]benzazepin‐2‐yl]amino]‐benzoic acid with allyl glucuronate. Copyright © 2009 John Wiley & Sons, Ltd.     

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 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 [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 empagliflozin,a novel and selective sodium‐glucose co‐transporter‐2 inhibitor,labeled with carbon‐14 and carbon‐13

Empagliflozin, (2S,3R,4R,5S,6R)‐2‐[4‐chloro‐3‐[[4‐[(3S)‐oxolan‐3‐yl]oxyphenyl]methyl]phenyl]‐6‐(hydroxymethyl)oxane‐3,4,5‐triol was recently approved by the FDA for the treatment of chronic type 2 diabetes mellitus. Herein, we report the synthesis of carbon‐13 and carbon‐14 labeled empagliflozin. Carbon‐13 labeled empagliflozin was prepared in five steps and in 34% overall chemical yield starting from the commercially available α‐D‐glucose‐[¹³C₆]. For the radiosynthesis, the carbon‐14 atom was introduced in three different positions of the molecule. In the first synthesis, Carbon‐14 D‐(+)‐gluconic acid δ‐lactone was used to prepare specifically labeled empagliflozin in carbon‐1 of the sugar moiety in four steps and in 19% overall radiochemical yield. Carbon‐14 labeled empagliflozin with the radioactive atom in the benzylic position was obtained in eight steps and in 7% overall radiochemical yield. In the last synthesis carbon‐14 uniformly labeled phenol was used to give [¹⁴C]empagliflozin in eight steps and in 18% overall radiochemical yield. In all these radiosyntheses, the specific activities of the final compounds were higher than 53 mCi/mmol, and the radiochemical purities were above 98.5%.     

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.     

Potent and selective inhibitors of 11β‐hydroxysteroid dehydrogenase type 1 labeled with carbon‐13 and carbon‐14

(S )‐6‐(2‐Hydroxy‐2‐methylpropyl)‐3‐((S )‐1‐(4‐(1‐methyl‐2‐oxo‐1,2‐dihydropyridin‐4‐yl)phenyl)ethyl)‐6‐phenyl‐1,3‐oxazinan‐2‐one (1) and (4aR ,9aS )‐1‐(1H‐benzo[d]midazole‐5‐carbonyl)‐2,3,4,4a,9,9a‐hexahydro‐1‐H‐indeno[2,1‐b]pyridine‐6‐carbonitrile hydrochloride (2) are potent and selective inhibitor of 11β‐hydroxysteroid dehydrogenase type 1 enzyme. These 2 drug candidates developed for the treatment of type‐2 diabetes were prepared labeled with carbon‐13 and carbon‐14 to enable drug metabolism, pharmacokinetics, bioanalytical, and other studies. In the carbon‐13 synthesis, benzoic‐¹³C ₆ acid was converted in 7 steps and in 16% overall yield to [¹³C₆]‐(1). Aniline‐¹³C ₆ was converted in 7 steps to 1H‐benzimidazole‐1‐2,3,4,5,6‐¹³C₆‐5‐carboxylic acid and then coupled to a tricyclic chiral indenopiperidine to afford [¹³C₆]‐(2) in 19% overall yield. The carbon‐14 labeled (1) was prepared efficiently in 2 radioactive steps in 41% overall yield from an advanced intermediate using carbon‐14 labeled methyl magnesium iodide and Suzuki‐Miyaura cross coupling via in situ boronate formation. As for the synthesis of [¹⁴C]‐(2), 1H‐benzimidazole‐5‐carboxylic‐¹⁴C acid was first prepared in 4 steps using potassium cyanide‐¹⁴C , then coupled to the chiral indenopiperidine using amide bond formation conditions in 26% overall yield.     

Syntheses of [14C]BAY 59‐7939 and its radiolabeled metabolite M‐4

BAY 59‐7939 is a novel, oral, direct Factor Xa inhibitor in clinical development for the prevention and treatment of thromboembolic diseases. Radiolabeled BAY 59‐7939 was required for drug absorption, distribution, metabolism and excretion (ADME studies). The BAY 59‐7939 was labeled with carbon‐14 in the carboxamide group in one step in an overall radiochemical yield of 85% starting from 4‐{4‐[(5S)‐5‐(aminomethyl)‐2‐oxo‐1,3‐oxazolidin‐3‐yl]phenyl}mor‐pholin‐3‐one and 5‐chlorothiophene‐2‐[¹⁴C]carboxylic acid. The radiolabeled metabolite M‐4 was prepared in 77% yield starting from [1‐¹⁴C]glycine and 5‐chlorothiophene‐5‐carboxylic acid. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of two potent glucocorticoid receptor agonists labeled with carbon‐14 and stable isotopes

Two potent glucocorticoid receptor agonists were prepared labeled with carbon‐14 and with stable isotopes to perform drug metabolism, pharmacokinetics, and bioanalytical studies. Carbon‐14 labeled (1) was obtained from an enantiopure alkyne (5) via a Sonogashira coupling to a previously reported 5‐amino‐4‐iodo‐[2‐¹⁴C]pyrimidine [¹⁴C]‐(6), followed by a base‐mediated cyclization (1) in 72% overall radiochemical yield. Carbon‐14 labeled (2) was prepared in five steps employing a key benzoic acid intermediate [¹⁴C]‐(13), which was synthesized in one pot from enolization of trifluoromethylketone (12), followed by bromine–magnesium exchange and then electrophile trapping reaction with [¹⁴C]‐carbon dioxide. A chiral auxiliary (S)‐1‐(4‐methoxyphenyl)ethylamine was then coupled to this acid to give [¹⁴C]‐(15). Propargylation and separation of diastereoisomers by crystallizations gave the desired diastereomer [¹⁴C]‐(17) in 34% yield. Sonogashira coupling to iodopyridine (10) followed by cyclization to the azaindole [¹⁴C]‐(18) and finally removal of the chiral auxiliary gave [¹⁴C]‐(2) in 7% overall yield. For stable isotope syntheses, [¹³C₆]‐(1) was obtained in three steps using [¹³C₄]‐(6) and trimethylsilylacetylene‐[¹³C₂] in 26% yield, while [²H₅]‐(2) was obtained by first preparing the iodopyridine [²H₅]‐(10) in five steps. Then, Sonogashira coupling to chiral alkyne (24) and cyclization gave [²H₅]‐(2) in 42% overall yield.     

Synthesis of potent lymphocyte function‐associated antigen‐1 inhibitors labeled with carbon‐14 and deuterium,part 1

The lymphocyte function‐associated antigen‐1 (LFA‐1) is an essential component in normal immune system function and is a target for drug discovery for its broad therapeutic potential in treating inflammatory diseases. Here, we report the synthesis of three potent antagonists of LFA‐1 labeled with carbon‐14 and deuterium to support drug metabolism and pharmacokinetics studies. Carbon‐14 labeled (R)‐1‐acetyl‐5‐(4‐bromobenzyl)‐3‐(3,5‐dichlorophenyl)‐5‐methyl‐imidazolidine‐2,4‐dione (1) was prepared in 27% radiochemical yield in two steps and with a specific activity of 2.1 GBq/mmol by using [¹⁴C]‐phosgene. Carbon‐14 labeled 5‐bromopyrimidine was used to prepare (R)‐5‐(1‐piperazinylsulfonyl)‐1‐(3,5‐dichlorophenyl)‐3‐[4‐(5‐pyrimidinyl)benzyl]‐3‐methyl‐1‐H‐imidazo[1,2a]imidazol‐2‐one (2) and (R)‐1‐[7‐(3,5‐dichlorophenyl)‐5‐methyl‐6‐oxo‐5‐(4‐pyrimidin‐5‐yl‐benzyl)‐6,7‐dihydro‐5H‐imidazo[1,2‐a]imidazole‐3‐sulfonyl]piperidin‐4‐carboxylic acid amide (3) via a Suzuki reaction with the corresponding boronic acid esters in 42% and 67% radiochemical yield and specific activities of 1.85 GBq/mmol and 1.95 GBq/mmol, respectively. Deuterium labeled piperazine was reacted with the sulfonyl chloride derivative (7), followed by a Suzuki coupling to the pyrimidine boronic ester to give deuterium labeled (2) in 47% yield. Deuterium labeled isonipecotamide was reacted in a similar way with the sulfonyl chloride derivative (14) to furnish deuterium labeled (3) in one step and in 94% yield. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of carbon‐14 and stable isotope labeled Avagacestat: a novel gamma secretase inhibitor for the treatment of Alzheimer's disease

Bristol‐Myers Squibb and others are developing drugs that target novel mechanisms to combat Alzheimer's disease. γ‐Secretase inhibitors are one class of potential therapies that have received considerable attention. (R)‐2‐(4‐Chloro‐N‐(2‐fluoro‐4‐(1,2,4‐oxadiazol‐3‐yl)benzyl)phenylsulfonamido)‐5,5,5‐trifluoropentanamide (Avagacestat) is a γ‐secretase‐inhibiting drug that has been investigated by Bristol‐Myers Squibb in preclinical and clinical studies. An important step in the development process was the synthesis of a carbon‐14‐labeled analog for use in a human absorption, distribution, metabolism, and excretion study and a stable isotope labeled analog for use as a standard in bioanalytical assays to accurately quantify the concentration of the drug in biological samples. Carbon‐14 labeled Avagacestat was synthesized in seven steps in a 33% overall yield from carbon‐14 labeled potassium cyanide. A total of 5.95 mCi was prepared with a specific activity of 0.81 μCi/mg and a radiochemical purity of 99.9%. ¹³C₆‐Labeled Avagacestat was synthesized in three steps in a 15% overall yield from 4‐chloro[¹³C₆]aniline. A total of 585 mg was prepared with a ultraviolet purity of 99.9%.     

Synthesis of selectively labeled histidine and its methylderivatives with deuterium,tritium, and carbon‐14

Isotopologues of l ‐histidine and its N‐methylderivatives labeled with deuterium and tritium at the 5‐position in the imidazole ring were obtained using the isotope exchange method. The deuterium‐labeled isotopologues [5‐²H]‐l ‐histidine, [5‐²H]‐N^τ‐methyl‐l ‐histidine, [5‐²H]‐N^π‐methyl‐l ‐histidine, and [2,5‐²H₂]‐l ‐histidine were synthesized by isotope exchange method carried out in a fully deuterated medium with. The same reaction conditions were applied to synthesize [5‐³H]‐N^τ‐methyl‐l ‐histidine, [5‐³H]‐N^π‐methyl‐l ‐histidine, and [5‐³H]‐l ‐histidine with specific activity of 2.0, 5.0, and 2.6 MBq/mmol, respectively. The N^π‐[methyl‐¹⁴C]‐histamine was obtained with specific activity of 0.23 MBq/mmol in a one‐step reaction by the direct methylation of histamine by [¹⁴C]iodomethane.     

Synthesis of carbon‐14 and stable isotope labelled NN414: a potent potassium channel opener

Currently, NN414, a potent β‐cell selective potassium channel opener, is undergoing clinical trials for the treatment of type 2 diabetes. Here, we report the synthesis of carbon‐14 and stable isotope labelled NN414 for use in metabolic studies and as an internal standard in pharmacokinetic assays, respectively. The carbon‐14 labelling was performed in two steps starting from an advanced intermediate. This provided [¹⁴C]NN414 in 60% overall radiochemical yield with a specific activity of 58mCi/mmol. The stable isotope labelling was accomplished from benzyl tert‐butyl malonate in eight steps using [¹³C,²H₃]iodomethane and [²H₂]dibromomethane as the source of carbon‐13/deuterium. The synthetic sequence, which included a Mannich reaction followed by deamination, a Simmons–Smith‐type cyclopropanation and a modified Curtius reaction, provided [¹³C,²H₅]NN414 in 8.6% overall yield. Copyright © 2004 John Wiley & Sons, Ltd.     

A novel five‐lipoxygenase activity protein inhibitor labeled with carbon‐14 and deuterium

2‐[4‐(3‐{(1R)‐1‐[4‐(2‐Aminopyrimidin‐5‐yl)phenyl]‐1‐cyclopropylethyl}‐1,2,4‐oxadiazol‐5‐yl)‐1H‐pyrazol‐1‐yl]‐N,N‐dimethylacetamide (1), is a novel and selective five‐lipoxygenase activity protein (FLAP) inhibitor with excellent pharmacokinetics properties. The availability of a key chiral intermediate allowed the synthesis of [¹⁴C]‐(1) in six radiochemical steps and in 47% overall radiochemical yield with a specific activity of 51 mCi/mmol using carbon‐14 zinc cyanide. 2‐Chloro‐N,N‐dimethyl‐²H₆‐acetamide was prepared and condensed with a penultimate intermediate to give [²H₆]‐(1) in very high yield and in more than 99% isotopic enrichment.     

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.     

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.     

Synthesis of [3H], [13C215N] and [14C]Sch 66336 (Sarasar™)

[³H]Sch 66336 was prepared at a specific activity of 1.35 Ci/mmol by Ru(Ph₃P)₃Cl₂ catalysed exchange with tritiated water. [¹³CN]Sch 66336 was synthesized from potassium [¹³C]cyanide and [¹³C¹⁵N₂]urea in 29% overall yield from potassium [¹³C]cyanide. [¹⁴C]Sch 66336 was synthesized from potassium [¹⁴C]cyanide in 31% yield. A second synthesis, from N‐Boc‐4‐hydroxy[¹⁴C]piperidine, gave [¹⁴C]Sch 66336 labelled in a different site in 19% overall yield. Copyright © 2004 John Wiley & Sons, Ltd.