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 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.     

Buscopan labeled with carbon‐14 and deuterium

Hyosine butyl bromide, the active ingredient in Buscopan, is an anticholinergic and antimuscarinic drug used to treat pain and discomfort caused by abdominal cramps. A straightforward synthesis of carbon‐14– and deuterium‐labeled Buscopan was developed using scopolamine, n‐butyl‐1‐¹⁴C bromide, and n‐butyl‐²H₉ bromide, respectively. In a second carbon‐14 synthesis, the radioactive carbon was incorporated in the tropic acid moiety to follow its metabolism. Herein, we describe the detailed preparations of carbon‐14– and deuterium‐labeled Buscopan.     

Potent and selective CC chemokine receptor 1 antagonists labeled with carbon‐13, carbon‐14, and tritium

1‐(4‐Fluorophenyl)‐1H‐pyrazolo[3,4‐c]pyridine‐4‐carboxylic acid (2‐methanesulfonyl‐pyridin‐4‐ylmethyl)‐amide ( 1 ) and its analogs ( 2 ) and ( 3 ) are potent CCR1 antagonists intended for the treatment of rheumatoid arthritis. The detailed syntheses of these 3 compounds labeled with carbon‐13 as well as the preparation of ( 1 ) and ( 2 ) labeled with carbon‐14, and ( 1 ) labeled with tritium, are described.     

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 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%.     

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.     

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.     

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 [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 carbon‐14 labeled pyraoxystrobin,a novel fungicide

SYP‐3343, (E)‐2‐(2‐((3‐(4‐chlorophenyl)‐1‐methyl‐1H‐pyrazole‐5‐yloxy)methyl)) phenyl)‐3‐methoxyacrylate, is a novel fungicide with broad‐spectrum and high activity against fungi. In this paper, radioactive pyraoxystrobin, labeled in the pyrazole ring system was achieved from ¹⁴C labeled 4‐chlorobenzoic acid through substitution, cyclization, and condensation, in an overall chemical and radiochemical yield of 44%. The chemical and radiochemical purity of the title compound was 98.5% and 98.2%, respectively. This labeled SYP‐3343 was used as a radiotracer for metabolism, toxicology, mode of action, and other environmental studies. 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.     

Synthesis of deuterium‐, tritium‐, and carbon‐14‐labeled BILN2061, a potent hepatitis C virus protease inhibitor

Hepatitis C virus (HCV) serine protease is a target for antiviral therapy against HCV infection, a leading cause of liver transplantation in the US. BILN2061, (1S, 4R, 6S, 7Z, 14S, 18R)‐14‐cyclopentyloxycarbonylamino‐18‐[2‐(2‐isopropylamino‐thiazol‐4‐yl)‐7‐methoxyquinolin‐4‐yloxy]‐2,15‐dioxo‐3,16‐diazatricyclo[14.3.0.0^4,6]nonadec‐7‐ene‐4‐carboxylic acid, is a potent inhibitor of HCV and the first compound in this class of cyclic peptides in human trials. Here, we report the synthesis of deuterium‐labeled BILN2061 with isotopic enrichment of 99%, tritium‐labeled BILN2061 with a specific activity of 17.1 GBq/mmol, and carbon‐14‐labeled BILN2061 with a specific activity of 1.83 GBq/mmol. The isotopes were incorporated via a Hantzsch thiazole synthesis of labeled isopropyl thiourea and α‐bromoketone intermediate. The preparation of labeled isopropyl thiourea is reported. Copyright © 2005 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.     

Synthesis of the olanzapine labeled by carbon‐14

Olanzapine is one of the most widely used antipsychotic drugs, which acts as an antagonist for multiple neurotransmitter receptor sites. 2‐Methyl‐4‐(4‐methyl‐1‐piperazinyl)‐10H‐thieno [2,3‐b][1,5] benzodiazepine (Olanzapine) labeled with carbon‐14 in the four positions has been synthesized as part of a three‐step sequence from 2‐amino‐5‐methylthiophene‐3‐carbonitrile‐[carbonitrile‐¹⁴C].     

The synthesis of a tritium,carbon‐14, and stable isotope‐labeled cathepsin C inhibitors

As part of a medicinal chemistry program aimed at developing a highly potent and selective cathepsin C inhibitor, tritium, carbon‐14, and stable isotope‐labeled materials were required. The synthesis of tritium‐labeled methanesulfonate 5 was achieved via catalytic tritiolysis of a chloro precursor, albeit at a low radiochemical purity of 67%. Tritium‐labeled AZD5248 was prepared via a 3‐stage synthesis, utilizing amide‐directed hydrogen isotope exchange. Carbon‐14 and stable isotope‐labeled AZD5248 were successfully prepared through modifications of the medicinal chemistry synthetic route, enabling the use of available labeled intermediates.     

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.     

Enzymatic synthesis of phenylpyruvic acid labeled with deuterium,tritium, and carbon‐14

The synthesis of isotopomers of phenylpyruvic acid, PPA, selectively labeled with hydrogen isotopes in the 3‐position of the side‐chain is reported. Three deuterium or tritium labeled isotopomers of L‐phenylalanine, L‐Phe, i.e. [(3S)‐²H]‐L‐, [(3S)‐³H]‐L‐, and doubly labeled [(3S)‐²H/³H]‐L‐Phe were synthesized using the enzyme phenylalanine ammonia lyase (EC 4.3.1.5). In the second step these isotopomers of L‐Phe were converted into [(3S)‐²H], [(3S)‐³H]‐, and [(3S)‐²H/³H]‐isotopomers of PPA using the enzyme L‐phenylalanine dedydrogenase (EC 1.4.1.20). The isotopomer of PPA labeled with ¹⁴C in carboxylic group, [1‐¹⁴C]‐PPA, was obtained in a two‐step enzymatic reaction using [1‐¹⁴C]‐cinnamic acid as the starting substrate. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of carbon‐14 labeled dibutyltin dichloride

This report describes the preparation of carbon‐14 labeled dibutyltin dichloride from carbon‐14 labeled barium carbonate in 30% overall radiochemical yield. The key steps were (a) the preparation of carbon‐14 labeled butyl bromide from carbon‐14 labeled barium carbonate via carbon‐14 labeled butyl mesylate, and (b) the direct preparation of tetrabutyltin by the lithium‐mediated reaction of dibutyltin dichloride with carbon‐14 labeled butyl bromide. Copyright © 2007 John Wiley & Sons, Ltd.     

Hepatitis C virus serine protease: synthesis of radioactive and stable isotope‐labeled potent inhibitors

Drug candidates labeled with radioactive and stable isotopes are required for absorption, distribution, metabolism, and excretion (ADME) studies, pharmacokinetics, autoradiography, bioanalytical, and other research activities. The findings from these studies are crucial in the development of a drug candidate and its approval for human use. Herein, we report the synthesis of potent and selective hepatitis C virus serine protease inhibitors related to BILN 2061 and BI 201335 labeled with radioactive and stable isotopes. Synthetic efforts were focused on the common substituted thiazole moiety, which is easily accessible via a Hantzsch's reaction of α‐bromoketones and mono‐substituted thioureas. In the radioactive synthesis, commercially available carbon‐14 thiourea was utilized to prepare mono‐substituted thioureas, which upon condensation with α‐bromoketones in isopropanol followed by ester hydrolysis gave the desired carbon‐14‐labeled protease inhibitors. The same strategy was used to prepare these inhibitors labeled with stable isotopes. Mono‐substituted thioureas were obtained from commercially available deuterium‐labeled intermediates and then condensed with α‐bromoketones followed by ester hydrolysis to give the deuterium‐labeled inhibitors.