Synthesis of tritium‐labeled (R,R)‐4‐methoxyfenoterol

The preparation of 2′,4′,6′‐[³H₃]‐(R,R)‐4‐methoxyfenoterol, a tritium‐labeled derivative of (R,R)‐4‐methoxyfenoterol was demonstrated on a 15 mCi scale providing material with a specific activity of 57 Ci/mmol. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of tritium‐labeled puerarin—a potential antidipsotropic agent

Puerarin 1 (8‐β‐D ‐Glucopyranosyl‐4′‐7‐dihydroxyisoflavone, NPI‐031G) is the major isoflavone C‐glycoside isolated from Pueraria lobata, a traditional Chinese medicine widely used for the treatment of alcohol intoxication. In order to understand the mode of action of puerarin in the reward pathway of the central nervous system and to study its bioavailability and pharmacokinetics, we developed a synthetic route for the preparation of tritium‐labeled puerarin. The key intermediate 4 was obtained by trimethylsilyl protection of all hydroxyl groups followed by selective deprotection. The corresponding aldehyde 5 was obtained through the subsequent oxidation of the primary alcohol. Standard NaB[³H]₄ reduction and hydrolysis produced the tritium‐labeled puerarin 6 . Copyright © 2007 John Wiley & Sons, Ltd.     

Microscale synthesis of isotopically labeled 6R‐N5, N10 methylene‐5, 6, 7, 8‐tetrahydrofolate

A one‐pot chemo‐enzymatic microscale synthesis of isotopically labeled R‐[6‐^YH; 11‐^XH] N⁵, N¹⁰ methylene‐5, 6, 7, 8‐tetrahydrofolate (CH₂H₄folate) is presented, where Y=1 or 2 represents protium or deuterium, and X=1, 2 or 3 represents protium, deuterium or tritium, respectively. In this procedure, Thermoanaerobium brockii alcohol dehydrogenase (tbADH) and Escherichia coli dihydrofolate reductase (ecDHFR) were used simultaneously in the reaction mixture. First, tbADH stereospecifically catalyzes a hydride transfer from [2‐^YH] iPrOH to the re face of C‐4 NADP⁺. The ecDHFR then reduced 7, 8‐dihydrofolate (H₂folate) to form (6S)‐H₄folate. Finally, the enzymatic reactions were followed by chemical trapping with isotopically labeled formaldehyde ([^XH]‐HCHO) to form the final product. The preparation of deuterium‐ and tritium‐labeled formaldehyde is also presented. Two reverse phase HPLC methods were developed for analysis and purification of product R‐[6‐^YH; 11‐^XH] CH₂H₄folate. This isotopically labeled cofactor can be used to study 1° and 2° kinetic isotope effects (KIEs) with any CH₂H₄folate dependent enzyme as demonstrated by studies with E. coli thymidylate synthase (TS). Copyright © 2005 John Wiley & Sons, Ltd.     

The synthesis of isotopically labeled (+)‐2‐aminobicyclo[3.1.0]hexane‐2,6‐carboxylic acid and its 2‐oxa‐ and 2‐thia‐analogs

As part of a program aimed at the design of conformationally constrained analogs of glutamic acid, (+)‐2‐aminobicyclo[3.1.0]hexane‐2,6‐carboxylic acid ( 1 ), identified as a highly potent, selective, group II metabotropic glutamate receptor agonist has been synthesized and studied clinically. Heterocyclic analogs of 1 were subsequently synthesized in which the C‐2 methylene has been replaced by an oxygen atom ( 2 ) or a sulfur atom ( 3 ). C‐14 labeled isotopomers of 1 , 2 and 3 have been synthesized to facilitate pre‐clinical ADME studies. A tritium labeled isotopomer of 1 was also synthesized for use in in vitro experiments. A stable labeled isotopomer of rac‐1 was prepared for use as an internal standard for bioanalytical assays. The key step in each of these syntheses was the reaction of chiral ketone 4 , 5 or 6 with K¹⁴CN/(NH₄)₂CO₃ using the Bucherer–Berg protocol. In the preparation of the stable labeled isotopomer, rac‐4 ‐[¹³ C ₂] was prepared in two steps from ethyl bromoacetate‐[UL‐¹³C₂]; subsequent reaction of rac‐4 ‐[¹³ C ₂] with K¹³CN/¹⁵NH₄Cl/Na₂CO₃, followed by hydrolysis of the hydantoin yielded rac‐1 ‐[¹³ C ₃,¹⁵ N ]. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and characterization of tritium labeled N‐((R)‐1‐((S)‐4‐(4‐chlorophenyl)‐4‐hydroxy‐3,3‐dimethylpiperidin‐1‐yl)‐3‐methyl‐1‐oxobutan‐2‐yl)‐3‐sulfamoylbenzamide

N‐((R)‐1‐((S)‐4‐(4‐chlorophenyl)‐4‐hydroxy‐3,3‐dimethylpiperidin‐1‐yl)‐3‐methyl‐1‐oxobutan‐2‐yl)‐3‐sulfamoylbenzamide is a potent C‐C chemokine receptor 1 (CCR1) antagonist. The compound, possessing benzamide functionality, successfully underwent tritium/hydrogen (T/H) exchange with an organoiridium catalyst (Crabtree's catalyst). The labeling pattern in the product was studied with liquid chromatography–mass spectrometry, time‐of‐flight mass spectrometry, and ³H‐NMR. Overall, multiple labeled species were identified. In addition to the anticipated incorporation of tritium in the benzamide moiety, tritium labeling was observed in the valine portion of the molecule including substitution at its chiral carbon. Using authentic standards, liquid chromatography analysis of the labeled compound showed complete retention of stereochemical configuration.     

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.     

Synthesis of deuterium,tritium, and carbon‐14 labeled BIRB 796, a p38 MAP kinase inhibitor

1‐(5‐tert‐Butyl‐2‐p‐tolyl‐2H‐pyrazol‐3‐yl)‐3‐[4‐(2‐morpholin‐4‐yl‐ethoxy)naphthalen‐1‐yl]urea (BIRB 796), currently in clinical trials for the treatment of inflammatory diseases, is a potent inhibitor of p38 MAP kinase. Labeled BIRB 796 with stable and radioactive isotopes was required for metabolism, distribution, and absorption studies. We first report the synthesis of carbon‐14 labeled BIRB 796 with a specific activity of 2 GBq/mmol (54.2 mCi/mmol), using [¹⁴C]‐phosgene under modified Schotten–Baumann conditions; second the preparation of tritium‐labeled BIRB 796 with a specific activity of 659 GBq/mmol (17.81 Ci/mmol) by reductive dehalogenation of iodo‐BIRB 796 with tritium gas; and finally, the synthesis of ²H₈‐BIRB 796 using morpholine‐2,2,3,3,5,5,6,6‐²H₈ with isotopic enrichment of 98.9 at% ²H. Copyright © 2004 John Wiley & Sons, Ltd.     

Syntheses of AZ12320927 labeled with H‐3, C‐14, and H‐2

In support of a program to develop a treatment for depression, three isotopically labeled forms of the 5‐HT_1B antagonist AZ12320927 were synthesized. A tritium labeled version was synthesized for autoradiography using Ir‐catalyzed hydrogen–tritium exchange. A C‐14 labeled version was prepared for use in metabolism studies in four‐steps from [u‐¹⁴C]p‐nitrophenol. A stable isotope labeled version was synthesized for use as an internal standard for LC/MS/MS quantitation in two steps from chromenone 1. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 2H‐ and 3H‐labeled N‐cyclopropylmethyl‐7α‐[(R)‐1‐hydroxy‐1‐methyl‐3‐(2thienyl)‐propyl]‐6,14‐endoethano‐6,7,8,14‐tetrahydro nororipavine

A procedure for deuterium and tritium labeling of the titled compound, an analgesic agent, was developed. A secondary amine intermediate was acylated to an acylamide, then the carbonyl function was reduced by LiAlD₄ to yield the tertiary amine. In the tritium‐labeled synthesis, the process utilized a bromo‐substituted precursor, which was subsequently reduced with ³H₂ in the presence of a Pd/C catalyst. The labeled compounds were successfully applied in pharmacokinetic and pharmacological studies. Copyright © 2005 John Wiley & Sons, Ltd.     

Preparation of tritium‐labeled PF‐622, a novel fatty acid amide hydrolase inhibitor

To make a detailed characterization of the mechanism of inhibition and selectivity of a novel fatty acid amide hydrolase inhibitor PF‐622 , 3 tritium isotopomers were prepared. [³H] PF‐622a labeled at the piperazine ring B and [³H] PF‐622b labeled at both the ring B and phenyl ring A were synthesized via catalytic H(hydrogen)‐T(tritium) exchange, utilizing 1 equiv and excess of Crabtree's catalyst, respectively. The preparation of [³H] PF‐622c labeled only at the phenyl ring A was achieved via tritiodebromination of the bromide precursor, using Pd(PPh₃)₄ as a catalyst. The observations from these tritiation reactions might open a new perspective in the labeling for the targets having a similar moiety.     

Synthesis of herbicidal ZJ0273 labeled with tritium and carbon‐14

ZJ0273, propyl 4‐(2‐(4,6‐dimethoxypyrimidin‐2‐yloxy)benzylamino)benzoate, is a broad‐spectrum herbicidal ingredient used for weed control in oilseed rape in China. Two mono‐labeled ZJ0273, propyl 4‐(2‐(4,6‐dimethoxypyrimidin‐2‐yloxy)[phenyl‐3,4,5,6‐³H₄]benzylamino)benzoate (7) and propyl 4‐(2‐(4,6‐dimethoxy[4,6‐¹⁴C₂]pyrimidin‐2‐yloxy)benzylamino)benzoate (12), were synthesized separately from [2,3,4,5,6‐³H₅]phenol in a four‐step yield of 27% and from 4,6‐dichloro‐2‐(methylthio)[4,6‐¹⁴C₂]pyrimidine in a three‐step yield of 54%. In addition, two dual‐labeled analogues of ZJ0273 were prepared by homogeneously mixing tritium‐labeled ZJ0273 (7) in the benzyl ring separately with two carbon‐14‐labeled ZJ0273 (2, 12) in the benzoate ring and the pyrimidine ring. These labeled ZJ0273 could be used as radiotracers in the studies on the metabolism, mode of action, environmental behavior, and fate of ZJ0273. Copyright © 2008 John Wiley & Sons, Ltd.     

Syntheses of dual‐radioisotope‐labeled CP‐I,a GABAA receptor partial agonist

CP‐I is a potent subtype‐selective GABA _A receptor partial agonist. Owing to its significant metabolic cleavage at C₈ observed in preliminary biotransformation studies with non‐radiolabeled CP‐I, the syntheses of CP‐I labeled at the right or left hand side with ¹⁴C or labeled with 3H at the right hand side were required. The two compounds labeled with ¹⁴C at the left or right hand side were synthesized in 2 and 5 radio‐synthetic steps using [¹⁴C]2‐chloroacetyl chloride and [¹⁴C]NaCN as starting radiolabeled materials, respectively. CP‐I was labeled with tritium at the right hand side by a tritium de‐halogenation method. Batches of radiolabeled CP‐I were mixed to give dual‐radioisotope‐labeled CP‐I. An efficient approach to [¹⁴C]fluoropyridinyl imidazole was developed, and a short synthesis of iodo‐substituted fluoropyridinyl imidazole was also achieved. The details of these syntheses are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of tritium labeled isotopomers of L‐tyrosine

The synthesis of four selectively labeled isotopomers of L ‐tyrosine, (L ‐Tyr), using chemical and enzymatic methods is reported. Four tritium labeled isotopomers of L ‐phenylalanine (L ‐Phe) – [2‐³H]‐, [2′,6′‐³H₂]‐, [3R‐³H]‐ and [3S‐³H]‐ have been synthesized using a combination of chemical and enzymatic methods. The labeled isotopomers of L ‐Phe have been converted into [2 ‐³H]‐, [2′,6′‐³H₂]‐, [3R‐³H]‐, and [3S‐³H]‐L ‐Tyr by using the enzyme L ‐phenyl‐alanine 4′‐monooxygenase. Copyright © 2002 John Wiley & Sons, Ltd.     

Enantiospecific tritium labeling of 28‐homocastasterone

A regiospecific and enantiospecific synthesis of tritium‐labeled 28‐homocastasterone is reported. Appropriate chlorocarbonate, efficiently synthesized from the starting 28‐homocastasterone in an overall yield of 46%, undergoes catalytic tritium dechlorination by the T₂/Pd[0]/Et₃N system, providing 28‐[3β‐³H]homocastasterone, in a good yield, radiochemical purity (>97%), and with a high specific activity (5.8 Ci/mmol).     

Synthesis of isotopomers of dopamine labeled with deuterium or tritium

The synthesis of four isotopomers of dopamine labeled with deuterium or tritium is reported. The ring labeled [2′,5′,6′‐²H₃]‐, and [2′,5′,6′‐³H₃]‐dopamine were obtained using acid catalyzed isotopic exchange between dopamine and heavy or tritiated water respectively. Two selectively labeled isotopomers, i.e. [1R‐²H]‐, and [1R‐³H]‐dopamine were synthesized by enzymatic decarboxylation of L ‐DOPA using the enzyme tyrosine decarboxylase (EC 4.1.1.25) from Streptococcus faecalis. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of the tritiated isotopomers of enzastaurin and its N‐des‐pyridylmethyl metabolite for use in ADME studies

Enzastaurin (3‐(1‐methyl‐1H‐indol‐3‐yl)‐4‐[1‐[1‐(2‐pyridinylmethyl)‐4‐piperidinyl]‐1H‐indol‐3‐yl]‐1H‐pyrrole‐2,5‐dione, 1), an agent with potential utility in the treatment of solid tumors, is currently in phase II clinical trials. Enzastaurin undergoes metabolism in vitro and in vivo to several products of oxidative metabolism, the major one of which is 3‐(1‐methyl‐1H‐indol‐3‐yl)‐4‐(1‐piperidin‐4‐yl‐1H‐indol‐3‐yl)‐1H‐pyrrole‐2,5‐dione (2). In a model study, the attempted synthesis 1‐[²H] by reaction of 1 with deuterium gas in the presence of Ir[(COD)(Cy₃P)pyr]PF₆ (Crabtree's catalyst) was unsuccessful. Alternatively, it was decided to prepare tritiated 2 as both a final product and the starting material for the tritiation of 1. We have reported herein a route that was developed for use in the preparation of tritium‐labeled 2‐[³H] and its successful conversion to 1‐[³H]. Copyright © 2008 John Wiley & Sons, Ltd.     

Tritium labeling of a γ‐secretase inhibitor and two modulators as in vitro imaging agents

The γ‐secretase inhibitor dibenzazepine ( DBZ ) and the γ‐secretase modulators 1 and AZ8349 were prepared as tritium‐labeled compounds with high specific activity and radiochemical purity. [³H] DBZ was labeled via an iodinated precursor, [³H] 1 was labeled by [³H]methylation of an O‐desmethyl precursor, and [2‐³H] AZ8349 was labeled via a tribromoacetyl precursor by catalytic hydrogenation. [³H]DBZ , [³H]1 , and [2‐³H]AZ8349 are promising in vitro imaging radioligands and have the potential to provide key information with regard to γ‐secretase expression, function, stoichiometry, and pharmacology.     

Enzymatic synthesis of tritium‐labelled isotopomers of histamine

Three tritium‐labelled isotopomers of histamine (HA) have been synthesized using combined chemical and enzymatic methods. In the first step the tritium‐labelled isotopomers of histidine have been obtained by catalysed exchange with tritiated water. These intermediates have been converted into [1S‐³H]‐HA, [1R‐³H]‐HA and [2′,4′,1S,‐³H₃]‐HA using the enzyme histidine decarboxylase (HDC, EC 4.1.1.22) from Lactobacillus 30a. Copyright © 2004 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.     

Syntheses of halogen derivatives of L‐tryptophan,L‐tyrosine and L‐phenylalanine labeled with hydrogen isotopes

Halogenated, labeled with tritium and doubly with deuterium and tritium, derivatives of L ‐tryptophan, i.e. 5′‐bromo‐[2‐³H]‐, 5′‐bromo‐[2‐²H/³H]‐, 5′‐fluoro‐[2‐³H]‐5′‐fluoro‐[2‐²H/³H]‐, 6′‐fluoro‐[2‐³H]‐, 6′‐fluoro‐[2‐²H/³H]‐L ‐tryptophan, as well as, L ‐tyrosine, i.e. 3′‐fluoro‐[2‐³H]‐, 3′‐fluoro‐[2‐²H/³H]‐, 3′‐chloro‐[2‐³H]‐, and 3′‐chloro‐[2‐²H/³H]‐L ‐tyrosine, and also L ‐phenylalanine, i.e. 2′‐fluoro‐[(3S)‐³H]‐, 2′‐fluoro‐[(3S)‐²H/³H]‐, 2′‐chloro‐[(3S)‐³H]‐, 2′‐chloro‐[(3S)‐²H/³H]‐, 4′‐chloro‐[(3S)‐³H]‐, and 4′‐chloro‐[(3S)‐²H/³H]‐L ‐phenylalanine were synthesized using enzymatic methods. Isotopomers of L ‐tryptophan were synthesized by coupling of halogenated indoles with S‐methyl‐L ‐cysteine carried out in deuteriated or tritiated incubation media. Labeled halogenated derivatives of L ‐tyrosine were obtained by the enzymatically supported exchange between halogenated L ‐tyrosine and isotopic water. Labeled halogenated isotopologues of L ‐Phe were synthesized by the enzymatic addition of ammonia to halogenated cinnamic acid. As a source of hydrogen tritiated water (HTO) and heavy water (D₂O) with addition of HTO were used.