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 [1‐13C]‐para‐xylene and [2‐13C]‐para‐xylene

An efficient synthesis of [1‐¹³C]‐para‐xylene ( 1a ) and [2‐¹³C]‐para‐xylene ( 1b ) is described. The incorporation of the label has been achieved by cyclocondensation of suitable 1,5‐bis(bromomagnesio)alkanes with either ethyl [1‐¹³C]acetate or ethyl [¹³C]formate which gave [ring‐¹³C]‐labelled dimethylcyclohexanols. Dehydration of these alcohols followed by dehydrogenation of the intermediate dimethylcyclohexenes furnished the title compounds in 32 and 40% overall yield, respectively. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of [13C2]nifedipine

[¹³C₂]Nifedipine (3 ) was synthesized from [¹³C]methanol (&1macr;) in two steps. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of 4‐thia[5‐13C]lysine

This report describes the synthesis of 4‐thia[5‐¹³C]lysine, an isotopomer of 4‐thialysine that is an analog of lysine. It was synthesized from 2‐amino[1‐¹³C]ethanol hydrochloride (1) in two steps. In the first step, 1 was converted to 2‐bromo[2‐¹³C]ethylamine hydrobromide (2). The reaction of cysteine with 2 in basic condition followed by acidification afforded 4‐thia[5‐¹³C]lysine hydrochloride (3).     

Synthesis of [guanido‐13C]‐γ‐hydroxyarginine

This report describes an efficient method of synthesizing [guanido‐¹³C]‐γ‐hydroxyarginine HCl salt. Iodolactonization of N‐Boc‐protected allylglycine mainly provided the cis iodo compound 2. This was converted to an amine through azide 4. The amine 5 was reacted with N‐Boc‐protected [¹³C]thiourea to afford N‐Boc‐protected [¹³C]guanidine 6, which underwent base catalyzed ring opening. Removal of the N‐Boc group afforded [guanido‐¹³C]‐γ‐hydroxyarginine HCl salt 7 giving a 30% overall yield of the final product from N‐Boc protected allylglycine 1 in five steps. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 5‐[4,5‐13C2]‐ and 5‐[1,5‐13C2]aminolevulinic acid

5‐[4,5‐¹³C₂]‐ and 5‐[1,5‐¹³C₂]Aminolevulinic acid (ALA) have been synthesized by the Gabriel condensation of potassium phthalimide with ethyl bromo[1,2‐¹³C₂]acetate (derived from [1,2‐¹³C₂]acetic acid) or ethyl bromo[2‐¹³C]‐acetate (derived from sodium [2‐¹³C]acetate), followed by conversion to the chloride, coupling reaction with 2‐ethoxycarbonylethylzinc iodide derived from ethyl 3‐iodopropionate or 2‐methoxy[¹³C]carbonylethylzinc iodide derived from methyl 3‐iodo[1‐¹³C]propionate (generated from potassium [¹³C]cyanide), and hydrolysis. Copyright © 2002 John Wiley & Sons, Ltd.     

One‐pot radiosynthesis of [13N]urea and [13N]carbamate using no‐carrier‐added [13N]NH3

The aim of this study was to develop a practical labeling method of [¹³N]ligands using no‐carrier‐added [¹³N]NH₃ with high specific activity. [¹³N]urea analogues [¹³N]1a and [¹³N]2a or [¹³N]carbamate [¹³N]3a were synthesized by reacting isocyanate 5a, carbamoyl chloride 6a or chloroformate 7a with [¹³N]NH₃. The precursors 5a–7a were prepared by treating amines 8a and 9a and alcohol 10a with triphosgene in situ. These reaction mixtures were not purified and were used directly for [¹³N]ammonolysis, respectively. Using the one‐pot method, we synthesized [¹³N]carbamazepine ([¹³N]4), a putative positron emission tomography ligand for brain imaging. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of 13C and 15N multilabeled 5‐aminolevulinic acid

5‐[4‐¹³C,¹⁵N]‐ and 5‐[5‐¹³C,¹⁵N]Aminolevulinic acid (ALA) were simply synthesized in four steps by the condensation of [1‐¹³C,¹⁵N]‐ or [2‐¹³C,¹⁵N]glycine, respectively, with phthalic anhydride, followed by conversion to the chloride, coupling reaction with a three‐carbon unit and hydrolysis. Copyright © 2002 John Wiley & Sons, Ltd.     

A method for the preparation of [13C6]‐labelled 2‐substituted naphthalenes

A reliable route is described for the preparation of various 2‐substituted derivatives of [1,2,3,4,4a,8a‐¹³C₆]‐naphthalene via the bromide 10. The approach is used to prepare [naphthalene‐1,2,3,4,4a,8a‐¹³C₆]‐2‐(2‐bromoethyl)naphthalene (1), a key intermediate in the synthesis of labelled SR57746A, Xaliproden (2). Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and purification of [2‐13C]‐5‐fluorouracil

[2‐¹³C]‐5‐Fluoropyrimidine‐2,4(1H,3H)‐dione ([2‐¹³C]‐5‐fluorouracil or [2‐¹³C]‐5‐FU) is a potential diagnostic agent for measuring 5‐FU‐induced toxicity in cancer patients. It was prepared and purified with isotopic and chemical purity of>99% on a multigram scale in a two‐step synthesis from [¹³C]‐urea. Preparative separation of [2‐¹³C]‐FU and [2‐¹³C]‐uracil was carried out by automated medium pressure silica gel column chromatography. The method is applicable to a broader range of 5‐FU isotopic analogs derived from labeled uracil. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis,radiosynthesis and in vivo evaluation of [123I]‐4‐(2‐(bis(4‐fluorophenyl)methoxy)ethyl)‐1‐(4‐iodobenzyl)piperidine as a selective tracer for imaging the dopamine transporter

Dopamine transporter (DAT) neuroimaging is a useful tool in Parkinson's disease diagnosis, staging and follow‐up providing information on the integrity of the dopaminergic neurotransmitter system in vivo. 4‐(2‐(Bis(4‐fluorophenyl)methoxy)ethyl)‐1‐(4‐iodobenzyl)piperidine (7) has nanomolar affinity for DAT and better selectivity over the other monoamine transporters compared with the existing SPECT radioligands for DAT. The aim of this study was to synthesize and evaluate [¹²³I]‐7 as an in vivo tracer for DAT. The tributylstannyl precursor was synthesized with an overall yield of 25%. [¹²³I]‐7 was synthesized by electrophilic destannylation with a yield of 40±10%. Radiochemical purity appeared to be >98%, whereas specific activity was at least 667 GBq/µmol. Biodistribution studies in mice showed brain uptake of 0.96±0.53%ID/g at 30 s post injection (p.i.) and 0.26±0.02%ID/g at 3 h p.i. High blood activity was observed at all time points. Pretreatment with Cyclosporin A raised brain uptake indicating that [¹²³I]‐7 is transported by P‐glycoprotein (P‐gp) pumps. In rats, regional brain distribution of [¹²³I]‐7 was not in agreement with DAT distribution. These results indicate that [¹²³I]‐7 is not suitable for mapping DAT in vivo but could be a useful tracer for the P‐gp transporter. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of 14C‐labelled myosmine, [2′‐14C] ‐3‐(1‐pyrrolin‐2‐yl)pyridine

¹⁴C‐Labelled myosmine ([2′‐¹⁴C]‐3‐(1‐pyrrolin‐2‐yl)pyridine) was synthesized for autoradiography studies starting from [carboxyl‐¹⁴C]‐nicotinic acid by initial esterification of the latter in the presence of 1,1,1‐triethoxyethane. Without any purification the ethyl nicotinate formed was directly reacted with N‐vinyl‐2‐pyrrolidinone in the presence of sodium hydride, yielding ¹⁴C‐labelled myosmine. The product was purified by silica gel column chromatography. The radiochemical yield was 15% and the specific activity 55.2 mCi/mmol. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of 1‐(2′‐deoxy‐2′‐fluoro‐β‐D‐arabinofuranosyl)‐[Methyl‐11C]thymine ([11C]FMAU) via a Stille cross‐coupling reaction with [11C]methyl iodide

1‐(2′‐deoxy‐2′‐fluoro‐β‐D‐arabinofuranosyl)‐[methyl‐¹¹C]thymine ([¹¹C]FMAU) [¹¹C]‐ 1 was synthesised via a palladium‐mediated Stille coupling reaction of 1‐(2′‐deoxy‐2′‐fluoro‐β‐D‐arabinofuranosyl)‐5‐(trimethylstannyl)uracil 2 with [¹¹C]methyl iodide in a one‐pot procedure. The reaction conditions were optimized by screening various catalysts and solvents, and by altering concentrations and reaction temperatures. The highest yield was obtained using Pd₂(dba)₃ and P(o‐tolyl)₃ in DMF at 130°C for 5 min. Under these conditions the title compound [¹¹C]‐ 1 was obtained in 28±5% decay‐corrected radiochemical yield calculated from [¹¹C]methyl iodide (number of experiments=7). The radiochemical purity was >99% and the specific radioactivity was 0.1 GBq/μmol at 25 min after end of bombardment. In a typical experiment 700–800 MBq of [¹¹C]FMAU [¹¹C]‐ 1 was obtained starting from 6–7 GBq of [¹¹C]methyl iodide. A mixed ¹¹C/¹³C synthesis to yield [¹¹C]‐ 1 /(¹³C)‐ 1 followed by ¹³C‐NMR analysis was used to confirm the labelling position. The labelling procedure was found to be suitable for automation. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of isotope‐labeled HSP90 inhibitor: [13CD3] and [14C]‐TAK‐459

[¹³CD₃]‐TAK‐459 (1A), an HSP90 inhibitor, was synthesized from [¹³CD₃]‐sodium methoxide in three steps in an overall yield of 29%. The key intermediate [¹³CD₃]‐2‐methoxy‐6‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)pyridine was synthesized in two steps from 2,6‐dibromopyridine and stable isotope‐labeled sodium methoxide. [¹⁴C]‐TAK‐459 (1B) was synthesized from [¹⁴C(U)]‐guanidine hydrochloride in five steps in an overall radiochemical yield of 5.4%. The key intermediate, [¹⁴C]‐(R)‐2‐amino‐7‐(2‐bromo‐4‐fluorophenyl)‐4‐methyl‐7,8‐dihydropyrido[4,3‐d]pyrimidin‐5(6H)‐one, was prepared by microwave‐assisted condensation.     

Synthesis of [N‐methyl‐13C]clarithromycin

We describe a simple synthesis of [N‐methyl‐¹³C]clarithromycin ( 3 ) via the N‐desmethylation of clarithromycin. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of a delta opioid agonist in [2H6], [2H4], [11C], and [14C] labeled forms

In support of a program to develop a treatment for depression, four labeled forms of a delta opioid agonist were prepared. The [²H₄] labeled form was prepared using a relatively straightforward conversion of [²H₄]bromoethanol to [²H₄]N‐methyl‐2‐hydroxyethylamine. The key step in the synthesis of the [²H₆] labeled form involved the Pd‐catalyzed exchange in D₂O of 8‐quinolin‐8‐ol to give [²H₆] 8‐quinolin‐8‐ol. The C‐14 labeled form was synthesized in one step using [¹⁴C]carbonylation, and the C‐11 labeled form was prepared in two steps from ¹¹CH₃I. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of (S)‐cyano(3‐phenoxyphenyl)methyl (1R,3R)‐ 3‐[(1Z)‐2‐chloro‐3,3,3‐trifluoro‐1‐propenyl]‐2,2‐dimethylcyclopropanecarboxylate‐1‐14C

γ‐Cyhalothrin ( 1a ), (S)‐cyano(3‐phenoxyphenyl)methyl (1R,3R)‐3‐[(1Z)‐2‐chloro‐3,3,3‐trifluoro‐1‐propenyl]‐2,2‐dimethylcyclopropanecarboxylate, is a single‐isomer, synthetic pyrethroid insecticide marketed by Pytech Chemicals GmbH, a joint venture between Dow AgroSciences and Cheminova A/S. As a part of the registration process there was a need to incorporate a carbon‐14 label into the cyclopropyl ring of this molecule. A high yielding radiochemical synthesis of γ‐cyhalothrin was developed from readily available carbon‐14 labeled N‐t‐Boc protected glycine. This seven step synthesis, followed by a preparative normal phase HPLC separation of diastereomers, provided 21.8 mCi of γ‐cyhalothrin‐1‐¹⁴C ( 1b ) with >98% radiochemical purity. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of [13C4]Baraclude® (entecavir)

Entecavir, labeled as 1H‐[¹³C₄]purin‐6(9H)‐one, was prepared from commercially available [¹³C]guanidine HCl, 1 and diethyl [1,2,3‐¹³C₃]malonate, 2 . The reagents were condensed together to give 2‐amino‐4,6‐dichloro[2,4,5,6‐¹³C₄]pyrimidine 3 , which in turn was coupled to an optically active amino cyclopentanol derivative, 9 . A further sequence of eight reaction steps completed the constructions of the purine ring system and the exocyclic olefin attachment on the cyclic pentyl portion, 18 . The removal of the methoxide and benzyl protecting groups gave [¹³C₄]entecavir, 20 in an overall yield of 6.8%. The chemical purity of the title compound was determined by HPLC to be 99.23%. The percent isotopic [¹³C₄] abundance was found by mass spectral analysis to be 96.7%. No detectable level of the unlabeled entecavir was found by LC‐MS analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Lack of specificity of [35S]‐ATPγS and [35S]‐ADPβS as radioligands for ionotropic and metabotropic P2 receptor binding

Adenosine‐5′‐O‐3‐thio[³⁵S]triphosphate ([³⁵S]‐ATPγS) has been reported to specifically bind several P2X receptor subtypes, including P2X₁, P2X₂, P2X₃, and P2X₄. Similarly, adenosine‐5′‐O‐2‐thio[³⁵S]diphosphate ([³⁵S]‐ADPβS) has been reported to label putative P2Y receptors. To address whether these radioligands selectively label P2 receptors, the functional activity of various P2 ligands was compared with their ability to compete for [³⁵S]‐ATPγS and [³⁵S]‐ADPβS binding to cell membrane preparations from rat brain, HEK293 cells, and to native and P2X₄ transfected 1321N1 astrocytoma cells. [³⁵S]‐ATPγS (0.2 nM) and [³⁵S]‐ADPβS (0.1 nM) displayed a high percentage of specific binding to membranes prepared from 1321N1 human astrocytoma cells, which were found to be devoid of detectable P2X and P2Y functional activity. [³⁵S]‐ATPγS and [³⁵S]‐ADPβS also exhibited equivalent high percentages of specific binding to HEK293 cell membranes, which endogenously express the P2Y₁ and P2Y₂ receptor subtypes, to 1321N1 cells stably transfected with the human P2X₄ receptor, and to rat brain membranes, which have previously been shown to contain both P2X and P2Y receptor subtypes. The potency order of P2 agonists to compete for radioligand binding to these cell membrane preparations was significantly different from the functional rank order potencies determined in HEK293 cells and 1321N1 cells expressing the P2X₄ receptor, as measured by cytosolic calcium flux. These data indicate that [³⁵S]‐ATPγS and [³⁵S]‐ADPβS appear to bind sites that do not correspond to known functional P2 receptor subtypes. The apparent lack of specificity of these radioligands for labeling P2 receptors is similar to that reported for other radiolabeled nucleotides and illustrates the need for caution in interpreting the apparent pharmacology of native P2 receptors on the basis of binding data alone. Drug Dev. Res. 48:84–93, 1999. © 1999 Wiley‐Liss, Inc.     

Syntheses of stable‐isotope labeled [M+7] and [M+6] 2‐(methylamino)imidazole

Stable isotope‐labeled 2‐methylaminoimidazole (M+7 and M+6) was required as an intermediate in the synthesis of mass labeled drug candidates. These two isotopomers were synthesized with total yields of 24 and 36%, respectively. Labeled 2‐aminoimidazole (M+4) was prepared from labeled isothiourea (M+3) and 2‐aminoacetaldehyde dimethyl acetal (M+1 and M+2). The (M+1) version of 2‐aminoacetaldehyde dimethyl acetal was obtained in two steps starting with potassium [¹⁵N]phthalimide, while the (M+2) version was prepared from the reduction of diethoxyacetamide with LiAlD₄. Two different approaches for the preparation of 2‐methylaminoimidazole from aminoimidazole were explored. Attempts to prepare protected 2‐aminoimidazole to couple with CH₃I (M+4) to form the desired labeled 2‐methyl‐aminoimidazole failed. However, methylation was achieved by applying N‐formamidation followed by deutero‐reduction. These successful syntheses allowed us to selectively label with nitrogen, carbon or hydrogen isotopes at most of the positions of 2‐methylaminoimidazole. Copyright © 2002 John Wiley & Sons, Ltd.