Synthesis of tritium labelled [2′,6′]‐L‐tyrosine

The synthesis of a specifically ring labelled isotopomer of L ‐tyrosine, (L ‐Tyr), using a combination of chemical and enzymatic methods is reported. The tritium labelled [2′,6′]‐L ‐Tyr has been synthesized via catalytic exchange of phenol with tritiated water in the presence of K₂PtCl₄, reverse acid catalysed removal of tritium from the o‐ and p‐positions of phenol, and subsequent condensation of the resulting [3′,5‐³H₂]‐phenol with S‐methyl‐L ‐cysteine using the enzyme β‐tyrosinase from Citrobacter freundii. Copyright © 2004 John Wiley & Sons, Ltd.     

Rac‐ and R‐(+)‐[4,4′,5,5′‐2H4]‐2‐(1′‐[2′′,6′′‐dichlorophenoxy]‐ethyl)‐Δ2‐imidazoline (lofexidine)

The synthesis of the d₄‐forms of rac‐ and R‐lofexidine was accomplished. Two methods are described; one method is a two‐step synthesis of rac‐d₄‐lofexidine from 2‐chloropropionitrile, the second method is a three‐step preparation of R‐d₄‐lofexidine in absolute enantiomeric purity from S‐methyl lactate. The commercial availability of R‐methyl lactate makes this latter enantioselective synthesis applicable also to the synthesis of S‐d₄‐ lofexidine. These procedures also conserve the utilization of the relatively expensive [1,1′,2,2′‐²H₄]ethylene diamine precursor. The availability of S‐ and R‐d₄‐lofexidines will enable pharmacokinetic studies to be carried out to determine if differential in vivo metabolism of the two enantiomers of lofexidine occurs. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of [2H8]‐enterolactone and [2H10]‐enterodiol

Enterolactone and enterodiol are the main mammalian metabolites of dietary butyrolactone type lignans. The study of biological properties and potential health effects of these compounds requires isotopically labelled compounds as standards for quantitative measurements. An expedient deutero‐labelling method for enterolactone is to use the D₃PO₄·BF₃/D₂O complex at room temperature which will exchange all eight aromatic hydrogens, even from inactivated meta positions, to form [2,4,5,6,2′,4′,5′,6′‐²H₈]‐enterolactone in 74% yield and 99% isotopic purity. [2,4,5,6,9,9,2′,4′,5′,6′‐²H₁₀]‐Enterodiol was prepared from [2,4,5,6,2′,4′,5′,6′‐²H₈]‐enterolactone by reduction with LiAlD₄ which introduces two more deuterium atoms into the molecule. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of (E)‐2,3′,4,5′‐tetramethoxy[2‐11C]stilbene

In this paper, we describe the radiosynthesis of the compound (E)‐2,3′,4,5′‐tetramethoxy[2‐¹¹C]stilbene, a potential, universal tumour positron emission tomography imaging agent. The production of (E)‐2,3′,4,5′‐tetramethoxy[2‐¹¹C]stilbene was carried out via ¹¹C‐methylation of (E)‐2‐(hydroxy)‐3′,4,5′‐trimethoxystilbene by using [¹¹C]methyl trifluoromethanesulfonate ([¹¹C]methyl triflate). (E)‐2,3′,4,5′‐tetramethoxy[2‐¹¹C]stilbene was obtained with a radiochemical purity greater than 95% in a 20 ± 2% decay‐corrected radiochemical yield, based upon [¹¹C]carbon dioxide. Synthesis, purification and formulation were completed on an average of 30 min following the end of bombardment (EOB). The specific radioactivity obtained was 1.9 ± 0.6 GBq/µmol at EOB. Copyright © 2007 John Wiley & Sons, Ltd.     

Radiosynthesis of 1′‐[18F]fluoroethyl‐β‐D‐lactose ([18F]‐FEL) for early detection of pancreatic carcinomas with PET

Introduction: The hepatocellular carcinoma–intestine–pancreas and pancreatitis‐associated proteins, also known as lactose‐binding protein, is upregulated in peritumoral pancreatic tissue. Previously, we reported ethyl‐ β ‐D ‐galactopyranosyl‐(1,4′)‐2′‐deoxy‐2′‐[¹⁸F]fluoro‐ β ‐D ‐glucopyranoside (Et‐[¹⁸F]‐FDL), a radiofluorinated lactose analog for positron emission tomography (PET) of small pancreatic carcinomas in mice. However, synthesis of the precursor for Et‐[¹⁸F]‐FDL involves 11 steps, which is quite lengthy, and produces overall low yields. Here, we report on synthesis and radiolabeling of another analog of lactose, the 1′‐[¹⁸F]fluoroethyl‐ β ‐D ‐lactose for PET imaging of pancreatic carcinomas. Methods: Two precursor compounds, 1′‐bromoethyl‐2′,3′,6′,2,3,4,6‐hepta‐O‐acetyl‐ β ‐D ‐lactose 4, and 1′‐p‐toluenesulfonylethyl‐2′,3′,6′,2,3,4,6‐hepta‐O‐acetyl‐ β ‐D ‐lactose 5, were synthesized in two and three steps, respectively; then, cold fluorination and radiofluorination of these precursors were performed. The reaction mixture was passed through a silica gel Sep‐pack cartridge, eluted with EtOAc, and the 1′‐[¹⁸F]fluoroethyl‐2′,3′,6′,2,3,4,6‐hepta‐O‐acetyl‐ β ‐D ‐lactose ([¹⁸F]‐6) purified by HPLC. After hydrolysis of the protecting groups, the 1′‐[¹⁸F]fluoroethyl‐ β ‐D ‐lactose [¹⁸F]‐7 was neutralized, diluted with saline, filtered through a sterile Millipore filter, and analyzed by radio‐TLC. Results: The average decay‐corrected radiochemical yield was 9% (n = 7) with>99% radiochemical purity and specific activity of 55.5 GBq/ µ mol. Conclusion : A new analog of lactose, 1′‐[¹⁸F]fluoroethyl‐ β ‐D ‐lactose, has been synthesized in good yields, with high purity and high specific activity suitable for PET imaging of early pancreatic carcinomas. Copyright © 2011 John Wiley & Sons, Ltd.     

Radiosynthesis of 3‐(2′‐[18F]fluoro)‐flumazenil ([18F]FFMZ)

Recently, two fluorine‐18 labelled derivatives of flumazenil were described: 5‐(2′‐[¹⁸F]fluoroethyl)‐5‐desmethylflumazenil (ethyl 8‐fluoro‐5‐[¹⁸F]fluoroethyl‐6‐oxo‐5,6‐dihydro‐4H‐benzo‐[f]imidazo[1,5‐a] [1,4]diazepine‐3‐carboxylate; [¹⁸F]FEFMZ) and 3‐(2′‐[¹⁸F]fluoro)‐flumazenil (2′‐[¹⁸F]fluoroethyl 8‐fluoro‐5‐methyl‐6‐oxo‐5,6‐dihydro‐4H‐benzo‐[f]imidazo[1,5‐a]‐[1,4]diazepine‐3‐carbo‐ xylate; [¹⁸F]FFMZ). Since the biodistribution data of the latter were superior to those of the former we developed a synthetic approach for [¹⁸F]FFMZ starting from a commercially available precursor, thereby obviating the need to prepare a precursor by ourselves. The following two‐step procedure was developed: First, [¹⁸F]fluoride was reacted with 2‐bromoethyl triflate using the kryptofix/acetonitrile method to yield 2‐bromo‐[¹⁸F]fluoroethane ([¹⁸F]BFE). In the second step, distilled [¹⁸F]BFE was reacted with the tetrabutylammonium salt of 3‐desethylflumazenil (8‐fluoro‐5‐methyl‐6‐oxo‐5,6‐dihydro‐4H‐benzo‐[f]imidazo[1,5‐a] [1,4]diazepine‐3‐carboxylic acid) to yield [¹⁸F]FFMZ. The synthesis of [¹⁸F]FFMZ allows for the production of up to 7 GBq of this PET‐tracer, enough to serve several patients. [¹⁸F]FFMZ synthesis was completed in less than 80 min and the radiochemical purity exceeded 98%. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of N‐(2‐chloro‐5‐methylthiophenyl)‐ N′‐(3‐methyl‐thiophenyl)‐ N′‐[3H3]methylguanidine, {[3H3]CNS‐5161}

The preparation of the title compound, [³H₃]CNS‐5161, was accomplished in three steps starting with the production of [³H₃]iodomethane (CT₃I). The intermediate N‐[³H₃]methyl‐3‐(thiomethylphenyl)cyanamide was prepared in 77% yield by the addition of CT₃I to 3‐(thiomethylphenyl)cyanamide, previously treated with sodium hydride. Reaction of this tritiated intermediate with 2‐chloro‐5‐thiomethylaniline hydrochloride formed the guanidine compound [³H₃]CNS‐5161. Purification by HPLC gave the desired labeled product in an overall yield of 9% with >96% radiochemical purity and a final specific activity of 66 Ci mmol^?1. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of 3H‐ and 2H4‐labelled versions of the hypoxia‐activated pre‐prodrug 2‐[(2‐bromoethyl)‐2,4‐dinitro‐6‐ [[[2‐(phosphonooxy)ethyl]amino]carbonyl]anilino]ethyl methanesulfonate (PR‐104)

³H‐ and ²H₄‐versions of the hypoxia‐activated pre‐prodrug PR‐104 [2‐[(2‐bromoethyl)‐2,4‐dinitro‐6‐[[[2‐(phosphonooxy)ethyl]amino]carbonyl]anilino]ethyl methanesulfonate], labelled in the ethylcarboxamide side chain, have been prepared, respectively, by [³H]NaBH₄ reduction of a precursor late stage aldehyde, and by late stage incorporation of deuterium with 2‐amino[1,1,2,2‐²H₄]ethanol. Copyright © 2007 John Wiley & Sons, Ltd.     

A convenient synthesis of 2′,3′‐dideoxyinosine‐13C5 and related 2′,3′‐dideoxyadenosine‐13C5

2′,3′‐Dideoxyinosine‐¹³C₅ (ddI‐¹³C₅) and the related 2′,3′‐dideoxyadenosine‐¹³C₅ (ddA‐¹³C₅) were prepared from (S)‐5‐[¹³C₅]2,3‐dideoxyribonolactone 1 . From a batch of this starting material ddI‐¹³C₅ was made in 27% overall yield in seven steps and ddA‐¹³C₅ in five steps and 14% overall yield. The known synthesis of ddI‐¹³C₅ from glucose‐¹³C₆ took 18‐steps_; therefore the present work is a substantial improvement. Copyright © 2010 John Wiley & Sons, Ltd.     

The synthesis of [3,4,1′‐13C3]genistein

A facile synthesis is described for [3,4,1′‐¹³C₃]genistein for use as an internal standard in isoflavone analysis by mass spectrometric methods. Ethyl 4‐hydroxy[1‐¹³C]benzoate was first prepared from the reaction of diethyl [2‐¹³C]malonate and 4H‐pyran‐4‐one. Two further ¹³C atoms were incorporated using potassium [¹³C]cyanide as the source to give 4′‐benzyloxy‐[1,2,1′‐¹³C₃]phenylacetonitrile. [3,4,1′‐¹³C₃]Genistein was then constructed through coupling of the isotopically labelled phenylacetonitrile with phloroglucinol under Hoesch conditions, followed by formylation and cyclization. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of stable isotopically labelled 3‐methylfuran‐2(5H)‐one and the corresponding strigolactones

Conventional synthetic procedures of strigolactones (SLs) involve the independent synthesis of ring ABC and ring D, followed by a coupling of the two fragments. Here we prepared three kinds of stable, isotopically labelled D‐ring analogues productively using a facile protocol. Then, a coupling of the D‐rings to ring ABC produced three isotope‐labelled SL derivatives. Moreover, (+)‐D₃‐2′‐epi‐ 1A and (?)‐ent‐D₃‐2′‐epi‐ 1A with high enantiomeric purity were obtained via chiral resolution.     

Total synthesis of [13C]2‐, [13C]3‐, and [13C]5‐isotopomers of xanthohumol,the principal prenylflavonoid from hops

Xanthohumol [(E )‐6′‐methoxy‐3′‐(3‐methylbuten‐2‐yl)‐2′,4′,4″‐trihydroxychalcone], he principal prenylated flavonoid from hops, has a complex bioactivity profile, and ¹³C‐labeled isotopomers of this compound are of potential use as molecular probes and as analytical standards to study metabolism and mode of action. 1,3‐[¹³C]₂‐Xanthohumol was prepared by an adaptation of the total synthesis of Khupse and Erhardt in 7 steps and 5.7% overall yield from phloroglucinol by a route incorporating a cascade Claisen‐Cope rearrangement to install the 3′‐prenyl moiety from a 5′‐prenyl aryl ether and an aldol condensation between 1‐[¹³C]‐2′,4′‐bis(benzyloxymethyloxy)‐6′‐methoxy‐3′‐(3‐methylbuten‐2‐yl)acetophenone and 1′‐[¹³C]‐4‐(methoxymethyloxy)benzaldehyde. The ¹³C‐atom in the methyl ketone was derived from 1‐[¹³C]‐acetyl chloride while that in the aryl aldehyde was derived from [¹³C]‐iodomethane. Tri‐ and penta‐¹³C‐labeled xanthohumols were similarly prepared by applying minor modifications to the route.     

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.     

1,3-Bis(pyridin-2-ylthio)propan-2-one,Bis(thieno[2,3-b]pyridin-2-yl)-ketone und 5H-Bispyrido[3′,2′:4,5]thieno[2,3-b:2′,3′-e]pyridin-11-one

1,3-Bis(pyridin-2-ylthio)propan-2-ones, Bis(thieno[2,3-b]pyridin-2-yl)ketones and 5H-Bispyrido[3′,2′:4,5]thieno[2,3-b:2′,3′-e]pyridin-11-ones Reaction of 1a-d with 1,3-dichloroacetone gives the bissulphides 2a-d . Base catalyzed cyclization of 2a-d affords heterocyclically substituted ketones 3a-e . Treatment of 3a and 3b in conc. H₃PO₄ leads to the bispyridothienopyridines 5a and 5b .     

Synthesis and 11C‐labelling of (E,E)‐1‐(3′,4′‐dihydroxystyryl)‐4‐(3′‐methoxy‐4′‐hydroxystyryl) benzene for PET imaging of amyloid deposits†

Carboxylic acid derivatives of the amyloid‐binding dye Congo red do not enter the brain well and are thus unable to serve as in vivo amyloid‐imaging agents. A neutral amyloid probe, (E,E)‐1‐(3′,4′‐dihydroxystyryl)‐4‐(3′‐methoxy‐4′‐hydroxystyryl)benzene ( 3 ), devoid of any carboxylate groups has been designed and synthesized via a 12‐step reaction sequence with a total yield of 30%. The unsymmetric compound 3 has also been labelled with C‐11 via [¹¹C]methyl iodide ([¹¹C]CH₃I) methylation of a symmetric 4,4′‐dimesyl protected precursor followed by deprotection. Preliminary evaluation indicated that compound 3 selectively stained plaques and neurofibrillary tangles in post‐mortem AD brain, and exhibited good binding affinity (K_i=38±8 nM) for Aβ(1–40) fibrils in vitro. In vivo pharmacokinetic studies indicated that [¹¹C] 3 exhibited higher brain uptake than its carboxylic acid analogs and good clearance from normal control mouse brain. [¹¹C] 3 also exhibited specific in vivo binding to pancreatic amyloid deposits in the NOR‐beta transgenic mouse model. These results justify further investigation of 3 and similar derivatives as surrogate markers for in vivo quantitation of amyloid deposits. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of 13C‐labeled 5‐aminoimidazole‐4‐carboxamide‐1‐β‐D‐[13C5] ribofuranosyl 5′‐monophosphate

5‐Aminoimidazole‐4‐carboxamide‐1‐β‐D‐[¹³C₅] ribofuranosyl 5′‐monophosphate ([¹³C₅ ribose] AICAR‐PO₃H₂) ( 6 ) has been synthesized from [¹³C₅]adenosine. Incorporation of the mass‐label into [¹³C₅ ribose] AICAR‐PO₃H₂ provides a useful standard to aid in metabolite identification and quantification in monitoring metabolic pathways. A synthetic route to the ¹³C‐labeled compound has not been previously reported. Our method employs a hybrid enzymatic, and chemical synthesis approach that applies an enzymatic conversion from adenosine to inosine followed by a ring‐cleavage of the protected inosine. A direct phosphorylation of the resulting 2′,3′‐isopropylidine acadesine ( 5 ) was developed to yield the title compound in 99% purity following ion exchange chromatography.     

Microscale synthesis and kinetic isotope effect analysis of (4R)‐[Ad‐14C,4‐2H] NADPH and (4R)‐[Ad‐3H,4‐2H] NADPH

We present a one‐pot chemo‐enzymatic microscale synthesis of NADPH with two different patterns of isotopic labels: (4R)‐[Ad‐¹⁴C,4‐²H] NADPH and (4R)‐[Ad‐³H,4‐²H] NADPH. These co‐factors are required by an enormous range of enzymes, and isotopically labeled nicotinamides are consequently of significant interest to researchers. In the current procedure, [Ad‐¹⁴C] NAD⁺ and [Ad‐³H] NAD⁺ were phosphorylated by NAD⁺ kinase to produce [Ad‐¹⁴C] NADP⁺ and [Ad‐³H] NADP⁺, respectively. Thermoanaerobium brockii alcohol dehydrogenase was then used to stereospecifically transfer deuterium from C2 of isopropanol to the re face of C4 of NADP⁺. After purification by HPLC, NMR analysis indicated that the deuterium content at the 4R position is more than 99.7%. The labeled cofactors were then used to successfully and sensitively measure kinetic isotope effects for R67 dihydrofolate reductase, providing strong evidence for the utility of this synthetic methodology. Copyright © 2009 John Wiley & Sons, Ltd.     

Radiosynthesis of microtubule‐targeted theranostic methyl N‐[5‐(3’‐radiohalobenzoyl)‐1H‐benzimidazol‐2‐yl]carbamates

Microtubules are a target for a broad spectrum of drugs used as chemotherapeutics to treat hematological malignancies and solid tumors. Most of these drugs have significant dose‐limiting toxicities including peripheral neuropathies that can be debilitating and permanent. In an ongoing effort to develop safer and more effective drugs, benzimidazole‐based compounds are being developed as replacement for vincristine and similar agents. In this report, we describe radiosyntheses of novel microtubule‐targeting methyl N‐[5‐(3’‐radiohalobenzoyl)‐1H‐benzimidazol‐2‐yl]carbamates 4 that are intended as potential imaging agents and molecular radiotherapeutics. ¹²⁵I‐ and ¹³¹I‐radiolabeled derivatives were prepared either by direct radioiodination of methyl N‐(6‐benzoyl‐1H‐benzimidazol‐2‐yl)carbamate 1 or radioiododestannylation of the corresponding stannane precursor 3 . The direct radioiodination was conducted in a solution of 1 in triflic acid and produced after ~1 hour at elevated temperatures and HPLC purification on average 62% of the no‐carrier added products ¹²⁵I‐ 4 and ¹³¹I‐ 4 . Radioiododestannylation of 3’‐trimethylstannane 3 proceeded with ease at room temperature in the presence of H₂O₂ as the oxidant and produced no‐carrier‐added ¹²⁵I‐ 4 and ¹³¹I‐ 4 in high isolated yields, on average 85%. The radiohalodestannylation protocol is universal and can be applied to other radiohalides including ¹²⁴I to produce ¹²⁴I‐ 4 , a positron emission tomography agent, and ²¹¹At to produce ²¹¹At‐ 4 , an α‐particle emitting radiotherapeutic.     

A new synthesis of [26,28‐2H6]brassinolide and [26,28‐2H6]castasterone via an unusual methyl migration

Deuterium‐labelled brassinosteroids, namely [26,28‐²H₆]castasterone, 8 , and [26,28‐²H₆]brassinolide, 9 , were synthesized starting from 6,6‐ ethylenedioxy‐20‐formyl‐2α,3α‐isopropylidenedioxy‐5α‐pregnane, 1 , and 3‐[²H₃]methyl‐but‐1‐yne‐[4,4,4‐²H₃], 11 . Upon alkylating cleavage of the epoxide 6 with trimethylaluminium‐n‐butyllithium an unusual migration of a neighbouring [²H₃]methyl group takes place to afford deuteriation at positions 26 and 28. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of [2H3]‐dextromethorphan and its major urinary metabolites [2H3]‐dextrorphan and [2H3]‐dextrorphan‐β‐glucuronide

Starting from dextromethorphan, [²H₃]‐dextrorphan‐β‐glucuronide was synthesized in four steps with [²H₃]‐dextromethorphan and [²H₃]‐dextrorphan as intermediates with an overall yield of 11%. Copyright © 2002 John Wiley & Sons, Ltd.