Investigations into the C‐deuteriation of enol acetates derived from aryl alkyl ketones

Results are reported on the regioselective C‐deuteriation of a series of enol acetates (derived from the aryl alkyl ketones) using molecular deuterium as the D‐source and palladium‐on‐barium sulphate as the mediator. The results presented highlight potential problems associated with the deuteriation of enol acetates. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigations into the regioselective C‐deuteriation of enolates derived from 2‐methyl tetralone using piperidine‐d11

Results are reported on the regioselective C‐deuteriation of 2‐methyl tetralone using piperidine‐d₁₁ as a deuterium source. The results presented further aid the understanding of kinetic deuteriation of amine–enolate complexes. Copyright © 2004 John Wiley & Sons, Ltd.     

Investigations into the C‐deuteriation of aryl alkyl ketones using urea as a pro‐base in the presence of a deuterium donor

Results are reported on the regioselective C‐deuteriation of a series of enolates derived from the deprotonation of aryl alkyl ketones using dilithiated urea as the pro‐base in the presence of a suitable deuterium donor. Copyright © 2006 John Wiley & Sons, Ltd.     

Probing the regioselective C‐deuteriation of lithium enolates derived from 2‐methyl‐tetralone in the presence of substituted tertiary amines

Results are reported on the regioselective C‐deuteriation of 2‐methyl‐tetralone using a series of D‐sources and tertiary amines as potential mediators. The results presented further aid the understanding of kinetic deuteriation of both ‘base‐containing’ and ‘base‐free’ enolates. Copyright © 2006 John Wiley & Sons, Ltd.     

A facile synthesis of 5,5‐dideutero‐4‐dimethyl(phenyl)silyl‐6‐undecyl‐tetrahydropyran‐2‐one as a deuterium labeled synthon for (−)‐tetrahydrolipstatin and (+)‐δ‐hexadecanolide

Deuterium‐labeled biologically active compounds are gaining importance because they can be utilized as tracers or surrogate compounds to understand the mechanism of action, absorption, distribution, metabolism, and excretion. Deuterated drug molecules (heavy drugs) become novel as well as popular because of better stability and bioavailability compared with their hydrogen analogs. Labeling of organic molecules with deuterium at specific positions is thus gaining popularity. In this work, we have exploited a highly regioselective and enantioselective direct Michael addition of methyl‐d₃ alkyl ketones to dimethyl(phenyl)silylmethylene malonate that was catalyzed by (S)‐N‐(2‐pyrrolidinylmethyl)pyrrolidine/trifluoroacetic acid/ D₂O combination with high yield and isotopic purity. The 5,5‐dideutero‐4‐dimethyl(phenyl)silyl‐6‐undecyl‐tetrahydropyran‐2‐one was obtained from the adduct of methyl‐d₃ undecanyl ketone and dimethyl(phenyl)silylmethylene malonate by a silicon controlled diastereoselective ketone reduction, lactonization, and deethoxycarbonylation. The dideuterated silylated tetrahydropyran‐2‐one is the precursor for geminal ²H₂‐labeled (+)‐4‐hydroxy‐6‐undecyl‐tetrahydropyran‐2‐one, an advanced intermediate for gem‐dideutero (–)‐tetrahydrolipstatin and (+)‐δ‐hexadecanolide syntheses.     

A gram‐scale synthesis of [3,4‐13C2,1α,7‐2H2]cortisone

A gram‐scale synthesis of [3,4‐¹³C₂,1α,7‐²H₂]cortisone from prednisone was developed. The deuterium atom at the C‐1 position was introduced through a regioselective and stereoselective deuteration of the 1,2‐double bond of the 1,4‐diene‐3‐one using Wilkinson's catalyst. After the oxidative cleavage of the A‐ring, two carbon‐13 atoms were introduced via acetylation of an A‐ring enol lactone with [1,2‐¹³C₂]acetyl chloride. The steroidal A‐ring was then reconstructed to incorporate the carbon‐13 atoms into the C‐3 and C‐4 positions. The deuterium atom at C‐7 was introduced through a regioselective deuteration of the 6,7‐double bond of a 4,6‐diene‐3‐one intermediate using palladium on strontium carbonate. The M + 4 stable isotope labeled cortisone was thus prepared in ca. 4% overall yield. In addition, [3,4‐¹³C₂,1α,7‐²H₂]‐11‐dehydrocorticosterone, [3,4‐¹³C₂,1α,7‐²H₂]cortisol, and [3,4‐¹³C₂,1α,7‐²H₂]corticosterone were also prepared. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigations into the regioselective C‐deuteriation of enolates using a diisopropylammonium salt

Results are reported on the regioselective C‐deuteriation of 2‐methyl tetralone using a series of diisopropylamine derived D‐sources. The results presented further aid the understanding of kinetic deuteriation of both ‘base‐containing’ and ‘base‐free’ enolates. Copyright © 2002 John Wiley & Sons, Ltd.     

Acetyl cedrene and its follower. An Isotopic,NMR and MS Structure elucidation and deuteriation study

Acetylation of cedarwood oil (Virginia) leads besides acetyl cedrene also to a minor product, 1,7,7‐trimethyl‐2,3‐(3′,4′‐dimethylbenzo)bicyclo[3.2.1]octane (follower). This product is identified by 2D NMR. Acetylation of cedarwood oil with ¹³C‐1 labeled acetic acid anhydride leads to a product labeled at the aromatic carbon C‐3′. From the ¹³C‐labeled compound ¹³C‐¹³C coupling constants could be measured. Acetyl cedrene is conveniently deuteriated by an acid‐catalysed exchange reaction using trifluoroacetic anhydride and D₂O. The product is found to be deuteriated both at the acetyl group and at the methyl group at the double bond (carbon 6). The reaction condition during deuteriation of cedrol leads to the elimination of the hydroxyl group at C‐6 with the formation of α ‐cedrene deuteriated at H‐5 and the methyl group at C‐6. Deuteriation of the follower leads to deuterium exchange at the aromatic carbons C‐5′ and C‐6′. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of deuterated dihydrochalcones

The dihydrochalcones phloretin and phloridzin are major phenolic constituents of apple fruit. Phloretin‐d₄, deuterated at both the α and β positions, was prepared by hydrogenolysis of naringenin and by deuterium exchange from unlabelled phloretin using Pd/C and sodium formate with methanol‐d₁ as the source of deuterium. Deuterated derivatives of the glycosides, phloridzin and naringin dihydrochalcone, were similarly prepared. Copyright © 2006 John Wiley & Sons, Ltd.     

NMR analysis of t‐butyl‐catalyzed deuterium exchange at unactivated arene localities

Regioselective labelling of arene rings via electrophilic exchange is often dictated by the electronic environment caused by substituents present on the aromatic system. Previously, we observed the presence of a t‐butyl group, either covalently bond or added as an external reagent, could impart deuterium exchange to the unactivated, C1‐position of estrone. Here, we provide nuclear magnetic resonance analysis of this exchange in a solvent system composed of 50:50 trifluoroacetic acid and D₂O with either 2‐t‐butylestrone or estrone in the presence of t‐butyl alcohol has shed insights into the mechanism of this t‐butyl‐catalyzed exchange. Fast exchange of the t‐butyl group concurrent with the gradual reduction of the H1 proton signal in both systems suggest a mechanism involving ipso attack of the t‐butyl position by deuterium. The reversible addition/elimination of the t‐butyl group activates the H1 proton towards exchange by a mechanism of t‐butyl incorporation, H1 activation and exchange, followed by eventual t‐butyl elimination. Density functional calculations are consistent with the observation of fast t‐butyl exchange concurrent with slower H1 exchange. The σ‐complex resulting from ipso attack of deuterium at the t‐butyl carbon was 6.6 kcal/mol lower in energy than that of the σ‐complex resulting from deuterium attack at C1. A better understanding of the t‐butyl‐catalyzed exchange could help in the design of labelling recipes for other phenolic metabolites.     

Syntheses of [2H3, 15N], [14C]Nexavar™ and its labeled metabolites

Nexavar?, Sorafenib tosylate (BAY 43‐9006 tosylate) is a potent small molecule Raf kinase inhibitor for the treatment of hyperproliferative disorders such as cancer. Both radiolabeled and stable isotope labeled compounds were required for drug absorption, distribution, metabolism and excretion (ADME) and quantitative mass spectrometry bio‐analytical studies. Nexavar? labeled with carbon‐14 in the carboxamide group was prepared in two steps in an overall radiochemical yield of 42% starting from 4‐chloro‐N‐methyl‐2‐pyridine‐[¹⁴C]carboxamide. The [²H₃,¹⁵N] version of Nexavar? was prepared in 75% yield based on 4‐chloro‐N‐[²H₃]methyl‐2‐pyridine‐[¹⁵N]carboxamide. The pyridine N‐oxide metabolite labeled with carbon‐14 as well as with deuterium and nitrogen‐15 and was synthesized by oxidation in yields of 59% and 87%, respectively. Starting from [²H₂, ¹³C]formaldehyde the N‐hydroxymethyl metabolite was labeled with carbon‐13 and deuterium in one step in a 45% overall yield. Copyright © 2006 John Wiley & Sons, Ltd.     

A two‐step synthesis of deuterium labeled 8, 8, 9, 9‐d4‐hexadecane from nonanoic acid

Labeled compounds are essential in elucidating metabolic mechanisms and reaction pathways. A two‐step synthesis of deuterium‐labeled 8, 8, 9, 9‐d₄‐hexadecane from nonanoic acid is described here. The synthesis procedures involved hydrogen–deuterium exchange of nonanoic acid with 3.00 m DCl‐D₂O and then Kolbe electrolysis of the deuterated nonanoic acid to achieve the desired n‐alkane that was confirmed by gas chromatography‐mass spectrometry and ¹H nuclear magnetic resonance. This method might provide an alternative route for the preparation of specifically deuterated alkanes of different chain lengths (C > 4) in which deuterium atoms are located at two adjacent carbons of the alkane's carbon chain. Copyright © 2012 John Wiley & Sons, Ltd.     

Uncatalyzed microwave deuterium exchange labeling of bleomycin A2

Bleomycin sulfate in D₂O was deuterated using microwave irradiation under catalyst free conditions. Following the removal of labile deuterium and purification, bleomycin A₂ with mass M + 1 to M + 7 was obtained. Successful selective uncatalyzed microwave deuterium exchange reactions on examples from the following classes of heterocycles are also described: imidazole, thiazole, indole, purine, and quinazoline. The described method was used as a test for non‐labile active protons. Copyright © 2004 John Wiley & Sons, Ltd.     

Combining microwave‐enhanced deuteriation reactions with parallel synthesis procedures

The development of combined microwave‐enhanced/parallel synthesis procedures and their application to the deuteriation of organic compounds via examples of solid‐state hydrogenation is reported. Other labelling procedures, such as solution state catalytic dehalogenations, hydrogenations as well as hydrogen isotope exchange reactions also benefit from the combined technology. Copyright © 2003 John Wiley & Sons, Ltd.     

Proton exchange reactions in isotope chemistry (I)

Direct H–D exchange reactions were applied to the preparations of stable isotope‐labeled TKI258 and two TKI258 metabolites. Each compound was made in one single H–D exchange reaction with excellent isotope incorporation. The number of deuterium incorporation and deuterium distribution in the molecules was similar in all three compounds. Stable isotope‐labeled TKI258 was also prepared from d₈‐methylpiperazine in a multistep synthesis.     

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.     

Unusual base‐catalyzed exchange in the synthesis of deuterated PF‐2413873a

The preparation of deuterated PF‐2413873 (4‐[3‐cyclopropyl‐1‐(methanesulfonylmethyl)‐5‐methyl‐1H‐pyrazol‐4‐yl]oxy‐2,6‐dimethylbenzonitrile, 1) is described for use as a bioanalytical standard in clinical trials. Two strategies were investigated. The sulfone‐containing substituent was labelled by base‐catalyzed exchange, but unacceptable deuterium loss was noted under assay conditions. Alternatively, labelling 4‐cyano‐3,5‐dimethylphenol was achieved by heating with deuterium oxide over platinum oxide. After building up the pyrazole ring we discovered that, during the subsequent alkylation to attach the methylthiomethyl group, the base, potassium t‐butoxide, caused unwanted scrambling of deuteriums on the aromatic portion and the methylthiomethyl group. Thus, it was necessary to remove all base‐labile hydrogens to prevent their exchange. This was accomplished by alkylating the pyrazole with per‐deuterated chloromethyl methylsulfide, oxidation to the sulfone, and selective removal of its deuteriums by treatment with sodium hydroxide. The unusual sensitivity and selectivity of these base‐promoted exchange reactions are discussed. Thus, 4‐[3‐cyclopropyl‐1‐(methanesulfonylmethyl)‐5‐methyl‐1H‐pyrazol‐4‐yl]oxy‐[²H₆]2,6‐dimethyl‐[3,5‐²H]benzonitrile (17) was obtained, labelled with eight deuterium atoms and an acceptable D₀/D₈ ratio. Copyright © 2009 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.     

Synthesis of deuterium‐labelled 5′‐O‐[N‐(Salicyl)sulfamoyl]adenosine (Sal‐AMS‐d4) as an internal standard for quantitation of Sal‐AMS

5′‐O‐[N‐(Salicyl)sulfamoyl]adenosine (Sal‐AMS, 1) is a potent inhibitor of the bifunctional enzyme salicyl‐AMP ligase in Mycobacterium tuberculosis. This inhibitor acts by disrupting the biosynthesis of the mycobactin siderophores that are essential for the process of iron acquisition. To aid with in vitro metabolism and in vivo pharmacokinetic studies of Sal‐AMS, a stable deuterium‐labelled Sal‐AMS analog (Sal‐AMS‐d₄) was synthesized. This deuterium‐labelled analog was used as an internal standard to conduct in vitro plasma and microsomal stability studies. Sal‐AMS was found to be stable for 24 h in human plasma and 1 h in human liver microsomes at 37°C. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of deuterium‐labelled amlexanox and its metabolic stability against mouse,rat, and human microsomes

As part of a program toward making analogues of amlexanox ( 1 ), currently under clinical investigation for the treatment of type 2 diabetes and obesity, we have synthesized derivative 5 in which deuterium has been introduced into two sites of metabolism on the C‐7 isopropyl function of amlexanox. The synthesis of 5 was completed in an efficient three‐step process utilizing reduction of key olefin 7b to 8 by Wilkinson's catalyst to provide specific incorporation of di‐deuterium across the double bond. Compound 5 displayed nearly equivalent potency to amlexanox (IC₅₀, 1.1μM vs 0.6μM, respectively) against recombinant human TBK1. When incubated with human, rat, and mouse liver microsomes, amlexanox ( 1 ) and d₂‐amlexanox ( 5 ) were stable (t_1/2 > 60 minutes) with 1 showing marginally greater stability relative to 5 except for rat liver microsomes. These data show that incorporating deuterium into two sites of metabolism does not majorly suppress Cyp‐mediated metabolism relative to amlexanox.