Deuterium isotope effects on drug pharmacokinetics. I. System-dependent effects of specific deuteration with aldehyde oxidase cleared drugs

The pharmacokinetic properties of drugs may be altered by kinetic deuterium isotope effects. With specifically deuterated model substrates and drugs metabolized by aldehyde oxidase, we demonstrate how knowledge of the enzyme's reaction mechanism, species differences in the role played by other enzymes in a drug's metabolic clearance, and differences in systemic clearance mechanisms are critically important for the pharmacokinetic application of deuterium isotope effects. Ex vivo methods to project the in vivo outcome using deuterated carbazeran and zoniporide with hepatic systems demonstrate the importance of establishing the extent to which other metabolic enzymes contribute to the metabolic clearance mechanism. Differences in pharmacokinetic outcomes in guinea pig and rat, with the same metabolic clearance mechanism, show how species differences in the systemic clearance mechanism can affect the in vivo outcome. Overall, to gain from the application of deuteration as a strategy to alter drug pharmacokinetics, these studies demonstrate the importance of understanding the systemic clearance mechanism and knowing the identity of the metabolic enzymes involved, the extent to which they contribute to metabolic clearance, and the extent to which metabolism contributes to the systemic clearance.     

Stereoselective synthesis of L‐[2,3,4,5‐D4] ornithine

Synthesis of L ‐[2,3,4,5‐D₄]ornithine in which all of the diastereotopic hydrogens were stereoselectively labeled with deuterium was investigated. The chirally deuterated 3‐aminopropanal derivative, a key intermediate in this synthesis, was prepared by a catalytic deuteration of an unsaturated γ‐lactone derived for L ‐glutamic acid followed by several functional group interconversions. Condensation of the obtained deuterium‐labeled 3‐aminopropanal derivative with a chiral glycine template afforded unsaturated ornithine. The dehydroornithine was then subjected to a catalytic deuteration followed by deprotection to give the L ‐[2,3,4,5‐D₄]ornithine. Copyright © 2002 John Wiley & Sons, Ltd.     

Deuterated drugs: where are we now?

Introduction: Deuterated versions of existing drugs can exhibit improved pharmacokinetic or toxicological properties due the stronger deuterium– carbon bond modifying their metabolism. There is great interest in the current state of development of this approach.

Areas covered: This review covers recent US patent applications and prosecutions in this area that are based on beneficial modifications in metabolism of deuterated versions of existing drugs. The current state of 35 U.S.C. §103 ‘obviousness’ rejections are emphasized, as is the development of strategies to overcome such rejections. Current trials and market considerations are also discussed.

Expert opinion: Deuterated drugs collectively are worth at least US$1 billion. It would seem that the likelihood of obviousness rejections is increasing in this area. However, careful elucidation of metabolic outcomes from deuteration that would not be anticipated from the prior art, and are instead unexpected and unobvious, has enabled allowance. Showing that drug deuteration alters pharmacokinetics by mechanisms not currently part of the prior art surrounding deuterated drugs has also been successful. Development of these and other strategies, combined with developing the extensive base of issued patents will enable the field to remain commercially attractive for some time.     

A simple method for α‐position deuterated carbonyl compounds with pyrrolidine as catalyst

A simple, cost‐effective method for deuteration of carbonyl compounds employing pyrrolidine as catalyst and D₂O as deuterium source was described. High degree of deuterium incorporation (up to 99%) and extensive functional group tolerance were achieved. It is the first time that secondary amines are used as catalysts for H/D exchange of carbonyl compounds, which also allow the deuteration of complex pharmaceutically interesting substrates. A possible catalytic mechanism, based on the hydrolysis of 1‐pyrrolidino‐1‐cyclohexene, for this pyrrolidine‐catalyzed H/D exchange reaction has been proposed.     

Convenient and efficient deuteration of functionalized aromatics with deuterium oxide: catalysis by cycloocta‐1,5‐dienyliridium(I) 1,3‐dionates

Aromatic compounds bearing an ortho‐directing substituent may be deuterated by exchange with deuterium oxide in the presence of a range of cycloocta‐1,5‐dienyliridium(I)1,3‐dionate catalysts. The exchange takes place in several dipolar aprotic solvents and is directly applicable to the deuteration of polar compounds. Isotope incorporation is efficient and regiospecific. The method is applicable to a wide range of ortho‐directing groups some of which are only weak directors for alternative ortho‐labelling approaches. In addition, the application of microwaves enables labelling within minutes even with sub‐stituents which are poor directors. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of chronic deuterated and non-deuterated phenelzine on rat brain monoamines and monoamine oxidase

Summary The effects of phenelzine and 1,1-dideuterophenelzine (0.5 or 2.5 mg/kg/day) administered s.c. via miniosmotic pumps for 13 days were compared. Striatal levels of p-tryrosine and tryptophan were unaffected by either treatment. The concentrations of DOPAC, HVA and 5-HIAA were dose-dependently decreased by phenelzine and deuterated phenelzine; furthermore, the deuterated compound decreased the amounts of these acids more than the same dose of phenelzine. Dopamine levels were increased by a rather small amount by all drug treatments; no effects of drug dose or drug type (deuterated or nondeuterated) were observed. With the exception of phenylethylamine, qualitatively similar effects were found with all other amines measured; their amounts were increased dose-dependently and the effects of deuterated phenelzine were greater than those of phenelzine. Rat cerebral MAO activity was inhibited dose-dependently by phenelzine and by deuterated phenelzine. Type A MAO was inhibited more than type B, and deuterated phenelzine inhibited both types more than did phenelzine. The present study shows that the efficacy of phenelzine was increased about 5-fold by deuteration, that deuterated phenelzine increased tryptamine, m-tyramine and p-tyramine levels much more than it did the other monoamines, that phenylethylamine levels were least affected by the drug treatments, and that deuterated phenelzine inhibited MAO more than did phenelzine.Abbreviations D deuterium - DOPAC 3,4-dihydroxyphenylacetic acid - 5HIAA 5-hydroxyindole acetic acid - HVA homovanillic acid - MAO monoamine oxidase - 3MT 3-methoxytyramine - 5-HT 5-hydroxytryptamine Send offprint requests to L. E. Dyck     

Highly selective catalytic transfer hydrodeuteration of cyclic alkenes

Selective deuterium installation into small molecules is becoming increasingly desirable not only for the elucidation of mechanistic pathways and studying biological processes but also because of deuterium's ability to favorably adjust the pharmacokinetic parameters of bioactive molecules. Fused bicyclic moieties, especially those containing heteroatoms, are prevalent in drug discovery and pharmaceuticals. Herein, we report a copper-catalyzed transfer hydrodeuteration of cyclic and heterocyclic alkenes, which enables the synthesis of chromans, quinolinones, and tetrahydronaphthalenes that are precisely deuterated at the benzylic position. We also demonstrate the ability to place one deuterium atom at the homobenzylic site of these scaffolds with high regioselectivity by swapping transfer reagents for their isotopic analogs. Furthermore, examples of chemoselective transfer hydrogenation and transfer deuteration are disclosed, allowing for the simultaneous incorporation of two vicinal hydrogen or deuterium atoms into a double bond.     

Benzylic deuteration of alkylnitroaromatics via amine-base catalysed exchange with deuterium oxide

This paper describes the deuterium-labelling of alkylnitroaromatics by base-catalysed exchange with deuterium oxide. As the alkyl protons alpha to the aromatic ring are the most acidic sites in the molecule, regioselective hydrogen isotope exchange at this benzylic location leads to a regiospecifically deuterated product. The exchange labelling takes place in good yields and with high atom% abundance in the presence of an appropriate nitrogen base. Alkylated 2,4-dinitrobenzenes deuterate at room temperature under catalysis by triethylamine, whilst alkylated 2-nitro- or 4-nitrobenzenes and related mono-nitroaromatics require higher temperatures and catalysis by 1,5-diazobicyclo[4.3.0]non-5-ene (DBN). The labelling reactions require an inert gas atmosphere, but otherwise are simple and high yielding with no obvious byproducts. Those compounds in which the benzylic protons are in an ortho-orientation with respect to the nitro group label somewhat more slowly than the analogues where there is a para relationship. In addition, higher alkyl homologues undergo benzylic deuteration at slower rates than methyl.     

Deuterium substitution enhances the effects of β-phenylethylamine on spontaneous motor activity in the rat

The effects of β-phenylethylamine (PEA) and α,α,β,β-tetradeutero-β-phenylethylamine (deuterated PEA) on spontaneous motor activity and conditioned taste aversion learning in the rat were examined. The intensity and duration of certain behavioural components elicited by PEA, namely, sniffing, headweaving, splayed hindlimbs and hyperreactivity, were significantly increased by deuterium substitution. In contrast, deuteration had no effect on the ability of PEA to elicit a conditioned taste aversion. The potentiation of the amine's effects on activity seemed to be directly related to the longer persistence of PEA in the brain due to the kinetic isotope effect since it appears that tetra-deuterated PEA is a poorer substrate for monoamine oxidase than the protonated amine.     

Synthesis of side chain specifically deuterated (−)‐Δ9‐tetrahydrocannabinols

(?)‐Δ⁹‐Tetrahydrocannabinols specifically deuterated at the n‐pentyl side chain were prepared using the corresponding resorcinols as key intermediates. To obtain the deuterated resorcinols we developed conditions under which no deuterium scrambling or loss was observed. The methodology allows for the preparative scale synthesis of deuterated resorcinols and corresponding (?)‐Δ⁹‐tetrahydrocannabinols. Copyright © 2002 John Wiley & Sons, Ltd.     

Iridium‐mediated β‐deuteration of enones

Exposure of captodative enone systems to deuterium in the presence of Crabtree's catalyst ( 1 ) results in deuteration at the vinylic site β‐ to the ketone carbonyl, as well as at any accessible ortho‐position. β‐exchange is also observed during the reduction of ethyl cinnamate ( 3 ) catalyzed by 1 . Copyright © 2003 John Wiley & Sons, Ltd.     

Deuterium isotope effect on the metabolism of N-nitrosodimethylamine and related compounds by cytochrome P4502E1.

1. Deuteration of N-nitrosodimethylamine (NDMA) decreases its carcinogenicity, and produces an isotope effect on its metabolism in vivo. Consistent with these results are the observations that deuteration caused a 5-fold increase in the apparent Km, but not the Vmax for the demethylation and denitrozation of NDMA in acetone-induced rat liver microsomes. These microsomes are a good source of cytochrome P4502E1. 2. For demethylation of Z-[2H3]NDMA and E-[2H3]NDMA, the Km values were indistinguishable, and were between the values for those of NDMA and [2H6]NDMA. Almost all the formaldehyde formed was derived from the non-deuterated methyl group, indicating a lack of stereoselectivity in the demethylation of NDMA. 3. NDMA and [2H6]NDMA displayed apparent Ki values of 59 and 441 microM, respectively, for N-nitrosodiethylamine deethylase, showing an apparent isotope effect of 0.13, and displayed an isotope effect of 0.21 in the Ki values for p-nitrophenol hydroxylase. 4. With acetone and deuterated acetone as inhibitors for p-nitrophenol hydroxylase, the isotope effect on the Ki was 0.11. Similar deuterium isotope effects were also observed with acetone and dimethylformamide as competitive inhibitors for NDMA demethylase. 5. In the microsomal oxidation of ethanol, a deuterium isotope effect of about five was observed in the Vmax/Km when carbon-1 was deuterated, but was not observed in the Vmax. 6. Results illustrate a unique deuterium isotope effect on the Km values of reactions catalysed by P4502E1.     

Deuterium isotope effect on the metabolism of N-nitrosodimethylamine and related compounds by cytochrome P4502E1

1. Deuteration of N-nitrosodimethylamine (NDMA) decreases its carcinogenicity, and produces an isotope effect on its metabolism in vivo. Consistent with these results are the observations that deuteration caused a 5-fold increase in the apparent K_m, but not the V_max the demethylation and denitrozation of NDMA in acetone-induced rat liver microsomes. These microsomes are a good source of cytochrome P4502E1.

2. For demethylation of Z-[²H₃]NDMA and E-[²H₃)NDMA, the K_m values were indistinguishable, and were between the values for those of NDMA and [²H₆]NDMA. Almost all the formaldehyde formed was derived from the non-deuterated methyl group. indicating a lack of stereoselectivity in the demethylation of NDMA.

3. NDMA and [²H₆]NDMA displayed apparent K_i values of 59 and 441 μM, respectively, for N-nitrosodiethylamine deethylase, showing an apparent isotope effect of 0.13, and displayed an isotope effect of 0.21 in the K_i values for p-nitrophenol hydroxylase.

4. With acetone and deuterated acetone as inhibitors for p-nitrophenol hydroxylase, the isotope effect on the K_i was 0.11. Similar deuterium isotope effects were also observed with acetone and dimethylformamide as competitive inhibitors for NDMA demethylase.

5. In the microsomal oxidation of ethanol, a deuterium isotope effect of about five was observed in the V_max/K_m when carbon-1 was deuterated, but was not observed in the V_max.

6. Results illustrate a unique deuterium isotope effect on the K_m values of reactions catalysed by P4502E1.     

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.     

Practical approaches to labelling terminal alkynes with deuterium

Base catalysed exchange with sodium hydroxide, calcium oxide or N,N,N,N-tetramethylguanidine in deuterium oxide is a viable procedure for the preparation of terminally deuterated alkynes for those alkynes stable to strong base. The use of silver perchlorate as a catalyst is an alternative practical option when labelling alkynes which are sensitive to base or contain functionalities which would lead to labelling elsewhere in the molecule. Labelling with this catalyst takes place smoothly at ambient temperature in a mixture of N,N-dimethylformamide and deuterium oxide.     

Synthesis of ceramides NS and NP with perdeuterated and specifically ω deuterated N‐acyl residues

The synthesis of 12 deuterated ceramides with either a deuteration at the last carbon atom of the amide bound fatty acid or a perdeuterated fatty acid chain is described. The ceramides were prepared starting from sphingosine or phytosphingosine and ω deuterated or perdeuterated fatty acids with PyBOP® as activating agent in high yields. For the synthesis of the specifically deuterated fatty acids, dicarboxylic acids were transformed into ω deuterated alkyl bromide, which was chain elongated with blocked ω bromo alcohols by copper catalyzed Grignard coupling. Oxidation of regenerated alcohol function yields the ω deuterated fatty acids.     

Deuterium substitution enhances the effects of beta-phenylethylamine on spontaneous motor activity in the rat

The effects of beta-phenylethylamine (PEA) and alpha, alpha, beta, beta-tetradeutero-beta-phenylethylamine (deuterated PEA) on spontaneous motor activity and conditioned taste aversion learning in the rat were examined. The intensity and duration of certain behavioural components elicited by PEA, namely, sniffing, headweaving, splayed hindlimbs and hyperreactivity, were significantly increased by deuterium substitution. In contrast, deuteration had no effect on the ability of PEA to elicit a conditioned taste aversion. The potentiation of the amine's effects on activity seemed to be directly related to the longer persistence of PEA in the brain due to the kinetic isotope effect since it appears that tetra-deuterated PEA is a poorer substrate for monoamine oxidase than the protonated amine.     

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.     

Detection and mechanism of formation of the potent direct-acting mutagen 2-bromoacrolein from 1,2-dibromo-3-chloropropane

The nematocide 1,2-dibromo-3-chloropropane (DBCP) was converted to products which are mutagenic for Salmonella typhimurium TA 100 in the presence of rat liver microsomes, NADPH, and oxygen. Typical in vivo and in vitro inhibitors of cytochrome P-450 decreased DBCP mutagenicity in the presence of microsomes. Addition of glutathione to cytosolic preparations failed to bioactivate DBCP to mutagenic metabolites. Mutagenicity studies with selectively deuterated analogs showed that substitution of deuterium for hydrogen at C-1 or C-3 of DBCP modestly decreased mutagenicity, but that deuteration at both C-1 and C-3 markedly decreased mutagenicity. The formation rates of the potent direct-acting mutagen, 2-bromoacrolein (2-BA), in incubations of DBCP and its deuterated analogs with rat liver microsomes, correlated with the isotope effects on mutagenicity. Characterization of 2-BA was accomplished by gas chromatography-mass spectrometry using positive-ion chemical ionization. Mass spectral analysis of 2-BA formed from specifically deuterated analogs of DBCP indicated that initial oxidative dehalogenation at C-1 followed by a spontaneous beta-elimination reaction was the preferred pathway in the formation of 2-BA from DBCP. These results demonstrate that mutagenic metabolites of DBCP are formed by cytochrome P-450-mediated oxidative metabolism, and that 2-BA is a major mutagen formed.     

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.