Synopsis of Some Recent Tactical Application of Bioisosteres in Drug Design

Vinyl azides in organic synthesis: an overview

Among organic azides, vinyl azides have attracted significant attention, because of their unique properties in organic synthesis, which led to reports of many types of research on this versatile conjugated azide in recent years. This magical precursor can also be converted into intermediates such as iminyl radicals, 2H-azirines, iminyl metal complexes, nitrilium ions, and iminyl ions, making this compound useful in heterocycle synthesis.

Isosteric Replacement of Ester Linkage of Lysophospholipids with Heteroaromatic Rings Retains Potency and Subtype Selectivity

Our group has reported various derivatives of lysophosphatidylserine (LysoPS) as potent and subtype-selective agonists for G-protein-coupled receptors (GPCRs). However, the ester linkage between the glycerol moiety and fatty acid or fatty acid surrogate is present in all of them. In order to develop these LysoPS analogs as drug candidates, appropriate pharmacokinetic consideration is essential. Here, we found that the ester bond of LysoPS is highly susceptible to metabolic degradation in mouse blood. Accordingly, we examined isosteric replacement of the ester linkage with heteroaromatic rings. The resulting compounds showed excellent retention of potency and receptor subtype selectivity, as well as increased metabolic stability in vitro.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Four-Component Strain-Release-Driven Synthesis of Functionalized Azetidines

Despite the favorable properties that azetidine rings can engender on drug-compounds, methods for the diversity-oriented synthesis of azetidine-based structures are significantly underdeveloped. Herein, we report the successful realization of a multicomponent [1,2]-Brook rearrangement/strain-release-driven anion relay sequence and its application to the modular synthesis of substituted azetidines. The rapidity of the reaction, as confirmed by in situ infra-red spectroscopy, leverages the strain-release ring-opening of azabicyclo[1.1.0]butane to drive the equilibrium of the Brook rearrangement. The three electrophilic coupling partners, added sequentially to azabicyclo[1.1.0]butyl-lithium, could be individually varied to access a diverse compound library. The utility of this methodology was demonstrated in a 4-step synthesis of the EP2 receptor antagonist PF-04418948.

Versatile Fluorine-Containing Building Blocks: β-CF3-1,3-enynes

The development of diversity-oriented synthesis based on fluorine-containing building blocks has been one of the hot research fields in fluorine chemistry. β-CF₃-1,3-enynes, as one type of fluorine-containing building blocks, have attracted more attention in the last few years due to their distinct reactivity. Numerous value-added trifluoromethylated or non-fluorinated compounds which have biologically relevant structural motifs, such as O-, N-, and S-heterocycles, carboncycles, fused polycycles, and multifunctionalized allenes were synthesized from these fluorine-containing building blocks. This review summarizes the most significant developments in the area of synthesis of organofluorine compounds based on β-CF₃-1,3-enynes, providing a detailed overview of the current state of the art.

Different Behavior of 2-Substituted 3-Nitro-2H-chromenes in the Reaction with Stabilized Azomethine Ylides Generated from α-Iminoesters

The AgOAc-catalysed reaction of 3-nitro-2-phenyl-2H-chromenes with stabilized azomethine ylides generated from the imines based on methyl glycinate and arylaldehydes leads to a mixture of endo and endo' isomers of the corresponding chromeno[3,4-c]pyrrolidines in a ratio of 2.0-2.3:1 in 85-93% total yields as a result of a Michael addition/Mannich reaction sequence. In a similar reaction involving 2-trifluoromethyl-3-nitro-2H-chromenes, only endo chromeno[3,4-c]pyrrolidines are formed in 85-94% yields. 3-Nitro-2-(trichloromethyl)-2H-chromenes under the same conditions react with these azomethine ylides to give the corresponding Michael adducts as individual anti-isomers with the cis,trans-configuration of the chromane ring in 40-67% yields. Some 4-CF₃-substituted chromano[3,4-c]pyrrolidines exhibited high cytotoxic activity against HeLa human cervical carcinoma cells.

Transition-metal-free radical difluorobenzylation/cyclization of unactivated alkenes: access to ArCF2-substituted ring-fused quinazolinones

A mild and efficient transition-metal-free radical difluorobenzylation/cyclization of unactivated alkenes toward the synthesis of difluorobenzylated polycyclic quinazolinone derivatives with easily accessible α,α-difluoroarylacetic acids has been developed. This transformation has the advantages of wide functional group compatibility, a broad substrate scope, and operational simplicity. This methodology provided a highly attractive access to pharmaceutically valuable ArCF₂-containing polycyclic quinazolinones.

Facile Entry to Pharmaceutically Important 3-Difluoromethyl-quinoxalin-2-ones Enabled by Visible-Light-Driven Difluoromethylation of Quinoxalin-2-ones

CF₂H moiety has a significant potential utility in drug design and discovery, and the incorporation of CF₂H into biologically active molecules represents an important and efficient strategy for seeking lead compounds and drug candidates. On the other hand, quinoxalin-2-one is of great interest to pharmaceutical chemists as a common skeleton frequently occurring in plenty of natural products and bioactive compounds. Herein, we reported a practical and efficient protocol for the synthesis of 3-CF₂H-quinoxalin-2-ones. Thus, in the presence of 3 mol% of photocatalyst and S-(difluoromethyl)sulfonium salt as difluoromethyl radical sources, a wide range of quinoxalin-2-ones readily underwent a visible-light redox-catalyzed difluoromethylation reaction, to deliver structurally diverse 3-difluoromethyl-quinoxalin-2-ones. We believe that this would facilitate increasing chances and possibilities for seeking potential lead compounds and drug candidates and further boost the development of fluorine-containing pharmaceuticals.

Gem-Difluoroallylation of Aryl Sulfonium Salts

The unprecedented photochemical late-stage defluorinative gem-difluoroallylation of aryl sulfonium salts, which are formed site-selectively by direct C(sp²)─H functionalization, is herein disclosed. This method is distinguished by its mild reaction conditions, wide scope, and excellent site-selectivity. As showcase examples, a Flurbiprofen and Pyriproxyfen derivatives could be late stage C(sp²)─H gem-difluoroallylated with high yields. Experimental and computational investigations were conducted.

Diverse reactivity of the gem-difluorovinyl iodonium salt for direct incorporation of the difluoroethylene group into N- and O-nucleophiles

The synthesis of gem-difluoroethylene compounds remains a difficult task in organic synthesis. Here, the direct difluoroethylation reactions of N- and O-nucleophiles including amides and acids were realized with a hypervalent iodine reagent: gem-difluorovinyl iodonium salt (DFVI). The reactions were accomplished via a neighbouring group rearrangement. The gem-difluorovinyl iodonium salt was found to display diverse reactivity due to its unique electronic effect and was applied to the incorporation of difluoroethylene group, including difluorovinylation of carboxylic acids, difluorovinylation and 1,3-cyclic fluorovinylation of amides and 1,1-cyclic difluoroethylation of amines.

Synthesis of β-Deuterated Amino Acids via Palladium-Catalyzed H/D Exchange

Despite several synthetic approaches that have been developed for α-deuterated amino acids, the synthesis of β-deuterated amino acids has remained a challenge. Herein, we disclose a palladium catalyzed H/D exchange protocol for a β-deuterated N-protected amino amide, which can be converted to a β-deuterated amino acid simply by removal of protecting groups. This protocol is highly efficient, simply manipulated, and appliable for deuterium-labeling of many amino amides. In addition, deuterium labeling of phenylalanine derivatives was also successful when pivalic acid served as an additive to promote the H/D exchange process.

Skeletal Ring Contractions via I(I)/I(III) Catalysis: Stereoselective Synthesis of cis-α,α-Difluorocyclopropanes

The clinical success of α,α-difluorocyclopropanes, combined with limitations in the existing synthesis portfolio, inspired the development of an operationally simple, organocatalysis-based strategy to access cis-configured derivatives with high levels of stereoselectivity (up to >20:1 cis:trans). Leveraging an I(I)/I(III)-catalysis platform in the presence of an inexpensive HF source, it has been possible to exploit disubstituted bicyclobutanes (BCBs) as masked cyclobutene equivalents for this purpose. In situ generation of this strained alkene, enabled by Brønsted acid activation, facilitates an unprecedented 4 → 3 fluorinative ring contraction, to furnish cis-α,α-difluorinated cyclopropanes in a highly stereoselective manner (up to 88% yield). Mechanistic studies are disclosed together with conformational analysis (X-ray crystallography and NMR) to validate cis-α,α-difluorocyclopropanes as isosteres of the 1,4-dicarbonyl moiety. Given the importance of this unit in biology and the foundational n_o → π* interactions that manifest themselves in this conformation (e.g., collagen), it is envisaged that the title motif will find application in focused molecular design.

Designing of kinase hinge binders: A medicinal chemistry perspective

Protein kinases are key regulators of cellular signaling and play a critical role in oncogenesis. Inhibitors of protein kinases are pursued by both industry and academia as a promising target for cancer therapy. Within the protein kinases, the ATP site has produced more than 40 FDA-approved drugs. The ATP site is broadly composed of a hinge region, gatekeeper residues, DFG-loop, ribose pocket, and other hydrophobic regions. The hinge region in the ATP site can be used for designing potent inhibitors. In this review, we discuss some representative studies that will highlight the interactions of heterocyclic compounds with hinge regions of different kinases like BRAF kinase, EGRF kinase, MAP kinase, and Mps1 kinase.

Novel 2-phenyl-4H-chromen derivatives: synthesis and anti-inflammatory activity evaluation in vitro and in vivo

It is significant to design, synthesise and optimise flavonoid derivatives with better anti-inflammatory activity. This study aims to design and synthesise a series of novel 2-phenyl-4H-chromen-4-one compounds with anti-inflammatory; among them, compound 8 was discovered as the best one. And then, the effects of compound 8 on the TLR4/MAPK signalling pathway was carried out in vivo, the results indicated that compound 8 could downregulate NO, IL-6, and TNF-α expression, and suppress LPS-induced inflammation by inhibiting the TLR4/MAPK pathways. Furthermore, compound 8 reduced inflammation by a mouse model of LPS-induced inflammatory disease in vivo. The results suggest that compound 8 has the potential against inflammation through regulating TLR4/MAPK pathway and can be assessed further for drug development.

Visible-Light-Induced C-F Bond Activation for the Difluoroalkylation of Indoles

An aryl disulfide mediated C-F bond activation of the trifluoromethyl group to generate valuable gem-difluoroalkylindoles is described. This method relies on readily available commodity reagents under mild reaction conditions and represents the first transition-metal-free redox-neutral C-F bond activation strategy. The reaction employs various substituted indoles and α-fluoro-substituted esters. Further, this mode of C-F activation was also amenable to the activation of trifluoromethylated arenes for the preparation of bis-benzylic gem-difluoromethylenes between indole and arene substructures, providing access to a unique chemical space.

Electrochemical Synthesis of gem-Difluoro- and γ-Fluoro-Allyl Boronates and Silanes

The electrochemical synthesis of fluorinated allyl silanes and boronates was disclosed. The addition of electrogenerated boryl or silyl radicals onto many α-trifluoromethyl or α-difluoromethylstyrenes in an undivided cell allowed the formation of a large panel of synthetically useful gem-difluoro and γ-fluoroallyl boronates and silanes (64 examples, from 31 % to 95 % yield). In addition, a scale up of the reactions under continuous flow was showcased using an electrochemical reactor with promising volumetric productivity (688 g.L-1 .h-1 and 496 g.L-1 .h-1 ). Moreover, the synthetic utility of these building blocks was highlighted through versatile transformations. Finally, plausible reaction mechanisms were suggested to explain the formation of the products.

Computational study of nitro-benzylidene phenazine as dengue virus-2 NS2B-NS3 protease inhibitor

According to the World Health Organisation (WHO), as of week 23 of 2022, there were more than 1,311 cases of dengue in Malaysia, with 13 deaths reported. Furthermore, there was an increase of 65.7% during the same period in 2021. Despite the increase in cumulative dengue incidence, there is no effective antiviral drug available for dengue treatment. This work aimed to evaluate several nitro-benzylidene phenazine compounds, especially those that contain 4-hydroxy-3,5-bis((2-(4-nitrophenyl)hydrazinylidene)-methyl)benzoate through pharmacophore queries selection method as potential dengue virus 2 (DENV2) NS2B-NS3 protease inhibitors. Herein, molecular docking was employed to correlate the energies of selected hits' free binding and their binding affinities. Pan assay interference compounds (PAINS) filter was also adopted to identify and assess the drug-likeness, toxicity, mutagenicity potentials, and pharmacokinetic profiles to select hit compounds that can be considered as lead DENV2 NS2B-NS3 protease inhibitors. Molecular dynamics assessment of two nitro-benzylidene phenazine derivatives bearing dinitro and hydroxy groups at the benzylidene ring showed their stability at the main binding pocket of DENV2 protease, where their MM-PBSA binding energies were between -22.53 and -17.01 kcal/mol. This work reports those two nitro-benzylidene phenazine derivatives as hits with 52-55% efficiency as antiviral candidates. Therefore, further optimisation is required to minimise the lead compounds' toxicity and mutagenicity.

Palladium Hydride-Enabled Hydroalkenylation of Strained Molecules

We report the first palladium hydride enabled hydroalkenylation of strained molecules. This new mild protocol proceeds via a regio- and chemoselective hydropalladation step, followed by a photoinduced radical alkyl Heck reaction. This methodology represents a new reactivity mode for strained molecules and opens new avenues for photoinduced palladium catalysis. The reaction is compatible with a wide range of functional groups and can be applied to complex structures, delivering a diverse array of highly valuable and modifiable alkenylated cyclobutanes and cyclopropanes. A hydroalkenylation/diastereoselective rearrangement cascade toward a cyclopentene scaffold has also been demonstrated.

Sulfenofunctionalization of Chiral α-Trifluoromethyl Allylboronic Acids: Asymmetric Synthesis of SCF3 , SCF2 R, SCN and SAr Compounds

We report herein a new method for the synthesis of densely functionalized chiral allyl SCF3 , SCF2 R, SCN and SAr species with a separate CF3 functionality. The synthetic approach is based on selenium-catalyzed sulfenofunctionalization of chiral α-CF3 allylboronic acids. The reactions proceeded with remarkably high stereo-, diastereo- and site-selectivity, based on the formation of a stable thiiranium ion followed by rapid deborylative ring opening.

Synthesis and Antimicrobial Activity of Sulfenimines Based on Pinane Hydroxythiols

The widespread presence of multidrug-resistant pathogenic microorganisms challenges the development of novel chemotype antimicrobials, insensitive to microbial tools of resistance. To date, various monoterpenoids have been shown as potential antimicrobials. Among many classes of molecules with antimicrobial activity, terpenes and terpenoids are an attractive basis for the design of antimicrobials because of their low toxicity and availability for various modifications. In this work, we report on the synthesis of sulfenimines from chiral trifluoromethylated and non-fluorinated pinane-type thiols. Final compounds were obtained with yields of up to 81%. Among the 13 sulfenimines obtained, 3 compounds were able to repress the growth of both bacteria (S. aureus, both MSSA and MRSA; P. aeruginosa) and fungi (C. albicans) with an MIC of 8-32 µg/mL. Although compounds exhibited relatively high cytotoxicity (the therapeutic index of 3), their chemotype can be used as a starter point for the development of disinfectants and antiseptics for targeting multidrug-resistant pathogens.

Advances in nonclassical phenyl bioisosteres for drug structural optimization

The phenyl group is the most prevalent ring system and plays an essential role as a pharmacophore or scaffold in marketed drugs. However, the indiscriminate employment of phenyl is also a major cause of poor physicochemical properties of active molecules. Nonclassical phenyl bioisosteres (NPBs) have emerged as effective replacements for phenyl in structural optimization due to their unique steric structures and physicochemical properties. Herein, the effects of widely reported NPBs on physicochemical properties and biological activities, including bicyclo[1.1.1]pentane (BCP), bicyclo[2.1.1]hexanes (BCH), bicyclo[2.2.2]octane (BCO), cubane (CUB) and closo-carboborane, are reviewed. Issues that require consideration while using NPBs and practical solutions to problems frequently encountered in structural optimization using NPBs are also discussed.

Aldehyde oxidase mediated drug metabolism: an underpredicted obstacle in drug discovery and development

Aldehyde oxidase (AO) has garnered curiosity as a non-CYP metabolizing enzyme in drug development due to unexpected consequences such as toxic metabolite generation and high metabolic clearance resulting in the clinical failure of new drugs. Therefore, poor AO mediated clearance prediction in preclinical nonhuman species remains a significant obstacle in developing novel drugs. Various isoforms of AO, such as AOX1, AOX3, AOX3L1, and AOX4 exist across species, and different AO activity among humans influences the AO mediated drug metabolism. Therefore, carefully considering the unique challenges is essential in developing successful AO substrate drugs. The in vitro to in vivo extrapolation underpredicts AO mediated drug clearance due to the lack of reliable representative animal models, substrate-specific activity, and the discrepancy between absolute concentration and activity. An in vitro tool to extrapolate in vivo clearance using a yard-stick approach is provided to address the underprediction of AO mediated drug clearance. This approach uses a range of well-known AO drug substrates as calibrators for qualitative scaling new drugs into low, medium, or high clearance category drugs. So far, in vivo investigations on chimeric mice with humanized livers (humanized mice) have predicted AO mediated metabolism to the best extent. This review addresses the critical aspects of the drug discovery stage for AO metabolism studies, challenges faced in drug development, approaches to tackle AO mediated drug clearance's underprediction, and strategies to decrease the AO metabolism of drugs.

Structure-Uptake Relationship Studies of Oxazolidinones in Gram-Negative ESKAPE Pathogens

The clinical success of linezolid for treating Gram-positive infections paired with the high conservation of bacterial ribosomes predicts that if oxazolidinones were engineered to accumulate in Gram-negative bacteria, then this pharmacological class would find broad utility in eradicating infections. Here, we report an investigative study of a strategically designed library of oxazolidinones to determine the effects of molecular structure on accumulation and biological activity. Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa strains with varying degrees of compromise (in efflux and outer membrane) were used to identify motifs that hinder permeation across the outer membrane and/or enhance efflux susceptibility broadly and specifically between species. The results illustrate that small changes in molecular structure are enough to overcome the efflux and/or permeation issues of this scaffold. Three oxazolidinone analogues (3e, 8d, and 8o) were identified that exhibit activity against all three pathogens assessed, a biological profile not observed for linezolid.

Copper-Catalyzed Reaction of 2,3-Allenols with Silylzinc Reagents: Access to 2-Silyl-1,3-butadienes

Reaction of 2,3-allenols with PhMe₂SiZnCl or Ph₂MeSiZnCl under catalysis of IPrCuCl or SIPrCuCl was carried out, affording 2-silyl-1,3-butadienes. Secondary and tertiary 2,3-allenols could be used as coupling partners. Reaction of secondary 2,3-allenols gave (E)-2-silyl-1,3-butadienes as the only products.

Synthesis of Trifluoromethylated Monoterpene Amino Alcohols

For the first time, monoterpene trifluoromethylated β-hydroxy-benzyl-O-oximes were synthesized in 81–95% yields by nucleophilic addition of the Ruppert–Prakash reagent (TMSCF3) to the corresponding β-keto-benzyl-O-oximes based on (+)-nopinone, (−)-verbanone and (+)-camphoroquinone. Trifluoromethylation has been determined to entirely proceed chemo- and stereoselective at the C=O rather than C=N bond. Trifluoromethylated benzyl-O-oximes were reduced to the corresponding α-trifluoromethyl-β-amino alcohols in 82–88% yields. The structure and configuration of the compounds obtained have been established.

Cu-Catalyzed Switchable Asymmetric Defluoroalkylation and [3 + 2] Cycloaddition of Trifluoropropene

Chiral fluorinated amino esters and pyrrolidines are privileged scaffolds in synthetic chemistry and exhibit unique biological properties. We report the facile preparation of these compounds through copper-catalyzed switchable defluoroalkylation and [3 + 2] cycloaddition of trifluoropropene in an asymmetric fashion. The choice of solvent and chiral ligand was crucial for the efficient transformation and exquisite chemoselectivity pattern from identical starting materials that rapidly and reliably incorporate gem-difluoroalkene and trifluoromethyl (CF₃) motifs to generate a diverse range of enantioenriched fluorinated building blocks in good to excellent yields with high asymmetric induction.

Reagent-Controlled Highly Stereoselective Difluoromethylation: Efficient Access to Chiral α-Difluoromethylamines from Ketimines

A reagent-controlled highly stereoselective reaction between (S)-difluoromethyl phenyl sulfoximine 1 and imines is reported, and this synthetic method provides a variety of enantiomerically enriched α-difluoromethyl amines. The main pros of this approach include high efficiency, high stereoselectivity, and a broad substrate scope, which is probably achieved through a non-chelating transition state.

[2]-Ladderanes as isosteres for meta-substituted aromatic rings and rigidified cyclohexanes

Aromatic ring isosteres and rigidified saturated hydrocarbons are important motifs to enable drug discovery. Herein we disclose [2]-ladderanes as a class of meta-substituted aromatic ring isosteres and rigidified cyclohexanes. A straightforward synthesis of the building blocks is presented along with representative derivatization. Preliminary studies reveal that the [2]-ladderanes offer similar metabolic and physicochemical properties thus establishing this class of molecules as interesting motifs.

Recent Scaffold Hopping Applications in Central Nervous System Drug Discovery

The concept of bioisosterism and the implementation of bioisosteric replacement is fundamental to medicinal chemistry. The exploration of bioisosteres is often used to probe key structural features of candidate pharmacophores and enhance pharmacokinetic properties. As the understanding of bioisosterism has evolved, capabilities to undertake more ambitious bioisosteric replacements have emerged. Scaffold hopping is a broadly used term in the literature referring to a variety of different bioisosteric replacement strategies, ranging from simple heterocyclic replacements to topological structural overhauls. In this work, we have highlighted recent applications of scaffold hopping in the central nervous system drug discovery space. While we have highlighted the benefits of using scaffold hopping approaches in central nervous system drug discovery, these are also widely applicable to other medicinal chemistry fields. We also recommend a shift toward the use of more refined and meaningful terminology within the realm of scaffold hopping.

Difluoromethylsulfonyl Imidazolium Salt for Difluoromethylation of Alkenes

Herein, we describe the design and synthesis of a difluoromethylsulfonyl imidazolium salt, which can act as a radical difluoromethylation reagent to achieve the challenging amino- and oxy-difluoromethylation of alkenes. Notably, the three steps for the synthesis of the imidazolium salt do not require any tedious distillation or column chromatography purification process, and the amino- and oxy-difluoromethylation paths are simply determined by the selection of reaction solvents.

Visible-Light-Promoted bis(Difluoromethylation)/Cyclization of 2-Vinyloxy Arylalkynes to Prepare Benzofuran Derivatives

A visible-light-promoted difluoromethylation/cyclization of 2-vinyloxy arylalkynes was developed, providing a variety of bis(difluoromethyl)-substituted benzofurans in moderate to good yields. A plausible mechanism involving difluoromethyl radical cascade cyclization and solvent-promoted ionic addition was proposed. This protocol has the advantages of having mild reaction conditions, simple operation, and good functional group tolerance.

Selective deuteration of bupropion slows epimerization and reduces metabolism

Strategically replacing hydrogen with deuterium at sites of metabolism in small molecule drugs can significantly alter clearance and potentially enhance clinical safety. Bupropion is an antidepressant and smoking cessation medication with the potential to cause seizures. We hypothesized that incorporating deuterium at specific sites in bupropion may greatly reduce epimerization, potentially slow metabolism, and reduce the formation of toxic metabolites, namely hydroxybupropion which has been associated with bupropion's toxicity. Four deuterated analogues were synthesized incorporating deuterium at sites of metabolism and epimerization with the aim of altering the metabolic profile of bupropion. Spectroscopic binding and metabolism studies with bupropion and R-or S-d4 and R-or S-d10 analogs were performed with recombinant CYP2B6, human liver microsomes, and human hepatocytes. Results demonstrate that deuterated bupropion analogues exhibited 20-25% decrease in racemization and displayed a significant decrease in the formation of CYP2B6-mediated R,R - or S,S-hydroxybupropion with recombinant protein and human liver microsomes. In primary human hepatocytes, metabolism of deuterated analogs to R,R - and S,S-hydroxybupropion and threo- and erythro-hydrobupropion was significantly less than R/S-d0 bupropion. Selective deuterium substitution at metabolic soft spots in bupropion has the potential to provide a drug with a simplified pharmacokinetic profile, reduced toxicity and improved tolerability in patients.