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We report our recent development of a conceptually new generation of exceptionally potent non-peptidic HIV-1 protease inhibitors that displayed excellent pharmacological and drug-resistance profiles. Our X-ray structural studies of darunavir and other designed inhibitors from our laboratories led us to create a variety of inhibitors incorporating fused ring polycyclic ethers and aromatic heterocycles to promote hydrogen bonding interactions with the backbone atoms of HIV-1 protease as well as van der Waals interactions with residues in the S2 and S2' subsites. We have also incorporated specific functionalities to enhance van der Waals interactions in the S1 and S1' subsites. The combined effects of these structural templates are critical to the inhibitors' exceptional potency and drug-like properties. We highlight here our molecular design strategies to promote backbone hydrogen bonding interactions to combat drug-resistance and specific design of polycyclic ether templates to mimic peptide-like bonds in the HIV-1 protease active site. Our medicinal chemistry and drug development efforts led to the development of new generation inhibitors significantly improved over darunavir and displaying unprecedented antiviral activity against multidrug-resistant HIV-1 variants.

COVID-19, caused by SARS-CoV-2 infection, continues to be a major public health crisis around the globe. Development of vaccines and the first cluster of antiviral drugs has brought promise and hope for prevention and treatment of severe coronavirus disease. However, continued development of newer, safer, and more effective antiviral drugs are critically important to combat COVID-19 and counter the looming pathogenic variants. Studies of the coronavirus life cycle revealed several important biochemical targets for drug development. In the present review, we focus on recent drug design and medicinal chemistry efforts in small molecule drug discovery, including the development of nirmatrelvir that targets viral protein synthesis and remdesivir and molnupiravir that target viral RdRp. These are recent FDA approved drugs for the treatment of COVID-19.

The emergence of multidrug resistant (MDR) HIV strains severely reduces the effectiveness of antiretroviral therapy. Clinical inhibitor darunavir (1) has picomolar binding affinity for HIV-1 protease (PR), however, drug resistant variants like PR(S17) show poor inhibition by 1, despite the presence of only two mutated residues in the inhibitor-binding site. Antiviral inhibitors that target MDR proteases like PR(S17) would be valuable as therapeutic agents. Inhibitors 2 and 3 derived from 1 through substitutions at P1, P2 and P2ʹ positions exhibit 3.4- to 500-fold better inhibition than clinical inhibitors for PR(S17) with the exception of amprenavir. Crystal structures of PR(S17)/2 and PR(S17)/3 reveal how these inhibitors target the two active site mutations of PR(S17). The substituted methoxy P2 group of 2 forms new interactions with G48V mutation, while the modified bis-fluoro-benzyl P1 group of 3 forms a halogen interaction with V82S mutation, contributing to improved inhibition of PR(S17).

Antiretroviral drug resistance is a therapeutic obstacle for people with HIV. HIV protease inhibitors darunavir and lopinavir are recommended for resistant infections. We characterized a protease mutant (PR10x) derived from a highly resistant clinical isolate including 10 mutations associated with resistance to lopinavir and darunavir. Compared to the wild-type protease, PR10x exhibits ∼3-fold decrease in catalytic efficiency and K

Asymmetric 1,2-carbamoyl rearrangement of lithiated 2-alkenyl carbamates has been investigated. Deprotonation of chiral 2-alkenyl oxazolidine carbamates with sec-butyllithium in ether at -78 °C followed by warming of the resulting 1-lithio-2-alkenyl derivatives to room temperature resulted in 1,2-carbamoyl rearrangement to provide α-hydroxy amides. The rearrangement proceeded with excellent diastereoselectivity and in good to excellent isolated yield of the α-hydroxy amide derivatives. The substrate scope of the reaction was investigated with a variety of 2-alkenyl and benzyl oxazolidine carbamates. A stereochemical model is provided to explain the stereochemical outcome associated with the rearrangement. Acid-catalyzed removal of the chiral oxazolidine afforded α-hydroxy acid in high optical purity.

The design, synthesis, X-ray structural, and biological evaluation of a series of highly potent HIV-1 protease inhibitors are reported herein. These inhibitors incorporated novel cyclohexane-fused tricyclic bis-tetrahydrofuran as P2 ligands in combination with a variety of P1 and P2’-ligands. The inhibitor with a difluoromethylphenyl P1 ligand and a cyclopropylaminobenzothiazole P2’ ligand exhibited the most potent antiviral activity. Also, it maintained potent antiviral activity against a panel of highly multidrug-resistant HIV-1 variants. The corresponding inhibitor with an enantiomeric ligand was significantly less potent in these antiviral assays. The new P2 ligands were synthesized in optically active form using enzymatic desymmetrization of meso-diols as the key step. To obtain molecular insight, two high resolution X-ray structures of inhibitor-bound HIV-1 protease were determined and structural analyses have been highlighted.

Small molecules that target the spliceosome SF3B complex are potent inhibitors of cancer cell growth. The compounds affect an early stage of spliceosome assembly when U2 snRNP first engages the branch point sequence of an intron. Employing an inactive herboxidiene analog (iHB) as a competitor, we investigated factors that influence inhibitor interactions with SF3B to inhibit pre-mRNA splicing in vitro. Order-of addition experiments show that inhibitor interactions are long lasting and affected by both temperature and the presence of ATP. Our data are also consistent with the idea that not all SF3B conformations observed in structural studies are conducive to productive inhibitor interactions. Notably, SF3B inhibitors do not impact an ATP-dependent rearrangement in U2 snRNP that exposes the branch binding sequence for base pairing. We also report extended structure activity relationship analysis of the splicing inhibitor herboxidiene. We identified features of the tetrahydropyran ring that mediate its interactions with SF3B and its ability to interfere with splicing. Analyzing our data in the context of recent structural models of SF3B interactions with inhibitors, our results lead us to extend the model for early spliceosome assembly and inhibitor mechanism. We postulate that interactions between a carboxylic acid substituent of herboxidiene and positively charged SF3B1 sidechains in the inhibitor binding channel are required to maintain inhibitor occupancy while counteracting the SF3B transition to a closed state that is required for stable U2 snRNP interactions with the intron.

The ability to perform routine structure-guided drug design for selective BACE inhibitors has been limited because of the lack of robust platform for BACE2 expression, purification, and crystallization. To overcome this limitation, we developed a platform that produces 2–3 mg of pure BACE2 protein per liter of E. coli culture, and we used this protein to design macrocyclic compounds that potently and selectively inhibit BACE1 over BACE2. Compound 2 was found to potently inhibit BACE 1 (K(i) = 5 nM) with a selectivity of 214-fold over BACE2. The X-ray crystal structures of unbound BACE2 (2.2 Å) and BACE2 bound to compound 3 (3.0 Å and K(i) = 7 nM) were determined and compared to the X-ray structures of BACE1 revealing the S1–S3 subsite as a selectivity determinant. This platform should enable a more rapid development of new and selective BACE inhibitors for the treatment of Alzheimer’s disease or type II diabetes.

We describe an enantioselective synthesis of (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-ol which is a key subunit of darunavir, a widely used HIV-1 protease inhibitor drug for the treatment of HIV/AIDS patients. The synthesis was achieved in optically pure form utilizing commercially available sugar derivatives as the starting material. The key steps involve a highly stereoselective substrate-controlled hydrogenation, a Lewis acid catalyzed anomeric reduction of a 1,2-O-isopropylidene-protected glycofuranoside, and a Baeyer-Villiger oxidation of a tetrahydrofuranyl-2-aldehyde derivative. This optically active ligand alcohol was converted to darunavir efficiently.

To date, there are no specific treatment regimens for HIV-1-related central nervous system (CNS) complications, such as HIV-1-associated neurocognitive disorders (HAND). Here, we report that two newly generated CNS-targeting HIV-1 protease (PR) inhibitors (PIs), GRL-08513 and GRL-08613, which have a P1-3,5-bis-fluorophenyl or P1-para-monofluorophenyl ring and P2-tetrahydropyrano-tetrahydrofuran (Tp-THF) with a sulfonamide isostere, are potent against wild-type HIV-1 strains and multiple clinically isolated HIV-1 strains (50% effective concentration [EC(50)]: 0.0001 to ∼0.0032 μM). As assessed with HIV-1 variants that had been selected in vitro to propagate at a 5 μM concentration of each HIV-1 PI (atazanavir, lopinavir, or amprenavir), GRL-08513 and GRL-08613 efficiently inhibited the replication of these highly PI-resistant variants (EC(50): 0.003 to ∼0.006 μM). GRL-08513 and GRL-08613 also maintained their antiviral activities against HIV-2(ROD) as well as severely multidrug-resistant clinical HIV-1 variants. Additionally, when we assessed with the in vitro blood-brain barrier (BBB) reconstruction system, GRL-08513 and GRL-08613 showed the most promising properties of CNS penetration among the evaluated compounds, including the majority of FDA-approved combination antiretroviral therapy (cART) drugs. In the crystallographic analysis of compound-PR complexes, it was demonstrated that the Tp-THF rings at the P2 moiety of GRL-08513 and GRL-08613 form robust hydrogen bond interactions with the active site of HIV-1 PR. Furthermore, both the P1-3,5-bis-fluorophenyl- and P1-para-monofluorophenyl rings sustain greater contact surfaces and form stronger van der Waals interactions with PR than is the case with darunavir-PR complex. Taken together, these results strongly suggest that GRL-08513 and GRL-08613 have favorable features for patients infected with wild-type/multidrug-resistant HIV-1 strains and might serve as candidates for a preventive and/or therapeutic agent for HAND and other CNS complications.

The enoyl-ACP reductase (FabI) enzyme is a well validated target for anti-staphylococcal drug discovery and development. With the goal of finding alternate therapeutics for drug-resistant strains of Staphylococcus aureus, such as methicillin-resistant S. aureus (MRSA), our previously published series of benzimidazole-based inhibitors of the FabI enzyme from Francisella tularensis (FtFabI) have been evaluated against FabI from S. aureus (SaFabI). We report here the preliminary structure-activity relationship of this series and the prioritization of compounds toward lead optimization. Mutational studies have identified key residues that contribute toward stabilizing the inhibitors in the active site of FabI. Mutations that do not significantly impact enzyme function but destabilize inhibitor binding are more likely to occur in nature as organisms evolve to evade the action of antibiotics leading to resistance. Identifying these residues provides guidance for minimizing susceptibility to resistance. Additionally, we have identified compounds that elicit antibacterial activity through off-target effects and observe that close analogs can display differing modes of action (on-target vs off-target) and need to be individually evaluated early on to prioritize compounds for lead optimization. Overall, our data suggest that the benzimidazole scaffold is a promising scaffold for anti-staphylococcal drug development.

Lewis acid-catalyzed rearrangements of 4,5-dihydro-1,3-dioxepines have been investigated. Rearrangement of vinyl acetals under a variety of conditions resulted in cis- and trans-2,3-disubstituted tetrahydrofuran derivatives in a highly stereoselective manner. Rearrangements at lower temperatures typically provided the cis-2,3-disubstituted tetrahydrofuran carbaldehydes. At higher temperatures, the corresponding trans-2,3-disubstituted tetrahydrofuran carbaldehydes are formed. The requisite substrates for the vinyl acetal rearrangement were synthesized via ring-closing olefin metathesis of bis(allyoxy)methyl derivatives using Grubbs second-generation catalyst followed by olefin isomerization using a catalytic amount of RuCl2(PPh3)3. We examined the substrate scope using substituted aromatic and aliphatic derivatives. Additionally, the rearrangement was utilized in the synthesis of a stereochemically-defined bis-tetrahydrofuran (bis-THF) derivative, which is one of the key structural elements of darunavir, an FDA-approved drug for the treatment of HIV/AIDS.

Drug-resistance threatens effective treatment of HIV/AIDS. Clinical inhibitors, including darunavir (1), are ineffective for highly resistant protease mutant PR20, however, antiviral compound 2 derived from 1 with fused tricyclic group at P2, extended amino-benzothiazole P2’ ligand and two fluorine atoms on P1 shows 16-fold better inhibition of PR20 enzyme activity. Crystal structures of PR20 and wild-type PR complexes reveal how the extra groups of 2 counteract the expanded ligand-binding pocket, dynamic flaps, and faster dimer dissociation of PR20.

BACE1 (Beta-site Amyloid Precursor Protein (APP) Cleaving Enzyme 1) is a promising therapeutic target for Alzheimer’s Disease (AD). However, efficient expression, purification, and crystallization systems are not well described or detailed in the literature nor are approaches for treatment of enzyme kinetic data for potent inhibitors well described. We therefore developed a platform for expression and purification of BACE1, including protein refolding from E.coli inclusion bodies, in addition to optimizing a reproducible crystallization procedure of BACE1 bound with inhibitors. We also report a detailed approach to the proper analysis of enzyme kinetic data for compounds that exhibit either rapid-equilibrium or tight-binding mechanisms. Our methods allow for the purification of ~15 mg of BACE1 enzyme from 1 L of culture which is higher than reported yields in the current literature. To evaluate the data analysis approach developed here, a well-known potent inhibitor and two of its derivatives were tested, analyzed, and compared. The inhibitory constants (K(i)) obtained from the kinetic studies are in agreement with dissociation constants (K(d)) that were also determined using isothermal titration calorimetry (ITC) experiments. The X-ray structures of these three compounds in complex with BACE1 were readily obtained and provide important insight into the structure and thermodynamics of the BACE1-inhibitor interactions.

Here, we report the synthesis, structure-activity relationship studies, enzyme inhibition, antiviral activity, and X-ray crystallographic studies of 5-chloropyridinyl indole carboxylate derivatives as a potent class of SARS-CoV-2 chymotrypsin-like protease inhibitors. Compound 1 exhibited a SARS-CoV-2 3CLpro inhibitory IC50 value of 250 nM and an antiviral EC50 value of 2.8 µM in VeroE6 cells. Remdesivir, an RNA-dependent RNA polymerase inhibitor, showed an antiviral EC50 value of 1.2 µM in the same assay. Compound 1 showed comparable antiviral activity with remdesivir in immunocytochemistry assays. Compound 7d with an N-allyl derivative showed the most potent enzyme inhibitory IC50 value of 73 nM. To obtain molecular insight into the binding properties of these molecules, X-ray crystal structures of compounds 2, 7b, and 9d-bound to SARS-CoV 3CLpro were determined, and their binding properties were compared.

We report the design and synthesis of a series of new 5-chloropyridinyl esters of salicylic acid, ibuprofen, indomethacin, and related aromatic carboxylic acids for evaluation against SARS-CoV-2 3CL protease enzyme. These ester derivatives were synthesized using EDC in the presence of DMAP to provide various esters in good to excellent yields. Compounds are stable and purified by silica gel chromatography and characterized using 1H-NMR, 13C-NMR, and mass spectral analysis. These synthetic derivatives were evaluated in our in vitro SARS-CoV-2 3CLpro inhibition assay using authentic SARS-CoV-2 3CLpro enzyme. Compounds were also evaluated in our in vitro antiviral assay using quantitative VeroE6 cell-based assay with RNAqPCR. A number of compounds exhibited potent SARS-CoV-2 3CLpro inhibitory activity and antiviral activity. Compound 9a was the most potent inhibitor, with an enzyme IC50 value of 160 nM. Compound 13b exhibited an enzyme IC50 value of 4.9 µM. However, it exhibited a potent antiviral EC50 value of 24 µM in VeroE6 cells. Remdesivir, an RdRp inhibitor, exhibited an antiviral EC50 value of 2.4 µM in the same assay. We assessed the mode of inhibition using mass spectral analysis which suggested the formation of a covalent bond with the enzyme. To obtain molecular insight, we have created a model of compound 9a bound to SARS-CoV-2 3CLpro in the active site.

U2 snRNP is an essential component of the spliceosome. It is responsible for branch point recognition in the spliceosome A-complex via base-pairing of U2 snRNA with an intron to form the branch helix. Small molecule inhibitors target the SF3B component of the U2 snRNP and interfere with A-complex formation during spliceosome assembly. We previously found that the first SF3B inhibited-complex is less stable than A-complex and hypothesized that SF3B inhibitors interfere with U2 snRNA secondary structure changes required to form the branch helix. Using RNA chemical modifiers, we probed U2 snRNA structure in A-complex and SF3B inhibited splicing complexes. The reactivity pattern for U2 snRNA in the SF3B inhibited-complex is indistinguishable from that of A-complex, suggesting that they have the same secondary structure conformation, including the branch helix. This observation suggests SF3B inhibited-complex instability does not stem from an alternate RNA conformation and instead points to the inhibitors interfering with protein component interactions that normally stabilize U2 snRNP’s association with an intron. In addition, we probed U2 snRNA in the free U2 snRNP in the presence of SF3B inhibitor and again saw no differences. However, increased protection of nucleotides upstream of Stem I in the absence of SF3A and SF3B proteins suggests a change of secondary structure at the very 5′ end of U2 snRNA. Chemical probing of synthetic U2 snRNA in the absence of proteins results in similar protections and predicts a previously uncharacterized extension of Stem I. Because this stem must be disrupted for SF3A and SF3B proteins to stably join the snRNP, the structure has the potential to influence snRNP assembly and recycling after spliceosome disassembly.

Intron selection during the formation of prespliceosomes is a critical event in pre-mRNA splicing. Chemical modulation of intron selection has emerged as a route for cancer therapy. Splicing modulators alter the splicing patterns in cells by binding to the U2 snRNP (small nuclear ribonucleoprotein)—a complex chaperoning the selection of branch and 3′ splice sites. Here we report crystal structures of the SF3B module of the U2 snRNP in complex with spliceostatin and sudemycin FR901464 analogs, and the cryo-electron microscopy structure of a cross-exon prespliceosome-like complex arrested with spliceostatin A. The structures reveal how modulators inactivate the branch site in a sequence-dependent manner and stall an E-to-A prespliceosome intermediate by covalent coupling to a nucleophilic zinc finger belonging to the SF3B subunit PHF5A. These findings support a mechanism of intron recognition by the U2 snRNP as a toehold-mediated strand invasion and advance an unanticipated drug targeting concept., Chemical modulation of intron selection has emerged as a route for cancer therapy. Here, structures of the U2 snRNP’s SF3B module and of prespliceosome- both in complexes with splicing modulators- provide insight into the mechanisms of intron recognition and branch site inactivation.

We have the investigated base mediated asymmetric intramolecular oxidopyrylium-alkene [5 + 2]-cycloaddition reaction which resulted in the synthesis of functionalized tricyclic ring systems containing an 8-oxabicyclo[3.2.1]octane core. Intramolecular cycloaddition constructed two new rings, three new stereogenic centers, and provided a tricyclic cycloadduct with high diastereoselectivity and isolated yield. We incorporated an α-chiral center and an alkoxy alkene tether on the substrates and examined the effect of the size of alkyl groups and alkene tether length on diastereoselectivity. The requisite substrates for the oxidopyrylium-alkene cycloaddition reaction were synthesized in a few steps involving alkylation of optically active α-hydroxy amide, furyllithium addition, reduction of resulting ketone, and Achmatowicz reaction followed by acylation of a lactol intermediate. We have proposed stereochemical models for the [5 + 2] cycloaddition reaction via the oxidopyrylium ylide. Interestingly, the alkoxy substituent on the stereocenter and the chain length are responsible for the degree of stereoselectivity of the cycloadduct.

Spliceostatins and thailanstatins are intriguing natural products due to their structural features as well as their biological significance. This family of natural products has been the subject of immense synthetic interest because they exhibit very potent cytotoxicity in representative human cancer cell lines. The cytotoxic properties of these natural products are related to their ability to inhibit spliceosomes. FR901564 and spliceostatins have been shown to inhibit spliceosomes by binding to their SF3B component. Structurally, these natural products contain two highly functionalized tetrahydropyran rings with multiple stereogenic centers joined by a diene moiety and an acyclic side chain linked with an amide bond. Total syntheses of this family of natural products led to the development of useful synthetic strategies, which enabled the synthesis of potent derivatives. The spliceosome modulating properties of spliceostatins and synthetic derivatives opened the door for understanding the underlying spliceosome mechanism as well as the development of new therapies based upon small-molecule splicing modulators. This review outlines the total synthesis of spliceostatins, synthetic studies of structural derivatives, and their bioactivity.

We describe here an enantioselective synthesis of (+)-EBC-23, a potent anticancer agent from the Australian rainforest. Our convergent synthesis features a [3+2] dipolar cycloaddition of an olefin-bearing 1,3-syn diol unit and an oxime segment containing 1,2-syn diol functionality as the key step. The segments were synthesized in a highly enantioselective manner using Noyori asymmetric hydrogenation of a β-keto ester and Sharpless asymmetric dihydroxylation of an α,β-unsaturated ester. Cycloaddition provided isoxazoline derivative which upon hydrogenolysis furnished the β-hydroxy ketone expediently. A one-pot, acid-catalyzed reaction removed the isopropylidene group, promoted spirocyclization, constructed the complex spiroketal lactone core, and furnished EBC-23 and its C11 epimer. The C11 epimer was also converted to EBC-23 by chemoselective oxidation and reduction sequence. The present synthesis provides convenient access to this family of natural products in an efficient manner.

We have designed, synthesized, and evaluated a new class of potent HIV-1 protease inhibitors with novel bicyclic oxazolidinone derivatives as the P2 ligand. We have developed an enantioselective synthesis of these bicyclic oxazolidinones utilizing a key o-iodoxybenzoic acid mediated cyclization. Several inhibitors displayed good to excellent activity toward HIV-1 protease and significant antiviral activity in MT-4 cells. Compound 4k has shown an enzyme K(i) of 40 pM and antiviral IC(50) of 31 nM. Inhibitors 4k and 4l were evaluated against a panel of highly resistant multidrug-resistant HIV-1 variants, and their fold-changes in antiviral activity were similar to those observed with darunavir. Additionally, two X-ray crystal structures of the related inhibitors 4a and 4e bound to HIV-1 protease were determined at 1.22 and 1.30 Å resolution, respectively, and revealed important interactions in the active site that have not yet been explored.

Four HIV-1 protease (PR) inhibitors, clinical inhibitors lopinavir and tipranavir, and two investigational compounds 4 and 5, were studied for their effect on the structure and activity of PR with drug-resistant mutation L76V (PRL76V). Compound 5 exhibited the best Ki value of 1.9 nM for PRL76V, whereas the other three inhibitors had Ki values of 4.5–7.6 nM, 2–3 orders of magnitude worse than for wild-type enzymes. Crystal structures showed only minor differences in interactions of inhibitors with PRL76V compared to wild-type complexes. The shorter side chain of Val76 in the mutant lost hydrophobic interactions with Lys45 and Ile47 in the flap, and with Asp30 and Thr74 in the protein core, consistent with decreased stability. Inhibitors forming additional polar interactions with the flaps or dimer interface of PRL76V were unable to compensate for the decrease in internal hydrophobic contacts. These structures provide insights for inhibitor design.

A convenient protocol for amide bond formation for electron deficient amines and carboxylic acids is described. Amide coupling of aniline derivatives has been investigated with a number of reagents under a variety of reaction conditions. The use of 1 equivalent of EDC and 1 equivalent of DMAP, catalytic amount of HOBt and DIPEA provided the best results. This method is amenable to the synthesis of a range of functionalized amide derivatives with electron deficient and unreactive amines.

Small molecules that target the spliceosome SF3B complex are potent inhibitors of cancer cell growth. The compounds affect an early stage of spliceosome assembly when U2 snRNP first engages the branch point sequence of an intron. Recent cryo-EM models of U2 snRNP before and after intron recognition suggest several large-scale rearrangements of RNA and protein interactions involving SF3B. Employing an inactive herboxidiene analog as a competitor with SF3B inhibitors, we present evidence for multiple conformations of SF3B in the U2 snRNP, only some of which are available for productive inhibitor interactions. We propose that both thermodynamics and an ATP-binding event promote the conformation conducive to SF3B inhibitor interactions. However, SF3B inhibitors do not impact an ATP-dependent rearrangement in U2 snRNP that exposes the branch binding sequence for base pairing. We also report extended structure activity relationship analysis of herboxidiene, which identified features of the tetrahydropyran ring that mediate its interactions with SF3B and its ability to interfere with splicing. In combination with structural models of SF3B interactions with inhibitors, our data leads us to extend the model for early spliceosome assembly and inhibitor mechanism. We postulate that interactions between a carboxylic acid substituent of herboxidiene and positively charged SF3B1 sidechains in the inhibitor binding channel are required to maintain inhibitor occupancy and counteract the SF3B transition to a closed state that is promoted by stable U2 snRNA interactions with the intron.

Lewis acid-catalyzed rearrangements of 4,5-dihydro-1,3-dioxepines have been investigated. Rearrangement of vinyl acetals under a variety of conditions resulted in cis- and trans-2,3-disubstituted tetrahydrofuran derivatives in a highly stereoselective manner. Rearrangements at lower temperatures typically provided the cis-2,3-disubstituted tetrahydrofuran carbaldehydes. At higher temperatures, the corresponding trans-2,3-disubstituted tetrahydrofuran carbaldehydes are formed. The requisite substrates for the vinyl acetal rearrangement were synthesized via ring-closing olefin metathesis of bis(allyoxy)methyl derivatives using Grubbs second-generation catalyst followed by olefin isomerization using a catalytic amount of RuCl(2)(PPh(3))(3). We examined the substrate scope using substituted aromatic and aliphatic derivatives. Additionally, the rearrangement was utilized in the synthesis of a stereochemically-defined bis-tetrahydrofuran (bis-THF) derivative, which is one of the key structural elements of darunavir, an FDA-approved drug for the treatment of HIV/AIDS.

We describe here our investigation of the asymmetric Diels-Alder reaction of chiral 3-(acyloxy)acryloyl oxazolidinones as dienophiles in various Lewis-acid promoted reactions with cyclopentadiene. The resulting highly functionalized cycloadducts are useful intermediates for the synthesis, particularly for the optically active synthesis of 6-5-5 tricyclic hexahydro-4H-3,5-methanofuro[2,3-b]pyranol (3) with five contiguous chiral centers. This stereochemically defined crown-like heterocyclic derivative is an important high affinity ligand for a variety of highly potent HIV-1 protease inhibitors. Among the various dienophiles and Lewis acid-mediated reactions surveyed, 3-(4-methoxybenzoyl)acryloyl oxazolidinone as the dienophile and diethylaluminum chloride as the Lewis-acid provided the desired endo product with excellent diastereoselectivity. The cycloaddition was carried out in multi-gram scale and the cycloadduct was efficiently converted to alcohol 3 with high enantiomeric purity. The optically active ligand was then transformed into potent HIV-1 protease inhibitor 2.

HIV-1 protease inhibitors (PIs), such as darunavir (DRV), are the key component of antiretroviral therapy. However, HIV-1 often acquires resistance to PIs. Here, seven novel PIs were synthesized, by introducing single atom changes such as an exchange of a sulfur to an oxygen, scission of a single bond in P2′-cyclopropylaminobenzothiazole (or -oxazole), and/or P1-benzene ring with fluorine scan of mono- or bis-fluorine atoms around DRV’s scaffold. X-ray structural analyses of the PIs complexed with wild-type Protease (PRWT) and highly-multi-PI-resistance-associated PRDRVRP51 revealed that the PIs better adapt to structural plasticity in PR with resistance-associated amino acid substitutions by formation of optimal sulfur bond and adaptation of cyclopropyl ring in the S2′-subsite. Furthermore, these PIs displayed increased cell permeability and extreme anti-HIV-1 potency compared to DRV. Our work provides the basis for developing novel PIs with high potency against PI-resistant HIV-1 variants with a high genetic barrier.

An efficient palladium-free Stille cross-coupling reaction of allylic bromides and functionalized organostannylfuran using catalytic copper halide has been developed. The coupling reaction was optimized using CuI and low catalyst loading (down to 5 mol %). The reaction was conveniently carried out at ambient temperature in the presence of inorganic base to afford the coupling product in good-to-excellent yields. The utility of this reaction was demonstrated in the synthesis of a furan with sensitive functionalities. A sulfolene moiety was utilized as a masking group for the sensitive diene. Noyori asymmetric reduction, Achmatowicz reaction, and Kishi reduction steps converted sulfolene to a highly substituted tetrahydropyran intermediate used in the synthesis of the highly potent antitumor agents, spliceostatins, and their derivatives.

Except remdesivir, no specific antivirals for SARS-CoV-2 infection are currently available. Here, we characterize two small-molecule-compounds, named GRL-1720 and 5h, containing an indoline and indole moiety, respectively, which target the SARS-CoV-2 main protease (Mpro). We use VeroE6 cell-based assays with RNA-qPCR, cytopathic assays, and immunocytochemistry and show both compounds to block the infectivity of SARS-CoV-2 with EC50 values of 15 ± 4 and 4.2 ± 0.7 μM for GRL-1720 and 5h, respectively. Remdesivir permitted viral breakthrough at high concentrations; however, compound 5h completely blocks SARS-CoV-2 infection in vitro without viral breakthrough or detectable cytotoxicity. Combination of 5h and remdesivir exhibits synergism against SARS-CoV-2. Additional X-ray structural analysis show that 5h forms a covalent bond with Mpro and makes polar interactions with multiple active site amino acid residues. The present data suggest that 5h might serve as a lead Mpro inhibitor for the development of therapeutics for SARS-CoV-2 infection., Here, using in vitro assays and structural analysis, the authors characterize the anti-SARS-CoV-2 properties of two small molcules, showing these to bind and target the virus main protease (Mpro), and to exhibit a synergistic antiviral effect when combined with remdesivir in vitro.