Structure-Based Design of Highly Potent HIV-1 Protease Inhibitors Containing New Tricyclic Ring P2-Ligands: Design, Synthesis, Biological, and X-ray Structural Studies

We describe here design, synthesis, and biological evaluation of a series of highly potent HIV-1 protease inhibitors containing stereochemically defined and unprecedented tricyclic furanofuran derivatives as P2 ligands in combination with a variety of sulfonamide derivatives as P2' ligands. These inhibitors were designed to enhance the ligand-backbone binding and van der Waals interactions in the protease active site. A number of inhibitors containing the new P2 ligand, an aminobenzothiazole as the P2' ligand and a difluorophenylmethyl as the P1 ligand, displayed very potent enzyme inhibitory potency and also showed excellent antiviral activity against a panel of highly multidrug-resistant HIV-1 variants. The tricyclic P2 ligand has been synthesized efficiently in an optically active form using enzymatic desymmetrization of meso-1,2-(dihydroxymethyl)cyclohex-4-ene as the key step. We determined high-resolution X-ray structures of inhibitor-bound HIV-1 protease. These structures revealed extensive interactions with the backbone atoms of HIV-1 protease and provided molecular insights into the binding properties of these new inhibitors.

Anomalous Hall effect in Cu doped Bi2Te3 topological insulator

The angle resolved photo-emission spectroscopy (ARPES) study and magneto-transport properties of Bi2Cu x Te3-x have been investigated. ARPES study indicates the clear existence of surface states in the as-prepared samples. The estimated bandgap from ARPES is found to be ∼5 meV and 16 meV respectively for x = 0.03 and x = 0.15 samples. Presence of larger Cu concentration (x = 0.15) introduces magnetic ordering. Observed non-linearity in the Hall data is due to the existence of anomalous Hall effect which can be attributed to the 2D transport. The observed magneto-transport features might be related to the surface carriers which is confirmed by ARPES study.

Fluorescent Probes for Monitoring Serine Ubiquitination

In a radical departure from the classical E1-E2-E3 three-enzyme mediated ubiquitination of eukaryotes, the recently described bacterial enzymes of the SidE family of Legionella pneumophila effectors utilize NAD⁺ to ligate ubiquitin onto target substrate proteins. This outcome is achieved via a two-step mechanism involving (1) ADP ribosylation of ubiquitin followed by (2) phosphotransfer to a target serine residue. Here, using fluorescent NAD⁺ analogues as well as synthetic substrate mimics, we have developed continuous assays enabling real-time monitoring of both steps of this mechanism. These assays are amenable to biochemical studies and high-throughput screening of inhibitors of these effectors, and the discovery and characterization of putative enzymes similar to members of the SidE family in other organisms. We also show their utility in studying enzymes that can reverse and inhibit this post-translational modification.

Asymmetric Diels-Alder reaction of 3-(acyloxy) acryloyl oxazolidinones: optically active synthesis of a high-affinity ligand for potent HIV-1 protease inhibitors

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.

Urea Derivatives in Modern Drug Discovery and Medicinal Chemistry

The urea functionality is inherent to numerous bioactive compounds, including a variety of clinically approved therapies. Urea containing compounds are increasingly used in medicinal chemistry and drug design in order to establish key drug-target interactions and fine-tune crucial drug-like properties. In this perspective, we highlight physicochemical and conformational properties of urea derivatives. We provide outlines of traditional reagents and chemical procedures for the preparation of ureas. Also, we discuss newly developed methodologies mainly aimed at overcoming safety issues associated with traditional synthesis. Finally, we provide a broad overview of urea-based medicinally relevant compounds, ranging from approved drugs to recent medicinal chemistry developments.

Potent HIV-1 Protease Inhibitors Containing Carboxylic and Boronic Acids: Effect on Enzyme Inhibition and Antiviral Activity and Protein-Ligand X-ray Structural Studies

We report the synthesis and biological evaluation of phenylcarboxylic acid and phenylboronic acid containing HIV-1 protease inhibitors and their functional effect on enzyme inhibition and antiviral activity in MT-2 cell lines. Inhibitors bearing bis-THF ligand as P2 ligand and phenylcarboxylic acids and carboxamide as the P2' ligands, showed very potent HIV-1 protease inhibitory activity. However, carboxylic acid containing inhibitors showed very poor antiviral activity relative to carboxamide-derived inhibitors which showed good antiviral IC₅₀ value. Boronic acid derived inhibitor with bis-THF as the P2 ligand showed very potent enzyme inhibitory activity, but it showed lower antiviral activity than darunavir in the same assay. Boronic acid containing inhibitor with a P2-Crn-THF ligand also showed potent enzyme K_i but significantly decreased antiviral activity. We have evaluated antiviral activity against a panel of highly drug-resistant HIV-1 variants. One of the inhibitors maintained good antiviral activity against HIV_DRV^R_P20 and HIV_DRV^R_P30 viruses. We have determined high resolution X-ray structures of two synthetic inhibitors bound to HIV-1 protease and obtained molecular insight into the ligand-binding site interactions.

Development of an Efficient Enzyme Production and Structure-Based Discovery Platform for BACE1 Inhibitors

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.

A novel HIV-1 protease inhibitor, GRL-044, has potent activity against various HIV-1s with an extremely high genetic barrier to the emergence of HIV-1 drug resistance

We designed, synthesized, and identified two novel nonpeptidic HIV-1 protease inhibitors (PIs), GRL- 037 and GRL-044, containing P2-tetrahydropyrano-tetrahydrofuran (Tp-THF), P1-benzene and P1-methoxybenzene, respectively, and P2'-isopropyl-aminobenzothiazole (Ip-Abt), based on the structure of the prototypic PI, darunavir (DRV). The 50% inhibitory concentrations (IC₅₀s) of GRL-037 and GRL-044 against wild-type HIV-1_NL4-3 were 0.042 and 0.0028-0.0033 nM with minimal cytotoxicity profiles compared to the IC₅₀ values of four most potent FDA-approved PIs, ranging from 2.6 to 70 nM. GRL-044 was also potent against HIV-2EHO (IC₅₀=0.0004 nM) and various PI-resistant HIV-1 variants (IC₅₀ ranging from 0.065 to 19 nM). In the selection assays we conducted, the emergence of HIV-1 variants resistant to GRL-044 was significantly delayed compared to that against DRV. Thermal stability test using differential scanning fluorimetry employing purified HIV-1 protease (PR) and SYPRO^® Orange showed that both GRL-037 and GRL-044 tightly bound to PR. A28S substitution emerged in the homologous recombination-based selection assays with GRL-044. Structural analyses showed that the larger size of GRL-044 over DRV, enabling GRL-044 to fit better to the hydrophobic cavity of protease, contributed to the greater potency of GRL- 044 against HIV-1. Structural analyses also suggested that the van der Waals surface contact of GRL-044 with A28' appears to be better compared to that of DRV because of the larger surface of Ip-Abt of GRL-044, which may be partially responsible for the emergence of A28S. The present antiviral data and structural features of GRL-044 should provide molecular insights for further design and development of potent and "resistance-repellant" novel PIs.

Potent antiviral HIV-1 protease inhibitor combats highly drug resistant mutant PR20

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.

P680The clinical value of CMR in the management of Cardio-Oncology patients - a tertiary centre experience

Background

There is increasing awareness of cardiotoxicity arising from cancer treatments. Early diagnosis and treatment is key, to ensure patients receive optimal oncological management. Cardiovascular magnetic resonance (CMR) offers gold standard measurement of cardiac function, alongside tissue characterisation and myocardial perfusion, thereby potentially providing additive value in the context of cardio-oncology.

Purpose

We sought to understand the clinical value of CMR in cardio-oncology at a tertiary cardio-oncology centre.

Methods

We retrospectively reviewed CMR scans requested in cardio-oncology patients at our institution within a ten-month period. We categorised clinical indications and assessed the impact on clinical management using previously-published criteria.

Results

102 CMR studies were requested in 93 cardio-oncology patients (mean age 56 (range 18 to 82), 49% male) between (March to December 2018). 41% of patients had haematological malignancies, 59% solid tumours.

15% of requests were for risk stratification prior to initiation of cancer therapy, 21% for screening for cardio-toxicity in patients currently receiving cardiotoxic agents (3% anthracyclines, 13% HER2 monoclonal antibodies, 4% fluoropyrimidines), 15% for investigation of patients with cardiac complications during cancer treatment, 35% assessment for late effects post cancer treatment, and 14% for cardiac malignancies/ infiltration.

The most common indications for CMR were monitoring of left ventricular ejection fraction (LVEF) in patients where quantification by echocardiography was non-diagnostic or significantly different between imaging studies (39%) and ischaemia assessment including for patients due to receive fluoropyrimidines (26%). Others were aetiology of LV dysfunction/cardiomyopathy (13%) and tissue characterisation (23%), including assessment for cardiac AL amyloid (11 patients), myocarditis (2), cardiac metastases (1), cardiac masses (6), and cardiac iron loading (1).

CMR findings had clinical impact in 61% of patients and assisted in adjudicating a new diagnosis in 29% of patients. 88% of patients were able to continue anthracycline/anti-HER2 therapies based on CMR findings of stable LVEF (93% of whose echocardiograms had suggested reductions). LVEF had reduced significantly in 12% of patients meaning chemotherapy was held/discontinued. 3 patients were recommended to receive non-fluoropyrimidine chemotherapy based on perfusion CMR (pCMR) findings, with one patient permitted to receive capecitabine following normal pCMR.

Conclusion

CMR provides a comprehensive assessment of myocardial structure and function with utility within the context of cardio-oncology for risk stratification pre-chemotherapy, screening for cardiotoxicity during treatment and investigation of cardiac complications of cancer treatment. The additional information derived from CMR generally provides reassurance enabling administration of optimal cancer therapies.

Potent HIV-1 protease inhibitors incorporating squaramide-derived P2 ligands: Design, synthesis, and biological evaluation

We describe the design, synthesis, and biological evaluation of novel HIV-1 protease inhibitors containing a squaramide-derived scaffold as the P2 ligand in combination with a (R)-hydroxyethylamine sulfonamide isostere. Inhibitor 3h with an N-methyl-3-(R)-aminotetrahydrofuranyl squaramide P2-ligand displayed an HIV-1 protease inhibitory Ki value of 0.51 nM. An energy minimized model of 3h revealed the major molecular interactions between HIV-1 protease active site and the tetrahydrofuranyl squaramide scaffold that may be responsible for its potent activity.

A Photochemical Route to Optically Active Hexahydro-4H-furopyranol, a High-Affinity P2 Ligand for HIV-1 Protease Inhibitors

We describe here the syntheses of optically pure (3aS,4S,7aR)-hexahydro-4H-furo[2,3-b]pyran-4-ol and (3aR,4R,7aS)-hexahydro-4H-furo[2,3-b]pyran-4-ol. These stereochemically defined heterocycles are important high-affinity P2 ligands for a variety of highly potent HIV-1 protease inhibitors. The key steps involve an efficient Paternò-Büchi [2 + 2] photocycloaddition, catalytic hydrogenation, acid-catalyzed cyclization to form the racemic ligand alcohol, and an enzymatic resolution with immobilized Amano Lipase PS-30. Optically active ligands (-)-6 and (+)-6 were obtained with high enantiomeric purity. Enantiomer (-)-6 has been converted to potent HIV-1 protease inhibitor 3.

Investigation of multi-mode spin-phonon coupling and local B-site disorder in Pr2CoFeO6 by Raman spectroscopy and correlation with its electronic structure by XPS and XAS studies

Electronic structure of Pr₂CoFeO₆ (at 300 K) was investigated by x-ray photoemission spectroscopy (XPS) and x-ray absorption spectroscopy techniques. All three cations, i.e. Pr, Co and Fe were found to be trivalent in nature. XPS valance band analysis suggested the system to be insulating in nature. The analysis suggested that Co³⁺ ions exist in low spin state in the system. Moreover, Raman spectroscopy study indicated the random distribution of the B-site ions (Co/Fe) triggered by same charge states. In temperature-dependent Raman study, the relative heights of the two observed phonon modes exhibited anomalous behaviour near magnetic transition temperature T _N ~ 270 K, thus indicating towards interplay between spin and phonon degrees of freedom in the system. Furthermore, clear anomalous softening was observed below T _N which confirmed the existence of strong spin-phonon coupling occurring for at least two phonon modes of the system. The line width analysis of the phonon modes essentially ruled out the role of magnetostriction effect in the observed phonon anomaly. The investigation of the lattice parameter variation across T _N (obtained from the temperature-dependent neutron diffraction measurements) further confirmed the existence of the spin-phonon coupling.

Enantioselective Total Synthesis of (+)-Monocerin, a Dihydroisocoumarin Derivative with Potent Antimalarial Properties

We describe here the enantioselective synthesis of (+)-monocerin and its acetate derivative. The present synthesis features an efficient optically active synthesis of the β-hydroxy-γ-lactone derivative with high enantiomeric purity using Sharpless dihydroxylation as the key step. The synthesis also highlights a tandem Lewis acid-catalyzed, oxocarbenium ion-mediated diastereoselective syn-allylation reaction, and a methoxymethyl group promoted methylenation reaction. We investigated this reaction with a variety of Lewis acids. A selective CrO3-mediated oxidation of isochroman provided the corresponding lactone derivative. The synthesis is quite efficient and may be useful for the preparation of derivatives.

Enantioselective Total Syntheses of (+)-Fendleridine and (+)-Acetylaspidoalbidine

Enantioselective syntheses of hexacyclic aspidoalbidine alkaloids (+)-fendleridine (2) and (+)-acetylaspidoalbidine (3) are described. These syntheses feature an asymmetric decarboxylative allylation and photocyclization of a highly substituted enaminone. Also, the synthesis highlights the formation of a C19-hemiaminal ether via a reduction/condensation/intramolecular cyclization cascade with the C21-alcohol. The present synthesis provides convenient access to the aspidoalbidine hexacyclic alkaloid family in an efficient manner.

Highly Selective and Potent Human β-Secretase 2 (BACE2) Inhibitors against Type 2 Diabetes: Design, Synthesis, X-ray Structure and Structure-Activity Relationship Studies

Herein we present the design, synthesis, and biological evaluation of potent and highly selective β-secretase 2 (memapsin 1, beta-site amyloid precursor protein cleaving enzyme 2, or BACE 2) inhibitors. BACE2 has been recognized as an exciting new target for type 2 diabetes. The X-ray structure of BACE1 bound to inhibitor 2 a {N³ -[(1S,2R)-1-benzyl-2-hydroxy-3-[[(1S,2S)-2-hydroxy-1-(isobutylcarbamoyl)propyl]amino]propyl]-5-[methyl(methylsulfonyl)amino]-N¹ -[(1R)-1-phenylpropyl]benzene-1,3-dicarboxamide} containing a hydroxyethylamine isostere was determined. Based on this structure, a computational docking study was performed which led to inhibitor 2 a-bound BACE2 models. These were used to optimize the potency and selectivity of inhibitors. A systematic structure-activity relationship study led to the identification of determinants of the inhibitors' potency and selectivity toward the BACE2 enzyme. Inhibitors 2 d [N³ -[(1S,2R)-1-benzyl-2-hydroxy-3-[[(1S,2S)-2-hydroxy-1-(isobutylcarbamoyl)pentyl]amino]propyl]-N¹ -methyl-N¹ -[(1R)-1-phenylpropyl]benzene-1,3-dicarboxamide; K_i =0.031 nm, selectivity over BACE1: ≈174 000-fold] and 3 l [N¹ -((2S,3R)-3-hydroxy-1-phenyl-4-((3-(trifluoromethyl)benzyl)amino)butan-2-yl)-N³ ,5-dimethyl-N³ -((R)-1-phenylethyl)isophthalamide; K_i =1.6 nm, selectivity over BACE1: >500-fold] displayed outstanding potency and selectivity. Inhibitor 3 l is nonpeptide in nature and may pave the way to the development of a new class of potent and selective BACE2 inhibitors with clinical potential.

Enantioselective Synthesis of a Cyclopropane Derivative of Spliceostatin A and Evaluation of Bioactivity

Spliceostatin A is a potent inhibitor of spliceosomes and exhibits excellent anticancer activity against multiple human cancer cell lines. We describe here the design and synthesis of a stable cyclopropane derivative of spliceostatin A. The synthesis involved a cross-metathesis or a Suzuki cross-coupling reaction as the key step. The functionalized epoxy alcohol ring was constructed from commercially available optically active tri- O-acetyl-d-glucal. The biological properties of the cyclopropyl derivative revealed that it is active in human cells and inhibits splicing in vitro comparable to spliceostatin A.

Design and Synthesis of Potent HIV-1 Protease Inhibitors Containing Bicyclic Oxazolidinone Scaffold as the P2 Ligands: Structure-Activity Studies and Biological and X-ray Structural Studies

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 IC₅₀ 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.

The Curtius Rearrangement: Applications in Modern Drug Discovery and Medicinal Chemistry

The Curtius rearrangement is the thermal decomposition of an acyl azide derived from carboxylic acid to produce an isocyanate as the initial product. The isocyanate can undergo further reactions to provide amines and their derivatives. Due to its tolerance for a large variety of functional groups and complete retention of stereochemistry during rearrangement, the Curtius rearrangement has been used in the synthesis of a wide variety of medicinal agents with amines and amine-derived functional groups such as ureas and urethanes. The current review outlines various applications of the Curtius rearrangement in drug discovery and medicinal chemistry. In particular, the review highlights some widely used rearrangement methods, syntheses of some key agents for popular drug targets and FDA-approved drugs. In addition, the review highlights applications of the Curtius rearrangement in continuous-flow protocols for the scale-up of active pharmaceutical ingredients.

Drug Resistance Mutation L76V Alters Nonpolar Interactions at the Flap-Core Interface of HIV-1 Protease

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 (PR_L76V). Compound 5 exhibited the best K _i value of 1.9 nM for PR_L76V, whereas the other three inhibitors had K _i 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 PR_L76V 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 PR_L76V were unable to compensate for the decrease in internal hydrophobic contacts. These structures provide insights for inhibitor design.

Enantioselective total synthesis of decytospolide A and decytospolide B using an Achmatowicz reaction

Enantioselective syntheses of decytospolide A and decytospolide B are described here. The current synthesis highlights an Achmatowicz rearrangement of an optically active furanyl alcohol followed by reduction of the resulting dihydropyranone hemiacetal with BF3·OEt2 and Et3SiH to provide the saturated tetrahydropyranyl alcohol directly. This reduction was investigated with a variety of other Lewis acids. The synthesis also features Noyori asymmetric transfer hydrogenation and Friedel-Crafts acylation. Overall, the synthesis provides ready access to the natural products and may be useful in the preparation of bioactive derivatives.

Design, synthesis, X-ray studies, and biological evaluation of novel BACE1 inhibitors with bicyclic isoxazoline carboxamides as the P3 ligand

We describe the design, synthesis, X-ray studies, and biological evaluation of novel BACE1 inhibitors containing bicyclic isoxazoline carboxamides as the P3 ligand in combination with methyl cysteine, methylsulfonylalanine and Boc-amino alanine as P2 ligands. Inhibitor 3a displayed a BACE1 Ki value of 10.9 nM and EC50 of 343 nM. The X-ray structure of 3a bound to the active site of BACE1 was determined at 2.85 Å resolution. The structure revealed that the major molecular interactions between BACE1 and the bicyclic tetrahydrofuranyl isoxazoline heterocycle are van der Waals in nature.

Nature Inspired Molecular Design: Stereoselective Synthesis of Bicyclic and Polycyclic Ethers for Potent HIV-1 Protease Inhibitors

We have developed a conceptually new generation of non-peptidic HIV-1 protease inhibitors incorporating novel structural templates inspired by nature. This has resulted in protease inhibitors with exceptional potency and excellent pharmacological and drug-resistance profiles. The design of a stereochemically defined bis-tetrahydrofuran (bis-THF) scaffold followed by modifications to promote hydrogen bonding interactions with the backbone atoms of HIV-1 protease led to darunavir, the first clinically approved drug for treatment of drug resistant HIV. Subsequent X-ray crystal structure-based design efforts led us to create a range of exceptionally potent inhibitors incorporating other intriguing molecular templates possessing fused ring polycyclic ethers with multiple stereocenters. These structural templates are critical to inhibitors' exceptional potency and drug-like properties. Herein, we will highlight the synthetic strategies that provided access to these complex scaffolds in a stereoselective and optically active form, enabling our medicinal chemistry and drug development efforts.