An Enzymatic Route to the Synthesis of Tricyclic Fused Hexahydrofuranofuran P2-Ligand for a Series of Highly Potent HIV-1 Protease Inhibitors

We describe a stereoselective synthesis of an optically active (1R, 3aS, 5R, 6S, 7aR)-octahydro-1,6-epoxy-isobenzo-furan-5-ol derivative. This stereochemically defined heterocycle serves as a high-affinity ligand for a variety of HIV-1 protease inhibitors. The key synthetic steps involve a highly enantioselective enzymatic desymmetrization of meso-1,2(dihydroxymethyl)cyclohex-4-ene and conversion of the resulting optically active alcohol to a methoxy hexahydroisobenzofuran derivative. A substrate controlled stereoselective dihydroxylation afforded syn-1,2-diols. Oxidation of diol provided the substituted 1,2-diketone and L-Selectride reduction provided the corresponding inverted syn-1,2-diols. Acid catalyzed cyclization furnished the ligand alcohol in optically active form.

Genome-wide mining of diversity and evolutionary signatures revealed selective hotspots in Indian Sahiwal cattle

The Sahiwal cattle breed is the best indigenous dairy cattle breed, and it plays a pivotal role in the Indian dairy industry. This is due to its exceptional milk-producing potential, adaptability to local tropical conditions, and its resilience to ticks and diseases. The study aimed to identify selective sweeps and estimate intrapopulation genetic diversity parameters in Sahiwal cattle using ddRAD sequencing-based genotyping data from 82 individuals. After applying filtering criteria, 78,193 high-quality SNPs remained for further analysis. The population exhibited an average minor allele frequency of 0.221 ± 0.119. Genetic diversity metrics, including observed (0.597 ± 0.196) and expected heterozygosity (0.433 ± 0.096), nucleotide diversity (0.327 ± 0.114), the proportion of polymorphic SNPs (0.726), and allelic richness (1.323 ± 0.134), indicated ample genomic diversity within the breed. Furthermore, an effective population size of 74 was observed in the most recent generation. The overall mean linkage disequilibrium (r2) for pairwise SNPs was 0.269 ± 0.057. Moreover, a greater proportion of short Runs of Homozygosity (ROH) segments were observed suggesting that there may be low levels of recent inbreeding in this population. The genomic inbreeding coefficients, computed using different inbreeding estimates (FHOM, FUNI, FROH, and FGROM), ranged from -0.0289 to 0.0725. Subsequently, we found 146 regions undergoing selective sweeps using five distinct statistical tests: Tajima's D, CLR, |iHS|, |iHH12|, and ROH. These regions, located in non-overlapping 500 kb windows, were mapped and revealed various protein-coding genes associated with enhanced immune systems and disease resistance (IFNL3, IRF8, BLK), as well as production traits (NRXN1, PLCE1, GHR). Notably, we identified interleukin 2 (IL2) on Chr17: 35217075-35223276 as a gene linked to tick resistance and uncovered a cluster of genes (HSPA8, UBASH3B, ADAMTS18, CRTAM) associated with heat stress. These findings indicate the evolutionary impact of natural and artificial selection on the environmental adaptation of the Sahiwal cattle population.

Exploration of P1 and P4 modifications of nirmatrelvir: Design, synthesis, biological evaluation, and X-ray structural studies of SARS-CoV-2 Mpro inhibitors

We report the synthesis, biological evaluation, and X-ray structural studies of a series of SARS-CoV-2 Mpro inhibitors based upon the X-ray crystal structure of nirmatrelvir, an FDA approved drug that targets the main protease of SARS-CoV-2. The studies involved examination of various P4 moieties, P1 five- and six-membered lactam rings to improve potency. In particular, the six-membered P1 lactam ring analogs exhibited high SARS-CoV-2 Mpro inhibitory activity. Several compounds effectively blocked SARS-CoV-2 replication in VeroE6 cells. One of these compounds maintained good antiviral activity against variants of concern including Delta and Omicron variants. A high-resolution X-ray crystal structure of an inhibitor bound to SARS-CoV-2 Mpro was determined to gain insight into the ligand-binding properties in the Mpro active site.

A lipid index for risk of hyperlipidemia caused by anti-retroviral drugs

HIV-associated lipodystrophy has been reported in people taking anti-retroviral therapy (ART). Lipodystrophy can cause cardiovascular diseases, affecting the quality of life of HIV-infected individuals. In this study, we propose a pharmacological lipid index to estimate the risk of hyperlipidemia caused by anti-retroviral drugs. Lipid droplets were stained in cells treated with anti-retroviral drugs and cyclosporin A. Signal intensities of lipid droplets were plotted against the drug concentrations to obtain an isodose of 10 μM of cyclosporin A, which we call the Pharmacological Lipid Index (PLI). The PLI was then normalized by EC50. PLI/EC50 values were low in early proteinase inhibitors and the nucleoside reverse transcriptase inhibitor, d4T, indicating high risk of hyperlipidemia, which is consistent with previous findings of hyperlipidemia. In contrast, there are few reports of hyperlipidemia for drugs with high PLI/EC50 scores. Data suggests that PLI/EC50 is a useful index for estimating the risk of hyperlipidemia.

Development of a new class of potent and highly selective G protein-coupled receptor kinase 5 inhibitors and structural insight from crystal structures of inhibitor complexes

G protein-coupled receptor kinase 5 (GRK5) is an important drug development target for heart failure, cardiac hypertrophy, and cancer. We have designed and developed a new class of highly selective, potent, and non-covalent GRK5 inhibitors. One of the inhibitors displayed GRK5 IC50 value of 10 nM and exhibited >100,000-fold selectivity over GRK2. The X-ray structure of a ketoamide-derived inhibitor-bound GRK5 showed the formation of a hemithioketal intermediate with active site Cys474 in the GRK5 active site and provided new insights into the ligand-binding site interactions responsible for high selectivity. The current studies serve as an important guide to therapeutic GRK5 inhibitor drug development.

Control of Biofilm Formation by an Agrobacterium tumefaciens Pterin-Binding Periplasmic Protein Conserved Among Pathogenic Bacteria

Biofilm formation and surface attachment in multiple Alphaproteobacteria is driven by unipolar polysaccharide (UPP) adhesins. The pathogen Agrobacterium tumefaciens produces a UPP adhesin, which is regulated by the intracellular second messenger cyclic diguanylate monophosphate (cdGMP). Prior studies revealed that DcpA, a diguanylate cyclase-phosphodiesterase (DGC-PDE), is crucial in control of UPP production and surface attachment. DcpA is regulated by PruR, a protein with distant similarity to enzymatic domains known to coordinate the molybdopterin cofactor (MoCo). Pterins are bicyclic nitrogen-rich compounds, several of which are formed via a non-essential branch of the folate biosynthesis pathway, distinct from MoCo. The pterin-binding protein PruR controls DcpA activity, fostering cdGMP breakdown and dampening its synthesis. Pterins are excreted and we report here that PruR associates with these metabolites in the periplasm, promoting interaction with the DcpA periplasmic domain. The pteridine reductase PruA, which reduces specific dihydro-pterin molecules to their tetrahydro forms, imparts control over DcpA activity through PruR. Tetrahydromonapterin preferentially associates with PruR relative to other related pterins, and the PruR-DcpA interaction is decreased in a pruA mutant. PruR and DcpA are encoded in an operon that is conserved amongst multiple Proteobacteria including mammalian pathogens. Crystal structures reveal that PruR and several orthologs adopt a conserved fold, with a pterin-specific binding cleft that coordinates the bicyclic pterin ring. These findings define a new pterin-responsive regulatory mechanism that controls biofilm formation and related cdGMP-dependent phenotypes in A. tumefaciens and is found in multiple additional bacterial pathogens.

SARS-CoV-2 papain-like protease (PLpro) inhibitory and antiviral activity of small molecule derivatives for drug leads

We report here the synthesis and biological evaluation of a series of small molecule SARS-CoV-2 PLpro inhibitors. We compared the activity of selected compounds in both SARS-CoV-1 and SARS-CoV-2 PLpro inhibitory and antiviral assays. We have synthesized and evaluated several new structural variants of previous leads against SARS-CoV-2 PLpro. The replacement of the carboxamide functionality with sulfonamide derivatives resulted in PLpro inhibitors with potent PLpro inhibitory and antiviral activity in VeroE6 cells similar to GRL0617. To obtain molecular insight, we created an optimized model of a potent sulfonamide derivative in the SARS-CoV-2 PLpro active site.

Stable isotope labeling as a promising tool for rapid drug susceptibility testing in Neisseria gonorrhoeae

The world is heading towards an era of intractable and impending untreatable N. gonorrhoeae, thereby underlining the significance of rapid and accurate prediction of drug resistance as an indispensable need of the hour. In the present study, we optimized and evaluated a stable isotope labeling-based approach using the MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry) for rapid and reliable detection of ciprofloxacin and azithromycin resistance in N. gonorrhoeae. All the isolates were cultured under three varied condition setups viz. medium supplemented with normal lysine, heavy lysine (isotope), and heavy lysine along with the antibiotics (ciprofloxacin/azithromycin), respectively. After incubation, spectra were acquired using the MALDI-TOF MS which were further screened for unique patterns (media-specific spectra) to differentiate drug-susceptible and resistant isolates. The results of the stable isotope labeling assay were comparable to the results of phenotypic methods used for susceptibility testing.

Four decades of continuing innovations in the development of antiretroviral therapy for HIV/AIDS: Progress to date and future challenges

The treatment of HIV-1 infection and AIDS represents one of the greatest challenges in medicine. While there is no cure for HIV/AIDS, truly remarkable progress has been made for treatment of HIV/AIDS patients today. The advent of combination antiretroviral therapy (cART) in the mid-1990s dramatically improved HIV-1 related morbidity, greatly prolonged life expectancy, and delayed progression of AIDS. Due to current antiretroviral therapy, the mortality rate for HIV infected patients is closely approaching the mortality rate for the general population. The long-term success of HIV-AIDS treatment requires continued enhancement of cART with further development of novel drugs that would exhibit fewer side effects, higher genetic barrier to the development of resistance, and longer action with durable virologic suppression. This editorial article provides a quick review of four decades of intense drug development research efforts targeting various viral enzymes and cellular host factors leading to the evolution of today's treatment of patients with HIV-1 infection and AIDS. It also touches on challenges of future treatment options.

Synthesis of optically active SARS-CoV-2 Mpro inhibitor drug nirmatrelvir (Paxlovid): an approved treatment of COVID-19

Nirmatrelvir (Paxlovid) is an FDA approved drug that targets SARS-COV-2 3CLprotease. We report an optically active synthesis of nirmatrelvir that avoids a critical epimerization step. Our initial coupling of gem-dimethyl bicyclo[3.1.0]proline methyl ester with tert-leucine-trifluoroacetamide using standard coupling reagents, EDC and HOBt, provided the corresponding dipeptide derivative in excellent yield, however, a significant epimerization was observed at the tert-leucine bearing chiral center. To circumvent this epimerization problem, we developed a ZnCl2-mediated direct N-trifluroacetylation of Boc-derivatives for the synthesis of nirmatrelvir. This protocol has been utilized for N-acyl bond formation with other anhydrides without epimerization. The present synthetic route can be useful for the synthesis of structural variants of nirmatrelvir without significant epimerization.

GRL-142 binds to and impairs HIV-1 integrase nuclear localization signal and potently suppresses highly INSTI-resistant HIV-1 variants

Nuclear localization signal (NLS) of HIV-1 integrase (IN) is implicated in nuclear import of HIV-1 preintegration complex (PIC). Here, we established a multiclass drug-resistant HIV-1 variant (HIVKGD) by consecutively exposing an HIV-1 variant to various antiretroviral agents including IN strand transfer inhibitors (INSTIs). HIVKGD was extremely susceptible to a previously reported HIV-1 protease inhibitor, GRL-142, with IC50 of 130 femtomolar. When cells were exposed to HIVKGD IN-containing recombinant HIV in the presence of GRL-142, significant decrease of unintegrated 2-LTR circular cDNA was observed, suggesting that nuclear import of PIC was severely compromised by GRL-142. X-ray crystallographic analyses revealed that GRL-142 interacts with NLS's putative sequence (DQAEHLK) and sterically blocks the nuclear transport of GRL-142-bound HIVKGD's PIC. Highly INSTI-resistant HIV-1 variants isolated from heavily INSTI-experienced patients proved to be susceptible to GRL-142, suggesting that NLS-targeting agents would serve as salvage therapy agents for highly INSTI-resistant variant-harboring individuals. The data should offer a new modality to block HIV-1 infectivity and replication and shed light on developing NLS inhibitors for AIDS therapy.

Total Synthesis of Neuroprotective Agents, (+)-Lycibarbarine A and (-)-Lycibarbarine B

We describe the convergent total syntheses of lycibarbarines A and B which are potent neuroprotective agents recently isolated from the fruits of Lycium barbarum. The synthesis highlights the construction of a unique spiro oxazine heterocyclic motif imbedded in these natural products. The synthesis is accomplished from the commercially available 8-hydroxyquinaline and 2-deoxy-d-ribose as key starting materials. The synthesis features a Reimer-Tiemann reaction, selective amine alkylation with a keto tosylate derivative, and spiroketalization to form an oxazine core.

Exploration of imatinib and nilotinib-derived templates as the P2-Ligand for HIV-1 protease inhibitors: Design, synthesis, protein X-ray structural studies, and biological evaluation

Structure-based design, synthesis, X-ray structural studies, and biological evaluation of a new series of potent HIV-1 protease inhibitors are described. These inhibitors contain various pyridyl-pyrimidine, aryl thiazole or alkylthiazole derivatives as the P2 ligands in combination with darunavir-like hydroxyethylamine sulfonamide isosteres. These heterocyclic ligands are inherent to kinase inhibitor drugs, such as nilotinib and imatinib. These ligands are designed to make hydrogen bonding interactions with the backbone atoms in the S2 subsite of HIV-1 protease. Various benzoic acid derivatives have been synthesized and incorporation of these ligands provided potent inhibitors that exhibited subnanomolar level protease inhibitory activity and low nanomolar level antiviral activity. Two high resolution X-ray structures of inhibitor-bound HIV-1 protease were determined. These structures provided important ligand-binding site interactions for further optimization of this class of protease inhibitors.

Evaluation of darunavir-derived HIV-1 protease inhibitors incorporating P2' amide-derivatives: Synthesis, biological evaluation and structural studies

We report here the synthesis and biological evaluation of darunavir derived HIV-1 protease inhibitors and their functional effect on enzyme inhibition and antiviral activity in MT-2 cell lines. The P2' 4-amino functionality was modified to make a number of amide derivatives to interact with residues in the S2' subsite of the HIV-1 protease active site. Several compounds exhibited picomolar enzyme inhibitory and low nanomolar antiviral activity. The X-ray crystal structure of the chloroacetate derivative bound to HIV-1 protease was determined. Interestingly, the active chloroacetate group converted to the acetate functionality during X-ray exposure. The structure revealed that the P2' carboxamide functionality makes enhanced hydrogen bonding interactions with the backbone atoms in the S2'-subsite.

HIV-1 protease with 10 lopinavir and darunavir resistance mutations exhibits altered inhibition, structural rearrangements and extreme dynamics

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 Ki values of 2-3 orders of magnitude worse for darunavir, lopinavir, and potent investigational inhibitor GRL-519. Crystal structures of the mutant were solved in a ligand-free form and in complex with GRL-519. The structures show altered interactions in the active site, flap-core interface, hydrophobic core, hinge region, and 80s loop compared to the corresponding wild-type protease structures. The ligand-free crystal structure exhibits a highly curled flap conformation which may amplify drug resistance. Molecular dynamics simulations performed for 1 μs on ligand-free dimers showed extremely large fluctuations in the flaps for PR10x compared to equivalent simulations on PR with a single L76V mutation or wild-type protease. This analysis offers insight about the synergistic effects of mutations in highly resistant variants.

Beyond darunavir: recent development of next generation HIV-1 protease inhibitors to combat drug resistance

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.

Recent Drug Development and Medicinal Chemistry Approaches for the Treatment of SARS-CoV-2 Infection and COVID-19

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.

Total Syntheses of the Proposed Structure of Iriomoteolide-1a, -1b and Synthesis of Three Derivatives for Structural Studies

Iriomoteolide-1a and iriomoteolide-1b are very potent cytotoxic agents, isolated from marine dinoflagellates. We carried out the enantioselective syntheses of the proposed structures of these natural products. However, our analysis of the NMR spectra of the synthetic iriomoteolide-1a and the natural products revealed that the structures of iriomoteolide-1a and iriomoteolide-1b were assigned incorrectly. Based upon our detailed analysis of the spectral data of the synthetic iriomoteolide-1a and the natural products, we rationally designed three diastereomers of the proposed structure of 1 in an effort to assign the correct structures. The key steps of our syntheses of the proposed structures of iriomoteolides involved a highly diastereoselective ene reaction, a carbocupration that utilized a Gilman reagent, a Julia-Kocienski olefination to couple fragments, and Yamaguchi macrolactonization to form the target macrolactone. This synthetic route was then utilized to carry out syntheses of three diastereomers to the proposed structure of 1. These diastereomeric structures show close similarities to natural iriomoteolide-1a; however, there were differences in their spectral data. While natural iriomoteolides exhibited potent cytotoxicies, our preliminary biological evaluation of synthetic iriomoteolide-1a, iriomoteolide-1b, and all three synthetic derivatives did not show any appreciable cytotoxic properties.

Remote ischaemic conditioning: defining critical criteria for success-report from the 11th Hatter Cardiovascular Workshop

The Hatter Cardiovascular Institute biennial workshop, originally scheduled for April 2020 but postponed for 2 years due to the Covid pandemic, was organised to debate and discuss the future of Remote Ischaemic Conditioning (RIC). This evolved from the large multicentre CONDI-2-ERIC-PPCI outcome study which demonstrated no additional benefit when using RIC in the setting of ST-elevation myocardial infarction (STEMI). The workshop discussed how conditioning has led to a significant and fundamental understanding of the mechanisms preventing cell death following ischaemia and reperfusion, and the key target cyto-protective pathways recruited by protective interventions, such as RIC. However, the obvious need to translate this protection to the clinical setting has not materialised largely due to the disconnect between preclinical and clinical studies. Discussion points included how to adapt preclinical animal studies to mirror the patient presenting with an acute myocardial infarction, as well as how to refine patient selection in clinical studies to account for co-morbidities and ongoing therapy. These latter scenarios can modify cytoprotective signalling and need to be taken into account to allow for a more robust outcome when powered appropriately. The workshop also discussed the potential for RIC in other disease settings including ischaemic stroke, cardio-oncology and COVID-19. The workshop, therefore, put forward specific classifications which could help identify so-called responders vs. non-responders in both the preclinical and clinical settings.

Asymmetric 1,2-Carbamoyl Rearrangement of Lithiated Chiral Oxazolidine Carbamates and Diastereoselective Synthesis of α-Hydroxy Amides

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.

Convergent synthesis of (+)-carambolaflavone A, an antidiabetic agent using a bismuth triflate-catalyzed C-aryl glycosylation

We describe a convergent total synthesis of carambolaflavone A, a natural flavonoid C-aryl glycoside with significant antihyperglycemic properties. The synthesis features a bismuth triflate-catalyzed stereoselective C-aryl glycosylation of a flavan derivative and an appropriately protected D-fucose derivative as the key step. Inexpensive and non-toxic bismuth triflate provided the best results among various other Lewis acids screened for this C-aryl glycosylation. The method can be utilized for the synthesis of other bioactive C-glycosyl flavonoids. The glycosylation partners were synthesized from commercially available (±)-naringenin and D-(+)-galactose, respectively. An oxidative bromination and elimination reaction sequence was utilized to construct the flavone. The natural product is obtained in 13 steps (longest linear sequence) from D-(+)-galactose.

Design, Synthesis and X-ray Structural Studies of Potent HIV-1 Protease Inhibitors Containing C-4 Substituted Tricyclic Hexahydro-furofuran derivatives as P2 ligands

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. Compound 4d with a difluoromethylphenyl P1 ligand and a cyclopropylaminobenzothiazole P2' ligand exhibited the most potent antiviral activity. Also, it maintained highly potent antiviral activity against a panel of highly multidrug-resistant HIV-1 variants. The corresponding inhibitor 5d 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, high resolution X-ray structures of inhibitors 4b and 5d -bound HIV-1 protease were determined and structural analyses are highlighted here.

U2 snRNA structure is influenced by SF3A and SF3B proteins but not by SF3B inhibitors

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.

Indole Chloropyridinyl Ester-Derived SARS-CoV-2 3CLpro Inhibitors: Enzyme Inhibition, Antiviral Efficacy, Structure-Activity Relationship, and X-ray Structural Studies

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.

Association of ischemic electrocardiographic changes in high-altitude areas with coronary angiography

Background

Soldiers native to lowlands, while sojourning at high altitude (HA), are referred to tertiary care centers with electrocardiographic (ECG) abnormalities. Exposure to HA may precipitate myocardial ischemia in subjects with underlying coronary artery disease (CAD). Conversely, it may produce physiological ECG changes mimicking those of CAD, causing a diagnostic dilemma. This study sought to correlate the presence of CAD on coronary angiography (CAG) with a putative diagnosis of CAD based on clinical findings and ECG.

Methods

A prospective study was conducted on patient's from HA areas, referred for evaluation for CAD to a single center at near-sea-level. Thirty-five minimally symptomatic/asymptomatic soldiers with ECG changes suggestive of CAD, underwent CAG. Correlation was sought between ECG and CAG evidence of CAD.

Results

The association of CAD on CAG with clinical and ECG diagnosis of CAD was not significant, 4 of the 35 soldiers (11.4%) showing CAG evidence of CAD (chi square 3.849, p = 0.697). The association between symptoms and coronary artery lesions was, also, not significant, only four of twenty-three (17.4%) minimally symptomatic subjects having CAD on CAG.

Conclusion

Insignificant numbers of previously healthy persons, who present with minimal symptoms and ECG changes suggestive of CAD while sojourning at HA, have coronary artery involvement on CAG. Those with incidental ECG changes, without symptomatology, do not have CAD on CAG.

Association between overcrowded households, multigenerational households, and COVID-19: a cohort study

OBJECTIVES

The role of overcrowded and multigenerational households as a risk factor for COVID-19 remains unmeasured. The objective of this study is to examine and quantify the association between overcrowded and multigenerational households and COVID-19 in New York City (NYC).

STUDY DESIGN

Cohort study.

METHODS

We conducted a Bayesian ecological time series analysis at the ZIP Code Tabulation Area (ZCTA) level in NYC to assess whether ZCTAs with higher proportions of overcrowded (defined as the proportion of the estimated number of housing units with more than one occupant per room) and multigenerational households (defined as the estimated percentage of residences occupied by a grandparent and a grandchild less than 18 years of age) were independently associated with higher suspected COVID-19 case rates (from NYC Department of Health Syndromic Surveillance data for March 1 to 30, 2020). Our main measure was an adjusted incidence rate ratio (IRR) of suspected COVID-19 cases per 10,000 population. Our final model controlled for ZCTA-level sociodemographic factors (median income, poverty status, White race, essential workers), the prevalence of clinical conditions related to COVID-19 severity (obesity, hypertension, coronary heart disease, diabetes, asthma, smoking status, and chronic obstructive pulmonary disease), and spatial clustering.

RESULTS

39,923 suspected COVID-19 cases were presented to emergency departments across 173 ZCTAs in NYC. Adjusted COVID-19 case rates increased by 67% (IRR 1.67, 95% CI = 1.12, 2.52) in ZCTAs in quartile four (versus one) for percent overcrowdedness and increased by 77% (IRR 1.77, 95% CI = 1.11, 2.79) in quartile four (versus one) for percent living in multigenerational housing. Interaction between both exposures was not significant (β_interaction = 0.99, 95% CI: 0.99-1.00).

CONCLUSIONS

Overcrowdedness and multigenerational housing are independent risk factors for suspected COVID-19. In the early phase of the surge in COVID cases, social distancing measures that increase house-bound populations may inadvertently but temporarily increase SARS-CoV-2 transmission risk and COVID-19 disease in these populations.

Structural basis of intron selection by U2 snRNP in the presence of covalent inhibitors

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.

Design and synthesis of herboxidiene derivatives that potently inhibit in vitro splicing

Herboxidiene is a potent antitumor agent that targets the SF3B subunit of the spliceosome. Herboxidiene possesses a complex structural architecture with nine stereocenters and design of potent less complex structures would be of interest as a drug lead as well as a tool for studying SF3B1 function in splicing. We investigated a number of C-6 modified herboxidiene derivatives in an effort to eliminate this stereocenter and, also to understand the importance of this functionality. The syntheses of structural variants involved a Suzuki-Miyaura cross-coupling reaction as the key step. The functionalized tetrahydrofuran core has been constructed from commercially available optically active tri-O-acetyl-d-glucal. We investigated the effect of these derivatives on splicing chemistry. The C-6 alkene derivative showed very potent splicing inhibitory activity similar to herboxidiene. Furthermore, the C-6 gem-dimethyl derivative also exhibited very potent in vitro splicing inhibitory activity comparable to herboxidiene.

Highly Diastereoselective Intramolecular Asymmetric Oxidopyrylium-olefin [5 + 2] Cycloaddition and Synthesis of 8-Oxabicyclo[3.2.1]oct-3-enone Containing Ring Systems

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 Derivatives: Chemical Syntheses and Biological Properties of Potent Splicing Inhibitors

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.

Enantioselective Total Synthesis of (+)-EBC-23, a Potent Anticancer Agent from the Australian Rainforest

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.

Herboxidiene Features That Mediate Conformation-Dependent SF3B1 Interactions to Inhibit Splicing

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 interfere with 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 model 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. In the context of recent structures of SF3B bound to inhibitor, 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 side chains in the inhibitor binding channel are needed to maintain inhibitor occupancy while counteracting the SF3B transition to a closed state that is required for stable U2 snRNP interactions with the intron.

A Structure-Based Discovery Platform for BACE2 and the Development of Selective BACE Inhibitors

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.

A small molecule compound with an indole moiety inhibits the main protease of SARS-CoV-2 and blocks virus replication

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.

Synthesis of amide derivatives for electron deficient amines and functionalized carboxylic acids using EDC and DMAP and a catalytic amount of HOBt as the coupling reagents

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.

The Chiron Approach to (3R,3aS,6aR)-Hexahydrofuro[2,3-b]furan-3-ol, a Key Subunit of HIV-1 Protease Inhibitor Drug, Darunavir

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.

Design, Synthesis, and X-ray Studies of Potent HIV-1 Protease Inhibitors with P2-Carboxamide Functionalities

The design, synthesis, biological evaluation, and X-ray structural studies are reported for a series of highly potent HIV-1 protease inhibitors. The inhibitors incorporated stereochemically defined amide-based bicyclic and tricyclic ether derivatives as the P2 ligands with (R)-hydroxyethylaminesulfonamide transition-state isosteres. A number of inhibitors showed excellent HIV-1 protease inhibitory and antiviral activity; however, ligand combination is critical for potency. Inhibitor 4h with a difluorophenylmethyl as the P1 ligand, crown-THF-derived acetamide as the P2 ligand, and a cyclopropylaminobenzothiazole P2'-ligand displayed very potent antiviral activity and maintained excellent antiviral activity against selected multidrug-resistant HIV-1 variants. A high resolution X-ray structure of inhibitor 4h-bound HIV-1 protease provided molecular insight into the binding properties of the new inhibitor.

Lewis Acid-Catalyzed Vinyl Acetal Rearrangement of 4,5-Dihydro-1,3-dioxepines: Stereoselective Synthesis of cis- and trans-2,3-Disubstituted Tetrahydrofurans

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.

GRL-0920, an Indole Chloropyridinyl Ester, Completely Blocks SARS-CoV-2 Infection

We assessed various newly generated compounds that target the main protease (Mpro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and various previously known compounds reportedly active against SARS-CoV-2, employing RNA quantitative PCR (RNA-qPCR), cytopathicity assays, and immunocytochemistry. Here, we show that two indole-chloropyridinyl-ester derivatives, GRL-0820 and GRL-0920, exerted potent activity against SARS-CoV-2 in cell-based assays performed using VeroE6 cells and TMPRSS2-overexpressing VeroE6 cells. While GRL-0820 and the nucleotide analog remdesivir blocked SARS-CoV-2 infection, viral breakthrough occurred. No significant anti-SARS-CoV-2 activity was found for several compounds reportedly active against SARS-CoV-2 such as lopinavir, nelfinavir, nitazoxanide, favipiravir, and hydroxychroloquine. In contrast, GRL-0920 exerted potent activity against SARS-CoV-2 (50% effective concentration [EC50] = 2.8 μM) and dramatically reduced the infectivity, replication, and cytopathic effect of SARS-CoV-2 without significant toxicity as examined with immunocytochemistry. Structural modeling shows that indole and chloropyridinyl of the derivatives interact with two catalytic dyad residues of Mpro, Cys145 and His41, resulting in covalent bonding, which was verified using high-performance liquid chromatography-mass spectrometry (HPLC/MS), suggesting that the indole moiety is critical for the anti-SARS-CoV-2 activity of the derivatives. GRL-0920 might serve as a potential therapeutic for coronavirus disease 2019 (COVID-19) and might be optimized to generate more-potent anti-SARS-CoV-2 compounds.IMPORTANCE Targeting the main protease (Mpro) of SARS-CoV-2, we identified two indole-chloropyridinyl-ester derivatives, GRL-0820 and GRL-0920, active against SARS-CoV-2, employing RNA-qPCR and immunocytochemistry and show that the two compounds exerted potent activity against SARS-CoV-2. While GRL-0820 and remdesivir blocked SARS-CoV-2 infection, viral breakthrough occurred as examined with immunocytochemistry. In contrast, GRL-0920 completely blocked the infectivity and cytopathic effect of SARS-CoV-2 without significant toxicity. Structural modeling showed that indole and chloropyridinyl of the derivatives interacted with two catalytic dyad residues of Mpro, Cys145 and His41, resulting in covalent bonding, which was verified using HPLC/MS. The present data should shed light on the development of therapeutics for COVID-19, and optimization of GRL-0920 based on the present data is essential to develop more-potent anti-SARS-CoV-2 compounds for treating COVID-19.

Roles of Re-entrant cluster glass state and spin-lattice coupling in magneto-dielectric behavior of giant dielectric double perovskite La1.8Pr0.2CoFeO6

La based Co-Fe combined double perovskite (La1.8Pr0.2CoFeO6) was synthesized and the dielectric (zero-field and in-field), magnetic, x-ray absorption and Raman spectroscopy measurements have been investigated for La1.8Pr0.2CoFeO6 double perovskite. The existence of re-entrant cluster glass state is observed. The magneto-dielectric (MD) is found in two temperature regions (25-80 K and 125-275 K). It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin-lattice coupling. Furthermore, the very large dielectric constant and the low loss suggest that La1.8Pr0.2CoFeO6 is very important from the application point of view.

Single atom changes in newly synthesized HIV protease inhibitors reveal structural basis for extreme affinity, high genetic barrier, and adaptation to the HIV protease plasticity

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 (PR_WT) and highly-multi-PI-resistance-associated PR_DRV^R_P51 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.

Extraordinary magnetic properties of double perovskite Eu2CoMnO6 wide band gap semiconductor

Some novel magnetic behaviours in double perovskite Eu2CoMnO6 (ECMO) have been reported. The x-ray photoemission spectroscopy study shows the presence of mixed valence states of transition metal ions. The UV-visible absorption spectroscopic study suggests that the ECMO has a direct wide band gap. A second-order magnetic phase transition as a sudden jump in the magnetization curve has been observed around 124.5 K. The large bifurcation between the zero field cooling and field cooling, suggests existence of strong spin frustration in the system. The inverse DC susceptibility confirms the presence of the Griffiths like phase. Sharp steps in magnetization have been observed in the M-H curve at 2 K, which vanishes on increasing temperature. The AC susceptibility study demonstrates the Hopkinson like effect as well as the presence of volume spin-glass-like behaviour. The temperature dependent Raman spectrum shows the presence of spin-phonon coupling.

Copper-Catalyzed Stille Cross-Coupling Reaction and Application in the Synthesis of the Spliceostatin Core Structure

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.

Drug Development and Medicinal Chemistry Efforts toward SARS-Coronavirus and Covid-19 Therapeutics

The COVID-19 pandemic caused by SARS-CoV-2 infection is spreading at an alarming rate and has created an unprecedented health emergency around the globe. There is no effective vaccine or approved drug treatment against COVID-19 and other pathogenic coronaviruses. The development of antiviral agents is an urgent priority. Biochemical events critical to the coronavirus replication cycle provided a number of attractive targets for drug development. These include, spike protein for binding to host cell-surface receptors, proteolytic enzymes that are essential for processing polyproteins into mature viruses, and RNA-dependent RNA polymerase for RNA replication. There has been a lot of ground work for drug discovery and development against these targets. Also, high-throughput screening efforts have led to the identification of diverse lead structures, including natural product-derived molecules. This review highlights past and present drug discovery and medicinal-chemistry approaches against SARS-CoV, MERS-CoV and COVID-19 targets. The review hopes to stimulate further research and will be a useful guide to the development of effective therapies against COVID-19 and other pathogenic coronaviruses.

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.