Comparative pharmacokinetic profile of cyclosporine (CsA) with a decapeptide and a linear analogue.

The synthesis and in vivo pharmacokinetic profile of an analogue of cyclosporine is disclosed. An acyclic congener was also profiled in in vitro assays to compare cell permeability. The compounds possess similar calculated and measured molecular descriptors however have different behaviors in an RRCK assay to assess cell permeability.

Crystal structure of the polo-box domain of polo-like kinase 2.

Polo-like kinase 2 (PLK2) is a crucial regulator in cell cycle progression, DNA damage response, and neuronal activity. PLK2 is characterized by the conserved N-terminal kinase domain and the unique C-terminal polo-box domain (PBD). The PBD mediates diverse functions of PLK2 by binding phosphorylated Ser-pSer/pThr motifs of its substrates. Here, we report the first crystal structure of the PBD of PLK2. The overall structure of the PLK2 PBD is similar to that of the PLK1 PBD, which is composed by two polo boxes each contain ß6α structures that form a 12-stranded ß sandwich domain. The edge of the interface between the two polo boxes forms the phosphorylated Ser-pSer/pThr motifs binding cleft. On the hand, the peripheral regions around the core binding cleft of the PLK2 PBD is distinct from that of the PLK1 PBD, which might confer the substrate specificity of the PBDs of the polo-like kinase family.

Crystal structure of the death effector domains of caspase-8.

Caspase-8 is a key mediator in various biological processes such as apoptosis, necroptosis, inflammation, T/B cells activation, and cell motility. Caspase-8 is characterized by the N-terminal tandem death effector domains (DEDs) and the C-terminal catalytic protease domain. The DEDs mediate diverse functions of caspase-8 through homotypic interactions of the DEDs between caspase-8 and its partner proteins. Here, we report the first crystal structure of the DEDs of caspase-8. The overall structure of the DEDs of caspase-8 is similar to that of the DEDs of vFLIP MC159, which is composed of two tandem death effector domains that closely associate with each other in a head-to-tail manner. Structural analysis reveals distinct differences in the region connecting helices α2b and α4b in the second DED of the DEDs between caspase-8 and MC159, in which the helix α3b in MC159 is replaced by a loop in caspase-8. Moreover, the different amino acids in this region might confer the distinct features of solubility and aggregation for the DEDs of caspase-8 and MC159.

Structure-based design of benzo[e]isoindole-1,3-dione derivatives as selective GSK-3ß inhibitors to activate Wnt/ß-catenin pathway.

Deregulation of Wnt/ß-catenin pathway is closely related to the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), and glycogen synthase kinase 3ß (GSK-3ß), the central negative regulator of Wnt pathway, is regarded as an important target for these diseases. Here, we report a series of benzo[e]isoindole-1,3-dione derivatives as selective GSK-3ß inhibitors by rational-design and synthesis, which show high selectivity against GSK-3ß over Cyclin-dependent kinase 2 (CDK2), and significantly activate the cellular Wnt/ß-catenin pathway. The structure-activity relationship of these GSK-3ß inhibitors was also explored by in silico molecular docking.

Identification and semisynthesis of (-)-anisomelic acid as oral agent against SARS-CoV-2 in mice.

(-)-Anisomelic acid, isolated from Anisomeles indica (L.) Kuntze (Labiatae) leaves, is a macrocyclic cembranolide with a trans-fused α-methylene-γ-lactone motif. Anisomelic acid effectively inhibits SARS-CoV-2 replication and viral-induced cytopathic effects with an EC50 of 1.1 and 4.3 µM, respectively. Challenge studies of SARS-CoV-2-infected K18-hACE2 mice showed that oral administration of anisomelic acid and subcutaneous dosing of remdesivir can both reduce the viral titers in the lung tissue at the same level. To facilitate drug discovery, we used a semisynthetic approach to shorten the project timelines. The enantioselective semisynthesis of anisomelic acid from the naturally enriched and commercially available starting material (+)-costunolide was achieved in five steps with a 27% overall yield. The developed chemistry provides opportunities for developing anisomelic-acid-based novel ligands for selectively targeting proteins involved in viral infections.

Understanding the binding mode and function of BMS-488043 against HIV-1 viral entry.

A recently discovered small-molecule inhibitor, BMS-488043 (BMS-488), for the invasion of Human immunodeficiency virus Type 1 (HIV-1), shows a high activity against the entry of diversified HIV-1. Docking and molecular dynamic studies have been carried out to understand the binding mode of BMS-488 to gp120 as well as the effect of the small molecule on the conformational change of gp120 induced by CD4 binding. The results indicate that BMS-488 can accommodate in the CD4 binding pocket and interfere the CD4 binding in a noncompetitive mode. The piperazine group of BMS-488 prevents the bridging sheet formation of gp120 induced by the CD4 binding mainly through blocking the rotation of the Trp112 located on the α1 helix of gp120. The bridging sheet formation cannot be blocked for the W112A mutant of gp120 due to the reduced steric hindrance, in agreement with its significant resistance to the BMS inhibitor. The aza-indole ring is likely to interfere the exposure of gp41 by stacking within the ß3-ß5 and LB loops to disrupt the close packing of Pro212-His66-Phe210. The mode of action of BMS-488 also accommodates many mutagenesis results related to BMS-488 activity.

Intermediate-assisted multifunctional catalysis in the conversion of flavin to 5,6-dimethylbenzimidazole by BluB: a density functional theory study.

BluB is a distinct flavin destructase that catalyzes a complex oxygen-dependent conversion of reduced flavin mononucleotide (FMNH(2)) to form 5,6-dimethylbenzimidazole (DMB), the lower ligand of vitamin B(12). The catalyzed mechanism remains a challenge due to the discrepancy between the complexity of the conversion and the relative simplicity of the active site of BluB. In this study, we have explored the detailed conversion mechanism by using the hybrid density functional method B3LYP on an active site model of BluB consisting of 144 atoms. The results indicate that the conversion involves more than 14 sequential steps in two distinct stages. In the first stage, BluB catalyzes the incorporation of dioxygen, and the fragmentation of the isoalloxazine ring of FMNH(2) to form alloxan and the ribityl dimethylphenylenediimine (DMPDI); in the second stage, BluB exploits alloxan as a multifunctional cofactor, such as a proton donor, a proton acceptor, and a hydride acceptor, to catalyze the remaining no fewer than 10 steps of the reaction. The retro-aldol cleavage of the C1'-C2' bond of DMPDI is the rate-determining step with a barrier of about 21.6 kcal/mol, which produces D-erythrose 4-phosphate (E4P) and the ring-closing precursor of DMB. The highly conserved residue Asp32 plays critical roles in multiple steps of the conversion by serving as a proton acceptor or a proton shuttle, and another conserved residue Ser167 plays its catalytic role mainly in the rate-determining step by stabilizing the protonated retro-aldol precursor. These results are consistent with the available experimental observations. More significantly, the novel intermediate-assisted mechanism not only provides significant insights into understanding the mechanism underlying the power of the simple BluB catalyzing the complex conversion of FMNH(2) to DMB, but also represents a new type of intermediate-assisted multifunctional catalysis in an enzymatic reaction.

Theoretical studies on the mechanism and stereoselectivity of Rh(Phebox)-catalyzed asymmetric reductive aldol reaction.

Density functional theory calculations (B3LYP) have been carried out to understand the mechanism and stereochemistry of an asymmetric reductive aldol reaction of benzaldehyde and tert-butyl acrylate with hydrosilanes catalyzed by Rh(Phebox-ip)(OAc)(2)(OH(2)). According to the calculations, the reaction proceeds via five steps: (1) oxidative addition of hydrosilane, (2) hydride migration to carbon-carbon double bond of tert-butyl acrylate, which determines the chirality at C2, (3) tautomerization from rhodium bound C-enolate to rhodium bound O-enolate, (4) intramolecular aldol reaction, which determines the chirality at C3 and consequently the anti/syn-selectivity, and (5) reductive elimination to release aldol product. The hydride migration is the rate-determining step with a calculated activation energy of 23.3 kcal mol(-1). In good agreement with experimental results, the formation of anti-aldolates is found to be the most favorable pathway. The observed Si-facial selectivity in both hydride migration and aldol reaction are well-rationalized by analyzing crucial transition structures. The Re-facial attack transition state is disfavored because of steric hindrance between the isopropyl group of the catalyst and the tert-butyl acrylate.

Targeting Extracellular Cyclophilin A via an Albumin-Binding Cyclosporine A Analogue.

An albumin-binding CsA analogue 4MCsA was achieved by attachment of a thiol-reactive maleimide group at the side-chain of P4 position of CsA derivative. 4MCsA was semi-synthesized from CsA, and the cell-impermeability of albumin-4MCsA was detected by mass spectrometry and a competitive flow cytometry. 4MCsA exhibits inhibition of chemotaxis activity and inflammation by targeting extracellular CypA without immunosuppressive effect and cellular toxicity. These combined results suggested that 4MCsA can be restricted extracellularly through covalently binding to Cys34 of albumin with its maleimide group, and regulate the functions of cyclophilin A extracellularly.

A theoretical study on the catalytic mechanism of Mus musculus adenosine deaminase.

The catalytic mechanism of Mus musculus adenosine deaminase (ADA) has been studied by quantum mechanics and two-layered ONIOM calculations. Our calculations show that the previously proposed mechanism, involving His238 as the general base to activate the Zn-bound water, has a high activation barrier of about 28 kcal/mol at the proposed rate-determining nucleophilic addition step, and the corresponding calculated kinetic isotope effects are significantly different from the recent experimental observations. We propose a revised mechanism based on calculations, in which Glu217 serves as the general base to abstract the proton of the Zn-bound water, and the protonated Glu217 then activates the substrate for the subsequent nucleophilic addition. The rate-determining step is the proton transfer from Zn-OH to 6-NH(2) of the tetrahedral intermediate, in which His238 serves as a proton shuttle for the proton transfer. The calculated kinetic isotope effects agree well with the experimental data, and calculated activation energy is also consistent with the experimental reaction rate.

Oxa-bicyclocalixarenes: a new cage for anions via C-H...anion hydrogen bonds and anion...pi interactions.

Density functional theory calculations indicate that the cage molecule 4 can trap F- in the gas phase (-80.5 kcal/mol) as well as in CH2Cl2 (-14.7 kcal/mol) via strong C-H...F- hydrogen bonds and pi...F- interaction.

Theoretical study of the catalytic mechanism and metal-ion dependence of peptide deformylase.

The reaction pathway of deformylation catalyzed by E. coli peptide deformylase (PDF) has been investigated by the density functional theory method of PBE1PBE on a small model and by a two-layer ONIOM method on a realistic protein model. The deformylation proceeds in sequential steps involving nucleophilic addition of metal-coordinated water/hydroxide to the carbonyl carbon of the formyl group, proton transfer, and cleavage of the C-N bond. The first step is rate-determining for the deformylation, which occurs through a pentacoordinated metal center. The estimated activation energies with the ONIOM method are about 23.0, 15.0, and 14.9 kcal/mol for Zn-, Ni-, and Fe-PDFs, respectively. These calculated barriers are in close agreement with experimental observations. Our results demonstrate that the preference for metal coordination geometry exerts a significant influence on the catalytic activity of PDFs by affecting the activation of the carbonyl group of the substrate, the deprotonation of the metal-coordinated water, and the stabilization of the transition state. This preference for coordination geometry is mainly determined by the ligand environment and the intrinsic electronic structures of the metal center in the active site of the PDFs.

Oxygen insertion of o-quinone under catalytic hydrogenation conditions.

An oxygen-insertion reaction that transforms an o-quinone and a conjugated α-diketone substrate into an anhydride product or derivative under catalytic hydrogenation conditions is reported. The experiments and computations indicate that the oxygen insertion proceeds via a radical mechanism mediated by an acetoxyl radical.

Understanding of the bridging sheet formation of HIV-1 glycoprotein gp120.

As the initial step of the entry of HIV-1 into cells, the interaction of CD4 with gp120 is a central area of concern in HIV-1 biology and intervention studies. CD4 binding induces large conformational changes to gp120, such as the formation of the bridging sheet between the V1/V2 stem and beta20/beta21. Understanding the dynamic process and the mechanism that leads to the formation of the bridging sheet is important. We have studied the formation of the bridging sheet via extensive molecular dynamics simulations on a modeled intermediate state. The intermediate state is derived from the crystal structure of the gp120/CD4 complex with rotation of the alpha1 helix and separation of the V1/V2 stem from beta20/beta21. The molecular dynamics simulations reveal that CD4-bound gp120 leads to the refolding of the bridging sheet but the CD4-free gp120 leads to structures similar to unliganded structures of SIV gp120. The bridging sheet refolds with the S375W mutant, but it does not refold with the W112A and S375W/T257S mutants. Our simulation results are in agreement with experimental observations, and they reveal the importance of the formation of the hydrophobic core to the conformational change of CD4-induced gp120. Other experimental observations, including variations in the binding entropy in different mutants, are also qualitatively reproduced.

One-pot synthesis of quinoline-based tetracycles by a tandem three-component reaction.

A practical one-pot synthetic strategy for the efficient synthesis of a range of structurally interesting and bioactive quinoline-based tetracycles has been developed. A key step in the synthesis is a tandem three-component reaction of heteroaromatic amine, methyl 2-formylbenzoate and (t)butyl isonitrile, followed by TFA-mediated lactamization via intramolecular aminolysis of an adjacent ester. Results related to a kinase-panel screening for several selected compounds are also discussed in this article.

A catalytic mechanism revealed by the crystal structures of the imidazolonepropionase from Bacillus subtilis.

Imidazolonepropionase (EC 3.5.2.7) catalyzes the third step in the universal histidine degradation pathway, hydrolyzing the carbon-nitrogen bonds in 4-imidazolone-5-propionic acid to yield N-formimino-l-glutamic acid. Here we report the crystal structures of the Bacillus subtilis imidazolonepropionase and its complex at 2.0-A resolution with substrate analog imidazole-4-acetic acid sodium (I4AA). The structure of the native enzyme contains two domains, a TIM (triose-phosphate isomerase) barrel domain with two insertions and a small beta-sandwich domain. The TIM barrel domain is quite similar to the members of the alpha/beta barrel metallo-dependent hydrolase superfamily, especially to Escherichia coli cytosine deaminase. A metal ion was found in the central cavity of the TIM barrel and was tightly coordinated to residues His-80, His-82, His-249, Asp-324, and a water molecule. X-ray fluorescence scan analysis confirmed that the bound metal ion was a zinc ion. An acetate ion, 6 A away from the zinc ion, was also found in the potential active site. In the complex structure with I4AA, a substrate analog, I4AA replaced the acetate ion and contacted with Arg-89, Try-102, Tyr-152, His-185, and Glu-252, further defining and confirming the active site. The detailed structural studies allowed us to propose a zinc-activated nucleophilic attack mechanism for the hydrolysis reaction catalyzed by the enzyme.