(5S)-5-Benzylswainsonines as potent and selective inhibitors of Golgi α-mannosidase II: synthesis, enzyme evaluation and molecular modelling.

Development of novel anti-cancer therapeutics based on Golgi α-mannosidase II (GMII) inhibition is considerably impeded by an undesired co-inhibition of lysosomal α-mannosidase leading to severe side-effects. In this contribution, we describe a fully stereoselective synthesis of (5S)-5-[4-(halo)benzyl]swainsonines as highly potent and selective inhibitors of GMII. The synthesis starts from a previously reported aldehyde readily available from l-ribose, and the key features include an intramolecular reductive amination with substrate-controlled stereoselectivity and a late-stage derivatisation of the benzyl group via ipso-substitution. These novel swainsonine analogues were found to be nanomolar inhibitors of the Golgi-type α-mannosidase AMAN-2 (Ki = 23-75 nM) with excellent selectivity (selectivity index = 205-870) over the lysosomal-type Jack bean α-mannosidase. Finally, molecular docking and pKa calculations were performed to provide more insight into the structure of the inhibitor:enzyme complexes, and a pair interaction energy analysis (FMO-PIEDA) was carried out to rationalise the observed potency and selectivity of the inhibitors.

A Comparison of the Antibacterial Efficacy of Carbohydrate Lipid-like (Thio)Ether, Sulfone, and Ester Derivatives against Paenibacillus larvae.

Paenibacillus larvae is the causative agent of American foulbrood (AFB), the most serious bacterial disease affecting developing honeybee larvae and pupas. In this study, a library of 24 (thio)glycosides, glycosyl sulfones, 6-O-esters, and ethers derived from d-mannose, d-glucose, and d-galactose having C10 or C12 alkyl chain were evaluated for their antibacterial efficacy against two P. larvae strains. The efficacy of the tested compounds determined as minimal inhibitory concentrations (MICs) varied greatly. Generally, dodecyl derivatives were found to be more potent than their decylated analogs. Thioglycosides were more efficient than glycosides and sulfones. The activity of the 6-O-ether derivatives was higher than that of their ester counterparts. Seven derivatives with dodecyl chain linked (thio)glycosidically or etherically at C-6 showed high efficacy against both P. larvae strains (MICs ranged from 12.5 µM to 50 µM). Their efficacies were similar or much higher than those of selected reference compounds known to be active against P. larvae-lauric acid, monolaurin, and honeybee larval food components, 10-hydroxy-2-decenoic acid, and sebacic acid (MICs ranged from 25 µM to 6400 µM). The high efficacies of these seven derivatives suggest that they could increase the anti-P. larvae activity of larval food and improve the resistance of larvae to AFB disease through their application to honeybee colonies.

Synthesis, α-mannosidase inhibition studies and molecular modeling of 1,4-imino-á´ -lyxitols and their C-5-altered N-arylalkyl derivatives.

A synthesis of 1,4-imino-ᴅ-lyxitols and their N-arylalkyl derivatives altered at C-5 is reported. Their inhibitory activity and selectivity toward four GH38 α-mannosidases (two Golgi types: GMIIb from Drosophila melanogaster and AMAN-2 from Caenorhabditis elegans, and two lysosomal types: LManII from Drosophila melanogaster and JBMan from Canavalia ensiformis) were investigated. 6-Deoxy-DIM was found to be the most potent inhibitor of AMAN-2 (K i = 0.19 µM), whose amino acid sequence and 3D structure of the active site are almost identical to the human α-mannosidase II (GMII). Although 6-deoxy-DIM was 3.5 times more potent toward AMAN-2 than DIM, their selectivity profiles were almost the same. N-Arylalkylation of 6-deoxy-DIM resulted only in a partial improvement as the selectivity was enhanced at the expense of potency. Structural and physicochemical properties of the corresponding inhibitor:enzyme complexes were analyzed by molecular modeling.

Molecular Modeling Insights into the Structure and Behavior of Integrins: A Review.

Integrins are heterodimeric glycoproteins crucial to the physiology and pathology of many biological functions. As adhesion molecules, they mediate immune cell trafficking, migration, and immunological synapse formation during inflammation and cancer. The recognition of the vital roles of integrins in various diseases revealed their therapeutic potential. Despite the great effort in the last thirty years, up to now, only seven integrin-based drugs have entered the market. Recent progress in deciphering integrin functions, signaling, and interactions with ligands, along with advancement in rational drug design strategies, provide an opportunity to exploit their therapeutic potential and discover novel agents. This review will discuss the molecular modeling methods used in determining integrins' dynamic properties and in providing information toward understanding their properties and function at the atomic level. Then, we will survey the relevant contributions and the current understanding of integrin structure, activation, the binding of essential ligands, and the role of molecular modeling methods in the rational design of antagonists. We will emphasize the role played by molecular modeling methods in progress in these areas and the designing of integrin antagonists.

1,4-Dideoxy-1,4-imino-D- and L-lyxitol-based inhibitors bind to Golgi α-mannosidase II in different protonation forms.

The development of effective inhibitors of Golgi α-mannosidase II (GMII, E.C.3.2.1.114) with minimal off-target effects on phylogenetically-related lysosomal α-mannosidase (LMan, E.C.3.2.1.24) is a complex task due to the complicated structural and chemical properties of their active sites. The pKa values (and also protonation forms in some cases) of several ionizable amino acids, such as Asp, Glu, His or Arg of enzymes, can be changed upon the binding of the inhibitor. Moreover, GMII and LMan work under different pH conditions. The pKa calculations on large enzyme-inhibitor complexes and FMO-PIEDA energy decomposition analysis were performed on the structures of selected inhibitors obtained from docking and hybrid QM/MM calculations. Based on the calculations, the roles of the amino group incorporated in the ring of the imino-D-lyxitol inhibitors and some ionizable amino acids of Golgi-type (Asp270-Asp340-Asp341 of Drosophila melanogaster α-mannosidase dGMII) and lysosomal-type enzymes (His209-Asp267-Asp268 of Canavalia ensiformis α-mannosidase, JBMan) were explained in connection with the observed inhibitory properties. The pyrrolidine ring of the imino-D-lyxitols prefers at the active site of dGMII the neutral form while in JBMan the protonated form, whereas that of imino-L-lyxitols prefers the protonation form in both enzymes. The calculations indicate that the binding mechanism of inhibitors to the active-site of α-mannosidases is dependent on the inhibitor structure and could be used to design new selective inhibitors of GMII. A series of novel synthetic N-substituted imino-D-lyxitols were evaluated with four enzymes from the glycoside hydrolase GH38 family (two of Golgi-type, Drosophila melanogaster GMIIb and Caenorhabditis elegans AMAN-2, and two of lysosomal-type, Drosophila melanogaster LManII and Canavalia ensiformis JBMan, enzymes). The most potent structures [N-9-amidinononyl and N-2-(1-naphthyl)ethyl derivatives] inhibited GMIIb (Ki = 40 nM) and AMAN-2 (Ki = 150 nM) with a weak selectivity index (SI) toward Golgi-type enzymes of IC50(LManII)/IC50(GMIIb) = 35 or IC50(JBMan)/IC50(AMAN-2) = 86. On the other hand, weaker micromolar inhibitors, such as N-2-naphthylmethyl or 4-iodobenzyl derivatives [IC50(GMIIb) = 2.4 µM and IC50 (AMAN-2) = 7.6 µM], showed a significant SI in the range from 111 to 812.

Synthesis of N-benzyl substituted 1,4-imino-l-lyxitols with a basic functional group as selective inhibitors of Golgi α-mannosidase IIb.

Inhibition of the biosynthesis of complex N-glycans in the Golgi apparatus is one of alternative ways to suppress growth of tumor tissue. Eight N-benzyl substituted 1,4-imino-l-lyxitols with basic functional groups (amine, amidine, guanidine), hydroxyl and fluoro groups were prepared, optimized their syntheses and tested for their ability to inhibit several α-mannosides from the GH family 38 (GMIIb, LManII and JBMan) as models for human Golgi and lysosomal α-mannoside II. All compounds were found to be selective inhibitors of GMIIb. The most potent structure bearing guanidine group, inhibited GMIIb at the micromolar level (Ki = 19 ±â€¯2 µM) while no significant inhibition (>2 mM) of LManII and JBMan was observed. Based on molecular docking and pKa calculations this structure may form two salt bridges with aspartate dyad of the target enzyme improving its inhibitory potency compared with other N-benzyl substituted derivatives published in this and previous studies.

N-Benzyl Substitution of Polyhydroxypyrrolidines: The Way to Selective Inhibitors of Golgi α-Mannosidase†II.

Inhibition of the biosynthesis of complex N-glycans in the Golgi apparatus influences progress of tumor growth and metastasis. Golgi α-mannosidase II (GMII) has become a therapeutic target for drugs with anticancer activities. One critical task for successful application of GMII drugs in medical treatments is to decrease their unwanted co-inhibition of lysosomal α-mannosidase (LMan), a weakness of all known potent GMII inhibitors. A series of novel N-substituted polyhydroxypyrrolidines was synthesized and tested with modeled GH38 α-mannosidases from Drosophila melanogaster (GMIIb and LManII). The most potent structures inhibited GMIIb (Ki =50-76 µm, as determined by enzyme assays) with a significant selectivity index of IC50 (LManII)/IC50 (GMIIb) >100. These compounds also showed inhibitory activities in in vitro assays with cancer cell lines (leukemia, IC50 =92-200 µm) and low cytotoxic activities in normal fibroblast cell lines (IC50 >200 µm). In addition, they did not show any significant inhibitory activity toward GH47 Aspergillus saitoiα1,2-mannosidase. An appropriate stereo configuration of hydroxymethyl and benzyl functional groups on the pyrrolidine ring of the inhibitor may lead to an inhibitor with the required selectivity for the active site of a target α-mannosidase.

Using DFT methodology for more reliable predictive models: Design of inhibitors of Golgi α-Mannosidase II.

Human Golgi α-mannosidase II (GMII), a zinc ion co-factor dependent glycoside hydrolase (E.C.3.2.1.114), is a pharmaceutical target for the design of inhibitors with anti-cancer activity. The discovery of an effective inhibitor is complicated by the fact that all known potent inhibitors of GMII are involved in unwanted co-inhibition with lysosomal α-mannosidase (LMan, E.C.3.2.1.24), a relative to GMII. Routine empirical QSAR models for both GMII and LMan did not work with a required accuracy. Therefore, we have developed a fast computational protocol to build predictive models combining interaction energy descriptors from an empirical docking scoring function (Glide-Schrödinger), Linear Interaction Energy (LIE) method, and quantum mechanical density functional theory (QM-DFT) calculations. The QSAR models were built and validated with a library of structurally diverse GMII and LMan inhibitors and non-active compounds. A critical role of QM-DFT descriptors for the more accurate prediction abilities of the models is demonstrated. The predictive ability of the models was significantly improved when going from the empirical docking scoring function to mixed empirical-QM-DFT QSAR models (Q(2)=0.78-0.86 when cross-validation procedures were carried out; and R(2)=0.81-0.83 for a testing set). The average error for the predicted ΔGbind decreased to 0.8-1.1kcalmol(-1). Also, 76-80% of non-active compounds were successfully filtered out from GMII and LMan inhibitors. The QSAR models with the fragmented QM-DFT descriptors may find a useful application in structure-based drug design where pure empirical and force field methods reached their limits and where quantum mechanics effects are critical for ligand-receptor interactions. The optimized models will apply in lead optimization processes for GMII drug developments.

'Click chemistry' synthesis of 1-(α-D-mannopyranosyl)-1,2,3-triazoles for inhibition of α-mannosidases.

Three new triazole conjugates derived from d-mannose were synthesized and assayed in in vitro assays to investigate their ability to inhibit α-mannosidase enzymes from the glycoside hydrolase (GH) families 38 and 47. The triazole conjugates were more selective for a GH47 α-mannosidase (Aspergillus saitoi α1,2-mannosidase), showing inhibition at the micromolar level (IC50 values of 50-250 µM), and less potent towards GH38 mannosidases (IC50 values in the range of 0.5-6 mM towards jack bean α-mannosidase or Drosophila melanogaster lysosomal and Golgi α-mannosidases). The highest selectivity ratio [IC50(GH38)/IC50(GH47)] of 100 was exhibited by the phenyltriazole conjugate. To understand structure-activity properties of synthesized compounds, 3-D complexes of inhibitors with α-mannosidases were built using molecular docking calculations.

Theoretical study of enzymatic catalysis explains why the trapped covalent intermediate in the E303C mutant of glycosyltransferase GTB was not detected in the wild-type enzyme.

Hybrid quantum mechanics/molecular mechanics calculations were used to study the catalytic mechanism of the retaining human α-(1,3)-galactosyltransferase (GTBWT) and its E303C mutant (GTBE303C). Both backside (via covalent glycosyl-enzyme intermediate, CGEI) and frontside SNi-like mechanisms (via oxocarbenium-ion intermediate, OCII) were investigated. The calculations suggest that both mechanisms are feasible in the enzymatic catalysis. The nucleophilic attack of the acceptor substrate to the anomeric carbon of OCII is the rate-determining step with an overall reaction barrier (ΔE(‡) = 19.5 kcal mol(-1)) in agreement with an experimental rate constant (kcat = 5.1 s(-1)). A calculated α-secondary kinetic isotope effect (α-KIE) of 1.27 (GTBWT) and 1.26 (GTBE303C) predicts dissociative character of the transition state in agreement with experimentally measured α-KIE of other retaining glycosyltransferases. Remarkably, stable CGEI in GTBE303C compared with its counterpart in GTBWT may explain why the CGEI has been detected by mass spectrometry only in GTBE303C ( Soya N, Fang Y, Palcic MM, Klassen JS. 2011. Trapping and characterization of covalent intermediates of mutant retaining glycosyltransferases. Glycobiology, 21: 547-552).

A theoretical study on the catalytic mechanism of the retaining α-1,2-mannosyltransferase Kre2p/Mnt1p: the impact of different metal ions on catalysis.

Glycosyltransferases are sugar-processing enzymes that require a specific metal ion cofactor for catalysis. In the presence of other ions the catalysis is often impaired. Here, for the first time, the enzymatic catalysis in the presence of various metal ions was modeled for a glycosyltransferase using a large enzymatic model. The catalytic mechanism of α-1,2-mannosyltransferase Kre2p/Mnt1p in the presence of Mn(2+) and other ions (Mg(2+), Zn(2+) and Ca(2+)) was modeled at the two hybrid DFT-QM/MM (M06-2X/OPLS2005 and B3LYP/OPLS2005) levels. Kinetic and structural parameters of transition states and intermediates, as well as kinetic isotope effects, were predicted and compared with available experimental and theoretical data. The catalysis in the presence of the metal ions is predicted as a stepwise SNi-like nucleophilic substitution reaction (DNint*AN(‡)DhAxh) via oxocarbenium ion intermediates. In the rate-determining step the leaving phosphate group of the donor substrate plays a role of the base catalyst. The predicted increased enzymatic reactivity (kcat: Zn(2+) ≈ Mg(2+) < Mn(2+) < Ca(2+)) correlated with the metal ion ability to polarize the Kre2p environment (Mg(2+) > Zn(2+) > Mn(2+) > Ca(2+)). The formation of the retained anomeric configuration in the product is controlled by a strict geometry of the active site of Kre2p. The 6-OH group of the attacking acceptor substrate may assist in protection of the anomeric carbon against unwanted hydrolysis by a through-space interaction with the electron deficient C1[double bond, length as m-dash]O5(+) moiety of the oxocarbenium-ion-like transition state.

PEGylated nanoparticles bind to and alter amyloid-beta peptide conformation: toward engineering of functional nanomedicines for Alzheimer's disease.

We have demonstrated that the polyethylene glycol (PEG) corona of long-circulating polymeric nanoparticles (NPs) favors interaction with the amyloid-beta (Aß(1-42)) peptide both in solution and in serum. The influence of PEGylation of poly(alkyl cyanoacrylate) and poly(lactic acid) NPs on the interaction with monomeric and soluble oligomeric forms of Aß(1-42) peptide was demonstrated by capillary electrophoresis, surface plasmon resonance, thioflavin T assay, and confocal microscopy, where the binding affected peptide aggregation kinetics. The capture of peptide by NPs in serum was also evidenced by fluorescence spectroscopy and ELISA. Moreover, in silico and modeling experiments highlighted the mode of PEG interaction with the Aß(1-42) peptide and its conformational changes at the nanoparticle surface. Finally, Aß(1-42) peptide binding to NPs affected neither complement activation in serum nor apolipoprotein-E (Apo-E) adsorption from the serum. These observations have crucial implications in NP safety and clearance kinetics from the blood. Apo-E deposition is of prime importance since it can also interact with the Aß(1-42) peptide and increase the affinity of NPs for the peptide in the blood. Collectively, our results suggest that these engineered long-circulating NPs may have the ability to capture the toxic forms of the Aß(1-42) peptide from the systemic circulation and potentially improve Alzheimer's disease condition through the proposed "sink effect".

α-D-mannose derivatives as models designed for selective inhibition of Golgi α-mannosidase II.

Human Golgi α-mannosidase II (hGM) is a pharmaceutical target for the design of inhibitors with anti-tumor activity. Nanomolar inhibitors of hGM exhibit unwanted co-inhibition of the human lysosomal α-mannosidase (hLM). Hence, improving specificity of the inhibitors directed toward hGM is desired in order to use them in cancer chemotherapy. We report on the rapid synthesis of D-mannose derivatives having one of the RS-, R(SO)- or R(SO(2))- groups at the α-anomeric position. Inhibitory properties of thirteen synthesized α-D-mannopyranosides were tested against the recombinant enzyme Drosophila melanogaster homolog of hGM (dGMIIb) and hLM (dLM408). Derivatives with the sulfonyl [R(SO(2))-] group exhibited inhibitory activities at the mM level toward both dGMIIb (IC(50) = 1.5-2.5 mM) and dLM408 (IC(50) = 1.0-2.0 mM). Among synthesized, only the benzylsulfonyl derivative showed selectivity toward dGMIIb. Its inhibitory activity was explained based on structural analysis of the built 3-D complexes of the enzyme with the docked compounds.

Hybrid QM/MM Calculations on the First Redox Step of the Catalytic Cycle of Bovine Glutathione Peroxidase GPX1.

The first reaction step of the redox cycle of bovine erythrocyte glutathione peroxidase from class 1 (GPX1) was investigated using hybrid quantum mechanics/molecular mechanics (QM/MM) calculations using the ONIOM methodology. The reduction of hydrogen peroxide by the active-site selenocysteine in selenolate form assisted by the Arg177 residue was modeled based on a proposal from previous molecular dynamics simulations and pKa calculations (J. Chem. TheoryComput. 2010, 6, 1670-1681). The redox reaction is predicted as a concerted SN2 nucleophilic substitution with a concomitant proton transfer from Arg177 onto leaving hydroxide ion upon reduction of hydrogen peroxide. The height of the reaction barrier was predicted in range of 6-11 kcal mol(-1), consistent with an experimental rate constant of ca. 10(7) M(-1) s(-1). The proposed GPX1-Se(-)-Arg177H(+) mechanism for GPX1 is compared with the GPX3-SeH-Gln83 one proposed for human glutathione peroxidase from class 3 (GPX3) and with the solvent-assisted proton exchange mechanism proposed for GPX-like organic selenols. The structural and energetic parameters predicted by various density functional theory methods (B3LYP, MPW1PW91, MPW1K, BB1K, M05-2X, M06-2X, and M06) are also discussed.

Theoretical prediction of pKa values of seleninic, selenenic, sulfinic, and carboxylic acids by quantum-chemical methods.

Aqueous acid dissociation constants of substituted areneseleninic, areneselenenic, arenesulfinic, and benzoic acids are calculated by ab initio (MP2) and DFT (B3LYP) methods in combination with bulk solvation models (IEFPCM, CRSrad) from appropriate thermodynamic cycles. Mean absolute deviations (MAD) between experimental and calculated pK(a) values are quite large for basis sets without diffuse functions; however, trends are reasonably well described. Best agreement with experiment as described by MAD as well as correlation coefficient and slope of the correlation equation pK(a) = a*ΔG(calc)/RT ln(10) + b is obtained with the CPCM solvation model using the defaults optimized within COSMO-RS (CRSrad; MAD = 1.54, R(2) = 0.94, a = 0.83). Sulfenic (selenenic) acid tautomers are significantly more stable than the corresponding sulfoxide (selenoxide) forms.

Theoretical Study on the Redox Cycle of Bovine Glutathione Peroxidase GPx1: pKa Calculations, Docking, and Molecular Dynamics Simulations.

Three approaches of computational chemistry [quantum mechanics (QM) calculations, docking, and molecular dynamics (MD) simulations] were used to investigate the redox cycle of bovine erythrocyte glutathione peroxidase from class 1 (GPx1, EC 1.11.1.9). The pKa calculations for two redox states of the active-site selenocysteine of GPx1 (selenol, Sec45-SeH, and selenenic acid, Sec45-SeOH) were estimated using a bulk solvent model (B3LYP-IEFPCM and B3LYP-CPCM-COSMO-RS). The calculated pKa values of Sec45-SeH and Sec45-SeOH were corrected via a simple linear fit to a training set of organoselenium compounds, which consisted of aliphatic selenols and aromatic selenenic acids with available experimental pKa values. Based on docking calculations, binding sites for both molecules of the cofactor glutathione (GSH) are described. MD simulations on the dimer of GPx1 have been performed for all chemical states of the redox cycle: without GSH and with one or two molecules of GSH bound at the active site. Conformational analyses of MD trajectories indicate high mobility of the Arg177 and His79 residues. These residues can approach the vicinity of Sec45 and take part in the catalytic mechanism. On the basis of the calculated data, new atomistic details for a generally accepted mechanism of GPx1 are proposed.

Theoretical study on the mechanism of a ring-opening reaction of oxirane by the active-site aspartic dyad of HIV-1 protease.

Two possible mechanisms of the irreversible inhibition of HIV-1 protease by epoxide inhibitors are investigated on an enzymatic model using ab initio (MP2) and density functional theory (DFT) methods (B3LYP, MPW1K and M05-2X). The calculations predict the inhibition as a general acid-catalyzed nucleophilic substitution reaction proceeding by a concerted SN2 mechanism with a reaction barrier of ca. 15-21 kcal mol(-1). The irreversible nature of the inhibition is characterized by a large negative reaction energy of ca. -17-(-24) kcal mol(-1). A mechanism with a direct proton transfer from an aspartic acid residue of the active site onto the epoxide ring has been shown to be preferred compared to one with the proton transfer from the acid catalyst facilitated by a bridging catalytic water molecule. Based on the geometry of the transition state, structural data important for the design of irreversible epoxide inhibitors of HIV-1 protease were defined. Here we also briefly discuss differences between the epoxide ring-opening reaction in HIV-1 protease and epoxide hydrolase, and the accuracy of the DFT method used.

A combined molecular dynamics simulation and quantum chemical study on the mechanism for activation of the OxyR transcription factor by hydrogen peroxide.

Molecular dynamics (MD) simulations have been performed on the regulatory domain of the Escherichia coli OxyR transcription factor for the different chemical states along the mechanistic cycle for its activation by hydrogen peroxide. Conformational analysis indicates that His198 and Arg220 catalytic residues can be involved in the biochemical process of activation of OxyR. On the basis of the simulation data, a detailed mechanism for the oxidation process is suggested in which His198, in the presence of an arginine residue, functions as a unique acid-base catalyst in the successive oxidations of Cys199 and Cys208 by hydrogen peroxide. This mechanistic proposal has been tested by density functional theory (DFT-B3LYP) and ab initio (MP2) calculations on model systems. The two oxidations are both identified as nucleophilic substitution reactions of SN2 type with deprotonated cysteines functioning as nucleophiles. Both reactions have a calculated free energy of activation close to 15 kcal mol-1, which is consistent with the available experimental data on the kinetics of the activation process.