Combined 3D‐QSAR Modeling and Molecular Docking Study on Quinoline Derivatives as Inhibitors of P‐selectin

P‐selectin is a promising target for developing novel atherosclerosis drugs. To understand the structure–activity correlation of quinolines‐based P‐selectin inhibitors, we have carried out a combined molecular docking and three‐dimensional quantitative structure–activity relationship (3D‐QSAR) modeling study. The study has resulted in two types of satisfactory 3D‐QSAR models, including the CoMFA model (r², 0.863; q², 0.589) and CoMSIA model (r², 0.866; q², 0.636), to predict the biological activity of new compounds. The detailed microscopic structures of P‐selectin binding with inhibitors have been studied by molecular docking. We have also developed docking based 3D‐QSAR models (CoMFA with r², 0.934; q², 0.591; CoMSIA with r², 0.896; q², 0.573). The contour maps obtained from the 3D‐QSAR models in combination with the docked binding structures help to better interpret the structure–activity relationship. All of the structural insights obtained from both the 3D‐QSAR contour maps and molecular docking are consistent with the available experimental activity data. The satisfactory results strongly suggest that the developed 3D‐QSAR models and the obtained P‐selectin‐inhibitor binding structures are reasonable for the prediction of the activity of new inhibitors and in future drug design.     

Peptide analogs from E‐cadherin with different calcium‐binding affinities

Abstract: Cadherins are a family of calcium‐dependent cell‐surface proteins that are fundamental in controlling the development and maintenance of tissues. Motif B of E‐cadherin seems to be a crucial calcium‐binding site as single point mutations (D134A and D134K) completely inactivate its adhesion activity. We analyzed peptide models corresponding to motif B (amino acids 128–144) as well as selected mutations of this motif. Our NMR studies showed that this motif B sequence is actually an active calcium‐binding region, even in the absence of the rest of the cadherin molecule. We found that the binding affinity of this motif is very sensitive to mutations. For example, our peptide P128‐144 with the native calcium‐binding sequence has an affinity of K_d 0.4 mm , whereas the mutants P128‐144/D134A and P128‐144/D134K containing the replacement of Asp¹³⁴ by Ala and Lys, have K_d values of only 1.5 and 11 mm , respectively. Removing Asp at position 134, which correlates with the loss of adhesion activity, decreases calcium‐binding affinity 20‐fold. Ala¹³², along with residues Asp¹³⁴, Asp¹³⁶ and Asn¹⁴³, is involved in calcium binding in solution. We also demonstrated that the calcium‐binding affinity can be increased ≈ 3‐fold when an additional Asp is introduced at position 132. In 50% organic solvent, this binding affinity of peptide P128‐144/A132D (17‐mer) from E‐cadherin is similar to that of peptide P72–100/C73–77–91A (29‐mer) from α‐lactalbumin.     

Topography of the neurotensin (NT)(8−9) binding site of human NT receptor‐1 probed with NT(8–13) analogs

Abstract: A series of neurotensin (NT)(8–13) analogs featuring substitution of the Arg⁸ and/or Arg⁹ residues with non‐natural cationic amino acids was synthesized and evaluated for binding to the human NT receptor‐1 (hNTR‐1). The modifications were designed to probe specific steric and electrostatic requirements in the N‐terminal cationic region of NT(8–13) for receptor binding as a general evaluation of the feasibility of incorporating minor structural changes into a peptide at a crucial polar receptor binding site. Many of the non‐natural amino acids are more or less isosteric to Arg but more lipophilic as a result of addition of alkyl groups or through removal or replacement of NH character with methylene or methyl substituents, whereas others vary the distance between the cation and the α–amino acid carbon. Substitution of Arg⁸ with N^G‐alkylated Arg derivatives or homolysine (Hlys) maintained the subnanomolar affinity of NT(8–13) to the hNTR‐1. Position 8 incorporation of Hlys produced the most favorable primary amine side‐chain substitution to date. Moderate losses in affinity observed with position 9 substitutions were attributed to adverse steric effects. Doubly substituted [Hlys⁸, DAB⁹]NT(8–13), in which DAB is 2,4‐diaminobutyric acid, was also prepared and tested as the shorter side‐chain of DAB is known to be favored in position 9 of NT(8–13). This analog maintained 60% of NT(8–13) binding affinity making it the most favored des‐guanidinium‐containing analog known. These results demonstrate that adequate receptor binding affinity can be maintained over a structural range of Arg analogs, thus providing a range of peptides expected to exhibit altered pharmacokinetic properties. From the standpoint of the hNTR‐1 cationic binding sites, these results help to map out the structural stringency inherent in the formation of a tight binding complex with NT(8–13) and related analogs.     

NMR solution structure of a potent cyclic nonapeptide inhibitor of ICAM‐1‐mediated leukocyte adhesion produced by homologous amino acid substitution

Abstract: We have previously described a disulfide‐linked cyclic nonapeptide (inhibitory peptide‐01, IP01), with the sequence CLLRMRSIC, which binds to intercellular adhesion molecule‐1 (ICAM‐1), and blocks binding to its counter‐structure, the integrin α_Lβ₂ (leukocyte functional antigen‐1, LFA‐1) (Sillerud et al., J. Peptide Res. 62, 2003: 97). We now report the optimization of this peptide by means of single homologous amino acid substitutions to yield a new peptide (IP02‐K6; CLLRMKSAC) which shows an approximately sixfold improvement in inhibitory activity of multivalent leukocyte binding (inhibition constant for 50% inhibition, IC₅₀ = 90 μm ) compared with IP01 (IC₅₀ = 580 μm ). This improvement in activity gives IP02‐K6 potent in vivo activity in a murine model of ischemia reperfusion injury (Merchant et al., Am. J. Physiol. Heart Circ. 284, 2003: H1260). In order to determine the structural features relevant to ICAM‐1‐binding, we have determined the structure of IP02‐K6 using proton nuclear magnetic resonance (NMR) spectroscopy and restrained molecular modeling. In our previously reported study of solution models of IP01, we observed three interconverting conformations during low‐temperature molecular dynamics simulation. In the present study, we find a single conformation of IP02‐K6 similar to one of the previously found conformations of IP01 (family C). In particular, an R4‐S7 β‐turn is present in similar proportions in both conformation C of IP01 and in IP02‐K6; this motif is important in binding to ICAM‐1 because this turn enables the IP02‐K6 backbone to drape over proline‐36 on ICAM‐1. The NMR‐derived solution model of IP02‐K6 was found to dock at the α_Lβ₂‐binding site on ICAM‐1 with no changes in peptide backbone conformation. This docking model displaced five of the 15 α_Lβ₂ residues at the ICAM‐1‐binding site and provided a rationale for understanding the quantitative relationship between IP02‐K6 structure and biologic activity.     

Dapsone analogs as potential polyamine binding site modulators of the N‐methyl‐D‐aspartate receptor complex

A high‐throughput radioligand binding assay was used to screen a series of dapsone analogs for their capacity to displace [³H]‐spermidine and [³H]‐MK‐801 from their respective binding sites on the N‐methyl‐D‐aspartate (NMDA) receptor complex in rat brain homogenates. Dapsone did not alter [³H]‐spermidine or [³H]‐MK‐801 binding, suggesting that the neuroprotective properties that have been attributed to this compound may not be due to modulation of the NMDA receptor complex at the polyamine binding site. In contrast, structural analogs of dapsone, including N‐phenyl‐1,4‐phenyldiamine and 4,4′diaminoazobenzene, effectively displaced [³H]‐SPD and [³H]‐MK‐801. These active dapsone analogs may represent a new class of polyamine binding site ligands that may provide opportunities for the rational design of novel NMDA receptor modulators. Drug Dev. Res. 51:268–272, 2000. © 2001 Wiley‐Liss, Inc.     

Synthesis of novel gefitinib‐based derivatives and their anticancer activity

Drug latentiation is a process of modifying a drug molecule structurally to improve its binding affinity as well as increasing the drug–receptor interactions and potentiate its therapeutic potential. In the quest for discovering more potent epidermal growth factor receptor (EGFR) inhibitors, gefitinib‐based derivatives were designed by simple structural modification at the secondary amine of gefitinib by N‐alkylation. Three gefitinib derivatives (gefitinib‐NB, ‐NP, and ‐NIP) were synthesized by N‐alkylation and phase transfer catalysis. Structural characterization, physicochemical parameters such as solubility, log P, and p K _a were determined. Molecular docking studies were carried out to investigate the binding interactions at the active site. Further drug‐bovine serum albumin (BSA) protein and drug‐calf thymus (CT) DNA interactions were performed to understand the pharmacokinetics of the synthesized derivatives. All the compounds were screened for preliminary in vitro cytotoxic activity against A549, A431 lung, and MDA‐MB‐231 breast cancer cell lines by MTT assay. The gefitinib‐NP and gefitinib‐NB derivatives exhibited strong cytotoxic activity compared with gefitinib. They also showed higher drug‐BSA and drug‐DNA interactions. Molecular docking studies showed the orientation and binding interactions with the EGFR as well as with BSA and CT DNA. The results establish a strong correlation between the experimental and molecular docking studies. EGFR inhibition studies were also carried out for the derivatives and we identified the NP derivative of gefitinib as a potential lead compound. The gefitinib‐based derivatives reported herein are cytotoxic agents and can be tested for further pharmacokinetic profiles and toxicity studies which might be helpful for designing more potent gefitinib‐based derivatives in the future.     

Molecular modeling of salsolinol,a full Gi protein agonist of the μ‐opioid receptor,within the receptor binding site

(R/S)‐Salsolinol is a full agonist of the μ‐opioid receptor (μOR) G_i protein pathway via its (S)‐enantiomer and is functionally selective as it does not promote β‐arrestin recruitment. Compared to (S)‐salsolinol, the (R)‐enantiomer is a less potent agonist of the G_i protein pathway. We have now studied the interactions of the salsolinol enantiomers docked in the binding pocket of the μOR to determine the molecular interactions that promote enantiomeric specificity and functional selectivity of (R/S)‐salsolinol. Molecular dynamics simulations showed that (S)‐salsolinol interacted with 8 of the 11 residues of the μOR binding site, enough to stabilize the molecule. (R)‐Salsolinol showed higher mobility with fewer prevalent bonds. Hence, the methyl group bound to the (S)‐stereogenic center promoted more favorable interactions in the μOR binding site than in the (R)‐orientation. Because (S)‐salsolinol is a small molecule (179.2 Da), it did not interact with residues implicated in the binding of larger morphinan agonists that are located toward the extracellular portion of the binding pocket: W318^7.35, I322^7.39, and Y326^7.43. Our results suggest that contact with residues which (S)‐salsolinol interacts with are enough to elicit G_i protein activation, and possibly define a minimum set required by μOR ligands to promote activation of the G_i protein pathway.     

Synthesis and mode of action studies of novel {2‐(3‐R‐1H‐1,2,4‐triazol‐5‐yl)phenyl}amines to combat pathogenic fungi

Due to their high specificity and efficacy, triazoles have become versatile antifungals to treat fungal infections in human healthcare and to control phytopathogenic fungi in agriculture. However, azole resistance is an emerging problem affecting human health as well as food security. Here we describe the synthesis of 10 novel {2‐(3‐R‐1H‐1,2,4‐triazol‐5‐yl)phenyl}amines. Their structure was ascertained by liquid chromatography–mass spectrometry, ¹H and ¹³C NMR, and elemental analysis data. Applying an in vitro growth assay, these triazoles show moderate to significant antifungal activity against the opportunistic pathogen Aspergillus niger, 12 fungi (Fusarium oxysporum, Fusarium fujikuroi, Colletotrichum higginsianum, Gaeumannomyces graminis, Colletotrichum coccodes, Claviceps purpurea, Alternaria alternata, Mucor indicus, Fusarium graminearum, Verticillium lecanii, Botrytis cinerea, Penicillium digitatum) and three oomycetes (Phytophtora infestans GL‐1, P. infestans 4/91; R+ and 4/91; R?) in the concentration range from 1 to 50 µg/ml (0.003–2.1 μM). Frontier molecular orbital energies were determined to predict their genotoxic potential. Molecular docking calculations taking into account six common fungal enzymes point to 14α‐demethylase (CYP51) and N‐myristoyltransferase as the most probable fungal targets. With respect to effectiveness, structure–activity calculations revealed the strong enhancing impact of adamantyl residues. The shown nonmutagenicity in the Salmonella reverse‐mutagenicity assay and no violations of drug‐likeness parameters suggest the good bioavailability and attractive ecotoxicological profile of the studied triazoles.     

Importance of the C‐terminal phenylalanine of gastrin for binding to the human CCK2 receptor

Abstract: The importance of the C‐terminal Phe of gastrin and structural requirements at position 17 for binding to the human CCK₂ receptor were assessed using analogs of [Leu¹⁵]G(11?17). The following peptides were synthesized, Ac[Leu¹⁵]G(11?17), Ac[Leu¹⁵]G(11?16)NH₂, [Leu¹⁵]G(11?17), [Leu¹⁵,Ala¹⁷]G(11?17), [Leu¹⁵,Abu¹⁷]G(11?17), [Leu¹⁵,Val¹⁷]G(11?17), [Leu¹⁵,Leu¹⁷]G(11?17), [Leu¹⁵,Cha¹⁷]G(11?17), [Leu¹⁵,Trp¹⁷]G(11?17), [Leu¹⁵,Tic¹⁷]G(11?17), [Leu¹⁵, d ‐Phe¹⁷]G(11?17) and [Leu¹⁵,p‐X‐Phe¹⁷]G(11?17), where X = F, Cl, Br, I, OH, CH₃, NH₂ and NO_2. Competition binding experiments with [³H]CCK‐8 were performed using human CCK₂ receptors stably expressed in CHO cells. Phe¹⁷ was shown to be important for binding. A hydrophobic side‐chain larger than Leu is required at position 17 but aromaticity does not appear to be essential. Constraint of the aromatic side‐chain either in the g(+) or g(–) conformation, as in the case of Tic, results in a significant decrease in affinity. In addition, the peptide conformation induced by incorporation of d ‐Phe decreases binding. The size and electron withdrawing/donating properties of the para substituent are not important for interaction with the receptor. The current study shows that the use of des‐Phe analogs of gastrin is not a viable strategy for development of antagonists for the human CCK₂ receptor.     

Brief Challenges on Medicinal Plants: An Eye‐Opening Look at Ageing‐Related Disorders

Several studies have reported that nature‐derived antioxidants may prevent free radicals over‐production and therefore control the onset and prevent the exacerbation of different kinds of diseases caused by oxidative stress and redox‐derived stressors, including ageing, fundamentally by suppressing the oxidative by‐products‐mediated degradation. Naturally derived antioxidants exert their anti‐ageing action via a panoply of signalling systems, many of which engaging reactive oxygen and nitrogen species scavenging, with the Nrf2/Keap1‐ARE system and improving the many survival genes and functions (such as the pathway mTOR/Foxo/SIRT1) able to slow cellular senescence. Most of the research in this field has evaluated the regulative effects and even pathways of herbal extracts with antioxidant property in the ageing process, and various age‐related disorders such as cardiovascular disease, ischaemia‐reperfusion injury, coronary and myocardial circulatory perfusion, peripheral vascular resistance, and even neurodegenerative disorders are prevented plant phytochemicals often via their antioxidant potential. A much more complex ability to interact with survival functions makes these compounds successfully active in preventing ageing‐related disorders. This report aimed to discuss in more detail some selected medicinal plants including Allium sativum, Aloe vera, Crataegus spp., Cynara scolymus, Eleutherococcus senticosus, Ginkgo biloba, Hippophae rhamnoides, Panax ginseng, Rosmarinus officinalis, Schizandra chinensis, Vitis vinifera and seaweeds in the prevention of ageing‐related pathologies. A systematic overview of the relevant information in the antioxidant function of the many herbal products reviewed here for the control of the ageing process is proposed, to provide a new horizon on the design of anti‐ageing herbal medicines.     

111In‐ and 203Pb‐labeled cyclic arginine‐glycine‐aspartic acid peptide conjugate as an αvβ3 integrin‐binding radiotracer

Methodology for site‐specific modification and chelate conjugation of a cyclic arginine‐glycine‐aspartic acid (cRGD) peptide for the preparation of a radiotracer molecular imaging agent suitable for detecting α_vβ₃ integrin is described. The method involves functionalizing the peptide with an aldehyde moiety and conjugation to a 1,4,7,10‐tetraazacyclododecane‐N,N′,N″,N?‐tetraacetic acid derivative that possesses an aldehyde reactive aminooxy group. The binding assay of the ¹¹¹In‐labeled peptide conjugate with α_vβ₃ integrin showed 60% bound when four equivalents of the integrin was added, a reasonable binding affinity for a monovalent modified RGD peptide.     

Biological and conformational study of β‐substituted prolines in MT‐II template: steric effects leading to human MC5 receptor selectivity*

Abstract: To investigate the molecular basis for the interaction of the χ‐constrained conformation of melanotropin peptide with the human melanocortin receptors, a series of β‐substituted proline analogs were synthesized and incorporated into the Ac‐Nle‐c[Asp‐His‐d ‐Phe‐Arg‐Trp‐Lys]‐NH₂ (MT‐II) template at the His⁶ and d ‐Phe⁷ positions. It was found that the binding affinities generally diminished as the steric bulk of the p‐substituents of the 3‐phenylproline residues increased. From (2S, 3R)‐3‐phenyl‐Pro⁶ to (2S, 3R)‐3‐(p‐methoxyphenyl)‐Pro⁶ analogs the binding affinity decreased 23‐fold at the human melanocortin‐3 receptor (hMC3R), 17‐fold at the hMC4R, and eight‐fold at the hMC5R, but selectivity for the hMC5R increased. In addition, the substitution of the d ‐Phe⁷ residue with a (2R, 3S)‐3‐phenyl‐Pro resulted in greatly reduced binding affinity (10³–10⁵) at these melanocortin receptors. Macromodel's Large Scale Low Mode (LLMOD) with OPLS‐AA force field simulations revealed that both MT‐II and SHU‐9119 share a similar backbone conformation and topography with the exception of the orientation of the side chains of d ‐Phe⁷/d ‐Nal (2′)⁷ in χ space. Introduction of the dihedrally constrained phenylproline analogs into the His⁶ position (analogs 2 – 6 ) caused topographical changes that might be responsible for the lower binding affinities. Our findings indicate that hMC3 and hMC4 receptors are more sensitive to steric effects and conformational constraints than the hMC5 receptor. This is the first example for melanocortin receptor selectivity where the propensity of steric interactions in χ space of β‐modified Pro⁶ analogs of MT‐II has been shown to play a critical role for binding as well as bioefficacy of melanotropins at hMC3 and hMC4 receptors, but not at the hMC5 receptor.     

Synthesis,biological evaluation,and molecular docking studies of novel 3‐aryl‐5‐(alkyl‐thio)‐1H‐1,2,4‐triazoles derivatives targeting Mycobacterium tuberculosis

A small library of new 3‐aryl‐5‐(alkyl‐thio)‐1H‐1,2,4‐triazoles was synthesized and screened for the antimycobacterial potency against Mycobacterium tuberculosis H₃₇Ra strain and Mycobacterium bovis BCG both in active and dormant stage. Among the synthesized library, 25 compounds exhibited promising anti‐TB activity in the range of IC₅₀0.03–5.88 μg/ml for dormant stage and 20 compounds in the range of 0.03–6.96 μg/ml for active stage. Their lower toxicity (>100 μg/ml) and higher selectivity (SI = >10) against all cancer cell lines screened make them interesting compounds with potential antimycobacterial effects. Furthermore, to rationalize the observed biological activity data and to establish a structural basis for inhibition of M. tuberculosis, the molecular docking study was carried out against a potential target MTB CYP121 which revealed a significant correlation between the binding score and biological activity for these compounds. Cytotoxicity and in vivo pharmacokinetic studies suggested that 1,2,4‐triazole analogues have an acceptable safety index, in vivo stability and bio‐availability.     

Synthesis and AT2 receptor‐binding properties of angiotensin II analogues

Abstract: The present study investigates the importance of the amino acid side chains in the octapeptide angiotensin II (Ang II) for binding to the AT₂ receptor. A Gly scan was performed where each amino acid in Ang II was substituted one‐by‐one with glycine. The resulting set of peptides was tested for affinity to the AT₂ receptor (porcine myometrial membranes). For a comparison, the peptides were also tested for affinity to the AT₁ receptor (rat liver membranes). Only the substitution of Arg² reduced affinity to the AT₂ receptor considerably (92‐fold when compared with Ang II). For the other Gly‐substituted analogues the affinity to the AT₂ receptor was only moderately affected. To further investigate the role of the Arg² side chain for receptor binding, we synthesized some N‐terminally modified Ang II analogues. According to these studies a positive charge in the N‐terminal end of angiotensin III [Ang II (2–8)] is not required for high AT₂ receptor affinity but seems to be more important in Ang II. With respect to the AT₁ receptor, [Gly²]Ang II and [Gly⁸]Ang II lacked binding affinity (K_i > 10 μm ). Replacement of the Val³ or Ile⁵ residues with Gly produced only a slight decrease in affinity. Interestingly, substitution of Tyr⁴ or His⁶, which are known to be very important for AT₁ receptor binding, resulted in only 48 and 14 times reduction in affinity, respectively.     

Specific binding of amyloid‐β‐protein to IMR‐32 neuroblastoma cell membrane

In flow cytometry using two detecting methods, we have found that amyloid‐β‐protein(1–40) [Aβ(1–40)] has high affinity to IMR‐32 neuroblastoma cell membrane when it is aggregated to form β‐sheet conformation, whereas random coil small Aβ‐species has low affinity. The difference in the binding ability to the cell membranes well accounts for the cytotoxicity of Aβ(1–40); namely, aggregated β‐sheet Aβ(1–40) gives cytotoxicity higher than random coil Aβ(1–40). Specific binding between Aβ(1–40) and ganglioside GM1 of the raft‐like domain in lipid membrane is suggested from a surface plasmon resonance (SPR) experiment.     

Combined 1H‐NMR and Molecular Dynamics Studies on Conformational Behavior of a Model Heptapeptide,GRGDSPC

Among various strategies, the de novo design and in silico approaches are being used to develop the short peptides, models of modified peptides, and mimetics as clinically useful drugs with improved stability and bioavailability. The resulting models will help to isolate the factors behind the folded structure formation and contribute useful information about de novo peptide design. The combined ¹H‐NMR spectroscopic and molecular dynamics methods were used to investigate the conformational behavior of an Arg‐Gly‐Asp (RGD)‐containing peptide, GRGDSPC, the cell‐binding heptapeptide of extracellular matrix protein, fibronectin. The formation of two fused weak β‐turns of type II (HB, 4→1) and type II’ (HB, 7→4) from simulation studies has been consistent with NMR data. The sustainable ‘S’‐shaped molecular structure (which remained unchanged during the entire simulation) and the conformational transitions due to interconversions between multiple turns initiated at Asp⁴, Ser⁵, and Cys⁷ imply that the peptide is flexible in nature. Thus, the model of ‘S’‐shaped structure with flexible multiple turns for GRGDSPC peptide may provide the structural rationale for antagonistic properties of this heptapeptide toward the treatment of integrin‐mediated cellular abnormal behaviors such as thrombosis and metastasis.     

(Z)‐2‐(3‐Chlorobenzylidene)‐3,4‐dihydro‐N‐(2‐methoxyethyl)‐3‐oxo‐2H‐benzo[b][1,4]oxazine‐6‐carboxamide as GSK‐3β inhibitor: Identification by virtual screening and its validation in enzyme‐ and cell‐based assay

Glycogen synthase kinase 3β (GSK‐3β) is a widely investigated molecular target for numerous diseases including Alzheimer's disease, cancer, and diabetes mellitus. The present study was aimed to discover new scaffolds for GSK‐3β inhibition, through protein structure‐guided virtual screening approach. With the availability of large number of GSK‐3β crystal structures with varying degree of RMSD in protein backbone and RMSF in side chain geometry, herein appropriate crystal structures were selected based on the characteristic ROC curve and percentage enrichment of actives. The validated docking protocol was employed to screen a library of 50,000 small molecules using molecular docking and binding affinity calculations. Based on the GLIDE docking score, Prime MMGB/SA binding affinity, and interaction pattern analysis, the top 50 ligands were selected for GSK‐3β inhibition. (Z)‐2‐(3‐chlorobenzylidene)‐3,4‐dihydro‐N‐(2‐methoxyethyl)‐3‐oxo‐2H‐benzo[b][1,4]oxazine‐6‐carboxamide (F389‐0663, 7 ) was identified as a potent inhibitor of GSK‐3β with an IC₅₀ value of 1.6 μm . Further, GSK‐3β inhibition activity was then investigated in cell‐based assay. The treatment of neuroblastoma N2a cells with 12.5 μm of F389‐0663 resulted in the significant increase in GSK‐3β Ser9 levels, which is indicative of the GSK‐3β inhibitory activity of a compound. The molecular dynamic simulations were carried out to understand the interactions of F389‐0663 with GSK‐3β protein.     

Alginate as an auxiliary bacterial membrane: binding of membrane‐active peptides by polysaccharides*

Abstract: The chronicity of Pseudomonas aeruginosa infections in cystic fibrosis (CF) patients is characterized by overproduction of the exopolysaccharide alginate, in which biofilm bacteria are embedded. Alginate apparently contributes to the antibiotic resistance of bacteria in this form by acting as a diffusion barrier to positively charged antimicrobial agents. We have been investigating cationic antimicrobial peptides (CAPs) (prototypic sequence: KKAAAXAAAAAXAAWAAXAAAKKKK‐NH₂, where X is any of the 20 commonly occurring amino acids) that were originally designed as transmembrane mimetic peptides. Peptides of this group above a specific hydrophobicity threshold insert spontaneously into membranes and have antibacterial activity at micromolar concentrations. While investigating the molecular basis of biofilm resistance to peptides, we found that the anionic alginate polysaccharide induces conformational changes in the most hydrophobic of these peptides typically associated with insertion of such peptides into membrane environments [Chan et al., J. Biol. Chem. (2004) vol. 279 , pp. 38749–38754]. Through a combination of experiments measuring release of the fluorescent dye calcein from phospholipid vesicles, peptide interactions with vesicles in the presence and absence of alginate, and affinity of peptides for alginate as a function of net peptide core hydrophobicity, we show here that alginate offers a microenvironment that provides a protective mechanism for the encased bacteria by both binding and promoting the self‐association of the CAPs. The overall results indicate that hydrophilic alginate polymers contain a significant hydrophobic compartment, and behave as an ‘auxiliary membrane’ for bacteria, thus identifying a unique protective role for biofilm exopolysaccharide matrices.     

Design,Synthesis, and Evaluation of 7H‐thiazolo‐[3,2‐b]‐1,2,4‐triazin‐7‐one Derivatives as Dual Binding Site Acetylcholinesterase Inhibitors

New dual binding site acetylcholinesterase (AChE) inhibitors have been designed and synthesized as a new drug candidate for the treatment of Alzheimer's disease (AD) through the binding to both catalytic and peripheral sites of the enzyme. Therefore, a series of 7H‐thiazolo[3,2‐b]‐1,2,4‐triazin‐7‐one derivatives 6a – j were synthesized and investigated for their ability to inhibit the activity of human AChE (hAChE) in comparison with huperzine‐A. All the compounds were found to inhibit AChE activity, especially compounds 6c and 6i with the inhibition value of 76.10% and 77.82%, respectively. The molecular docking study indicated that they were nicely accommodated by AChE. The molecular docking study revealed that 6c and 6i possessed a more optimal binding conformation than 6a and can perfectly fit into the active and peripheral site of hAChE, and consequently exhibited highly improved inhibitor potency to hAChE.