β-turn tendency in N-methylated peptides with dehydrophenylalanine residue: DFT study

The tendency to adopt β‐turn conformation by model dipeptides with α,β‐dehydrophenylalanine (ΔPhe) residue in the gas phase and in solution is investigated by theoretical methods. We pay special attention to a dependence of conformational properties on the side‐chain configuration of dehydro residue and the influence of N‐methylation on β‐turn stability. An extensive computational study of the conformational preferences of Z and E isomers of dipeptides Ac‐Gly‐(E/Z)‐ΔPhe‐NHMe ( 1a / 1b ) and Ac‐Gly‐(E/Z)‐ΔPhe‐NMe₂ ( 2a / 2b ) by B3LYP/6‐311++G(d,p) and MP2/6‐311++G(d,p) methods is reported. It is shown that, in agreement with experimental data, Ac‐Gly‐(Z)‐ΔPhe‐NHMe has a great tendency to adopt β‐turn conformation. In the gas phase the type II β‐turn is preferred, whereas in the polar environment, the type I. On the other hand, dehydro residue in Ac‐Gly‐(E)‐ΔPhe‐NHMe has a preference to adopt extended conformations in all environments. N‐methylation of C‐terminal amide group, which prevents the formation of 1←4 intramolecular hydrogen bond, change dramatically the conformational properties of studied dehydropeptides. Especially, the tendency to adopt β‐turn conformations is much weaker for the N‐methylated Z isomer (Ac‐Gly‐(Z)‐ΔPhe‐NMe₂), both in vacuo and in the polar environment. On the contrary, N‐methylated E isomer (Ac‐Gly‐(E)‐ΔPhe‐NMe₂) can easier adopt β‐turn conformation, but the backbone torsion angles (?₁, ψ₁, ?₂, ψ₂) are off the limits for common β‐turn types. © 2012 Wiley Periodicals, Inc. Biopolymers 97:518–528, 2012.     

Toward engineering efficient peptidomimetics. Screening conformational landscape of two modified dehydroaminoacids

Effective peptidomimetics should posses structural rigidity and appropriate interaction pattern leading to potential spatial and electronic matching to the target receptor site. Rational design of such small bioactive molecules could push chemical synthesis and molecular modeling toward faster progress in medicinal chemistry. Conformational properties of N‐t‐butoxycarbonyl‐glycine‐(E/Z)‐dehydrophenylalanine N′,N′‐dimethylamides (Boc‐Gly‐(E/Z)‐ΔPhe‐NMe₂) in chloroform were studied by NMR and IR spectroscopy. The experimental findings were supported by extensive calculations at DFT(B3LYP, M06‐2X) and MP2 levels of theory and the β‐turn tendency for both isomers of the studied dipeptide were determined in vacuum and in solution. The theoretical data and experimental IR results were used as an additional information for the NMR‐based determination of the detailed solution conformations of the peptides. The obtained results reveal that N‐methylation of C‐terminal amide group changes dramatically the conformational properties of studied dehydropeptides. Theoretical conformational analysis reveals that the tendency to adopt β‐turn conformations is much weaker for the N‐methylated Z isomer (Boc‐Gly‐(Z)‐ΔPhe‐NMe₂), both in vacuum and in polar environment. On the contrary, N‐methylated E isomer (Boc‐Gly‐(E)‐ΔPhe‐NMe₂) can easily adopt β‐turn conformation, but the backbone torsion angles (φ₁, ψ₁, φ₂, ψ₂) are off the limits for common β‐turn types. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 28–40, 2014.     

The conformational properties of dehydrobutyrine and dehydrovaline: theoretical and solid‐state conformational studies

Dehydrobutyrine is the most naturally occurring dehydroamino acid. It is also the simplest dehydroamino acid having the geometrical isomers E/Z. To investigate its conformational properties, a theoretical analysis was performed on N‐acetyl‐α,β‐dehydrobutyrine N′‐methylamides, Ac‐(E)‐ΔAbu‐NHMe and Ac‐(Z)‐ΔAbu‐NHMe, as well as the dehydrovaline derivative Ac‐ΔVal‐NHMe. The ?, ψ potential energy surfaces and the localised conformers were calculated at the B3LYP/6‐311 + + G(d,p) level of theory both in vacuo and with inclusion of the solvent (chloroform, water) effect (SCRF method). The X‐ray crystal structures of Ac‐(Z)‐ΔAbu‐NHMe and Ac‐ΔVal‐NHMe were determined at 85 and 100 K, respectively. The solid‐state conformational preferences for the studied residues have been analysed and compared with the other related structures. Despite the limitations imposed by the C^α = C^β double bond on the topography of the side chains, the main chains of the studied dehydroamino acids are more flexible than in standard alanine. The studied dehydroamino acids differ in their conformational preferences, which depend on the polarity of the environment. This might be a reason why the nature quite precisely differentiates between ΔVal and each of the ΔAbu isomers, and why, particularly so with the latter, they are used as a conformational tool to influence the biological action of usually small, cyclic dehydropeptides. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

De novo design,synthesis and solution conformational study of two didehydroundecapeptides: effect of nature and number of amino acids interspersed between Phe residues

De novo design of peptides and proteins has recently surfaced as an approach for investigating protein structure and function. This approach vitally tests our knowledge of protein folding and function, while also laying the groundwork for the fabrication of proteins with properties not precedented in nature. The success relies heavily on the ability to design relatively short peptides that can espouse stable secondary structures. To this end, substitution with α,β‐didehydroamino acids, especially α,β‐didehydrophenylalanine (Δ^zPhe), comes in use for spawning well‐defined structural motifs. Introduction of ΔPhe induces β‐bends in small and 3₁₀‐helices in longer peptide sequences. The present work aims to investigate the effect of nature and the number of amino acids interspersed between two ΔPhe residues in two model undecapeptides, Ac‐Gly‐Ala‐ΔPhe‐Ile‐Val‐ΔPhe‐Ile‐Val‐ΔPhe‐Ala‐Gly‐NH₂ (I) and Boc‐Val‐ΔPhe‐Phe‐Ala‐Phe‐ΔPhe‐Phe‐Leu‐Ala‐ΔPhe‐Gly‐OMe (II). Peptide I was synthesized using solid‐phase chemistry and characterized using circular dichroism spectroscopy. Peptide II was synthesized using solution‐phase chemistry and characterized using circular dichroism and nuclear magnetic resonance spectroscopy. Peptide I was designed to examine the effect of incorporating β‐strand‐favoring residues like valine and isoleucine as spacers between two ΔPhe residues on the final conformation of the resulting peptide. Circular dichroism studies on this peptide have shown the existence of a 3₁₀‐helical conformation. Peptide II possesses three amino acids as spacers between ΔPhe residues and has been reported to adopt a mixed 3₁₀/α‐helical conformation using circular dichroism and nuclear magnetic resonance spectroscopy studies. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Controlling the helical screw sense of peptides with C‐terminal L‐valine

One chiral L ‐valine (L ‐Val) was inserted into the C‐terminal position of achiral peptide segments constructed from α‐aminoisobutyric acid (Aib) and α,β‐dehydrophenylalanine (Δ^ZPhe) residues. The IR, ¹H NMR and CD spectra indicated that the dominant conformations of the pentapeptide Boc‐Aib‐ΔPhe‐(Aib)₂‐L ‐Val‐NH‐Bn (3) and the hexapeptide Boc‐Aib‐ΔPhe‐(Aib)₃‐L ‐Val‐NH‐Bn (4) in solution were both right‐handed (P) 3₁₀‐helical structures. X‐ray crystallographic analyses of 3 and 4 revealed that only a right‐handed (P) 3₁₀‐helical structure was present in their crystalline states. The conformation of 4 was also studied by molecular‐mechanics calculations. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Effect of the ΔPhe residue configuration on a didehydropeptides conformation: A combined CD and NMR study

Conformations of two pairs of dehydropeptides with the opposite configuration of the ΔPhe residue, Boc‐Gly‐Δ^ZPhe‐Gly‐Phe‐OMe ( Z‐ OMe ), Boc‐Gly‐Δ^EPhe‐Gly‐Phe‐OMe ( E‐ OMe ), Boc‐Gly‐Δ^ZPhe‐Gly‐Phe‐p‐NA ( Z‐p‐ NA ), and Boc‐Gly‐Δ^EPhe‐Gly‐Phe‐p‐NA ( E‐p‐ NA ) were compared on the basis of CD and NMR studies in MeOH, trifluoroethanol (TFE), MeCN, chloroform, and dimethylsulfoxide (DMSO). The CD results were used as the additional input data for the NMR‐based determination of the detailed solution conformations of the peptides. It was found that E‐ OMe is unordered and Z‐ OMe , Z‐p‐ NA , and E‐p‐ NA adopt the β‐turn conformation. There are two overlapping β‐turns in each of those peptides: type II and type III′ in Z‐ OMe and Z‐p‐ NA , and two type III in E‐p‐ NA . The ordered structure‐inducing properties of Δ^ZPhe and Δ^EPhe in the peptides studied depend on the C‐terminal blocking group. In methyl esters, the Δ^ZPhe residue is a strong inducer of ordered conformations whereas the Δ^EPhe one has no such properties. In p‐nitroanilides, both isomers of ΔPhe cause the peptides to adopt ordered structures to a similar extent. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 1055–1064, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Solvent effects on the conformational preferences of model peptoids. MP2 study

The influence of aqueous environment on the main‐chain conformation (ω₀, ?, and ψ dihedral angles) of two model peptoids: N‐acetyl‐N‐methylglycine N’‐methylamide (Ac‐N(Me)‐Gly‐NHMe) ( 1 ) and N‐acetyl‐N‐methylglycine N’,N’‐dimethylamide (Ac‐N(Me)‐Gly‐NMe₂) ( 2 ) was investigated by MP2/6‐311++G(d,p) method. The Ramachandran maps of both studied molecules with cis and trans configuration of the N‐terminal amide bond in the gas phase and in water environment were obtained and all energy minima localized. The polarizable continuum model was applied to estimate the solvation effect on conformation. Energy minima of the Ac‐N(Me)‐Gly‐NHMe and Ac‐N(Me)‐Gly‐NMe₂ have been analyzed in terms of the possible hydrogen bonds and C = O dipole attraction. To validate the theoretical results obtained, conformations of the similar structures gathered in the Cambridge Crystallographic Data Centre were analyzed. Obtained results indicate that aqueous environment in model peptoids 1 and 2 favors the conformation F (? and ψ = ?70º, 180º), and additionally significantly increases the percentage of structures with cis configuration of N‐terminal amide bond in studied compounds. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

The conformational properties of α,β‐dehydroamino acids with a C‐terminal ester group

α,β‐Dehydroamino acid esters occur in nature. To investigate their conformational properties, a systematic theoretical analysis was performed on the model molecules Ac‐ΔXaa‐OMe [ΔXaa = ΔAla, (E)‐ΔAbu, (Z)‐ΔAbu, ΔVal] at the B3LYP/6‐311+ + G(d,p) level in the gas phase as well as in chloroform and water solutions with the self‐consistent reaction field‐polarisable continuum model method. The Fourier transform IR spectra in CCl₄ and CHCl₃ have been analysed as well as the analogous solid state conformations drawn from The Cambridge Structural Database. The ΔAla residue has a considerable tendency to adopt planar conformations C5 (?, ψ ≈ ? 180°, 180°) and β2 (?, ψ ≈ ? 180°, 0°), regardless of the environment. The ΔVal residue prefers the conformation β2 (?, ψ ≈ ? 120°, 0°) in a low polar environment, but the conformations α (?, ψ ≈ ? 55°, 35°) and β (?, ψ ≈ ? 55°, 145°) when the polarity increases. The ΔAbu residues reveal intermediate properties, but their conformational dispositions depend on configuration of the side chain of residue: (E)‐ΔAbu is similar to ΔAla, whereas (Z)‐ΔAbu to ΔVal. Results indicate that the low‐energy conformation β2 is the characteristic feature of dehydroamino acid esters. The studied molecules constitute conformational patterns for dehydroamino acid esters with various side chain substituents in either or both Z and E positions. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

A Cellular Automata Model of Proton Hopping Down a Channel

Proton hopping is the process where a H‐atom on a hydronium ion forms a H‐bond with the O‐atom of a neighboring H₂O molecule. There is then an exchange of bonding forces when that covalent bond of the H‐atom in the hydronium ion changes to a H‐bond, and the previous H‐bond changes to a covalent bond with the neighboring O‐atom. The neighboring molecule now becomes a hydronium (H₃O⁺) ion. This process repeats itself very rapidly among neighboring hydronium and H₂O molecules. There is a flow of protonic character through bulk H₂O, referred to as proton hopping. This process carries information through living systems where H₂O is present. A cellular automata model of proton hopping down a channel has been created and studied. Variations in the rate of proton entry into the channel and the effects of the polar character of the channel walls was studied using the model. The behavior of the models corresponds to experimental results.     

Structural versatility of peptides from Cα, α-disubstituted glycines: Crystal-state conformational analysis of homopeptides from Cα-methyl,Cα-benzylglycine [(αMe)Phe]n

The molecular and crystal structures of one derivative and three homopeptides (from the di-to the tetrapeptide level) of the chiral, C^{α, α}-disubstituted glycine C^α-methyl, C^α-benzylglycine [(αMe)Phe], have been determined by x-ray diffraction. The derivative is mClAc-D -(αMe)Phe-OH, and the peptides are pBrBz-[D -(αMe)Phe]₂-NHMe, pBrBz-[D -(αMe)Phe]₃-OH hemihydrate, and pBrBz-[D -(αMe)Phe]₄-OtBu sesquihydrate. All (αMe)Phe residues prefer ?,ψ torsion angles in the helical region of the conformational map. The dipeptide methylamide and the tripeptide carboxylic acid adopt a β-turn conformation with a 1 ← 4 C?O…?H? N intramolecular H bond. The structure of the tripeptide carboxylic acid is further stabilized by a 1 ← 4 C?O…?H? O intramolecular H bond, forming an “oxy-analogue” of a β-turn. The tetrapeptide ester is folded in a regular (incipient) 3₁₀-helix. In general, the relationship between (αMe)Phe chirality and helix screw sense is opposite to that exhibited by protein amino acids. A comparison is made with the conclusions extracted from published work on homopeptides from other C^α-methylated α-amino acids. © 1993 John Wiley & Sons, Inc.     

Fungicidal Properties of Some Novel Trifluoromethylphenyl Amides

Trifluoromethylphenyl amides (TFMPAs) were designed and synthesized as potential pesticides. Thirty‐three structures were evaluated for fungicidal activity against three Colletotrichum species using direct bioautography assays. Active compounds were subsequently tested against C. fragariae, C. gloeosporioides, C. acutatum, Phomopsis obscurans, P. viticola, Botrytis cinerea and Fusarium oxysporum. The study identified 2‐chloro‐N‐[2,6‐dichloro‐4‐(trifluoromethyl)phenyl]acetamide ( 7a ) as showing the strongest antifungal activity, and the broadest activity spectrum in this set against Colletotrichum acutatum (at 48 and 72 h) and Phomopsis viticola (at 144 h). The presence of triethylamine in its complex with N‐[2,6‐dichloro‐4‐(trifluoromethyl)phenyl]‐2,2,3,3,3‐pentafluoropropanamide ( 7b′ ) played an important role in the bioactivity, and depending on the concentration or fungal species it showed higher or lower activity than the parent amide. X‐Ray crystallography has shown that the complex ( 7b′ ) is an ion pair, (C₁₀H₂Cl₂F₈NO)^? (C₆H₁₆N)⁺, where a proton is transferred from the amide nitrogen to the triethylamine nitrogen and then connected by hydrogen bonding to the acyl oxygen (N?H 0.893 Å; H???O 1.850 Å; N???O 2.711 Å; N?H???O 161.2(13)°). Although none of these compounds were better than standards, this work revealed some potential lead structures for further development of active novel compounds.     

Sex pheromone components of the carpenterworm moth,Holcocerus vicarius

Extracts of the female sex pheromone gland of the carpenterworm moth, Holcocerus vicarius (Walker) (Lepidoptera: Cossidae), a pest of Ulmus pumila L. (Ulmaceae), were found to contain Z7‐tetradecenyl acetate (Z7‐14Ac), E3‐tetradecenyl acetate (E3‐14Ac), (Z3,E5)‐tetradecenyl acetate (Z3,E5‐14Ac), and Z7‐tetradecenyl alcohol (Z7‐14OH) by coupled gas chromatographic‐electroantennographic detection (GC‐EAD) and coupled gas chromatography‐mass spectrometry (GC‐MS). Field trapping studies with impregnated rubber septa indicated that Z7‐14Ac was essential for attraction of males of H. vicarius. However, the most attractive blend contained Z7‐14Ac, E3‐14Ac, Z3,E5‐14Ac, and Z7‐14OH in a 50:22:17:10 ratio. Our results demonstrated that a blend of Z7‐14Ac, E3‐14Ac, Z3,E5‐14Ac, and Z7‐14OH represented the sex pheromone of H. vicarius. The optimized four‐component lure blend may be useful for monitoring H. vicarius infestations and mating disruption.     

The effect of β‐methylation on the conformation of α, β‐dehydrophenylalanine: a DFT study

Dehydroamino acids are non‐coded amino acids that offer unique conformational properties. Dehydrophenylalanine (ΔPhe) is most commonly used to modify bioactive peptides to constrain the topography of the phenyl ring in the side chain, which commonly serves as a pharmacophore. The Ramachandran maps (in the gas phase and in CHCl₃ mimicking environments) of ΔPhe analogues with methyl groups at the β position of the side chain as well as at the C‐terminal amide were calculated using the B3LYP/6‐31 + G** method. Unexpectedly, β‐methylation alone results in an increase of conformational freedom of the affected ΔPhe residue. However, further modification by introducing an additional methyl group at C‐terminal methyl amide results in a steric crowding that fixes the torsion angle ψ of all conformers to the value 123°, regardless of the Z or E position of the phenyl ring. The number of conformers is reduced and the accessible conformational space of the residues is very limited. In particular, (Z)‐Δ(βMe)Phe with the tertiary C‐terminal amide can be classified as the amino acid derivative that has a single conformational state as it seems to adopt only the β conformation. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

Sex pheromone of a North American population of the spotted tentiform leafminer, Phyllonorycter blancardella

The major sex pheromone compound of the spotted tentiform leafminer, Phyllonorycter blancardella (F.) (Lepidoptera: Gracillariidae), from Ontario, Canada, was identified as (10E)‐dodecen‐1‐yl acetate (E10‐12:Ac) using chemical analysis and field trapping experiments. The minor compounds (10E)‐dodecen‐1‐ol (E10‐12:OH) (4.6%), dodecan‐1‐ol (12:OH) (2.3%), and (10Z)‐dodecen‐1‐yl acetate (Z10‐12:Ac) 1.6% were also identified. The dienic acetate (4E,10E)‐dodecadien‐1‐yl acetate (E4,E10‐12:Ac), a compound reported to be attractive to P. blancardella, was not found in the glands of this population. A two‐component blend of the major and one of each the three minor compounds, in ratios similar to those found in the sex pheromone gland, did not increase the attractiveness of traps baited with synthetic pheromone. The minor compounds E10‐12:OH and 12:OH were not attractive to P. blancardella when tested individually. Z10‐12:Ac was attractive to P. blancardella, although traps baited with this compound captured only 2% of the moths that were captured in traps baited with the main compound. A four‐component blend of the major and each of the three minor compounds (100 : 1 : 1 : 1) was not more attractive than the major compound alone. The related species Phyllonorycter mespilella was captured in traps baited with E10‐12:Ac.     

Solvent selection and optimization of α‐chymotrypsin‐catalyzed synthesis of N‐Ac‐Phe‐Tyr‐NH2 using mixture design and response surface methodology

A peptide, N‐Ac‐Phe‐Tyr‐NH₂, with angiotensin I‐converting enzyme (ACE) inhibitor activity was synthesized by an α‐chymotrypsin‐catalyzed condensation reaction of N‐acetyl phenylalanine ethyl ester (N‐Ac‐Phe‐OEt) and tyrosinamide (Tyr‐NH₂). Three kinds of solvents: a Tris–HCl buffer (80 mM, pH 9.0), dimethylsulfoxide (DMSO), and acetonitrile were employed in this study. The optimum reaction solvent component was determined by simplex centroid mixture design. The synthesis efficiency was enhanced in an organic‐aqueous solvent (Tris‐HCl buffer: DMSO: acetonitrile = 2:1:1) in which 73.55% of the yield of N‐Ac‐Phe‐Tyr‐NH₂ could be achieved. Furthermore, the effect of reaction parameters on the yield was evaluated by response surface methodology (RSM) using a central composite rotatable design (CCRD). Based on a ridge max analysis, the optimum condition for this peptide synthesis included a reaction time of 7.4 min, a reaction temperature of 28.1°C, an enzyme activity of 98.9 U, and a substrate molar ratio (Phe:Tyr) of 1:2.8. The predicted and the actual (experimental) yields were 87.6 and 85.5%, respectively. The experimental design and RSM performed well in the optimization of synthesis of N‐Ac‐Phe‐Tyr‐NH₂, so it is expected to be an effective method for obtaining a good yield of enzymatic peptide. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Crystal structures of two cyclic pseudopentapeptides containing ψ[CH2S] and ψ[CH2SO] backbone surrogates

The solid state conformations of cyclo[Gly–Proψ[CH₂S]Gly–D –Phe–Pro] and cyclo[Gly–Proψ[CH₂–(S)–SO]Gly–D –Phe–Pro] have been characterized by X-ray diffraction analysis. Crystals of the sulfide trihydrate are orthorhombic, P2₁2₁2₁, with a = 10.156(3) Å, b = 11.704(3) Å, c = 21.913(4) Å, and Z = 4. Crystals of the sulfoxide are monoclinic, P2₁, with a = 10.662(1) Å, b = 8.552(3) Å, c = 12.947(2) Å, β = 94.28(2), and Z = 2. Unlike their all-amide parent, which adopts an all-trans backbone conformation and a type II β-turn encompassing Gly-Pro-Gly-D -Phe, both of these peptides contain a cis Gly¹-Pro² bond and form a novel turn structure, i.e., a type II′ β-turn consisting of Gly–D –Phe–Pro–Gly. The turn structure in each of these peptides is stabilized by an intramolecular H bond between the carbonyl oxygen of Gly¹ and the amide proton of D -Phe⁴. In the cyclic sulfoxide, the sulfinyl group is not involved in H bonding despite its strong potential as a hydrogen-bond acceptor. The crystal structure made it possible to establish the absolute configuration of the sulfinyl group in this peptide. The two crystal structures also helped identify a type II′ β-turn in the DMSO-d₆ solution conformers of these peptides. © 1993 John Wiley & Sons, Inc.     

Sialic acid and sialyl‐lactose glyco‐conjugates: design,synthesis and binding assays to lectins and swine influenza H1N1 virus

The terminal parts of the influenza hemagglutinin (HA) receptors α2,6‐ and α2,3‐sialyllactoses were conjugated to an artificial carrier, named sequential oligopeptide carrier (SOC₄), to formulate human and avian receptor mimics, respectively. SOC₄, formed by the tripeptide unit Lys‐Aib‐Gly, adopts a rigid helicoids‐type conformation, which enables the conjugation of biomolecules to the Lys‐N^εH₂ groups. By doing so, it preserves their initial conformations and functionalities of the epitopes. We report that SOC₄‐glyco‐conjugate bearing two copies of the α2,6‐sialyllactose is specifically recognized by the biotinylated Sambucus nigra (elderberry) bark lectin, which binds preferentially to sialic acid in an α2,6‐linkage. SOC₄‐glyco‐conjugate bearing two copies of the α2,3‐sialyllactose was not recognized by the biotinylated Maackia amurensis lectin, despite its well‐known α2,3‐sialyl bond specificity. However, preliminary immune blot assays showed that H1N1 virus binds to both the SOC₄‐glyco‐conjugates immobilized onto nitrocellulose membrane. It is concluded that Ac‐SOC₄[(Ac)₂,(3′SL‐Aoa)₂]‐NH₂ 5 and Ac‐SOC₄[(Ac)₂,(6′SL‐Aoa)₂]‐NH₂ 6 mimic the HA receptors. These findings could be useful for easy screening of binding and inhibition assays of virus–receptor interactions. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Modulating the structure of phenylalanine‐incorporated ascidiacyclamide through fluorination

We designed four fluorinated Phe‐incorporated ascidiacyclamide ([Phe]ASC) analogs, (cyclo(?Xxx1‐oxazoline2‐d ‐Val3‐thiazole4‐Ile5‐oxazoline6‐d ‐Val7‐thiazole8‐)), [(4‐F)Phe]ASC (Xxx1: 4‐fluorophenylalanine), [(3,5‐F₂)Phe]ASC (Xxx1: 3,5‐difluorophenylalanine), [(3,4,5‐F₃)Phe]ASC (Xxx1: 3,4,5‐trifluorophenylalanine) and [(F₅)Phe]ASC (Xxx1: pentafluorophenylalanine), to modulate the π‐electron density of the aromatic ring of the Phe residue. X‐ray diffraction analysis, ¹H NMR and CD spectra all suggested that the interactions between the benzene ring of the Xxx1 residue and the alkyl groups of oxazoline2 contribute to the stability of the folded structure of these analogs. Substituting fluorines for the hydrogens progressively weakened those interactions through reducing the π‐electron density, thereby mediating transformation from the folded to square structure. As a result, [(F₅)Phe]ASC preferred the square form more than the other analogs did. Also contributing to the preference for the square form may be the hindrance of the rotation around the Cα–Cβ bond by the two ortho‐fluoro substituents of [(F₅)Phe]ASC. These findings demonstrate that the structure of ASC can be modulated by using fluorine as an electron‐withdrawing group. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Interactions of Phospholipid Vesicles with Murine Lymphocytes

The effect of unilamellar lipid vesicles composed of dioleoyl lecithin (DOL), egg yolk lecithin (EYL), 1:1 EYL:cholesterol (Chol), dipalmitoyl lecithin (DPL), and dimyristoyl lecithin (DML) on the mitogenic response in mouse lymphocytes was tested. Cortisone-resistant thymocytes were briefly treated with lipid vesicles and subsequently stimulated with concanavalin A (con A). All of the lipid vesicles induced an enhanced mitogenic response on day 3 as tested by [³H]TdR incorporation and by counting total cells. The order of enhanced [³H]TdR incorporation (?5.3 times the control) was DML>DPL>1:1 EYL:Chol>EYL?DOL> untreated control cells. These increases were paralleled by increased numbers of total cells. The response of spleen cells to a B-cell mitogen, bacterial lipopolysaccharide, was similarly enhanced by vesicle pretreatments in the same order. Vesicle treatments alone were not mitogenic.

Pretreatment of cells with lipid vesicles modified lectin binding: DML and DPL increased the binding of [¹²⁵I]con A by three to four times the control, whereas 1:1 EYL:Chol, EYL, or DOL had little or no effect. The binding of [125I]phytohemagglutinin-P (PHA-P) to vesicle-treated cells was indistinguishable from untreated cells. The lectin (con A; PHA-P)-induced agglutination of vesicle-treated cells was also modified by different lipid vesicles in the same order as the mitogenic response.

Based on the results presented in the accompanying report [6], we find that the cell surface adsorption properties of the applied lipid vesicles correlate with their ability to enhance the mitogenic response, and that they modify agglutinability and lectin binding. These results are further discussed in terms of the possible alteration of membrane properties and subsequent cellular activity.