Dagmara Tymecka

β-Homo-amino Acid Scan of Angiotensin IV

Angiotensin IV, a metabolite of angiotensin II, inhibits the enzyme insulin regulated aminopeptidase or IRAP and also, although with lower potency, aminopeptidase-N (AP-N). When both beta (2)-homo amino acid- and beta (3)-homo amino acid substitutions were used, allowed the identification of H-( R)beta (2)hVal-Tyr-Ile-His-Pro-beta (3)hPhe-OH as a potent and stable Ang IV analog with high selectivity for IRAP versus AP-N and the AT1 receptor.

HPLC enantioseparation of β2-homoamino acids using crown ether-based chiral stationary phase

RP high-performance liquid chromatographic methods were developed for the enantioseparation of eleven unusual beta(2)-homoamino acids. The underivatized analytes were separated on a chiral stationary phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as chiral selector. The effects of organic (alcoholic) and acidic modifiers, the mobile phase composition and temperature on the separation were investigated. The structures of the substituents in the alpha-position of the analytes substantially influenced the retention and resolution. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers.

Electron transfer across α-helical peptide monolayers: importance of interchain coupling.

Four helical peptides with the general formula (Boc)-Cys-(S-Acm)-(Ala-Leu)(n)-NH-(CH(2))(2)-SH (n = 4-7) were synthesized and further used for the preparation of self-assembled monolayers (SAMs) on gold substrates. The electron-transfer behavior of these systems was probed using current-sensing atomic force microscopy (CS-AFM). It was found that the electron transmission through SAMs of helical peptides trapped between an AFM conductive tip and a gold substrate occurs very efficiently and that the distance dependence obeys the exponential trend with a decay constant of 4.6 nm(-1). This result indicates that the tunneling mechanism is operative in this case. Conductance measurements under mechanical stress show that peptide-mediated electron transmission occurs with the possible contribution of intermolecular electron tunneling between adjacent helices. It was also demonstrated that an external electric field applied between metallic contacts can affect the structure of the peptide SAM by changing its thickness. This explains the asymmetry of the current-voltage response of metal-monolayer-metal junction.

Enantioseparation of β2-amino acids on cinchona alkaloid-based zwitterionic chiral stationary phases. Structural and temperature effects

The enantiomers of sixteen unusual β(2)-amino acids were directly separated on chiral stationary phases containing quinine- or quinidine-based zwitterionic selectors. The effects of the mobile phase composition, the structure of the analyte and temperature on the separations were investigated. Experiments were performed at constant mobile phase compositions in the temperature range -5 to 55°C in order to study the effects of temperature, and thermodynamic parameters were estimated from plots of lnk or lnα vs. 1/T. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. It was found that the enantiomeric separations were in most cases enthalpically driven, but entropically driven separation was also observed. The sequence of elution of the enantiomers was determined in some cases.

High-performance liquid chromatographic enantioseparation of β2-amino acids using a long-tethered (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid-based chiral stationary phase

Reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of eleven unnatural beta(2)-amino acids on a new chiral stationary phase, using the 11-methylene-unit spacer of aminoundecylsilica gel for the bonding of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as selector. The nature and concentration of the acidic and organic modifiers, the pH, the mobile phase composition, and the structures of the analytes substantially influenced the retention and resolution. Separations were carried out at constant mobile phase compositions in the temperature range 7-40 degrees C and the changes in enthalpy, Delta(DeltaH degrees ), entropy, Delta(DeltaS degrees ), and free energy, Delta(DeltaG degrees ) were calculated. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers.

High-performance liquid chromatographic chiral separation of β2-homoamino acids

Reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of eleven unnatural beta(2)-homoamino acids on chiral stationary phases containing macrocyclic glycopeptides (teicoplanin-containing Chirobiotic T and T2) or the macrocyclic peptide teicoplanin aglycone (Chirobiotic TAG) as chiral selectors. The effects of the organic modifier, the mobile phase composition, temperature, and the structures of the analytes on the separations were investigated. Separations were carried out at constant mobile phase compositions in temperature range 7-45 degrees C and the changes in enthalpy, Delta(DeltaH(o)), entropy, Delta(DeltaS(o)), and free energy, Delta(DeltaG(o)), were calculated. The -Delta(DeltaG(o)) values obtained on the three columns indicated that Chirobiotic TAG, without sugar units, may promote the interactions of the enantiomers of beta(2)-homoamino acids with branched alkyl or aryl side-chains, whereas for beta(2)-homoamino acids with alkyl side-chains Chirobiotic T and T2 seem to be more favorable. The elution sequence was determined in some cases and was observed to be R < S.

Comparison of the Separation Performances of Cinchona Alkaloid-Based Zwitterionic Stationary Phases in the Enantioseparation of β2- and β3-Amino Acids

The enantiomers of twelve unusual β2- and β3-homoamino acids containing the same side-chains were separated on chiral stationary phases containing a quinine- or quinidine-based zwitterionic ion-exchanger as chiral selector. The effects of the mobile phase composition, the nature and concentration of the acid and base additives and temperature on the separations were investigated. The changes in standard enthalpy, ∆(∆H°), entropy, ∆(∆S°), and free energy, ∆(∆G°), were calculated from the linear van’t Hoff plots derived from the ln α vs. 1/T curves in the studied temperature range (10–50 °C). The values of the thermodynamic parameters depended on the nature of the selectors, the structures of the analytes, and the positions of the substituents on the analytes. A comparison of the zwitterionic stationary phases revealed that the quinidine-based ZWIX(−)™ column exhibited much better selectivity for both β2- and β3-amino acids than the quinine-based ZWIX(+)™ column, and the separation performances of both the ZWIX(+)™ and ZWIX(−)™ columns were better for β2-amino acids. The elution sequence was determined in some cases and was observed to be R < S and S < R on the ZWIX(+)™ and ZWIX(−)™ columns, respectively.

Modulation of Activity of Ultrashort Lipopeptides toward Negatively Charged Model Lipid Films

Because of the increasing resistance of pathogens to commonly used antibiotics, there is an urgent need to find alternative antimicrobial compounds with different mechanisms of action. Among them, lipopeptides are recognized as promising candidates. In this work, the Langmuir technique and atomic force microscopy were employed to investigate the interactions of two novel lipopeptides with negatively charged phospholipid membranes, which served as a simplified model of inner membrane of Gram-negative bacteria. Lipid films contained phosphatidylethanolamine and phosphatidylglycerol extracts from E. coli bacteria. Lipopeptides were composed of palmitoyl chain covalently coupled to N-terminus of peptide with Trp-Lys-Leu-Lys amino acid sequence and the conformation of third residue was either d-Leu or l-Leu. It was found that chirality of leucine strongly affects interfacial behavior of these compounds, which was ascribed to the difference in effective size of the peptide portion of the molecules. Although the lipopeptides were the same in terms of amino acid sequence, charge, and identity of lipophilic chain, the experiments revealed that the barrier for their insertion into the lipid membrane is significantly different. Namely, it was lower for lipopeptide containing d-Leu residue. We have also found that insertion of the lipopeptides into the model membranes strongly alters lateral distribution of the membrane components and leads to its substantial fluidization. The dynamics of reorganization was noticeably faster in the presence of lipopeptide with smaller size of peptide moiety, i.e., containing d-Leu. It proves that effective size of the peptide headgroup is an important factor determining lipopeptide activity toward the lipid membranes.

Conformational latitude – activity relationship of KPPR tetrapeptide analogues toward their ability to inhibit binding of vascular endothelial growth factor 165 to neuropilin-1

Neuropilin‐1 (NRP‐1) has been found to be overexpressed in several kinds of malignant tumors, and it is postulated that in pathological angiogenesis, its interaction with the vascular endothelial growth factor 165 (VEGF165) leads to progression of tumor vascularization and growth. Herein, we present synthesis and in vitro evaluation of tetrapeptides with the general sequence KxxR, where xx represents two canonical amino acid residues or a single amino acid possessing hydrocarbon backbone. All synthesized compounds were found to be inhibitors of VEGF165/NRP‐1 interactions. The rationale behind their design was to elucidate the relationship between the xx flexibility and their inhibitory activity. Detailed molecular dynamics simulations for all synthesized compounds have been performed. A clear and quantitative relationship was found in the peptide analogues: the more flexible is the xx, the less active the analogue is. But surprisingly, highly flexible peptidomimetics with non‐natural amino acids (NH2‐(CH2)n‐COOH; n = 4,5) residues used possessed higher inhibitory activity than it was expected. Our molecular dynamics study of inhibitor/NRP‐1 complexes provides convincing explanations of divergence in the observed inhibitory activity; thus, it might give indication for design of the next generation NRP‐1 inhibitors. Copyright

Structure-activity relationship study of tetrapeptide inhibitors of the Vascular Endothelial Growth Factor A binding to Neuropilin-1

HIGHLIGHTS13 tetrapeptides were synthesized, tested for inhibitory activity on VEGF165/NRP‐1 binding and modeled by molecular dynamics.Arg or Har in 1st position allow optimal interactions with NRP‐1 (length and delocalized charge of guanidinium group).Rigidity of central part of molecule should be partially preserved, changes in position 2 more favorable than in position 3.Har‐Dab‐Pro‐Arg, exhibits a submicromolar IC50, is almost 10 times stronger than a reference inhibitor A7R.the results give an important insight into structural requirements for high inhibitory activity on VEGF165/NRP‐1 interaction. ABSTRACT Neuropilin‐1 is considered as one of the key receptors responsible for signaling pathways involved in pathological angiogenesis necessary for tumor progression, therefore targeting of VEGF165 binding to NRP‐1 could be a relevant strategy for antiangiogenic treatment. It was shown before that the VEGF165/NRP‐1 interaction can be inhibited by short tetrapeptides with K/RXXR sequence. Here, we present a structure–activity relationship study of the systematic optimization of amino acid residues in positions 1–3 in the above tetrapeptides. All the 13 synthesized analogs possessed C‐terminal arginine that is a necessary element for interaction with NRP‐1. The obtained results of the inhibitory activity and modeling by molecular dynamics indicate that simultaneous interactions of the basic amino acid residues in position 1 and 4 (Arg) with Neuropilin‐1 are crucial and their cooperation strongly affects the inhibitory activity. In addition, the binding strength is modulated by the flexibility of the peptide backbone (in the central part of the peptide), and the nature of the side chain of the amino acids at the second or third position. A dramatic decrease in the activity to the receptor is observed in flexible derivatives that are missing proline residues. The results described in this paper should prove useful for future studies aimed at establishing the best pharmacophore for inhibitors of VEGF165 binding to NRP‐1.