Stereochemistry-Driven Interactions of α,γ-Peptide Ligands with the Neuropeptide Y Y4-Receptor.

The G-protein-coupled Y4-receptor (Y4R) and its endogenous ligand, pancreatic polypeptide (PP), suppress appetite in response to food intake and, thus, are attractive drug targets for body-weight control. The C-terminus of human PP (hPP), T32-R33-P34-R35-Y36-NH2, penetrates deep into the binding pocket with its tyrosine-amide and di-arginine motif. Here, we present two C-terminally amidated α,γ-hexapeptides (1a/b) with sequence Ac-R31-γ-CBAA32-R33-L34-R35-Y36-NH2, where γ-CBAA is the (1R,2S,3R)-configured 2-(aminomethyl)-3-phenylcyclobutanecarboxyl moiety (1a) or its mirror image (1b). Both peptides bind the Y4R (Ki of 1a/b: 0.66/12 nM) and act as partial agonists (intrinsic activity of 1a/b: 50/39%). Their induced-fit binding poses in the Y4R pocket are unique and build ligand-receptor contacts distinct from those of the C-terminus of the endogenous ligand hPP. We conclude that energetically favorable interactions, although they do not match those of the native ligand hPP, still guarantee high binding affinity (with 1a rivaling hPP) but not the maximum receptor activation.

Synthesis and Characterization of Bidentate Isonitrile Iron Complexes.

The divalent iron complexes trans-[FeBr2(BINC)2], [Cp*FeCl(BINC)] (Cp* = Me5C5), and [FeBr2(CNAr3NC)2] with the chelating bis(isonitrile) ligands BINC (bis(2-isocyanophenyl)phenylphosphonate) and CNAr3NC (2,2″-diisocyano-3,5,3″,5"tetramethyl-1,1':3',1″-terphenyl) have been prepared and characterized. Their subsequent reduction yields the di- and trinuclear compounds [Fe3(BINC)6], [Cp*Fe(BINC)]2, [Fe(CNAr3NC)2]2, and [K(Et2O)]2[Fe(CNAr3NC)2]2. The molecular structures of all new species were determined by X-ray crystallography and compared to those of related iron carbonyl complexes, demonstrating that the bidentate isonitrile ligands are capable surrogates for two CO ligands with only minimal distortion of the tetrahedral or octahedral geometry of the parent complexes. The complexes were further characterized by NMR and IR spectroscopy, and the electrochemical properties of selected compounds were analyzed by UV-vis-NIR spectroelectrochemistry.

Cyclic RGD and isoDGR Integrin Ligands Containing cis-2-amino-1-cyclopentanecarboxylic (cis-ß-ACPC) Scaffolds.

Integrin ligands containing the tripeptide sequences Arg-Gly-Asp (RGD) and iso-Asp-Gly- Arg (isoDGR) were actively investigated as inhibitors of tumor angiogenesis and directing unit in tumor-targeting drug conjugates. Reported herein is the synthesis, of two RGD and one isoDGR cyclic peptidomimetics containing (1S,2R) and (1R,2S) cis-2-amino-1-cyclopentanecarboxylic acid (cis-ß-ACPC), using a mixed solid phase/solution phase synthetic protocol. The three ligands were examined in vitro in competitive binding assays to the purified αvß3 and α5ß1 receptors using biotinylated vitronectin (αvß3) and fibronectin (α5ß1) as natural displaced ligands. The IC50 values of the ligands ranged from nanomolar (the two RGD ligands) to micromolar (the isoDGR ligand) with a pronounced selectivity for αvß3 over α5ß1. In vitro cell adhesion assays were also performed using the human skin melanoma cell line WM115 (rich in integrin αvß3). The two RGD ligands showed IC50 values in the same micromolar range as the reference compound (cyclo[RGDfV]), while for the isoDGR derivative an IC50 value could not be measured for the cell adhesion assay. A conformational analysis of the free RGD and isoDGR ligands by NMR (VT-NMR and NOESY experiments) and computational studies (MC/EM and MD), followed by docking simulations performed in the αVß3 integrin active site, provided a rationale for the behavior of these ligands toward the receptor.

Functional changes of biomolecules and organocatalysts as a probe for pressure effects in solution.

High pressure acts as a mild and non-destructive activation mode for chemical reactions. However, in the context of organo-/biocatalysis, high pressure activation, has not been investigated systematically, although there are significant benefits such as rate acceleration, increased selectivity and the possibility of suppressing side product formation. The influence of hydrostatic pressure in solution on the catalytic performance of enzymes and small molecule organocatalysts such as amino acids, peptides, amines, cinchona alkaloids and thioureas is evaluated in this review, taking reactivity and selectivity as a probe to identify pressure effects on biomolecules.

Visible-light photoredox-catalyzed desulfurization of thiol- and disulfide-containing amino acids and small peptides.

A scalable protocol for the desulfurization of cysteine by using visible light, the photocatalyst Ir(dF(CF3 )ppy)2 (dtb-bpy)PF6 and triethylphosphite under biphasic reaction conditions has been developed. The loading of the catalyst can be as low as 0.01 mol%, which can be efficiently removed during the workup (≤0.3 ppm), giving rise to the corresponding desulfurized product in high yields. This method has been applied also to cystine, penicillamine, and reduced and oxidized glutathione. The desulfurization has been found to be pH sensitive, with an optimal pH value of 6.5 and 7.0 for the cysteine derivatives and glutathione, respectively. In addition, during the desulfurization of a decapeptide containing cysteine and methionine, concurrent oxidation of the two sulfur-containing residues to disulfide and sulfoxide has been observed. Therefore, whereas the presented protocol allows a straightforward visible light-mediated desulfurization of simple thiols by using very low catalyst loading and a cost-effective trialkylphosphite as thiyl radical trapping agent, its application to complex substrates needs to be carefully validated. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

High Affinity Agonists of the Neuropeptide Y (NPY) Y4 Receptor Derived from the C-Terminal Pentapeptide of Human Pancreatic Polypeptide (hPP): Synthesis, Stereochemical Discrimination, and Radiolabeling.

The diastereomeric mixture of d/l-2,7-diaminooctanedioyl-bis(YRLRY-NH2) (BVD-74D, 2) was described in the literature as a high affinity Y4 receptor agonist. Here we report on the synthesis and pharmacological characterization of the pure diastereomers (2R,7R)- and (2S,7S)-2 and a series of homo- and heterodimeric analogues in which octanedioic acid was used as an achiral linker. To investigate the role of the Arg residues, one or two arginines were replaced by Ala. Moreover, N(ω)-(6-aminohexylaminocarbonyl)Arg was introduced as an arginine replacement (17). (2R,7R)-2 was superior to (2S,7S)-2 in binding and functional cellular assays and equipotent with 17. [(3)H]Propionylation of one amino group in the linker of (2R,7R)-2 or at the primary amino group in 17 resulted in high affinity Y4R radioligands ([(3)H]-(2R,7R)-10, [(3)H]18) with subnanomolar Kd values.

Traceless stereoinduction for the enantiopure synthesis of substituted-2-cyclopentenones.

The pseudoenantiomeric 4-O-Boc- and 4-OPMP-cyclopent-2-enones, readily available from hydroxymethylenefurane on multigram scale, are demonstrated to be exceptional building blocks for the synthesis of enantiopure 4-alkyl-5-(1'-hydroxyalkyl) substituted 2-cyclopentenones and derivatives thereof. The 4-OR substituent acts as a traceless stereoinducing element, conferring not only 1,2- but also 1,4-stereocontrol with excellent selectivity. The methodology developed here was applied for the rapid synthesis of natural products and biologically active 2-cyclopentenones such as TEI-9826, guaianes, and pseudoguaianolides.

Peptides containing ß-amino acid patterns: challenges and successes in medicinal chemistry.

The construction of bioactive peptides using ß-amino acid-containing sequence patterns is a very promising strategy to obtain analogues that exhibit properties of high interest for medicinal chemistry applications. ß-Amino acids have been shown to modulate the conformation, dynamics, and proteolytic susceptibility of native peptides. They can be either combined with α-amino acids by following specific patterns, which results in backbone architectures with well-defined orientations of the side chain functional groups, or assembled in de novo-designed bioactive ß- or α,ß-peptidic sequences. Such peptides display various biological functions, including antimicrobial activity, inhibition of protein-protein interactions, agonism/antagonism of GPCR ligands, and anti-angiogenic activity.

Replacement of Thr32 and Gln34 in the C-terminal neuropeptide Y fragment 25-36 by cis-cyclobutane and cis-cyclopentane ß-amino acids shifts selectivity toward the Y(4) receptor.

Neuropeptide Y (NPY) and pancreatic polypeptide (PP) control central and peripheral processes by activating the G protein coupled receptors YxR (x = 1, 2, 4, 5). We present analogs of the C-terminal fragments 25-36 and 32-36 of NPY and PP containing (1R,2S)-cyclobutane (ßCbu) or (1R,2S)-cyclopentane (ßCpe) ß-amino acids, which display exclusively Y4R affinity. In particular, [ßCpe(34)]-NPY-(25-36) is a Y4R selective partial agonist (EC50 41 ± 6 nM, Emax 71%) that binds Y4R with a Ki of 10 ± 2 nM and a selectivity >100-fold relative to Y1R and Y2R and >50-fold relative to Y5R. Comparably, [Y(32), ßCpe(34)]-NPY(PP)-(32-36) selectively binds and activates Y4R (EC50 94 ± 21 nM, Emax 73%). The NMR structure of [ßCpe(34)]-NPY-(25-36) in dodecylphosphatidylcholine micelles shows a short helix at residues 27-32, while the C-terminal segment R(33)ßCpe(34)R(35)Y(36) is extended. The biological properties of the ßCbu- or ßCpe-containing NPY and PP C-terminal fragments encourage the future application of these ß-amino acids in the synthesis of selective Y4R ligands.

Synthesis and evaluation of 3-amino/guanidine substituted phenyl oxazoles as a novel class of LSD1 inhibitors with anti-proliferative properties.

A series of functionalized phenyl oxazole derivatives was designed, synthesized and screened in vitro for their activities against LSD1 and for effects on viability of cervical and breast cancer cells, and in vivo for effects using zebrafish embryos. These compounds are likely to act via multiple epigenetic mechanisms specific to cancer cells including LSD1 inhibition.

17ß-Estradiol induces vasorelaxation in a G-protein-coupled receptor 30-independent manner.

17ß-Estradiol (E2) exerts rapid non-genomic vascular effects through activation of its plasma membrane receptors. We tested the hypothesis that E2 induces vasorelaxation through activation of the G-protein-coupled receptor 30 (GPR30) in rat aorta. Rat aortic rings were mounted in organ baths and subjected to contraction followed by relaxation. Whether endothelium was intact or denuded, both E2 and G1, a GPR30 agonist, induced vasorelaxation in concentration-dependent manners. Although G15, a specific GPR30 antagonist, blocked G1-induced vasorelaxation, it did not block E2-induced vasorelaxation. In conclusion, 17ß-estradiol induces vasorelaxation in a GPR30-independent manner in rat aorta.

α/ß-Peptide foldamers: state of the art.

Interplay between proteins, nucleic acids, carbohydrates and/or lipids is involved in almost every process in life on earth. As a consequence, a wide range of diseases results from abnormal interactions of such biomolecules. The main motivation of foldamer science is the development of scaffolds that are capable of adopting defined structures, mimicking parts of biological protagonists in their function. Among the most fundamental interactions in living beings are those between proteins, the so called protein--protein interactions (PPIs). Therefore, peptidic foldamers bear the promise to be an important tool for the inhibition of PPIs, as they are structurally most similar to the original proteins. The great number of possible permutations given by the combination of proteinogenic α-amino acid residues along with ß-amino acids opens the door for a larger pool of accessible structures with potential applications. Despite the increasing amount of new secondary structure motifs, only few examples for tertiary and quaternary structure design, as well as inhibition of PPIs, have been realized so far. In this review, we summarize the current knowledge and recent progress made in the field of α/ß-peptide foldamers beginning from secondary structure design up to highly sophisticated biological applications, such as protein surface recognition and inhibition of HIV cell entry.

Synthesis of an adenine nucleoside containing the (8'R) epimeric carbohydrate core of amipurimycin and its biological study.

The (8'R) epimeric carbohydrate core 2 of amipurimycin was synthesized from D-glucose derived allylic alcohol 3 in 11 steps and 13% overall yield. The key steps involve an acid-catalyzed acetonide ring opening of 9 with concomitant formation of an unprecedented pyranose ring skeleton to give 2,7-dioxabicyclo[3.2.1]octane 10. The α-orientation of the furan ring in 10 readily allows the stereoselective ß-glycosylation and opening of the furanose ring that on removal of protecting groups affords the pyranosyl adenine nucleoside 2. The antifungal and anticancer activities of 2 were studied.

Iron(II)-bis(isonitrile) complexes: novel catalysts in asymmetric transfer hydrogenations of aromatic and heteroaromatic ketones.

Chiral iron(ii)-bis(isonitrile) complexes catalyse the transfer hydrogenation of aromatic ketones with enantioselectivities up to 91% ee, most likely via hydride transfer through imine intermediates, generated by in situ reduction of the isonitrile ligands, whereas iron acts as a Lewis acid to activate the ketone.

Synthesis of (S)- and (R)-5-oxo-piperazine-2-carboxylic acid and its application to peptidomimetics.

A straightforward synthesis of (S)- and (R)-N-Boc-5-oxo-piperazine-2-carboxylic acid is reported starting from L- or D-serine and ethyl glyoxylate. Those were evaluated as constituents in two tetrapeptides by studying their secondary structure by (1)H NMR spectroscopy. In the case of Boc-Val-(S)-PCA-Gly-Leu-OMe, two readily interconverting conformations (in a 40%:60% ratio) were observed, differing for the cis-trans isomerizaton of the tertiary amide bond, while Boc-Val-(R)-PCA-Gly-Leu-OMe displayed an equilibrium between a gamma-turn and a type II beta-turn conformation.

Residual dipolar couplings in short peptidic foldamers: combined analyses of backbone and side-chain conformations and evaluation of structure coordinates of rigid unnatural amino acids.

A flexible tool for rigid systems. Residual dipolar couplings (RDCs) have proven to be valuable NMR structural parameters that provide insights into the backbone conformations of short linear peptidic foldamers, as illustrated here. This study demonstrates that RDCs at natural abundance can provide essential structural information even in the case of short linear peptides with unnatural amino acids. In addition, they allow for the detection of proline side-chain conformations and are used as a quality check for the parameterizations of rigid unnatural amino acids.

Short alpha/beta-peptides as catalysts for intra- and intermolecular aldol reactions.

Short alpha/beta-peptides, containing conformationally restricted cis-beta-aminocyclopropylcarboxylic acid units as turn-inducing elements, have been found to be efficient catalysts for inter- and intramolecular aldol reactions. The tripeptide H-(L)-Pro-black triangle-(L)-Pro-OH was identified to perform especially well in homogeneous and heterogeneous aqueous solutions as well as in organic solvents.

Structural properties of orexins for activation of their receptors.

The closely related neuropeptides orexin A and orexin B mediate their actions, including the regulation of sleep and appetite, by the activation of the orexin 1 and 2 receptors. To elucidate the structural prerequisites for receptor activation and subtype selectivity, we performed multiple amino acid substitutions within the sequence of orexin A and human orexin B-(6-28)-peptide and analyzed their solution structures by CD spectroscopy and their activity at both receptors in Ca(2+) mobilization assays. For orexin A, we showed that the basic amino acids within the segment of residues 6-14 were important for the activation of both receptors. Furthermore, we showed that the restriction via disulfide bonds is not required to maintain the active structure of orexin A. The kink region of h orexin B has been shown to be important for Ox(2)R selectivity, which is not mediated by the restriction of the turn structure. Additionally, we showed that no particular secondary structure is required for receptor subtype selectivity.