Quest for New Generation Biocompatible Materials: Tailoring ß-Peptide Structure and Interactions via Synergy of Experiments and Modelling.

Peptide-based self-assembly has been used to produce a wide range of nanostructures. While most of these systems involve self-assembly of α-peptides, more recently ß-peptides have also been shown to undergo supramolecular self-assembly, and have been used to produce materials for applications in tissue engineering, cell culture and drug delivery. In order to engineer new materials with specific structure and function, theoretical molecular modelling can provide significant insights into the collective balance of non-covalent interactions that drive the self-assembly and determine the structure of the resultant supramolecular materials under different conditions. However, this approach has only recently become feasible for peptide-based self-assembled nanomaterials, particularly those that incorporate non α-amino acids. This perspective provides an overview of the challenges associated with computational modelling of the self-assembly of ß-peptides and the recent success using a combination of experimental and computational techniques to provide insights into the self-assembly mechanisms and fully atomistic models of these new biocompatible materials.

Unimolecular Chemiexcited Oxygenation of Pathogenic Amyloids.

Pathogenic protein aggregates, called amyloids, are etiologically relevant to various diseases, including neurodegenerative Alzheimer disease. Catalytic photooxygenation of amyloids, such as amyloid-ß (Aß), reduces their toxicity; however, the requirement for light irradiation may limit its utility in large animals, including humans, due to the low tissue permeability of light. Here, we report that Cypridina luciferin analogs, dmCLA-Cl and dmCLA-Br, promoted selective oxygenation of amyloids through chemiexcitation without external light irradiation. Further structural optimization of dmCLA-Cl led to the identification of a derivative with a polar carboxylate functional group and low cellular toxicity: dmCLA-Cl-acid. dmCLA-Cl-acid promoted oxygenation of Aß amyloid and reduced its cellular toxicity without photoirradiation. The chemiexcited oxygenation developed in this study may be an effective approach to neutralizing the toxicity of amyloids, which can accumulate deep inside the body, and treating amyloidosis.

Synthesis, Characterization, and Antimicrobial Activity of Ultra-Short Cationic ß-Peptides.

The development of new antibiotics is urgently required because of the rapidly growing resistance against conventional antibiotics. The antimicrobial peptides show potential as small antibiotic molecules. The stability of peptides is a primary concern for the use of peptides as drugs. Introducing ß-amino acids into peptide sequences can be useful in preventing biological degradation by proteolytic enzymes. Herein, we describe the synthesis, characterization, and antimicrobial activity of ultra-short cationic ß-peptides, LA-ß3,3-Pip-ß2,2-Ac6c-PEA, P1; LA-ß3,3-Pip(G)-ß2,2-Ac6c-PEA, P2; LAU-ß3,3-Pip-ß2,2-Ac6c-PEA, P3, and LAU-ß3,3-Pip(G)-ß2,2-Ac6c-PEA, P4. Peptides P1-P4 were evaluated against Gram-negative, Gram-positive, MRSA, and multi-drug resistant E. coli (MDR-E. coli). P3 exhibited the most potent antimicrobial activity against E. coli, S. epidermidis, S. aureus, K. pneumoniae, S. mutans, and E. faecalis, with MIC values 0.5, 2, 0.5, 1, 2, and 1 µg/mL, respectively. P3 exhibited time- and concentration-dependent bactericidal activities against E. coli, S. aureus, and E. faecalis with a killing rate of 1.6 logs/h. The treatment of E. coli with peptide P3 showed membrane disruption. In addition, P3 exhibited the inhibition of biofilm produced by E. coli, synergism with antibiotics (ciprofloxacin, streptomycin, and ampicillin), 100% cell viability against AML12, RAW 264.7, and HEK-293 cell lines at 1, and 10 µg/mL concentrations.

Advance in the Polymerization Strategy for the Synthesis of ß-Peptides and ß-Peptoids.

Peptide mimics, possessing excellent biocompatibility and protease stability, have attracted broad attention and research in the biomedical field. ß-Peptides and ß-peptoids, as two types of vital peptide mimics, have demonstrated great potential in the field of foldamers, antimicrobials and protein binding, etc. Currently, the main synthetic strategies for ß-peptides and ß-peptoids include solid-phase synthesis and polymerization. Among them, polymerization in one-pot can minimize the repeated separation and purification used in solid-phase synthesis, and has the advantages of high efficiency and low cost, and can synthesize ß-peptides and ß-peptoids with high molecular weight. This review summarizes the polymerization methods for ß-peptides and ß-peptoids. Moreover, future developments of the polymerization method for the synthesis of ß-peptides and ß-peptoids will be discussed.

Atomic zinc sites with hierarchical porous carbon for high-throughput chemical screening with high loading capacity and stability.

Alzheimer's disease (AD) is a neurodegenerative disease associated with aging, and the number of people affected is rapidly increasing. Abnormally hyperphosphorylated tau filaments and extracellular deposits of amyloid ß-peptides (Aß) fibrils are two important pathological hallmarks of AD. Currently, stopping the production of Aß and blocking its aggregation is the main strategy for the treatment of AD. Turmeric is effective in treating neurodegenerative diseases, but there is no effective way to identify active compounds from their complicated chemical compositions. Instead of using conventional extraction and separation methods with low efficiency and time-consuming, our group tried to use atomic materials in high-throughput chemical screening due to their structural characteristics and the unique advantages of surface atomic. Herein, a novel atomic zinc sites with hierarchical porous carbon (Zn-HPC) was synthesized to quickly screen potential inhibitors of Aß aggregation in turmeric. As-combined Aß@Zn-HPC demonstrates superior storage stability and high selectivity, outperforming the most reported supporters for ligand fishing. Five compounds with strong affinity on Aß@Zn-HPC were selected by high-performance liquid chromatography-hybrid linear ion trap/orbitrap mass spectrometer after incubation with turmeric extract. Finally, it was shown that curcumin and bisdemethoxycurcumin can inhibit Aß aggregation by using thioflavin-T fluorescence assay and biolayer interferometry. A new application for the accurate identification of Aß aggregation inhibitors from turmeric were developed based on the active compounds possessing binding affinity to Aß to inhibit its aggregation. The developed method could provide a promising tool for efficient drug discovery from natural product resources.

Synthesis of chimera oligopeptide including furanoid ß-sugar amino acid derivatives with free OHs: mild but successful removal of the 1,2-O-isopropylidene from the building block.

Complementary to hydrophobic five membered ring ß-amino acids (e.g. ACPC), ß-sugar amino acids (ß-SAAs) have found increasing application as hydrophilic building blocks of foldamers and α/ß chimeric peptides. Fmoc-protected ß-SAAs [e.g. Fmoc-RibAFU(ip)-OH] are indeed useful Lego elements, ready to use for SPPS. The removal of 1,2-OH isopropylidene protecting group increasing the hydrophilicity of such SAA is presented here. We first used N3-RibAFU(ip)-OH model compound to optimize mild deprotection conditions. The formation of the 1,2-OH free product N3-RibAFU-OH and its methyl glycoside methyl ester, N3-RibAFU(Me)-OMe were monitored by RP-HPLC and found that either 50% TFA or 8 eqv. Amberlite IR-120 H+ resin in MeOH are optimal reagents for the effective deprotection. These conditions were then successfully applied for the synthesis of chimeric oligopeptide: -GG-X-GG- [X=RibAFU(ip)]. We found the established conditions to be effective and-at the same time-sufficiently mild to remove 1,2-O-isopropylidene protection and thus, it is proposed to be used in the synthesis of oligo- and polypeptides of complex sequence combination.

Supramolecular Bait to Trigger Non-Equilibrium Co-Assembly and Clearance of Aß42.

In living systems, non-equilibrium states that control the assembly-disassembly of cellular components underlie the gradual complexification of life, whereas in nonliving systems, most molecules follow the laws of thermodynamic equilibrium to sustain dynamic consistency. Little is known about the roles of non-equilibrium states of interactions between supramolecules in living systems. Here, a non-equilibrium state of interaction between supramolecular lipopolysaccharide (LPS) and Aß42, an aggregate-prone protein that causes Alzheimer's disease (AD), was identified. Structurally, Aß42 presents a specific groove that is recognized by the amphiphilicity of LPS bait in a non-equilibrium manner. Functionally, the transient complex elicits a cellular response to clear extracellular Aß42 deposits in neuronal cells. Since the impaired clearance of toxic Aß42 deposits correlates with AD pathology, the non-equilibrium LPS and Aß42 could represent a useful target for developing AD therapeutics.

Protective effect of 2-dodecyl-6-methoxycyclohexa-2, 5-diene-1, 4-dione, isolated from Averrhoa carambola L., against Aß1-42-induced apoptosis in SH-SY5Y cells by reversing Bcl-2/Bax ratio.

BACKGROUND AND PURPOSE: Aß1-42-induced neurotoxicity has been considered as a possible mechanism to aggravate the onset and progression of Alzheimer's disease (AD). In this study, we aim to determine the protective effect of DMDD on the apoptosis of SH-SY5Y cells induced by Aß1-42 and elucidate potential mechanism of DMDD's protective function in apoptosis. EXPERIMENTAL APPROACH: CCK-8, AnnexinV-FITC/PI flow cytometry, and transmission electron microscopy analysis were used to determine the protection of DMDD on Aß1-42-evoked apoptosis of SH-SY5Y cells. Cytochrome c release, JC-1 staining, and measuring the protein of Bcl-2 family by Western blot were applied to elucidate the mechanism of DMDD's protective function in apoptosis. KEY RESULTS: Three concentration of DMDD (5 µmol/L, 10 µmol/L, and 20 µmol/L) rescues the cell viability loss and apoptosis of SH-SY5Y cells cultivated in Aß1-42. The expressions of cleaved Caspase-3, -8, -9, the cytochrome c release, and mitochondrial membrane potential loss were inhibited by DMDD in Aß1-42-insulted SH-SY5Y cells. The Western blot analysis showed that DMDD pretreatment clearly downregulated the protein of Bax and upregulated Bcl-2. Moreover, the Bcl-2/Bax ratio was obviously decreased in cells only exposed to Aß1-42, but, which was suppressed by treated with DMDD. CONCLUSION AND IMPLICATIONS: DMDD attenuated the apoptosis of SH-SY5Y cells induced by Aß1-42 through reversing the Bcl-2/Bax ratio.

High-Speed Atomic Force Microscopy Reveals the Structural Dynamics of the Amyloid-ß and Amylin Aggregation Pathways.

Individual Alzheimer's disease (AD) patients have been shown to have structurally distinct amyloid-ß (Aß) aggregates, including fibrils, in their brain. These findings suggest the possibility of a relationship between AD progression and Aß fibril structures. Thus, the characterization of the structural dynamics of Aß could aid the development of novel therapeutic strategies and diagnosis. Protein structure and dynamics have typically been studied separately. Most of the commonly used biophysical approaches are limited in providing substantial details regarding the combination of both structure and dynamics. On the other hand, high-speed atomic force microscopy (HS-AFM), which simultaneously visualizes an individual protein structure and its dynamics in liquid in real time, can uniquely link the structure and the kinetic details, and it can also unveil novel insights. Although amyloidogenic proteins generate heterogeneously aggregated species, including transient unstable states during the aggregation process, HS-AFM elucidated the structural dynamics of individual aggregates in real time in liquid without purification and isolation. Here, we review and discuss the HS-AFM imaging of amyloid aggregation and strategies to optimize the experiments showing findings from Aß and amylin, which is associated with type II diabetes, shares some common biological features with Aß, and is reported to be involved in AD.

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory-Impairing Anti-Parallel Aß Dimers.

Amyloid-ß (Aß) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aß oligomers. Herein parallel and anti-parallel variants of Aß(1-40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti-parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA-approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aß oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aß in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aß interactions with dimer-specific molecules.

Chemoselectivity issues of the asymmetric interaction between cyclohexanone, ß-nitrostyrene, and benzoic acid under 5-aryl prolinate's organocatalysis.

4-l-menthyloxycarbonyl 5-aryl prolinates were studied as organocatalysts of a novel three-component reaction of cyclohexanone, benzoic acid, and ß-nitrostyrene. The presence of ortho-halogen atom in 5-aryl fragment of the catalyst is favored for driving the formation of chiral 7a-hydroxyoctahydro-2H-indol-2-one scaffold. 5-(o-Chlorophenyl) prolinate selectively afforded 3-phenyl-7a-hydroxyoctahydro-2H-indol-2-one with ee 63%, whereas 5-phenyl prolinate led to conjugation of ß-nitrostyrene to cyclohexanone (the Michael adduct). Plausible chlorine effect is accounted for the specific interaction of the 5-aryl prolinate enamine intermediate with ß-nitrostyrene in the transition state.

A Glycosylated Cationic Block Poly(ß-peptide) Reverses Intrinsic Antibiotic Resistance in All ESKAPE Gram-Negative Bacteria.

Carbapenem-resistant Gram-negative bacteria (GNB) are heading the list of pathogens for which antibiotics are the most critically needed. Many antibiotics are either unable to penetrate the outer-membrane or are excluded by efflux mechanisms. Here, we report a cationic block ß-peptide (PAS8-b-PDM12) that reverses intrinsic antibiotic resistance in GNB by two distinct mechanisms of action. PAS8-b-PDM12 does not only compromise the integrity of the bacterial outer-membrane, it also deactivates efflux pump systems by dissipating the transmembrane electrochemical potential. As a result, PAS8-b-PDM12 sensitizes carbapenem- and colistin-resistant GNB to multiple antibiotics in vitro and in vivo. The ß-peptide allows the perfect alternation of cationic versus hydrophobic side chains, representing a significant improvement over previous antimicrobial α-peptides sensitizing agents. Together, our results indicate that it is technically possible for a single adjuvant to reverse innate antibiotic resistance in all pathogenic GNB of the ESKAPE group, including those resistant to last resort antibiotics.

Solution-Based Determination of Dissociation Constants for the Binding of Aß42 to Antibodies.

Amyloid ß-peptides (Aß) play a major role in the pathogenesis of Alzheimer's disease. Therefore, numerous monoclonal antibodies against Aß have been developed for basic and clinical research. The present study applied fluorescence based analytical ultracentrifugation and microscale thermophoresis to characterize the interaction between Aß42 monomers and three popular, commercially available antibodies, namely 6E10, 4G8 and 12F4. Both methods allowed us to analyze the interactions at low nanomolar concentrations of analytes close to their dissociation constants (K D) as required for the study of high affinity interactions. Furthermore, the low concentrations minimized the unwanted self-aggregation of Aß. Our study demonstrates that all three antibodies bind to Aß42 monomers with comparable affinities in the low nanomolar range. K D values for Aß42 binding to 6E10 and 4G8 are in good agreement with formerly reported values from SPR studies, while the K D for 12F4 binding to Aß42 monomer is reported for the first time.

Improved Modeling of Peptidic Foldamers Using a Quantum Chemical Parametrization Based on Torsional Minimum Energy Path Matching.

The increasing interest in novel foldamer constructs demands an accurate computational treatment on an extensive timescale. However, it is still a challenge to derive a force field (FF) that can reproduce the experimentally known fold while also allowing the spontaneous exploration of other structures. Here, aiming at a realistic reproduction of backbone torsional barriers, the relevant proper dihedrals of acyclic ß2-, ß3- and ß2,3-amino acids were added to the CHARMM FF and optimized using a novel, self-consistent iterative procedure based on quantum chemical relaxed scans. The new FF was validated by molecular dynamics simulations on three acyclic peptides. While they resided most of the time in their preferred fold (>80 % in helices and >50 % in hairpin), they also visited other conformations. Owing to the CHARMM36m-consistent parametrization, the proposed extension is suitable for exploring new foldamer structures and assemblies, and their interactions with diverse biomolecules.

Crystal structure of 4-[(1R,2S,5R)-2-isopropyl-5-methyl-cyclo-hex-yl] 2-methyl (2S,4S,5R)-1-[(2S,3R,5R)-5-meth-oxy-carbonyl-2-(2-methyl-phen-yl)pyrrolidine-3-carbon-yl]-5-(2-methyl-phen-yl)pyrrolidine-2,4-di-carboxyl-ate.

The title compound, C38H50N2O7, represents a chiral ß-proline dipeptide. Corresponding stereogenic centres of constituting pyrrolidine units have opposite absolute configurations. The central amide fragment is planar within 0.1 Šand adopts a Z configuration along the N-CO bond. In the crystal, the hydrogen atoms of the methyl-ene groups form several short inter-molecular C-H⋯O contacts with the carbonyl oxygen atoms of an adjacent mol-ecule. The only active amino hydrogen atom is not involved in hydrogen bonding.

ß-Aminopeptidases: Insight into Enzymes without a Known Natural Substrate.

ß-Aminopeptidases have the unique capability to hydrolyze N-terminal ß-amino acids, with varied preferences for the nature of ß-amino acid side chains. This unique capability makes them useful as biocatalysts for synthesis of ß-peptides and to kinetically resolve ß-peptides and amides for the production of enantiopure ß-amino acids. To date, six ß-aminopeptidases have been discovered and functionally characterized, five from Gram-negative bacteria and one from a fungus, Aspergillus Here we report on the purification and characterization of an additional four ß-aminopeptidases, one from a Gram-positive bacterium, Mycolicibacterium smegmatis (BapAMs), one from a yeast, Yarrowia lipolytica (BapAYlip), and two from Gram-negative bacteria isolated from activated sludge identified as Burkholderia spp. (BapABcA5 and BapABcC1). The genes encoding ß-aminopeptidases were cloned, expressed in Escherichia coli, and purified. The ß-aminopeptidases were produced as inactive preproteins that underwent self-cleavage to form active enzymes comprised of two different subunits. The subunits, designated α and ß, appeared to be tightly associated, as the active enzyme was recovered after immobilized-metal affinity chromatography (IMAC) purification, even though only the α-subunit was 6-histidine tagged. The enzymes were shown to hydrolyze chromogenic substrates with the N-terminal l-configurations ß-homo-Gly (ßhGly) and ß3-homo-Leu (ß3hLeu) with high activities. These enzymes displayed higher activity with H-ßhGly-p-nitroanilide (H-ßhGly-pNA) than previously characterized enzymes from other microorganisms. These data indicate that the new ß-aminopeptidases are fully functional, adding to the toolbox of enzymes that could be used to produce ß-peptides. Overexpression studies in Pseudomonas aeruginosa also showed that the ß-aminopeptidases may play a role in some cellular functions.IMPORTANCE ß-Aminopeptidases are unique enzymes found in a diverse range of microorganisms that can utilize synthetic ß-peptides as a sole carbon source. Six ß-aminopeptidases have been previously characterized with preferences for different ß-amino acid substrates and have demonstrated the capability to catalyze not only the degradation of synthetic ß-peptides but also the synthesis of short ß-peptides. Identification of other ß-aminopeptidases adds to this toolbox of enzymes with differing ß-amino acid substrate preferences and kinetics. These enzymes have the potential to be utilized in the sustainable manufacture of ß-amino acid derivatives and ß-peptides for use in biomedical and biomaterial applications. This is important, because ß-amino acids and ß-peptides confer increased proteolytic resistance to bioactive compounds and form novel structures as well as structures similar to α-peptides. The discovery of new enzymes will also provide insight into the biological importance of these enzymes in nature.

Preventing S. aureus biofilm formation on titanium surfaces by the release of antimicrobial ß-peptides from polyelectrolyte multilayers.

Staphylococcus aureus infections represent the major cause of titanium based-orthopaedic implant failure. Current treatments for S. aureus infections involve the systemic delivery of antibiotics and additional surgeries, increasing health-care costs and affecting patient's quality of life. As a step toward the development of new strategies that can prevent these infections, we build upon previous work demonstrating that the colonization of catheters by the fungal pathogen Candida albicans can be prevented by coating them with thin polymer multilayers composed of chitosan (CH) and hyaluronic acid (HA) designed to release a ß-amino acid-based peptidomimetic of antimicrobial peptides (AMPs). We demonstrate here that this ß-peptide is also potent against S. aureus (MBPC = 4 µg/mL) and characterize its selectivity toward S. aureus biofilms. We demonstrate further that ß-peptide-containing CH/HA thin-films can be fabricated on the surfaces of rough planar titanium substrates in ways that allow mammalian cell attachment and permit the long-term release of ß-peptide. ß-Peptide loading on CH/HA thin-films was then adjusted to achieve release of ß-peptide quantities that selectively prevent S. aureus biofilms on titanium substrates in vitro for up to 24 days and remained antimicrobial after being challenged sequentially five times with S. aureus inocula, while causing no significant MC3T3-E1 preosteoblast cytotoxicity compared to uncoated and film-coated controls lacking ß-peptide. We conclude that these ß-peptide-containing films offer a novel and promising localized delivery approach for preventing orthopaedic implant infections. The facile fabrication and loading of ß-peptide-containing films reported here provides opportunities for coating other medical devices prone to biofilm-associated infections. STATEMENT OF SIGNIFICANCE: Titanium (Ti) and its alloys are used widely in orthopaedic devices due to their mechanical strength and long-term biocompatibility. However, these devices are susceptible to bacterial colonization and the subsequent formation of biofilms. Here we report a chitosan and hyaluronic acid polyelectrolyte multilayer-based approach for the localized delivery of helical, cationic, globally amphiphilic ß-peptide mimetics of antimicrobial peptides to inhibit S. aureus colonization and biofilm formation. Our results reveal that controlled release of this ß-peptide can selectively kill S. aureus cells without exhibiting toxicity toward MC3T3-E1 preosteoblast cells. Further development of this polymer-based coating could result in new strategies for preventing orthopaedic implant-related infections, improving outcomes of these titanium implants.

Identifying the Coiled-Coil Triple Helix Structure of ß-Peptide Nanofibers at Atomic Resolution.

Peptide self-assembly represents a powerful bottom-up approach to the fabrication of nanomaterials. ß3-Peptides are non-natural peptides composed entirely of ß-amino acids, which have an extra methylene in the backbone, and we reported fibers derived from the self-assembly of ß3-peptides that adopt 14-helical structures. ß3-Peptide assemblies represent a class of stable nanomaterials that can be used to generate bio- and magneto-responsive materials with proteolytic stability. However, the three-dimensional structure of many of these materials remains unknown. To develop structure-based criteria for the design of ß3-peptide-based biomaterials with tailored function, we investigated the structure of a tri-ß3-peptide nanoassembly by molecular dynamics simulations and X-ray fiber diffraction analysis. Diffraction data was collected from aligned fibrils formed by Ac-ß3[LIA] in water and used to inform and validate the model structure. Models with 3-fold radial symmetry resulted in stable fibers with a triple-helical coiled-coil motif and measurable helical pitch and periodicity. The fiber models revealed a hydrophobic core and twist along the fiber axis arising from a maximization of contacts between hydrophobic groups of adjacent tripeptides on the solvent-exposed fiber surface. These atomic structures of macroscale fibers derived from ß3-peptide-based materials provide valuable insight into the effects of the geometric placement of the side chains and the influence of solvent on the core fiber structure which is perpetuated in the superstructure morphology.

Designed Macrocyclic Peptides as Nanomolar Amyloid Inhibitors Based on Minimal Recognition Elements.

Amyloid self-assembly is linked to the pathogenesis of Alzheimer's disease (AD) and type 2 diabetes (T2D), but so far, no anti-amyloid compound has reached the clinic. Macrocyclic peptides belong to the most attractive drug candidates. Herein we present macrocyclic peptides (MCIPs) designed using minimal IAPP-derived recognition elements as a novel class of nanomolar amyloid inhibitors of both Aß40(42) and IAPP or Aß40(42) alone and show that chirality controls inhibitor selectivity. Sequence optimization led to the discovery of an Aß40(42)-selective MCIP exhibiting high proteolytic stability in human plasma and human blood-brain barrier (BBB) crossing ability in a cell model, two highly desirable properties for anti-amyloid AD drugs. Owing to their favorable properties, MCIPs should serve as leads for macrocyclic peptide-based anti-amyloid drugs and scaffolds for the design of small-molecule peptidomimetics for targeting amyloidogenesis in AD or in both AD and T2D.

Theoretical and NMR Conformational Studies of ß-Proline Oligopeptides With Alternating Chirality of Pyrrolidine Units.

Synthetic ß-peptides are potential functional mimetics of native α-proteins. A recently developed, novel, synthetic approach provides an effective route to the broad group of ß-proline oligomers with alternating patterns of stereogenic centers. Conformation of the pyrrolidine ring, Z/E isomerism of ß-peptide bonds, and hindered rotation of the neighboring monomers determine the spatial structure of this group of ß-proline oligopeptides. Preferences in their structural organization and corresponding thermodynamic properties are determined by NMR spectroscopy, restrained molecular dynamics and quantum mechanics. The studied ß-proline oligopeptides exist in dimethyl sulfoxide solution in a limited number of conformers, with compatible energy of formation and different spatial organization. In the ß-proline tetrapeptide with alternating chirality of composing pyrrolidine units, one of three peptide bonds may exist in an E configuration. For the alternating ß-proline pentapeptide, the presence of an E configuration for at least of one ß-peptide bond is mandatory. In this case, three peptide bonds synchronously change their configurations. Larger polypeptides may only exist in the presence of several E configurations of ß-peptide bonds forming a wave-like extended structure.