The nucleation of monomeric parallel beta-sheet-like structures and their self-assembly in aqueous solution

A Comparative Study on the Self-Assembly of Peptide TGV-9 by In Situ Atomic Force Microscopy

Previous studies of amyloid diseases reported that the aggregating proteins share a similar conserved peptide sequence which can form the cross-β-sheet-containing nanostructures like nanofilaments. The template-assisted self-assembly (TASA) of peptides on inorganic substrates with different hydrophilicity could be an alternative approach to shed light on the fibrillization mechanism of proteins/peptides in vivo. To figure out the effect of interfaces on amyloid aggregation, we herein employed in situ atomic force microscopy (AFM) to investigate the self-assembling of a Parkinson disease-related core peptide sequence (TGV-9) on a hydrophobic liquid-solid interface via real-time observation of the dynamic fibrillization process. The results show that TGV-9 forms one-dimensional nanostructures on the surface of highly ordered pyrolytic graphite (HOPG) with three preferred growth orientations, which are consistent with the atomic lattice of HOPG, indicating an epitaxial growth or TASA. Conversely, the nanostructures formed in bulk solution can be free-standing nanofilaments, and the fibrillization mechanism is different from that on HOPG. These results could not only deepen the understanding of the protein/peptide aggregation mechanism but also benefit for the early diagnosis and clinic treatment of related diseases.

Improved Stability and Tunable Functionalization of Parallel β-Sheets via Multicomponent N-Alkylation of the Turn Moiety

In contrast to the myriad of methods available to produce α-helices and antiparallel β-sheets in synthetic peptides, just a few are known for the construction of stable, non-cyclic parallel β-sheets. Herein, we report an efficient on-resin approach for the assembly of parallel β-sheet peptides in which the N-alkylated turn moiety enhances the stability and gives access to a variety of functionalizations without modifying the parallel strands. The key synthetic step of this strategy is the multicomponent construction of an N-alkylated turn using the Ugi reaction on varied isocyano-resins. This four-component process assembles the orthogonally protected turn fragment and incorporates handles serving for labeling/conjugation purposes or for reducing peptide aggregation. NMR and circular dichroism analyses confirm the better-structured and more stable parallel β-sheets in the N-alkylated peptides compared to the non-functionalized variants.

The conjugates of ferrocene-1,1'-diamine and amino acids. A novel synthetic approach and conformational analysis

A novel synthetic approach toward a poorly explored bioorganometallic consisting of ferrocene-1,1'-diamine bearing structurally and chirally diverse amino acid sequences is reported. Until now, ferrocene-1,1'-diamine was suitable for accommodating only identical amino acid sequences at its N-termini, leading to the symmetrically disubstituted homochiral products stabilized through a 14-membered intramolecular hydrogen-bonded ring as is seen in antiparallel β-sheet peptides. The key step of the novel synthetic pathway is the transformation of Ac-Ala-NH-Fn-COOH (5) (Fn = 1,1'-ferrocenylene) to orthogonally protected Ac-Ala-NH-Fn-NHBoc (7). The spectroscopic analysis (IR, NMR, CD) of the novel compounds, corroborated with DFT studies, suggests the interesting feature of the ferrocene-1,1'-diamine scaffold. The same hydrogen-bonding pattern, i.e. a 14-membered hydrogen-bonded ring, was determined both in solution and in the solid state, thus making them promising, yet simple scaffolds capable of mimicking β-sheet peptides. In vitro screening of potential anticancer activity in Hep G2 human liver carcinoma cells and Hs 578 T human breast cancer cells revealed a cytotoxic pattern for novel compounds (150-500 μM) with significantly decreased cell proliferation.

Fourier transform infrared spectroscopy on external perturbations inducing secondary structure changes of hemoglobin

The secondary structure of proteins and their conformation are intimately related to their biological functions.

Impact of Strand Number on Parallel β-Sheet Stability

We have examined whether parallel β-sheet secondary structure becomes more stable as the number of β-strands increases, via comparisons among peptides designed to adopt two- or three-stranded parallel β-sheet conformations in aqueous solution. Our three-strand design is the first experimental model of a triple-stranded parallel β-sheet. Analysis of the designed peptides by nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy supports the hypothesis that increasing the number of β-strands, from two to three, increases the stability of the parallel β-sheet. We present the first experimental evidence for cooperativity in the folding of a triple-stranded parallel β-sheet, and we show how minimal model systems may enable experimental documentation of characteristic properties, such as CD spectra, of parallel β-sheets.

Cu(2+)-RGDFRGDS: exploring the mechanism and high efficacy of the nanoparticle in antithrombotic therapy

Thrombosis disease has been the leading cause of morbidity and mortality worldwide. In the discovery of antithrombotic agents, three complexes of Cu²⁺ and repetitive arginine-glycine-aspartic acid (RGD) sequences, Cu(II)-Arg-Gly-Asp-Ser-Arg-Gly-Asp-Ser (Cu[II]-4a), Cu(II)-Arg-Gly-Asp-Val-Arg-Gly-Asp-Val (Cu[II]-4b), and Cu(II)-Arg-Gly-Asp-Phe-Arg-Gly-Asp-Phe (Cu[II]-4c), were previously reported, of which Cu(II)-4a and Cu(II)-4c possessed the highest in vitro and in vivo activity, respectively. Transmission electron microscopy (TEM) images visualized that Cu(II)-4a and Cu(II)-4c formed nanoaggregates and nanoparticles, respectively. However, the details of the formation of the nanospecies complexes and of the mechanism for inhibiting thrombosis remain to be clarified. For this purpose, this study designed a novel complex of Cu(II) and the RGD octapeptide, Arg-Gly-Asp-Phe-Arg-Gly-Asp-Ser (RGDFRGDS), consisting of Arg-Gly-Asp-Phe of Cu(II)-4c and Arg-Gly-Asp-Ser of Cu(II)-4a, to colligate their biological and nanostructural benefits. In contrast with Cu(II)-4a, -4b, and -4c, Cu(II)-RGDFRGDS (Cu²⁺-FS) had high antiplatelet and antithrombotic activities, with the formed nanoparticles having a porous surface. Additionally, this paper evidenced the dimer had the basic structural unit of Cu²⁺-FS in water, theoretically simulated the formation of Cu²⁺-FS nanoparticles, and identified that Cu²⁺-FS activity in decreasing glycoprotein IIb/IIIa, P-selectin, and IL-8 was responsible for the antithrombotic action. Finally, adherence onto the surface and entry into the cytoplasm were considered the steps of a two-step model for the blocking of platelet activation by Cu²⁺-FS nanoparticles. Findings indicated that the antiplatelet aggregation activity of Cu²⁺-FS was 10–52 times higher than that of RGDFRGDS, while the effective dose for antithrombotic action was 5,000 times lower than that of RGDFRGDS.

Insoluble protein assemblies characterized by fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) spectroscopy is a useful tool for the structural characterization of insoluble protein assemblies, as it allows to obtain information on the protein secondary structures and on their intermolecular interactions. The protocols for FTIR spectroscopy and microspectroscopy measurements in transmission and attenuated total reflection modes will be presented and illustrated in the following examples: bacterial inclusion bodies, self-assembling peptides, thermal aggregates, and amyloid fibrils.

Novel Cu(II)-RGD-octapeptides: Synthesis, coordination mode, in vitro anti-platelet aggregation/in vivo anti-thrombotic evaluation and correlation of sequence with nano-structure

The synthesis, bioassays and nano-structure characterization of Cu(II)-RGD-octapeptide complexes Cu(II)-Arg-Gly-Asp-Ser-Arg-Gly-Asp-Ser [Cu(II)-4a], Cu(II)-Arg-Gly-Asp-Val-Arg-Gly-Asp-Val [Cu(II)-4b] and Cu(II)-Arg-Gly-Asp-Phe-Arg-Gly-Asp-Phe [Cu(II)-4c] were investigated. UV-vis, CD and CD/ESI-MS spectra suggested that the coordination of Cu(II)-4a-c met a 3 N mode. In the in vitro anti-platelet aggregation assay the IC(50) values of Cu(II)-RGD-octapeptide complexes were 10 - 110 folds lower than that of RGD-octapeptides. In the in vivo anti-thrombotic assay the effective dose of Cu(II)-RGD-octapeptide complexes was 5000 folds lower than that of RGD-octapeptides. In transmission electron microscopy measurement Cu(II)-4a-c offered distinct nano-images. The effect of the sequence on the in vitro anti-platelet aggregation/in vivo anti-thrombotic activity and the nano-structure of Cu(II)-4a-c was discussed.

FROM THE CLINICAL EDITOR

This basic science paper discusses the synthesis, coordination mode, in vitro anti-platelet aggregation and in vivo anti-thrombotic evaluation of novel Cu(II)-RGD-octapeptides.

Macrocyclic design strategies for small, stable parallel beta-sheet scaffolds

Pairs of short peptide strands can be induced to adopt an antiparallel beta-sheet secondary structure in aqueous solution via a macrocyclic constraint, as illustrated by many natural and designed peptides. We show that an analogous strategy is successful for creation of small units of parallel beta-sheet secondary structure in aqueous solution. Cyclization in this case requires nonpeptide segments for N-to-N and C-to-C interstrand linkage. Surprisingly, we find that only one of these segments needs to be preorganized.

Binding mechanisms in supramolecular complexes

Supramolecular chemistry has expanded dramatically in recent years both in terms of potential applications and in its relevance to analogous biological systems. The formation and function of supramolecular complexes occur through a multiplicity of often difficult to differentiate noncovalent forces. The aim of this Review is to describe the crucial interaction mechanisms in context, and thus classify the entire subject. In most cases, organic host-guest complexes have been selected as examples, but biologically relevant problems are also considered. An understanding and quantification of intermolecular interactions is of importance both for the rational planning of new supramolecular systems, including intelligent materials, as well as for developing new biologically active agents.

Early stages of misfolding and association of beta2-microglobulin: insights from infrared spectroscopy and dynamic light scattering

Conformational changes associated with the assembly of recombinant beta 2-microglobulin in vitro under acidic conditions were investigated using infrared spectroscopy and static and dynamic light scattering. In parallel, the morphology of the different aggregated species obtained under defined conditions was characterized by electron microscopy. The initial salt-induced aggregate form of beta 2-microglobulin, composed of small oligomers (dimers to tetramers), revealed the presence of beta-strands organized in an intramolecular-like fashion. Further particle growth was accompanied by the formation of intermolecular beta-sheet structure and led to short curved forms. An increase in temperature by only 25 degrees C was able to disaggregate these assemblies, followed by the formation of longer filamentous structures. In contrast, a rise in temperature up to 100 degrees C was associated with a reorganization of the short curved forms at the level of secondary structure and the state of assembly, leading to a species with a characteristic infrared spectrum different from those of all the other aggregates observed before, suggesting a unique overall structure. The infrared spectral features of this species were nearly identical to those of beta 2-microglobulin assemblies formed at low ionic strength with agitation, indicating the presence of fibrils, which was confirmed by electron microscopy. The observed spectroscopic changes suggest that the heat-triggered conversion of the short curved assemblies into fibrils involves a reorganization of the beta-strands from an antiparallel arrangement to a parallel arrangement, with the latter being characteristic of amyloid fibrils of beta 2-microglobulin.

Diacid linkers that promote parallel beta-sheet secondary structure in water

We report the development of diacid units that promote formation of a two-stranded parallel beta-sheet secondary structure between peptide segments attached via their N-termini. These linker units are formed by attaching glycine to one carboxyl group of cis-1,2-cyclohexanedicarboxylic acid (CHDA). Parallel sheet formation in water is observed when l-residue strands are attached to the CHDA-Gly unit with either of the two absolute configurations.

Time-resolved infrared spectroscopy of pH-induced aggregation of the Alzheimer Abeta(1-28) peptide

Aggregation of the Alzheimer's disease-related Abeta(1-28) peptide was induced by a rapid, sub-millisecond pH jump and monitored by time-resolved infrared spectroscopy on the millisecond to second time-scale. The release of protons was induced by the photolysis of a caged compound, 1-(2-nitrophenyl)ethyl sulfate (NPE-sulfate). The pH jump generated in our experimental setup is used to model the Abeta peptide structural conversions that may occur in the acidic endosomal/lysosomal cell compartment system. The aggregation of the Abeta(1-28) peptide induced by the pH jump from 8.5 to <6 yields an antiparallel beta-sheet structure. The kinetics of the structural transition is biphasic, showing an initial rapid phase with a transition from random coil to an oligomeric beta-sheet form with a time constant of 3.6 s. This phase is followed by a second slower transition, which yields larger aggregates during 48.0 s.

An artificial beta-sheet that dimerizes through parallel beta-sheet interactions

This Article introduces a simple chemical model of a beta-sheet (artificial beta-sheet) that dimerizes by parallel beta-sheet formation in chloroform solution. The artificial beta-sheet consists of two N-terminally linked peptide strands that are linked with succinic or fumaric acid and blocked along one edge with a hydrogen-bonding template composed of 5-aminoanisic acid hydrazide. The template is connected to one of the peptide strands by a turn unit composed of (S)-2-aminoadipic acid (Aaa). 1H NMR spectroscopic studies show that these artificial beta-sheets fold in CDCl3 solution to form well-defined beta-sheet structures that dimerize through parallel beta-sheet interactions. Most notably, all of these compounds show a rich network of NOEs associated with folding and dimerization. The compounds also exhibit chemical shifts and coupling constants consistent with the formation of folded dimeric beta-sheet structures. The aminoadipic acid unit shows patterns of NOEs and coupling constants consistent with a well-defined turn conformation. The present system represents a significant step toward modeling the type of parallel beta-sheet interactions that occur in protein aggregation.

Infrared spectroscopy of proteins

This review discusses the application of infrared spectroscopy to the study of proteins. The focus is on the mid-infrared spectral region and the study of protein reactions by reaction-induced infrared difference spectroscopy.

Thermodynamic analysis of autonomous parallel beta-sheet formation in water

We report the first thermodynamic analysis of parallel beta-sheet formation in a model system that folds in aqueous solution. NMR chemical shifts were used to determine beta-sheet population, and van't Hoff anaysis provided thermodynamic parameters. Our approach relies upon the d-prolyl-1,1-dimethyl-1,2-diaminoethane unit to promote parallel beta-sheet formation between attached peptide strands. The development of a macrocyclic reference molecule to provide chemical shift data for the fully folded state was crucial to the quantitative anaylsis.

The internal structure of self-assembled peptide amphiphiles nanofibers

The self-assembly of peptide amphiphiles (PAs) into nanofibers and their bioactivity as well as physical properties have been investigated by our laboratory over the past few years. We report here on the use of transmission infrared spectroscopy (IR) and polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) to characterize the internal structure of the nanofibers. Depositing nanofibers flat on surfaces, and using the surface selection rules in PM-IRRAS, we demonstrate that peptide amphiphiles form β-sheets oriented parallel to the long-axis of nanofibers that pack radially from the nanofiber core. We show also that the extent of internal order depends on the molecular architecture and peptide sequence of PAs, with branched PAs yielding nanofibers with the lowest degree of internal order. Measurements of intensity and spectral position of the alkyl bands suggest that the hydrophobic core of these nanofibers can have internal order to an extent that correlates with order in their peptidic domains. We expect that bioactivity and physical properties will be controlled by the degree of internal order in these self-assembling nanostructures.

One-Armed Artificial Receptors for the Binding of Polar Tetrapeptides in Water: Probing the Substrate Selectivity of a Combinatorial Receptor Library

We have recently developed a new class of one-armed artificial receptors 1 for the binding of the polar tetrapeptide N-Ac-D-Glu-L-Lys-D-Ala-D-Ala-OH (EKAA) 2 in water using a combined combinatorial and statistical approach. We have now further probed the substrate selectivity of this receptor library 1 by screening a second tetrapeptide substrate (3) with the inverse sequence N-Ac-D-Ala-D-Ala-L-Lys-D-Glu-OH (AAKE). This "inverse" substrate is also efficiently bound by our receptors, with K(ass) approximately 6000 M(-1) for the best receptors, as determined both by a quantitative on-bead binding assay and by UV and fluorescence titration studies in free solution. Hence, the inverse tetrapeptide 3 is in general bound two to three times less efficiently than the "normal" peptide 2 (K(ass) approximately 17,000 M(-1)), even though the complexation mainly involves long-range electrostatic interactions and both the receptor and substrate are rather flexible. Molecular modeling and ab initio calculations have been used to rationalize the observed substrate selectivity and to analyze the various binding interactions within the complex.

Peptide-based inhibitors of amyloid assembly

This review considers the design, synthesis, and mechanistic assessment of peptide-based fibrillogenesis inhibitors, mainly focusing on beta-amyloid, but generalizable to other aggregating proteins and peptides. In spite of revision of the "amyloid hypothesis," the investigation and development of fibrillogenesis inhibitors remain important scientific and therapeutic goals for at least three reasons. First, it is still premature to dismiss fibrils altogether as sources of cytotoxicity. Second, a "fibrillogenesis inhibitor" is typically identified experimentally as such, but these compounds may also bind to intermediates in the fibrillogenesis pathway and have hard-to-predict consequences, including improved clearance of more cytotoxic soluble oligomers. Third, inhibitors are valuable structural probes, as the entire field of enzymology attests. Screening procedures for selection of random inhibitory sequences are briefly considered, but the bulk of the review concentrates on rationally designed fibrillogenesis inhibitors. Among these are internal segments of fibril-forming peptides, amino acid substitutions and side chain modifications of fibrillogenic domains, insertion of prolines into or adjacent to fibrillogenic domains, modification of peptide termini, modification of peptide backbone atoms (including N-methylation), peptide cyclization, use of D-amino acids in fibrillogenic domains, and nonpeptidic beta-sheet mimics. Finally, we consider methods of assaying fibrillogenesis inhibitors, including pitfalls in these assays. We consider binding of inhibitor peptides to their targets, but because this is a specific application of the more general and much larger problem of assessing protein-protein interactions, this topic is covered only briefly. Finally, we consider potential applications of inhibitor peptides to therapeutic strategies.

Inhibition of hIAPP amyloid-fibril formation and apoptotic cell death by a designed hIAPP amyloid- core-containing hexapeptide

The pathogenesis of type II diabetes is associated with the aggregation of the 37-residue human islet amyloid polypeptide (hIAPP) into cytotoxic beta sheet aggregates and fibrils. We have recently shown that introduction of two N-methyl rests in the beta sheet- and amyloid-core-containing sequence hIAPP(22-27), or NFGAIL converted this amyloidogenic and cytotoxic sequence into nonamyloidogenic and noncytotoxic NF(N-Me)GA(N-Me)IL. Here, we show that NF(N-Me)GA(N-Me)IL is able to bind with high-affinity full-length hIAPP and to inhibit its fibrillogenesis. NF(N-Me)GA(N-Me)IL also inhibits hIAPP-mediated apoptotic beta cell death. By contrast, unmodified NFGAIL does not inhibit hIAPP amyloidogenesis and cytotoxicity, suggesting that N-methylation conferred on NFGAIL the properties of NF(N-Me)GA(N-Me)IL. These results support the concept that rational N-methylation of hIAPP amyloid-core sequences may be a valuable strategy to design pancreatic-amyloid diagnostics and therapeutics for type II diabetes.

beta-Sheet ligands in action: KLVFF recognition by aminopyrazole hybrid receptors in water

Little is known about the precise mechanism of action of beta-sheet ligands, hampered by the notorious solubility problems involved with protein misfolding and amyloid formation. Recently the nucleation site for the pathogenic aggregation of the Alzheimer's peptide was identified as the KLVFF sequence in the central region of Abeta. A combination of two aminopyrazole ligands with di- or tripeptides taken from this key fragment now furnished water-soluble Abeta-specific ligands which allow model investigations in water. A detailed conformational analysis provides experimental evidence for an increased beta-sheet content induced in the peptide. Strong indications were also found for the peptide backbone recognition via hydrogen bonds plus hydrophobic contributions between aminopyrazole nuclei and Phe residues. The affinity of these new ligands toward the KKLVFF fragment is highly dependent on their sequence and composition from natural and artificial amino acids. Thus, for the first time, detailed insight is gained into the complexation of beta-sheet ligands with model peptides taken directly from Abeta.

Prevention of Alzheimer's Disease-associated Aβ Aggregation by Rationally Designed Nonpeptidic β-Sheet Ligands

A new concept is introduced for the rational design of beta-sheet ligands, which prevent protein aggregation. Oligomeric acylated aminopyrazoles with a donor-acceptor-donor (DAD) hydrogen bond pattern complementary to that of a beta-sheet efficiently block the solvent-exposed beta-sheet portions in Abeta-(1-40) and thereby prevent formation of insoluble protein aggregates. Density gradient centrifugation revealed that in the initial phase, the size of Abeta aggregates was efficiently kept between the trimeric and 15-meric state, whereas after 5 days an additional high molecular weight fraction appeared. With fluorescence correlation spectroscopy (FCS) exactly those two, i.e. a dimeric aminopyrazole with an oxalyl spacer and a trimeric head-to-tail connected aminopyrazole, of nine similar aminopyrazole ligands were identified as efficient aggregation retardants whose minimum energy conformations showed a perfect complementarity to a beta-sheet. The concentration dependence of the inhibitory effect of a trimeric aminopyrazole derivative allowed an estimation of the dissociation constant in the range of 10(-5) m. Finally, electrospray ionization mass spectrometry (ESI-MS) was used to determine the aggregation kinetics of Abeta-(1-40) in the absence and in the presence of the ligands. From the comparable decrease in Abeta monomer concentration, we conclude that these beta-sheet ligands do not prevent the initial oligomerization of monomeric Abeta but rather block further aggregation of spontaneously formed small oligomers. Together with the results from density gradient centrifugation and fluorescence correlation spectroscopy it is now possible to restrict the approximate size of soluble Abeta aggregates formed in the presence of both inhibitors from 3- to 15-mers.

Dipeptide Binding in Water by a de Novo Designed Guanidiniocarbonylpyrrole Receptor

A new dipeptide receptor 9, which was designed de novo based on theoretical calculations, efficiently binds dipeptides in water with Kass > 104 M-1 by a combination of ion pairing and hydrogen bonds as can be shown by UV-titration and NMR experiments.

Formation of critical oligomers is a key event during conformational transition of recombinant syrian hamster prion protein

We have investigated the conformational transition and aggregation process of recombinant Syrian hamster prion protein (SHaPrP90-232) by Fourier transform infrared spectroscopy, circular dichroism spectroscopy, light scattering, and electron microscopy under equilibrium and kinetic conditions. SHaPrP90-232 showed an infrared absorbance spectrum typical of proteins with a predominant alpha-helical structure both at pH 7.0 and at pH 4.2 in the absence of guanidine hydrochloride. At pH 4.2 and destabilizing conditions (0.3-2 m guanidine hydrochloride), the secondary structure of SHaPrP90-232 was transformed to a strongly hydrogen-bonded, most probably intermolecularly arranged antiparallel beta-sheet structure as indicated by dominant amide I band components at 1620 and 1691 cm-1. Kinetic analysis of the transition process showed that the decrease in alpha-helical structures and the increase in beta-sheet structures occurred concomitantly according to a bimolecular reaction. However, the concentration dependence of the corresponding rate constant pointed to an apparent third order reaction. No beta-sheet structure was formed within the dead time (190 ms) of the infrared experiments. Light scattering measurements revealed that the structural transition of SHaPrP90-232 was accompanied by formation of oligomers, whose size was linearly dependent on protein concentration. Extrapolation to zero protein concentration yielded octamers as the smallest oligomers, which are considered as "critical oligomers." The small oligomers showed spherical and annular shapes in electron micrographs. Critical oligomers seem to play a key role during the transition and aggregation process of SHaPrP90-232. A new model for the structural transition and aggregation process of the prion protein is described.

The synthesis and study of side-chain lactam-bridged peptides

Side-chain lactam bridges linking amino acid residues that are spaced several residues apart in the linear sequence offer a convenient and flexible method for introducing conformational constraints into a peptide structure. The availability of a variety of selectively cleavable protecting groups for amines and carboxylic acids allows for several approaches to the synthesis of monocyclic, dicyclic, and bicyclic lactam-bridged peptides by solid-phase methods. Multicyclic structures are also accessible, but segment-condensation syntheses with solution-phase cyclizations are most likely to provide the best synthetic approach to these more complex constrained peptides. Lactam bridges linking (i, i + 3)-, (i, i + 4), and (i, i + 7)-spaced residue pairs have all proven useful for stabilization of alpha helices, and (i, i + 3)-linked residues have also been demonstrated to stabilize beta-turns. These structures are finding an increasing number of applications in protein biology, including studies of protein folding, protein aggregation, peptide ligand-receptor recognition, and the development of more potent peptide therapeutics. Defining the functional roles of the amphiphilic alpha-helices in medium-sized peptide hormones, and studying helix propagation from rigid, alpha-helix initiating bicyclic peptides are among the most exciting developments currently underway in this field.

Synthesis of enantiomerically pure 1,2-diamine derivatives of 7-azabicyclo[2.2.1]heptane. New leads as glycosidase inhibitors and rigid scaffolds for the preparation of peptide analogues

Enantiomerically pure alcohols (-)- and (+)-7-tert-butoxycarbonyl-6-endo-p-toluenesulfonyl-7-azabicyclo[2.2.1]hept-2-en-5-endo-ol ((-)-11 and (+)-11) have been obtained from the Diels-Alder adduct of N-(tert-butoxycarbonyl)pyrroel and 2-bromo-1-p-toluenesulfonylacetylene, including a resolution method. These two alcohols were converted into (+)- and (-)-5-exo-amino-7-(tert-butoxycarbonyl)-2,3-exo-isopropylidenedioxy-7-azabicyclo[2.2.1]heptane ((+)-18 and (-)-18) and (+)- and (-)-5-endo-amino-7-(tert-butoxycarbonyl)-2,3-exo-isopropylidenedioxy-7-azabicyclo[2.2.1]heptane ((+)-19 and (-)-19) after adequate functionalization and desulfonylation steps. The corresponding conformationally constrained bicyclic 1,2-diamines (+)-4, (-)-4, (+/-)-5, (+/-)-6, (+)-7, and (-)-7 were obtained from the protected precursors 18 and 19 and evaluated as glycosidase inhibitors. Diamines (+)-4, (-)-4, (+)-6, and (-)-6 can be seen as new nonpeptide molecular scaffolds for the design of peptide analogues.