Martin Ehlers

Incorporation of a Non-Natural Arginine Analogue into a Cyclic Peptide Leads to Formation of Positively Charged Nanofibers Capable of Gene Transfection

Functionalization of the tetracationic cyclic peptide (Ka)4 with a single guanidiniocarbonyl pyrrole (GCP) moiety, a weakly basic but highly efficient arginine analogue, completely alters the self-assembly properties of the peptide. In contrast to the nonfunctionalized peptide 2, which does not self-assemble, GCP-containing peptide 1 forms cationic nanofibers of micrometer length. These aggregates are efficient gene transfection vectors. DNA binds to their cationic surface and is efficiently delivered into cells.

A metal-free fluorescence turn-on molecular probe for detection of nucleoside triphosphates

We report a fluorescence probe 1, which contains a naphthalimide fluorophore with two symmetric peptidic arms equipped with a tailor-made anion-binding motif, the guanidiniocarbonyl pyrrole moiety, for the detection of nucleoside triphosphates. Upon binding to nucleoside triphosphates, especially ATP, 1 shows significant turn-on fluorescence response. Probe 1 can also be applied for the imaging of ATP in cells.

Use of an Octapeptide–Guanidiniocarbonylpyrrole Conjugate for the Formation of a Supramolecular β‐Helix that Self‐Assembles into pH‐Responsive Fibers

Peptides that adopt β-helix structures are predominantly found in transmembrane protein domains or in the lipid bilayer of vesicles. Constructing a β-helix structure in pure water has been considered difficult without the addition of membrane mimics. Herein, we report such an example; peptide 1 self-assembles into a supramolecular β-helix in pure water based on charge interactions between the individual peptides. Peptide 1 further showed intriguing transitions from small particles to helical fibers in a time-dependent process. The fibers can be switched to vesicles by changing the pH value.

Preparation and antimalarial activity of a novel class of carbohydrate-derived, fused thiochromans.

A novel class of fused thiochroman derivatives has been prepared by an efficient and versatile synthetic procedure involving nucleophilic displacement of the side-chain iodo substituent in 2-deoxy-2-C-iodomethyl glucosides by thiophenolate ions, and subsequent intramolecular C-glycoside formation. A range of aromatic substituents is tolerated, and the subsequent facile selective oxidation of the sulfur to the sulfoxide or sulfone level expands the range and molecular diversity of the series of compounds. A selection of the sulfoxide and sulfone derivatives bearing lipophilic substituents on the aromatic portion were found to have antimalarial activities in the low micromolar range.

Development of Antitrypanosomal and Antiplasmodial Nonpeptidic Cysteine Protease Inhibitors based on N-Protected-Guanidino-Furan and -Pyrrole Building Blocks

Infectious diseases, such as malaria, leishmaniasis, and African trypanosomiasis (sleeping sickness), are public health problems in more than 90 countries with millions of deaths per year. The drugs mainly used today for chemotherapy, especially against the neglected diseases leishmaniasis and trypanosomiasis, were developed decades ago, lack appropriate efficacy, and give rise to severe side effects. The absence of highly effective vaccines and the inadequate control of insect vectors demand new approaches to drug development. Furthermore, resistance of the pathogens causing malaria (Plasmodium falciparum) and African trypanosomiasis (sleeping sickness caused by Trypanosoma brucei gambiense and T. b. rhodesiense, and nagana in livestock, caused by T. b. brucei) against established drugs has been increasing. Therefore, research to identify new drugs, ideally addressing new targets, is more important than ever. Parasite cysteine proteases of clan CA, family C1 (papain family), are considered to be new promising therapeutic targets. These enzymes, namely falcipains in plasmodia, and rhodesain in T. b. rhodesiense, play important roles in the life cycles of the parasites. Cysteine protease inhibitors have been reported to kill African trypanosomes in vitro and in animal models of the disease, however, it is not yet clear whether rhodesain is the only target of the inhibitors. Proteases of malaria parasites play pivotal roles in the processes of host erythrocyte rupture, erythrocyte invasion, and hemoglobin degradation. Treatment with cysteine protease inhibitors blocks hemoglobin hydrolysis and development of the parasite. 8–12] Both enzymes belong to the cathepsin L subfamily of the papain family of cysteine proteases. In a general proteaseand cell-based screening using different proteases, we recently discovered hybrid compounds containing both a peptidic and a nonpeptidic moiety, namely a guanidinocarbonyl pyrrole, as potent inhibitors of falcipains with antiplasmodial activity (Scheme 1). The compounds were originally designed as new aspartic protease inhibitors but did not fulfill this expectation. However, the tert-butoxycarbonyl (Boc)-protected intermediates, for example, falcipain inhibitor A with a hybrid structure, unexpectedly displayed inhibitory activity against falcipains and plasmodia (FP-2: IC50 = 3.1 mm ; FP-3: no inhibition at 100 mm ; P. f. : IC50 = 1.7 mm). In order to evaluate which inhibitor fragment is responsible for the remarkable activity, the two building blocks B and C were tested individually. The peptidic fragment C was moderately active in the form of the ester (R = Et: FP-2: IC50 = 34 mm ; FP-3: IC50 = 49 mm ; P. f. : IC50 = 29 mm ; R = H: no inhibition at 100 mm) ; this was not unexpected, as Michael-acceptor-derived peptides have already been shown to be cysteine protease inhibitors. However, to our surprise, the Boc-protected guanidinocarbonyl moiety B was also an efficient falcipain inhibitor (FP-2: IC50 = 33 mm).

A fluorescent light-up probe as an inhibitor of intracellular β-tryptase.

A pyrene-functionalized peptidic inhibitor binds to and inhibits β-tryptase in a non-competitive and reversible manner even in cells. Upon protein binding a fluorescence increase of the two pyrene fluorophores is observed which allows using as a fluorescent light-up probe for this enzyme.

Two-Component Self-Assembly: Hierarchical Formation of pH-Switchable Supramolecular Networks by π-π Induced Aggregation of Ion Pairs.

Two-component self-assembly is a promising approach to construct functional nanomaterials. Interaction of a flexible guanidiniocarbonyl pyrrole tetra-cation (1) with naphthalene diimide dicarboxylic acid (NDIDC) in aqueous DMSO leads to the formation of supramolecular networks. First, the carboxylate groups of NDIDC bind to the guanidiniocarbonyl pyrrole cations of 1 in a 1:2 stoichiometry. Further π-π induced aggregation then leads to 3D networks, as established by dynamic light scattering studies (DLS), NMR, fluorescence titration, viscosity measurements, AFM, and TEM microscopy. Due to ion pairing, the resulting aggregates can be switched between the monomers and the aggregates reversibly using external stimuli like protonation or deprotonation. At high concentration, a stable colloidal solution is formed, which shows an extensive Tyndall effect. Increasing the concentrations even further leads to formation of a supramolecular gel.

Rational Design, Binding Studies, and Crystal‐Structure Evaluation of the First Ligand Targeting the Dimerization Interface of the 14‐3‐3ζ Adapter Protein

14‐3‐3 Proteins play a central role in signalling pathways in cells: they interact as gatekeeper proteins with a huge number of binding partners. Their function as hub for intracellular communication can explain why these adapter proteins are associated with a wide range of diseases. How they control the various cellular mechanisms is still unclear, but it is assumed that the dimeric nature of the 14‐3‐3 proteins plays a key role in their activity. Here, we present, to the best of our knowledge, the first example of a small molecule binding to the 14‐3‐3ζ dimerisation interface. This compound was designed by rational in silico optimisation of a peptidic ligand identified from biochemical screening of a peptidic library, and the binding was characterised by UV/Vis spectroscopy, microscale thermophoresis, multiscale simulations, and X‐ray crystallography.