Fragment-Based Interrogation of the 14-3-3/TAZ Protein-Protein Interaction.

The identification of chemical starting points for the development of molecular glues is challenging. Here, we employed fragment screening and identified an allosteric stabilizer of the complex between 14-3-3 and a TAZ-derived peptide. The fragment binds preferentially to the 14-3-3/TAZ peptide complex and shows moderate stabilization in differential scanning fluorimetry and microscale thermophoresis. The binding site of the fragment was predicted by molecular dynamics calculations to be distant from the 14-3-3/TAZ peptide interface, located between helices 8 and 9 of the 14-3-3 protein. This site was confirmed by nuclear magnetic resonance and X-ray protein crystallography, revealing the first example of an allosteric stabilizer for 14-3-3 protein-protein interactions.

Reversible Covalent Imine-Tethering for Selective Stabilization of 14-3-3 Hub Protein Interactions.

The stabilization of protein complexes has emerged as a promising modality, expanding the number of entry points for novel therapeutic intervention. Targeting proteins that mediate protein-protein interactions (PPIs), such as hub proteins, is equally challenging and rewarding as they offer an intervention platform for a variety of diseases, due to their large interactome. 14-3-3 hub proteins bind phosphorylated motifs of their interaction partners in a conserved binding channel. The 14-3-3 PPI interface is consequently only diversified by its different interaction partners. Therefore, it is essential to consider, additionally to the potency, also the selectivity of stabilizer molecules. Targeting a lysine residue at the interface of the composite 14-3-3 complex, which can be targeted explicitly via aldimine-forming fragments, we studied the de novo design of PPI stabilizers under consideration of potential selectivity. By applying cooperativity analysis of ternary complex formation, we developed a reversible covalent molecular glue for the 14-3-3/Pin1 interaction. This small fragment led to a more than 250-fold stabilization of the 14-3-3/Pin1 interaction by selective interfacing with a unique tryptophan in Pin1. This study illustrates how cooperative complex formation drives selective PPI stabilization. Further, it highlights how specific interactions within a hub proteins interactome can be stabilized over other interactions with a common binding motif.

Fragment-Based Stabilizers of Protein-Protein Interactions through Imine-Based Tethering.

Small-molecule stabilization of protein-protein interactions (PPIs) is a promising concept in drug discovery, however the question how to identify or design chemical starting points in a "bottom-up" approach is largely unanswered. We report a novel concept for identifying initial chemical matter for PPI stabilization based on imine-forming fragments. The imine bond offers a covalent anchor for site-directed fragment targeting, whereas its transient nature enables efficient analysis of structure-activity relationships. This bond enables fragment identification and optimisation using protein crystallography. We report novel fragments that bind specifically to a lysine at the PPI interface of the p65-subunit-derived peptide of NF-κB with the adapter protein 14-3-3. Those fragments that subsequently establish contacts with the p65-derived peptide, rather than with 14-3-3, efficiently stabilize the 14-3-3/p65 complex and offer novel starting points for molecular glues.

An Exploration of Chemical Properties Required for Cooperative Stabilization of the 14-3-3 Interaction with NF-κB-Utilizing a Reversible Covalent Tethering Approach.

Protein-protein modulation has emerged as a proven approach to drug discovery. While significant progress has been gained in developing protein-protein interaction (PPI) inhibitors, the orthogonal approach of PPI stabilization lacks established methodologies for drug design. Here, we report the systematic ″bottom-up″ development of a reversible covalent PPI stabilizer. An imine bond was employed to anchor the stabilizer at the interface of the 14-3-3/p65 complex, leading to a molecular glue that elicited an 81-fold increase in complex stabilization. Utilizing protein crystallography and biophysical assays, we deconvoluted how chemical properties of a stabilizer translate to structural changes in the ternary 14-3-3/p65/molecular glue complex. Furthermore, we explore how this leads to high cooperativity and increased stability of the complex.

Cellular model system to dissect the isoform-selectivity of Akt inhibitors.

The protein kinase Akt plays a pivotal role in cellular processes. However, its isoforms' distinct functions have not been resolved to date, mainly due to the lack of suitable biochemical and cellular tools. Against this background, we present the development of an isoform-dependent Ba/F3 model system to translate biochemical results on isoform specificity to the cellular level. Our cellular model system complemented by protein X-ray crystallography and structure-based ligand design results in covalent-allosteric Akt inhibitors with unique selectivity profiles. In a first proof-of-concept, the developed molecules allow studies on isoform-selective effects of Akt inhibition in cancer cells. Thus, this study will pave the way to resolve isoform-selective roles in health and disease and foster the development of next-generation therapeutics with superior on-target properties.

Set-up and screening of a fragment library targeting the 14-3-3 protein interface.

Protein-protein interactions (PPIs) are at the core of regulation mechanisms in biological systems and consequently became an attractive target for therapeutic intervention. PPIs involving the adapter protein 14-3-3 are representative examples given the broad range of partner proteins forming a complex with one of its seven human isoforms. Given the challenges represented by the nature of these interactions, fragment-based approaches offer a valid alternative for the development of PPI modulators. After having assembled a fragment set tailored on PPIs' modulation, we started a screening campaign on the sigma isoform of 14-3-3 adapter proteins. Through the use of both mono- and bi-dimensional nuclear magnetic resonance spectroscopy measurements, coupled with differential scanning fluorimetry, three fragment hits were identified. These molecules bind the protein at two different regions distant from the usual binding groove highlighting new possibilities for selective modulation of 14-3-3 complexes.

5H-furan-2-ones from fungal cultures of Aporpium caryae.

Four furanones 1-4 with an unusual skeleton containing an acetylene unit, named aporpinones, were isolated from the culture of the basidiomycete Aporpium caryae and their structures were elucidated by spectroscopic methods. Compounds 3 and 4 showed weak to moderate antibacterial activity against Bacillus subtilis, Staphylococcus aureus and Escherichia coli.

Efficient synthesis of the structural core of tetracyclines by a palladium-catalyzed domino Tsuji-Trost-Heck-Mizoroki reaction.

The Pd-catalyzed domino Tsuji-Trost-Heck-Mizoroki reactions of compounds 18, 27, and 34, respectively, each containing an allyl acetate and a halogen aryl moiety, lead to the formation of hexahydronaphthacenes 2 and 3 and octahydroanthracene 4 in 62-81 % yield. The octahydroanthracene and hexahydronaphthacene motifs are found in many natural products, for example, the tetracycline antibiotics.

Biaryl synthesis via Pd-catalyzed decarboxylative coupling of aromatic carboxylates with aryl halides.

A new strategy for the regiospecific construction of unsymmetrical biaryls is presented, in which easily available salts of carboxylic acids are decarboxylated in situ to give arylmetal species that serve as the nucleophilic component in a catalytic cross-coupling reaction with aryl halides. The catalyst system consists of a copper phenanthroline complex that mediates the extrusion of CO2 from aromatic carboxylates to generate arylcopper species, and a palladium complex that catalyzes the cross-coupling of these intermediates with aryl halides. This bimetallic system allows the direct coupling of various aryl, heteroaryl, or vinyl carboxylic acids with aryl or heteroaryl iodides, bromides, or chlorides at 160 degrees C in the presence of a mild base such as potassium carbonate. The present scope and potential economic impact of the reaction are demonstrated by the synthesis of 42 biaryls, some of which are of substantial industrial relevance. Remaining challenges and future perspectives of the new transformation are discussed.

Characterisation of fungal lanostane-type triterpene acids by electrospray ionisation mass spectrometry.

Lanostane-triterpene acids obtained from the culture of the fungus Coriolellus malicola were studied by electrospray mass spectrometry in the negative ion mode using quadrupole time-of-flight and quadrupole ion trap analysers. Despite the differences observed in the mass spectra recorded with these instruments, a set of fragment ions was found to be characteristic of the family, depending on the Delta(7,9(11)) or Delta(8) skeleton and the particular functional group at C-3.

Synthesis of biaryls via catalytic decarboxylative coupling.

We present a safe and convenient cross-coupling strategy for the large-scale synthesis of biaryls, commercially important structures often found in biologically active molecules. In contrast to traditional cross-couplings, which require the prior preparation of organometallic reagents, we use a copper catalyst to generate the carbon nucleophiles in situ, via decarboxylation of easily accessible arylcarboxylic acid salts. The scope and potential economic impact of the reaction are demonstrated by the synthesis of 26 biaryls, one of which is an intermediate in the large-scale production of the agricultural fungicide Boscalid.

Synthesis and enzymatic kinetic resolution of alpha,alpha-disubstituted cyclic hydroxy nitriles.

Herein, we describe the diastereoselective synthesis of five- and six-membered alpha,alpha-disubstituted cyclic beta-hydroxy nitriles and their resolution via enzymatic transesterification. By this method, all possible stereoisomers were obtained in enantiopure form and high yield.

Is the ring conformation the most critical parameter in lipase-catalysed acylation of cycloalkanols?

CAL-B catalysed the resolution of several five and six-membered cyclic beta-hydroxy esters efficiently with the exception of the cis-cyclohexanol (+/-)-4. When employing molecular modelling techniques the conformation turned out to be the most important determinant for their reactivity towards O-acetylation. In all cases, the R enantiomers reacted faster than the S enantiomers since the reactive intermediates of the former can adopt more favourable ring conformations and thus experience less steric hindrance in the active site. Furthermore, the minimised structure for the main conformer of R-4 showed that the axial hydrogens in the 3 and 5-positions with respect to the hydroxyl group prevent the enzymatic reaction.