Peptidmimetica – maßgeschneiderte Enzyminhibitoren

Design, Synthesis and Late-Stage Modification of Indane-Based Peptides via [2+2+2] Cyclotrimerization

Here, we prepared several dipeptides containing 2-aminoindane-2-carboxylic acid (Aic) and carried out further synthetic transformations. Synthesis and purification of modified peptides by using [2+2+2] cyclotrimerization is a challenging task. We are able to modify the unusual amino acids and peptide derivatives by late-stage incorporation of benzylhalo functionality. To incorporate benzylhalo moiety we used [2+2+2] cyclotrimerization in the presence of Mo(CO)₆ . These halo derivatives are potential substrates for further modification by Sonogashira reaction, Suzuki-Miyaura cross-coupling, sultine formation, and the Diels-Alder reaction sequence.

Oligo-Quinolylene-Vinylene Foldamers

Quinoline based aromatic amide foldamers are known to adopt stable folded conformations. We have developed a synthetic approach to produce similar oligomers where all amide bonds, or part of them, have been replaced by an isosteric vinylene group. The results of solution and solid state structural studies show that oligomers exclusively containing vinylene linkages are not well folded, and adopt predominantly flat conformations. In contrast, a vinylene segment flanked by helical oligoamides also folds in a helix, albeit with a slightly lower curvature. The presence of vinylene functions also result in an extension of π-conjugation across the oligomer that may change charge transport properties. Altogether, these results pave the way to foldamers in which both structural control and specific electronic properties may be engineered.

De novo synthesis of alkyne substituted tryptophans as chemical probes for protein profiling studies

De novo synthesis of alkynalted tryptophan moieties as chemical probes for protein profilling studies, via an unexpected synthesis of Michael acceptor 12 is reported. Friedel Craft's alkylation of 12 and alkyne substituted indoles gave alkynalated tryptophan moieties, which perform as chemical probe by incorporating into actively translating Escherichia coli cells, whereby the alkyne moiety enables multimodal analyses through click chemistry mediated attachment of reporting groups.

A Single Stereodynamic Center Modulates the Rate of Self-Assembly in a Biomolecular System

Chirality is a property of asymmetry important to both physical and abstract systems. Understanding how molecular systems respond to perturbations in their chiral building blocks can provide insight into diverse areas such as biomolecular self-assembly, protein folding, drug design, materials, and catalysis. Despite the fundamental importance of stereochemical preorganization in nature and designed materials, the ramifications of replacing chiral centers with stereodynamic atomic mimics in the context of biomolecular systems is unknown. Herein, we demonstrate that replacement of a single amino acid stereocenter with a stereodynamic nitrogen atom has profound consequences on the self-assembly of a biomolecular system. Our results provide insight into how the fundamental biopolymers of life would behave if their chiral centers were not configurationally stable, highlighting the vital importance of stereochemistry as a pre-organizing element in biomolecular folding and assembly events.

Constraining cyclic peptides to mimic protein structure motifs

Many proteins exert their biological activities through small exposed surface regions called epitopes that are folded peptides of well-defined three-dimensional structures. Short synthetic peptide sequences corresponding to these bioactive protein surfaces do not form thermodynamically stable protein-like structures in water. However, short peptides can be induced to fold into protein-like bioactive conformations (strands, helices, turns) by cyclization, in conjunction with the use of other molecular constraints, that helps to fine-tune three-dimensional structure. Such constrained cyclic peptides can have protein-like biological activities and potencies, enabling their uses as biological probes and leads to therapeutics, diagnostics and vaccines. This Review highlights examples of cyclic peptides that mimic three-dimensional structures of strand, turn or helical segments of peptides and proteins, and identifies some additional restraints incorporated into natural product cyclic peptides and synthetic macrocyclic peptidomimetics that refine peptide structure and confer biological properties.

Peptides and proteins as a continuing exciting source of inspiration for peptidomimetics

Despite their enormous diversity in biological function and structure, peptides and proteins are endowed with properties that have induced and stimulated the development of peptidomimetics. Clearly, peptides can be considered as the "stem" of a phylogenetic molecular development tree from which branches of oligomeric peptidomimetics such as peptoids, peptidosulfonamides, urea peptidomimetics, as well as β-peptides have sprouted. It is still a challenge to efficiently synthesize these oligomeric species, and study their structural and biological properties. Combining peptides and peptidomimetics led to the emergence of peptide-peptidomimetic hybrids in which one or more (proteinogenic) amino acid residues have been replaced with these mimetic residues. In scan-like approaches, the influence of these replacements on biological activity can then be studied, to evaluate to what extent a peptide can be transformed into a peptidomimetic structure while maintaining, or even improving, its biological properties. A central issue, especially with the smaller peptides, is the lack of secondary structure. Important approaches to control secondary structure include the introduction of α,α-disubstituted amino acids, or (di)peptidomimetic structures such as the Freidinger lactam. Apart from intra-amino acid constraints, inter-amino acid constraints for formation of a diversity of cyclic peptides have shaped a thick branch. Apart from the classical disulfide bridges, the repertoire has been extended to include sulfide and triazole bridges as well as the single-, double- and even triple-bond replacements, accessible by the extremely versatile ring-closing alkene/alkyne metathesis approaches. The latter approach is now the method of choice for the secondary structure that presents the greatest challenge for structural stabilization: the α-helix.

Asymmetric syntheses and Wnt signal inhibitory activity of melleumin A and four analogues of melleumins A and B

Guided by nature: A flexible and epimerization-free approach for the asymmetric syntheses of melleumin A and four analogues of melleumins A and B was developed, which allowed confirming the stereochemistry at C-4 of melleumin A, and revealed that the unnatural 4-epi-melleumin B possesses a modest inhibitory activity on Wnt signaling. The first total synthesis of melleumin A and four analogues of melleumins A and B is described. The N-acyl L-Thr-Gly/beta-hydroxy-gamma-amino acid coupling/macrolactamization strategy allowed the efficient assembly of the three segments being free of epimerization. While the Jouin-Castro method with minor modification allows a rapid entrance to the key syn-beta-hydroxy-gamma-amino acid segment, required for the synthesis of melleumin A, an extension of our malimide-based methodology using a changed N-protecting group affords a flexible access to several anti-beta-hydroxy-gamma-amino acids, and hence analogues of melleumins A and B. Among them, unnatural 4-epi-melleumin B (2 a) exhibits a modest inhibitory activity on Wnt signaling. The total synthesis of melleumin A allowed confirmation of its full structure.

Supramolecular bidentate ligands by metal-directed in situ formation of antiparallel beta-sheet structures and application in asymmetric catalysis

The principles of protein structure design, molecular recognition, and supramolecular and combinatorial chemistry have been applied to develop a convergent metal-ion-assisted self-assembly approach that is a very simple and effective method for the de novo design and the construction of topologically predetermined antiparallel beta-sheet structures and self-assembled catalysts. A new concept of in situ generation of bidentate P-ligands for transition-metal catalysis, in which two complementary, monodentate, peptide-based ligands are brought together by employing peptide secondary structure motif as constructing tool to direct the self-assembly process, is achieved through formation of stable beta-sheet motifs and subsequent control of selectivity. The supramolecular structures were studied by (1)H, (31)P, and (13)C NMR spectroscopy, ESI mass spectrometry, X-ray structure analysis, and theoretical calculations. Our initial catalysis results confirm the close relationship between the self-assembled sheet conformations and the catalytic activity of these metallopeptides in the asymmetric rhodium-catalyzed hydroformylation. Good catalyst activity and moderate enantioselectivity were observed for the selected combination of catalyst and substrate, but most importantly the concept of this new methodology was successfully proven. This work presents a perspective interface between protein design and supramolecular catalysis for the design of beta-sheet mimetics and screening of libraries of self-organizing supramolecular catalysts.

Ambient temperature synthesis of high enantiopurity N-protected peptidyl ketones by peptidyl thiol ester-boronic acid cross-coupling

alpha-Amino acid thiol esters derived from N-protected mono-, di-, and tripeptides couple with aryl, pi-electron-rich heteroaryl, or alkenyl boronic acids in the presence of stoichiometric Cu(I) thiophene-2-carboxylate and catalytic Pd(2)(dba)(3)/triethylphosphite to generate the corresponding N-protected peptidyl ketones in good-to-excellent yields and in high enantiopurity. Triethylphosphite plays a key role as a supporting ligand by mitigating an undesired palladium-catalyzed decarbonylation-beta-elimination of the alpha-amino thiol esters. The peptidyl ketone synthesis proceeds at room temperature under nonbasic conditions and demonstrates a high tolerance to functionality.

An Efficient Access to Novel Enantiomerically Pure Steroidal δ-Amino Acids

A highly chemoselective sequence of Stille and Heck couplings on the heterocyclic bromoenol triflates 2 a-c with the bicycloalkenylstannanes cis-3 and trans-3 furnished the intermediate bromobutadienes 4 a-c in good yields ranging from 73-94 %. A modified Heck coupling protocol employing the palladacycle 8 and an additional bidentate ligand such as 1,4-bis(diphenylphosphinyl)butane allowed a significant reduction in catalyst loading while still obtaining the heterocyclic 1,3,5-hexatrienes 5 a-c in good yields (71-94 %). The unsymmetrically substituted 1,3,5-hexatrienes 5 a-c in solution underwent 6pi-electrocyclizations following an optimized microwave-heating protocol to yield the steroidal tetracycles cis-7 a-c and trans-7 b (59-69 %). Tetracycles cis-7 a-c are the products of a subsequent 1,5-hydrogen shift to the thermodynamically more stable, more highly substituted diene units. Removal of the tert-butyl groups provided the novel steroidal delta-amino acid 9 a and the delta-amino acid derivatives 9 b, c in good yields (76-86 %).

Azabicycloalkenes as Synthetic Intermediates: Application to the Preparation of Diazabicycloalkane Scaffolds

[reaction: see text] A general method to synthesize bicyclic dipeptide mimetics is reported. Key intermediates are azabicycloalkenes 9 and 17, which are prepared via Diels-Alder reactions and subsequent mild deprotection. These unsaturated bicyclic heterocycles are versatile intermediates for different dipeptide mimetics of the aza- and diazabicycloalkane type, which is demonstrated by the synthesis of diazabicycloalkanes 11 and 19 in only 3-6 steps and good overall yield.