Synthesis of an optically active, bicyclic 2-pyridone dipeptide mimetic

Metal-Free, One-Pot Cascade Annulation of 2-Pyrones in Water for the Synthesis of Peptidomimetics

A one-pot, metal-free, double cyclization for the synthesis of bicyclic 2-pyridones as peptidomimetics was developed. In this process, the transformation of 2-pyrones bearing a tethered, homochiral α-amino acid started with the removal of the N-Boc protective group under acidic or neutral conditions at elevated temperature, followed by several key transformations, including cyclic enamine formation, decarboxylation or esterification, isomerization, and lactamization, to furnish bicyclic 2-pyridones in up to 98% yield with retention of the chirality at the α-carbon of the amino acid portion of the molecule. Exploration of the substrate scope revealed some selectivity between the decarboxylation and esterification pathways under thermal acidic conditions, while performing the reaction in boiling water yielded the decarboxylation products exclusively.

A one-pot, metal-free approach to bicyclic 2-pyridones

A practical one-pot process based on two-fold intramolecular cyclizations provides a more expedient entry into a variety of bicyclic 2-pyridones.

Structural diversity of bicyclic amino acids

Over the years biomedical research has been constantly oriented towards the development of new therapeutics based on bioactive peptides and their analogues. In particular, the generation of compounds having structures and functions similar to bioactive peptides, named "peptidomimetics", raised much interest among organic and medicinal chemists due to the possibility by using such compounds to improve both potency and stability of peptidic lead compounds. In the context of this research area, unnatural amino acids are of great interest in drug discovery, and their use as new building blocks for the development of peptidomimetics with high diversity level and possessing high-ordered structures is of special interest. In particular, medicinal chemistry has taken advantage of the use of amino acid homologues and of cyclic and polycyclic templates to introduce elements of diversity for the generation of new molecules as drug candidates. Bicyclic amino acids have been developed as reverse turn mimetics and dipeptide isosteres, and the constraint imposed by their structures has been reported as a tool for controlling the conformational preferences of modified peptides. Moreover, synthetic efforts have been driven to the generation of diverse structures based on the modulation of ring size and scaffold decoration by suitable functional groups. Herein is reported an overview of different classes of bicyclic amino acids, taking into account the strategies to achieve structurally diverse templates, and some implications in medicinal chemistry are also disclosed.

Tandem Michael Addition/Amino-Nitrile Cyclization from 2-Formyl-1,4-DHP in the Synthesis of Novel Dihydroindolizine-Based Compounds

A simple and efficient methodology for the synthesis of a small library of substituted indolizines with different degrees of saturation starting from the racemic 2-formyl-1,4-DHP reagent was described. The large synthetic possibilities of this reagent as well as of its Knoevenagel corresponding 2-dicyanovinyl-1,4-DHP reagent were investigated using four kinds of activated methylenes as nucleophiles. The key step of the sequential reaction was based on the highly diastereoselective tandem Michael addition/intramolecular amino-nitrile cyclization catalyzed by an organic base, which resulted in the formation of 1,7-dihydroindolizines in a diastereoselective manner. The process seems to be a straightforward one and can be extended to numerous active methylenes such as malononitrile, 1,3-diketones, and alkyl acetoacetates. The 1,3-hydrogen shift of partially hydrogenated indolizines was accomplished easily with a base at room temperature, giving rise to the corresponding 7,8-dihydroindolizines in very good yields. Interestingly, when the active methylene bears a leaving group, the latter process could not be accomplished because a rare cis-elimination of phenylsulfinic acid and nitrous acid preceded the hydrogen shift. The resulting 1,7-dihydroindolizines bearing an exo-methylene group at C1 were not isolated in all cases, as they turned rapidly to indolizines as the thermodynamically more stable products. During these investigations, oxidization of 1,7-dihydroindolizines with CuCl(2) resulted in the formation of polysubstituted pyridines. Also, the epimerization of certain 1,7-dihydroindolizines was evidenced in the solution studied by NMR spectroscopy, whereas in the solid state, they existed only in a unique form as shown by X-ray diffraction analysis of a representative structure. Finally, all products reported herein bear a primary amine and a nitrile function crucial for further transformations. These include the introduction of various pharmacophore groups at either NH(2) or CN groups as well as at both groups at the same time to access the more elaborated indolizines fused to N- or N,N-heterocycles.

Design, synthesis and evaluation of peptidomimetics based on substituted bicyclic 2-pyridones-targeting virulence of uropathogenic E. coli

Substituted bicyclic 2-pyridones, termed pilicides, are dipeptide mimetics that prevent pilus assembly in uropathogenic Escherichia coli. Here, we apply rational design to produce four classes of extended peptidomimetics based on two bioactive 2-pyridones. The key intermediate in the synthesis was an amino-functionalised 2-pyridone scaffold, which could be obtained via a mild and selective nitration and subsequent reduction. Procedures were then developed to further derivatize this amino-substituted core and a total of 24 extended peptidomimetics were synthesised and evaluated for chaperone affinity and in vivo antivirulence activity in P pili producing E. coli. Enhanced affinities for the target protein were observed within the generated set of compounds, while the ability to prevent pilus assembly in vivo was significantly decreased compared to the parent lead compounds. The results suggest that the limited in vivo potencies of the analogues are either uptake/distribution related or due to loss in binding specificity.

Design, synthesis, and application of azabicyclo[X.Y.0]alkanone amino acids as constrained dipeptide surrogates and peptide mimics

Azabicyclo[X.Y.0]alkanone amino acids are challenging synthetic targets and useful tools for studying structure-activity relationships of native peptide ligands. They have been employed to increase potency and stability in conformationally rigid enzyme inhibitors and receptor ligands. Since last reviewed in 1997, activity in their synthesis and application has increased significantly and access is now available to a wider diversity of these peptide mimics. This review focuses on recent syntheses of these heterocyclic amino acids and their application in the investigation of biologically active peptides and peptide mimics.