Polina M. Ivantcova

Alternating Asymmetric Self‐Induction in Functionalized Pyrrolidine Oligomers

Artificial structurally well-defined polymers have excited interest as functional mimetics of natural biomacromolecules, exhibiting additional properties not occurring in the living world. Specific conformational organization of natural and synthetic polymeric objects leading to unique folding accounts for the molecular recognition, which is one of the driving principles in important natural processes. Some nonnatural oligomeric species adopt specific and well-defined conformations dictated by the structure of monomeric units and intramolecular interactions and are defined as foldamers. One of the most studied unnatural foldamer types are bpeptides that adopt stable folded helical, sheet, and turn-like conformations. b-Peptides are stable towards natural enzymes, and appropriate design leads to discovery of bpeptide ligands for complicated pharmaceutical targets, such as protein–protein interactions. The application of pyrrolidine-3-carboxylic acid (Pca) for the construction of bpolypeptide chain rigidifies the molecular backbone and provides additional stabilization of the secondary structure of the oligomer in solution. The typical synthesis of a b-peptide backbone is based on the arsenal of peptide chemistry methods, including routine sequences of amino group protection–deprotection steps and multiple activations of carboxylic functionality for amide bond construction. Herein we disclose a fundamentally novel synthetic method towards well-defined highly functionalized short b-peptides that avoids protection, deprotection, and activation procedures and allows to generate efficiently stereoregular oligomeric pyrrolidine-based molecules. The developed method, called cycloadditive oligomerization, has been used for the synthesis of a set of racemic and enantiopure oligomers containing a Pca backbone. The realized approach determines highly diverse structural characteristics of b-peptide oligomers, which are characterized by various physicochemical methods, including X-ray analysis. The oligomerization utilized azomethine ylide 1,3-dipolar cycloaddition as a chain-growth approach (Scheme 1). 5Arylpyrrolidine-2,4-dicarboxylate units serve both as linked elements and as auxiliaries to determine stereoand enantioselectivities of the cycloaddition process. The starting 5arylpyrrolidine-2,4-dicarboxylic acid diesters 3a (X=H, Br) for oligomer synthesis were obtained from iminoesters 1 and tert-butyl acrylate in racemic and enantiopure forms by 1,3-dipolar cycloaddition using Lewis acids for the azomethine ylide generation step (Scheme 1, Table 1). Asymmetric synthesis of the monomer ( )-3a-H was effectively conducted with the enantiopure ligand 4 on a gram scale, and single recrystallization provided the target compound with more than 99% ee. Subsequent N-acryloylation of monomers 3a with acryloyl chloride transformed them into dipolarophiles 2b with a sterically hindered amide residue connected to the ethylene fragment. We supposed that these unique dipolarophiles would induce good diastereoand enantioselectivities under iterative cycloaddition steps with iminoesters 1 (Scheme 1). Indeed, dimers 3b were effectively synthesized by cycloaddition of acrylamides 2b with Schiff bases 1 (X=H, Br) in presence of AgOAc as a Lewis acid agent for azomethine ylide generation (Table 1, entries 4–6). Comparison of H NMR spectra of the cycloaddition reaction mixtures and

Menthols as Chiral Auxiliaries for Asymmetric Cycloadditive Oligomerization: Syntheses and Studies of β-Proline Hexamers

To produce a novel class of structurally ordered poly-β-prolines, an emergent method for synthesizing chiral β-peptide molecular frameworks was developed based on 1,3-dipolar cycloaddition chemistry of azomethine ylides. Functionalized short β-peptides with up to six monomeric residues were efficiently synthesized in homochiral forms using a cycloadditive oligomerization approach. X-ray, NMR, and CD structural analyses of the novel β-peptides revealed secondary structure features that were generated primarily by Z/E-β-peptide bond isomerism. Anticancer in cellulo activity of the new β-peptides toward hormone-refractory prostate cancer cells was observed and was dependent on the absolute configuration of the stereogenic centers and the chain length of the β-proline oligomers.

Structural Studies and Anticancer Activity of a Novel Class of β‐Peptides

Functionalized oligomeric organic compounds with well-defined β-proline scaffold have been synthesized by a cycloadditive oligomerization approach in racemic and enantiopure forms. The structure of the novel β-peptides was investigated by NMR spectroscopic and X-ray methods determining the conformational shapes of the β-proline oligomers in solution and solid states. The main structural elements subject to conformational switches are β-peptide bonds between 5-arylpyrrolidine-2-carboxylic acid units existing in Z/E configurations. The whole library of short β-peptides and intermediate acrylamides has been tested on antiproliferative activity towards the hormone-refractory prostate cancer cell line PC-3 revealing several oligomeric compounds with low micromolar and submicromolar activities. Bromine-substituted dimeric and trimeric acrylamides induced caspase-dependent apoptosis of PC-3 cells through cell-cycle arrest and mitochondrial damage.

Control of Azomethine Cycloaddition Stereochemistry by CF3 Group: Structural Diversity of Fluorinated β-Proline Dimers

β-Proline-functionalized dimers consisting of homochiral monomeric units were synthesized by a non-peptidic coupling method for the first time. The applied synthetic methodology is based on 1,3-dipolar cycloaddition chemistry of azomethine ylides and provides absolute control over the β-proline backbone stereogenic centers. An o-(trifluoromethyl)phenyl substituent contributes to appropriate stabilization of the definite acrylamide chiral cis conformation and to achieve the dipole reactivity that is not observed for aryl groups lacking strong electronegative character.

Enantiomerically pure β-dipeptide derivative induces anticancer activity against human hormone-refractory prostate cancer through both PI3K/Akt-dependent and -independent pathways

The use of peptides that target cancer cells and induce anticancer activities through various mechanisms is developing as a potential anticancer strategy. KUD983, an enantiomerically pure β-dipeptide derivative, displays potent activity against hormone-refractory prostate cancer (HRPC) PC-3 and DU145 cells with submicromolar IC50. KUD983 induced G1 arrest of the cell cycle and subsequent apoptosis associated with down-regulation of several related proteins including cyclin D1, cyclin E and Cdk4, and the de-phosphorylation of RB. The levels of nuclear and total c-Myc protein, which could increase the expression of both cyclin D1 and cyclin E, were profoundly inhibited by KUD983. Furthermore, it inhibited PI3K/Akt and mTOR/p70S6K/4E-BP1 pathways, the key signaling in multiple cellular functions. The transient transfection of constitutively active myristylated Akt (myr-Akt) cDNA significantly rescued KUD983-induced caspase activation but did not blunt the inhibition of mTOR/p70S6K/4E-BP1 signaling cascade suggesting the presence of both Akt-dependent and -independent pathways. Moreover, KUD983-induced effect was enhanced with the down-regulation of anti-apoptotic Bcl-2 members (e.g., Bcl-2, and Mcl-1) and IAP family members (e.g., survivin). Notably, KUD983 induced autophagic cell death using confocal microscopic examination, tracking the level of conversion of LC3-I to LC3-II and flow cytometric detection of acidic vesicular organelles-positive cells. In conclusion, the data suggest that KUD983 is an anticancer β-dipeptide against HRPCs through the inhibition of cell proliferation and induction of apoptotic and autophagic cell death. The suppression of signaling pathways regulated by c-Myc, PI3K/Akt and mTOR/p70S6K/4E-BP1 and the collaboration with down-regulation of Mcl-1 and survivin may explain KUD983-induced anti-HRPC mechanism.The use of peptides that target cancer cells and induce anticancer activities through various mechanisms is developing as a potential anticancer strategy. KUD983, an enantiomerically pure β-dipeptide derivative, displays potent activity against hormone-refractory prostate cancer (HRPC) PC-3 and DU145 cells with submicromolar IC50. KUD983 induced G1 arrest of the cell cycle and subsequent apoptosis associated with down-regulation of several related proteins including cyclin D1, cyclin E and Cdk4, and the de-phosphorylation of RB. The levels of nuclear and total c-Myc protein, which could increase the expression of both cyclin D1 and cyclin E, were profoundly inhibited by KUD983. Furthermore, it inhibited PI3K/Akt and mTOR/p70S6K/4E-BP1 pathways, the key signaling in multiple cellular functions. The transient transfection of constitutively active myristylated Akt (myr-Akt) cDNA significantly rescued KUD983-induced caspase activation but did not blunt the inhibition of mTOR/p70S6K/4E-BP1 signaling cascade suggesting the presence of both Akt-dependent and -independent pathways. Moreover, KUD983-induced effect was enhanced with the down-regulation of anti-apoptotic Bcl-2 members (e.g., Bcl-2, and Mcl-1) and IAP family members (e.g., survivin). Notably, KUD983 induced autophagic cell death using confocal microscopic examination, tracking the level of conversion of LC3-I to LC3-II and flow cytometric detection of acidic vesicular organelles-positive cells. In conclusion, the data suggest that KUD983 is an anticancer β-dipeptide against HRPCs through the inhibition of cell proliferation and induction of apoptotic and autophagic cell death. The suppression of signaling pathways regulated by c-Myc, PI3K/Akt and mTOR/p70S6K/4E-BP1 and the collaboration with down-regulation of Mcl-1 and survivin may explain KUD983-induced anti-HRPC mechanism.

Theoretical and NMR Conformational Studies of β-Proline Oligopeptides With Alternating Chirality of Pyrrolidine Units

Synthetic β-peptides are potential functional mimetics of native α-proteins. A recently developed, novel, synthetic approach provides an effective route to the broad group of β-proline oligomers with alternating patterns of stereogenic centers. Conformation of the pyrrolidine ring, Z/E isomerism of β-peptide bonds, and hindered rotation of the neighboring monomers determine the spatial structure of this group of β-proline oligopeptides. Preferences in their structural organization and corresponding thermodynamic properties are determined by NMR spectroscopy, restrained molecular dynamics and quantum mechanics. The studied β-proline oligopeptides exist in dimethyl sulfoxide solution in a limited number of conformers, with compatible energy of formation and different spatial organization. In the β-proline tetrapeptide with alternating chirality of composing pyrrolidine units, one of three peptide bonds may exist in an E configuration. For the alternating β-proline pentapeptide, the presence of an E configuration for at least of one β-peptide bond is mandatory. In this case, three peptide bonds synchronously change their configurations. Larger polypeptides may only exist in the presence of several E configurations of β-peptide bonds forming a wave-like extended structure.

(1SR,3RS,3aSR,6aRS)-Methyl 5-methyl-4,6-dioxo-3-[2-(trifluoro­meth­yl)phen­yl]octa­hydro­pyrrolo­[3,4-c]pyrrole-1-carboxyl­ate

In the title compound, C16H15F3N2O4, the relative stereochemistry of the four stereogenic C atoms has been determined. The carboxymethyl and 2-(trifluoromethyl)phenyl substituents of the pyrrolidine cycle have a cis mutual arrangement. The five-membered saturated azacycle adopts an envelope conformation with the N atom occupying the flap position. In the crystal, adjacent molecules are combined in centrosymmetric dimers by two weak N—H⋯O hydrogen bonds.