Turn-Mimic Hydantoin-Based Loops Constructed by a Sequential Multicomponent Reaction.

A collection of peptidomimetics characterized by having an aspartic acid motif embedded in a rigid hydantoin heterocycle are synthesized through a sequential multicomponent domino process followed by standard regioselective deprotection/coupling reactions based on acid-base liquid/liquid purification protocols. 1H nuclear magnetic resonance experiments, molecular modeling, and X-ray analysis showed that the resulting hydantoin-based loops I (in particular) and II (to a lesser extent) can be considered novel ß-turn inducer motifs being able to project two peptide-like strands in a U-shaped conformation driven by the formation of intermolecular hydrogen bonds.

Synthesis and Conformational Analysis of Hydantoin-Based Universal Peptidomimetics.

The synthesis of a collection of enantiomerically pure, systematically substituted hydantoins as structural privileged universal mimetic scaffolds is presented. It relies on a chemoselective condensation/cyclization domino process between isocyanates of quaternary or unsubstituted α-amino esters and N-alkyl aspartic acid diesters followed by standard hydrolysis/coupling reactions with amines, using liquid-liquid acid/base extraction protocols for the purification of the intermediates. Besides the nature of the α carbon on the isocyanate moiety, either a quaternary carbon or a more flexible methylene group, conformational studies in silico (molecular modeling), in solution (NMR, circular dichroism (CD), Fourier transform infrared (FTIR)), and in solid state (X-ray) showed that the presented hydantoin-based peptidomimetics are able to project their substituents in positions superimposable to the side chains of common protein secondary structures such as α-helix and ß-turn, being the open α-helix conformation slightly favorable according to molecular modeling, while the closed ß-turn conformation preferred in solution and in solid state.

Synthesis and Characterization of New Triazole-Bispidinone Scaffolds and Their Metal Complexes for Catalytic Applications.

Bispidines are a family of ligands that plays a pivotal role in various areas of coordination chemistry, with applications in medicinal chemistry, molecular catalysis, coordination polymers synthesis, and molecular magnetism. In the present work, triazole moieties were introduced using the CuAAC click-reaction, with the aim of expanding the number of coordination sites on the bispidine core. The 1,2,3-triazole rings were thus synthesized on propargyl-derived bispidines after reaction with different alkyl azides. The new class of triazole-bispidines was characterized, and their chelation capabilities were evaluated with different metals through NMR titration, ESI-MS spectrometry, and single-crystal X-ray diffraction (SC-XRD). Finally, the suitability of these molecules as metal ligands for the catalytic Henry reaction was demonstrated with copper and zinc.

Recycling of used vegetable oils by powder adsorption.

The treatment of used vegetable oil (UVO) with seven different adsorbents and through two different procedures (stirring and gravity filtration) was explored. Important differences in terms of density, turbidity, electrical resistance, free fatty acids (FFAs) content and relative fatty acid distribution were observed. Different outcomes were shown depending both on the adsorbent and on the procedure. Lower values of density and FFAs were registered for oils treated by gravity filtration with portland (respectively 0.6% and 0.81 g/ml) and celite (respectively 0.7% and 0.72 g/ml). Considering the undesired leaching from the powder to the oil, related to the turbidity, the celite resulted more suitable for the oil recycling (241 Nephelometric Turbidity Unit (NTU) for portland vs 184 NTU for celite). In addition, Fourier-transform infrared spectroscopy combined with multivariate analysis allowed to determine a chemical fingerprint relative characteristic of vegetable oils recycled by gravity or by adsorption by stirring.

Deep eutectic solvent as solvent and catalyst: one-pot synthesis of 1,3-dinitropropanes via tandem Henry reaction/Michael addition.

The Henry reaction was performed using microwave heating within the deep eutectic solvent (DES) choline chloride/urea (ChCl/urea) which acted as both the catalyst and solvent for the reaction. The optimisation of the conditions (temperature, heating mode, time, DES) allowed 1,3-dinitropropane derivatives to be obtained via tandem Henry reaction/Michael addition, in one step from a range of different aromatic aldehydes in high yields and under mild reaction conditions.

Ecdysteroid Derivatives that Reverse P-Glycoprotein-Mediated Drug Resistance.

The expression of multidrug resistance P-glycoprotein (P-gp) by cancer cells represents one of the major drawbacks to successful cancer therapy. Accordingly, the development of drugs that inhibit the activity of this transporter remains a major challenge in cancer drug discovery. In this context, several new ecdysteroid derivatives have been synthesized and evaluated as P-gp inhibitors. Two of them (compounds 9 and 14) were able to resensitize CEMVbl100 and LoVoDoxo resistant cell lines to vinblastine and doxorubicin, respectively. Indeed, both compounds 9 and 14 increased the cellular accumulation of rhodamine 123 in cells expressing P-gp and stimulated basal P-glycoprotein-ATPase activity at a 1 µM concentration, demonstrating their interference with the transport of other substrates in a competitive mode. Moreover, in a medulloblastoma cell line (DAOY), compounds 9 and 14 reduced the side population representing cancer stem cells, which are characterized by a high expression of ABC drug transporters. Further, in DAOY cells, the same two compounds synergized with cisplatin and vincristine, two drugs used commonly in the therapy of medulloblastoma. Molecular docking studies on the homology-modeled structure of the human P-glycoprotein provided a rationale for the biological results, validating the binding mode within the receptor site, in accordance with lipophilicity data and observed structure-activity relationship information. Altogether, the present results endorse these derivatives as promising P-gp inhibitors, and they may serve as candidates to reverse drug resistance in cancer cells.

Influence of the Core Formulation on Features and Drug Delivery Ability of Carbamate-Based Nanogels.

In the last years, nanogels have emerged as one of the most promising classes of novel drug delivery vehicles since they can be employed in multiple fields, such as various therapeutics or diagnostics, and with different classes of compounds and active molecules. Their features, such as a high volume to surface ratio, excellent drug loading and release ability, as well as biocompatibility and tunable behavior, are unique, and, nowadays, great efforts are made to develop new formulations that can be employed in a wider range of applications. Polyethylene glycol (PEG)-polyethylenimine (PEI) nanogels probably represent the baseline of this class of biomaterials and they are still largely employed and studied. In any way, the possibility to exploit new core formulations for nanogels is certainly very interesting in order to understand the influence of different polymer chains on the final properties of the system. In this research, we explore and make a comparison between PEG-PEI nanogels and two other different formulations: pluronic F127-PEI nanogels and PEG-Jeffamine nanogels. We propose nanogels synthesis methods, their chemical and physical characterization, as well as their stability analysis, and we focus on the different drug delivery ability that these structures exhibit working with different typologies of drug mimetics.

Synthesis and Antimicrobial Evaluation of Novel Chiral 2-Amino-4,5,6,7-tetrahydrothieno[2,3-c]pyridine Derivatives.

New N-substituted-2-amino-4,5,6,7-tetrahydrothieno[2,3-c]pyridine derivatives were synthesized employing a convenient one-pot three-component method and their structures were characterized by 1 H-NMR and single crystal X-ray diffraction analysis. All the synthesized compounds were in vitro screened for antimicrobial activity against Gram-positive (Sarcina lutea) and Gram-negative bacteria (Escherichia coli). In this work, we introduced a chiral residue on the tetrahydropyridine nitrogen, the hitherto the less investigated position on this pharmacophore in order to explore the effect. The antibacterial results showed that the synthesized compounds were active only against Gram-positive bacteria and the (R)-enantiomers displayed a greater antimicrobial potency than their (S)-counterparts. The structure-activity relationship here investigated may provide some interesting clues for future development of tetrahydrothienopyridine derivatives with higher antimicrobial activity.

Highly Dynamic and Tunable Behavior of 1D Coordination Polymers Based on the Bispidine Ligand.

Ligands L1 and L2 have been designed, synthesized, and used to build for the first time bispidine-based coordination polymers (CPs) in combination with MnII . The novel CPs have been structurally characterized by single-crystal (SC) and powder X-ray diffraction (P-XRD) techniques, showing that they are composed of 1D ribbon-like chains that adopt various arrangements depending on the trapped solvent species. These materials show highly dynamic behavior as they undergo heterogeneous solid/liquid and solid/vapor multiple solvent exchange processes, comprising crystalline-amorphous-crystalline, selective adsorption and SC-to-SC transformations, where major structural reorganization of the 1D ribbons are observed. By tuning inter-ribbon interactions through expansion of the ligand's accessible surface, the dynamic behavior can be effectively modulated.

Microwave-assisted synthesis of TEMPO-labeled hydrogels traceable with MRI.

Polymer functionalization strategies have recently attracted considerable attention for several applications in biomaterials science. In particular, technological advancements in medical imaging have focused on the design of polymeric matrices to improve non-invasive approaches and diagnostic accuracy. In this scenario, the use of microwave irradiation of aqueous solutions containing appropriate combinations of polymers is gaining increasing interest in the synthesis of sterile hydrogels without using monomers, eliminating the need to remove unreacted species. In this study, we developed a method for the in situ fabrication of TEMPO-labeled hydrogels based on a one-pot microwave reaction that can then be tracked by magnetic resonance imaging (MRI) without using toxic compounds that could be hostile for the target tissue. Click chemistry was used to link TEMPO to the polymeric scaffold. In an in vivo model, the system was able to preserve its TEMPO paramagnetic activity up to 1 month after hydrogel injection, showing a clear detectable signal on T1-weighted MRI with a longitudinal relaxivity value of 0.29 mM s-1, comparable to a value of 0.31 mM s-1 characteristic of TEMPO application. The uncleavable conjugation between the contrast agent and the polymeric scaffold is a leading point to record these results: the use of TEMPO only physically entrapped in the polymeric scaffold did not show MRI traceability even after few hours. Moreover, the use of TEMPO-labeled hydrogels can also help to reduce the number of animals sacrificed being a longitudinal non-invasive technique.

Organocatalytic Asymmetric Biginelli-like Reaction Involving Isatin.

The first asymmetric, Brønsted acid catalyzed Biginelli-like reaction of a ketone has been developed, employing N-substituted isatins as carbonyl substrates, and urea and alkyl acetoacetates as further components. BINOL-derived phosphoric acid catalysts have been used to achieve the synthesis of a small library of chiral, enantioenriched spiro(indoline-pyrimidine)-diones derivatives. The absolute configuration of the new spiro stereocenter was assessed on diastereoisomeric derivatives through computer-assisted NMR spectroscopy. X-ray diffractometry allowed the disclosure of the overall molecular conformation in the solid state and the characterization of the crystal packing of a Br-substituted Biginelli-like derivative, while computational studies on the reaction transition state allowed us to rationalize the stereochemical outcome.

Organocatalytic vinylogous Mannich reaction of trimethylsiloxyfuran with isatin-derived benzhydryl-ketimines.

A family of chiral quaternary 3-aminooxindole butenolides has been synthesized by BINOL-derived phosphoric acid-catalyzed addition of trimethylsiloxyfuran to isatin-derived ketimines. Such a vinylogous Mannich-type reaction was found to produce diastereoisomeric butenolides in good yields and in most cases high enantiomeric excesses. The configurational assignment of the obtained products was safely performed by chemical correlation. A computational study of the transition state allowed rationalizing the obtained stereochemical outcome, highlighting the possible binding modes of the catalyst-imine-nucleophile transition complex.

Spectroscopic, Structural, and Computational Characterization of Three Bispidinone Derivatives, as Ligands for Enantioselective Metal Catalyzed Reactions.

Three chiral derivatives of the alkaloid sparteine (bispidines), characterized by the 3,7-diazabicyclo[3.3.1]nonane moiety, were designed as efficient ligands in a number of enantioselective reactions due to their metal coordination properties. A full evaluation of the 3D properties of the compounds was carried out, as the geometrical features of the bicyclic framework are strictly related to the efficiency of the ligands in the asymmetric catalysis. The selected molecules have different molecular complexity for investigating the effects of different chiral groups on the bicycle conformation. We report here a thorough analysis of their molecular arrangement, by NMR spectroscopy, single crystal X-ray crystallography, and computational techniques, which put in evidence their conformational preferences and the parameters needed for the design of more efficient ligands in asymmetric synthetic routes. The results confirmed the high molecular flexibility of the compounds, and indicated how to achieve a control of the chair-chair/boat-chair conformational ratio, by adjusting the relative size of the substituents on the piperidine nitrogens.

Complementary isonitrile-based multicomponent reactions for the synthesis of diversified cytotoxic hemiasterlin analogues.

A small family of structural analogues of the antimitotic tripeptides, hemiasterlins, have been designed and synthesized as potential inhibitors of tubulin polymerization. The effectiveness of a multicomponent approach was fully demonstrated by applying complementary versions of the isocyanide-based Ugi reaction. Compounds strictly related to the lead natural products, as well as more extensively modified analogues, have been synthesized in a concise and convergent manner. In some cases, biological evaluation provided evidence for strong cytotoxic activity (six human tumor cell lines) and for potent inhibition of tubulin polymerization.

Hemiasterlin analogues incorporating an aromatic, and heterocyclic type C-terminus: design, synthesis and biological evaluation.

A representative series of structural analogs of the antimitotic tripeptides hemiasterlins have been designed and synthesized, as potential inhibitors of tubulin polymerization. Relying also on a computational approach, we aimed to explore unknown extensive changes at the C-fragment, by incorporating the conformationally required double bond into five- and six-membered rings. Key steps of the synthetic strategy are a dynamic resolution affording the A-fragment in 97 % ee and the preparation of six new cyclic C fragments, all potentially able to interact with tubulin by means of H bonds. Unexpectedly, biological evaluation of these analogs did not provide evidences neither for cytotoxic effect nor for inhibition of tubulin polymerization.

Asymmetric Ugi 3CR on isatin-derived ketimine: synthesis of chiral 3,3-disubstituted 3-aminooxindole derivatives.

An efficient Ugi three-component reaction of a preformed chiral ketimine derived from isatin with various isonitrile and acid components has been developed. The reactions proceeded smoothly and in a stereocontrolled manner with regard to the new center of the Ugi products due to the stereoinduction of the amine chiral residue. A wide variety of novel chiral 3,3-disubstituted 3-aminooxindoles were obtained, a selection of which were subjected to post-Ugi transformations, paving the way to application as peptidomimetics.

Tetrahydro-ß-carboline-based spirocyclic lactam as type II' ß-turn: application to the synthesis and biological evaluation of somatostatine mimetics.

The synthesis of novel spirocyclic lactams, embodying D-tryptophan (Trp) amino acid as the central core and acting as peptidomimetics, is presented. It relies on the strategic combination of Seebach's self-reproduction of chirality chemistry and Pictet-Spengler condensation as key steps. Investigation of the conformational behavior by molecular modeling, X-ray crystallography, and NMR and IR spectroscopies suggests very stable and highly predictable type II' ß-turn conformations for all compounds. Relying on this feature, we also pursued their application to two potential mimetics of the hormone somatostatin, a pharmaceutically relevant natural peptide, which contains a Trp-based type II' ß-turn pharmacophore.

Synthesis of robalzotan, ebalzotan, and rotigotine precursors via the stereoselective multienzymatic cascade reduction of α,ß-unsaturated aldehydes.

A stereoselective synthesis of bicyclic primary or secondary amines, based on tetralin or chroman structural moieties, is reported. These amines are precursors of important active pharmaceutical ingredients such as rotigotine (Neupro), robalzotan, and ebalzotan. The key step is based on a multienzymatic reduction of an α,ß-unsaturated aldehyde or ketone to give the saturated primary or secondary alcohol, in a high yield and with a high ee. The catalytic system consists of the combination of an ene-reductase (ER; i.e., OYE2 or OYE3 belonging to the Old Yellow Enzyme family) with an alcohol dehydrogenase (ADH), applying the in situ substrate feeding product removal technology. By this system the formation of the allylic alcohol side product and the racemization of the chirally unstable α-substituted aldehyde intermediate are minimized. The primary alcohols were elaborated via a Curtius rearrangement. The combination of OYE2 with a Prelog or an anti-Prelog ADH allowed the preparation of the secondary alcohols with ee > 99% and de > 87%. The absolute configuration of the primary amines was unambiguously assigned by comparison with authentic samples. The stereochemistry of secondary alcohols was assigned by X-ray crystal structure and NMR analysis of Mosher esters.

Substrate scope and synthetic applications of the enantioselective reduction of α-alkyl-ß-arylenones mediated by Old Yellow Enzymes.

The ene-reductases mediated bioreduction of a selection of open-chain α-alkyl-ß-aryl enones afforded the corresponding saturated α-chiral ketones in high yield and optical purity in several cases. The stereo-electronic requirements of the reaction have been investigated, considering the nature and location of substituents on the aromatic ring as well as the steric hindrance at the α-position and adjacent to the carbonyl functionality. The general considerations drawn allow us to guide the design of α,ß-unsaturated ketones to be employed as substrates of ene-reductases in future preparative applications. An interesting case of orthogonality between enzyme-based and substrate-based stereocontrol within the highly homologous ene-reductases from Saccharomyces species (OYE1-3) has been reported and rationalized with the help of computational docking studies. Furthermore, to demonstrate the synthetic versatility of the reaction, the key chiral precursors of biologically active compounds such as (2'R)-stenusines and (S)-iopanoic acid were obtained. The very robust protocol allowed us to run the reactions on preparative scale in quantitative yields, with a simple work-up and no chromatographic purification steps.

Quinazolinecarboline alkaloid evodiamine as scaffold for targeting topoisomerase I and sirtuins.

This paper reports the synthesis of a series of evodiamine derivatives. We assayed the ability to inhibit cell growth on three human tumour cell lines (H460, MCF-7 and HepG2) and we evaluated the capacity to interfere with the catalytic activity of topoisomerase I both by the relaxation assay and the occurrence of the cleavable complex. Moreover, whose effect on sirtuins 1, 2 and 3 was investigated. Finally, molecular docking analyses were performed in an attempt to rationalize the biological results.