Expanding the substrate scope of Ugi five-center, four-component reaction U-5C-4CR): ketones as coupling partners for secondary amino acids

Synthesis, docking study and inhibitory activity of 2,6-diketopiperazines derived from α-amino acids on HDAC8

Diketopiperazines (DKPs) have been regarded as an important scaffold from the viewpoint of synthesis due to their biological properties for the treatment of several diseases, including cancer. In this work, two novel series of enantiomeric 2,6-DKPs derived from α-amino acids were synthesized through nucleophilic substitution and intramolecular cyclization reactions. All the compounds were docked against histone deacetylase 8 (HDAC8), which is a promising target for the development of anticancer drugs. These compounds bound into the active site of HDAC8 in a similar way to Trichostatin A (TSA), which is an HDAC8 inhibitor. This study showed that the conformation of the 2,6-DKP ring, stereochemistry, and the type of substituent on the chiral center had an important role in the binding modes. The Gibbs free energies and dissociation constants values of HDAC8-ligand complexes showed that compounds (S)-4hBn, (S)-4m, (R)-4h, and (R)-4m were more stable and affine towards HDAC8 than TSA. The inhibitory activities of 4a, (S)-4h, (S)- and (R)-4(g, l, m) were evaluated in vitro on HDAC8. It was found that compounds (R)-4g (IC₅₀ = 21.54 nM) and (R)-4m (IC₅₀ = 10.81 nM) exhibited better inhibitory activities than TSA (IC₅₀ = 28.32 nM). These results suggested that 2,6-DKPs derivatives may be promising anticancer agents for further biological studies.

α-Amino Acids as Synthons in the Ugi-5-Centers-4-Components Reaction: Chemistry and Applications

Since the first reports, the Ugi four-component reaction (U-4CR) has been recognized as a keystone transformation enabling the synthesis of peptide mimetics in a single step and with high atom economy. In recent decades, the U-4CR has been a source of inspiration for many chemists fascinated by the possibility of identifying new efficient organic reactions by simply changing one of the components or by coupling in tandem the multicomponent process with a huge variety of organic transformations. Herein we review the synthetic potentialities, the boundaries, and the applications of the U-4CR involving α-amino acids, where the presence of two functional groups—the amino and the carboxylic acids—allowed a 5-center 4-component Ugi-like reaction, a powerful tool to gain access to drug-like multi-functionalized scaffolds.

Exploitation of the Ugi 5-Center-4-Component Reaction (U-5C-4CR) for the Generation of Diverse Libraries of Polycyclic (Spiro)Compounds

An Ugi multicomponent reaction with chiral cyclic amino acids, benzyl isocyanide and cyclic ketones (or acetone) has been exploited as key step for the generation of peptidomimetics. After a straightforward set of elaborations, the peptidomimetics were converted into polycyclic scaffolds displaying two orthogonally protected secondary amines. Libraries of compounds were obtained decorating the molecules through acylation/reductive amination reactions on these functional groups.

Methionine and seleno-methionine type peptide and peptoid building blocks synthesized by five-component five-center reactions

A first example of 5-component 5-center reactions with isonitriles [Ugi-5CRs] is described. The extended Ugi type reactions involve selenoaldehydes as well as ammonia, both challenging reactants in multicomponent (MCR) systems, to generate methionine and Se-methionine moieties and derivatives as protected building blocks or for direct ligation in peptides or peptoids. The peptoid/peptide building blocks proved to be non-cytotoxic but increased the expression of genes encoding for stress protective selenoproteins (Gpx1).

Multicomponent Cascade Reactions of Unprotected Ketoses and Amino Acids--Access to a Defined Configured Quaternary Stereogenic Center

A highly stereoselective multicomponent cascade reaction of ketones with unprotected amino acids was developed. This operationally simple methodology was expanded to reactions of unprotected ketohexoses and unprotected amino acids. By the careful choice of amino acid and isonitrile, an optional access to all possible enantiomers is given.

Synthesis of new perhydropyrrolo[1,2-a]pyrazine derivatives and their evaluation in animal models of epilepsy

A series of novel stereochemically pure derivatives of the investigative broad-spectrum anticonvulsant ADD408003 was designed and synthesized. Five-center four-component (U-5C-4CR) and four-center three-component (U-4C-3CR) variants of Ugi reaction were used in the key step of the synthetic pathways. The compounds obtained were evaluated for the anticonvulsant activitiy in the maximal electroshock seizure (MES), subcutaneous Metrazole (scMET) and minimal clonic seizure (6 Hz) animal models of epilepsy. The efficacies of most derivatives in the 6 Hz model of pharmacoresistant partial seizures were markedly higher than in the ‘classical’ MES and scMET models. The most active compounds, (4R,8aR)-3a, and (4S,8aS)-6 displayed median effective doses (ED₅₀) of 47.90 and 126.19 mg/kg, respectively, for the 6 Hz test.