Cis-Configured Aziridines Are New Pseudo-Irreversible Dual-Mode Inhibitors ofCandida albicans Secreted Aspartic Protease 2

Non-Aziridination Approaches to 3-Arylaziridine-2-carboxylic Acid Derivatives and 3-Aryl-(aziridin-2-yl)ketones

Highly functionalized aziridines, including compounds with aromatic moieties, are attractive substrates both in synthetic and medical areas of chemistry. There is a broad and interesting set of synthetic methods for reaching these compounds. Aziridination represents the most explored tool, but there are several other more specific, less well-known, but highly promising approaches. Therefore, the current review focuses on recently described or updated ways to obtain 3-arylated aziridines via different non-aziridination-based synthetic methods, reported mainly since 2000. The presented methods belong to two main directions of synthesis, namely, cyclization of open-chain substrates and rearrangement of other heterocycles. Cyclization of open-chain substrates includes the classic Gabriel-Cromwell type cyclization of halogenated substrates with amines, base-promoted cyclization of activated aminoalcohols (or its analogues), and the oxidative cyclization of β-dicarbonyls. Rearrangements of other heterocycles are presented as the Baldwin rearrangement of 4-isoxazolines, the cycloaddition of 1.3-dipoles or dienes to 2H-azirines, and the addition of C- and N-nucleophiles to the double bond of azirines.

β-Indolyloxy Functionalized Aspartate Analogs as Inhibitors of the Excitatory Amino Acid Transporters (EAATs)

The excitatory amino acid transporters (EAATs) mediate uptake of the major excitatory neurotransmitter l-glutamate (Glu). The essential functions governed by these transporters in regulating the central Glu level make them interesting therapeutic targets in a wide range of neurodegenerative and psychiatric disorders. l-Aspartate (Asp), another EAAT substrate, has served as a privileged scaffold for the development of EAAT inhibitors. In this study, we designed and synthesized the first β-indolyloxy Asp analogs 15a-d with the aim to probe a hitherto unexplored adjacent pocket to the substrate binding site. The pharmacological properties of 15a-d were characterized at hEAAT1-3 and rEAAT4 in a conventional [³H]-d-Asp uptake assay. Notably, thiophene analog 15b and the para-trifluoromethyl phenyl analog 15d were found to be hEAAT1,2-preferring inhibitors exhibiting IC₅₀ values in the high nanomolar range (0.21-0.71 μM) at these two transporters versus IC₅₀ values in the low micromolar range at EAAT3,4 (1.6-8.9 μM). In summary, the results presented herein open up for further structure-activity relationship studies of this new scaffold.

Targeting fungal virulence factor by small molecules: Structure-based discovery of novel secreted aspartic protease 2 (SAP2) inhibitors

Secreted aspartic protease 2 (SAP2), a kind of virulence factor, is an emerging new antifungal target. Using docking-based virtual screening and structure-based inhibitor design, a series of novel SAP2 inhibitors were successfully identified. Among them, indolone derivative 24a showed potent SAP2 inhibitory activity (IC₅₀ = 0.92 μM). It blocked fungi biofilm and hypha formation by down-regulating the expression of genes SAP2, ECE1, ALS3 and EFG1. As a virulence factor inhibitor, compound 24a was inactive in vitro and showed potent in vivo efficacy in a murine model of invasive candidiasis. It represents a promising lead compound for the discovery of novel antifungal agents.

Identification of plakortide E from the Caribbean sponge Plakortis halichondroides as a trypanocidal protease inhibitor using bioactivity-guided fractionation

In this paper, we report new protease inhibitory activity of plakortide E towards cathepsins and cathepsin-like parasitic proteases. We further report on its anti-parasitic activity against Trypanosoma brucei with an IC₅₀ value of 5 μM and without cytotoxic effects against J774.1 macrophages at 100 μM concentration. Plakortide E was isolated from the sponge Plakortis halichondroides using enzyme assay-guided fractionation and identified by NMR spectroscopy and mass spectrometry. Furthermore, enzyme kinetic studies confirmed plakortide E as a non-competitive, slowly-binding, reversible inhibitor of rhodesain.

New cis-configured aziridine-2-carboxylates as aspartic acid protease inhibitors

A series of 52 cis-configured 1-alkyl-3-phenylaziridine-2-carboxylates were synthesized as new pseudo-irreversible inhibitors of Candida albicans secreted aspartic acid protease 1 (SAP1), SAP2, SAP3, and SAP8. Some of the compounds, which were obtained as diastereomers with S,S- and R,R-configured aziridine rings by Cromwell synthesis of racemic (2R,3S+2S,3R)-dibromophenylpropionic acid ester with amines, followed by ester hydrolysis and coupling to hydrophobic amino acid esters, were separated by preparative HPLC. The absolute configuration of the aziridine ring was assigned by a combination of experimental circular dichroism (CD) investigations and quantum chemical CD calculations. In agreement with previous docking studies, the diastereomers all exhibit similar activity. The compounds were found to be more active against the related mammalian enzyme cathepsin D, presumably due to productive interactions of the N-alkyl substituent with the highly lipophilic S2 pocket. The most active inhibitors (5, 9, 10, 21, and 28), characterized by benzyl, cyclohexylmethyl, tert-butyl, or 1,4-dimethylpentyl moieties at the aziridine nitrogen atom, exhibit k(2nd) values between 500 and 900×10³ M⁻¹ min⁻¹ and K(i) values near or below 1 μM for cathepsin D.

Effect of electron-withdrawing substituents on the epoxide ring: an experimental and theoretical electron density analysis of a series of epoxide derivatives

A series of acceptor-substituted epoxide derivatives is scrutinized by means of experimental and theoretical electron-density investigations. Due to the possibility of nucleophilic ring-opening, the epoxide ring is not only a very useful functional group in organic synthesis, but acceptor-substituted epoxides are valuable building blocks for the design of protease inhibitors. Therefore, the electron-density analysis in this work focuses on two main aspects that can contribute to rational drug design: (i) the quantification of the electron-withdrawing substituent effects on the epoxide ring and (ii) the intermolecular interactions involving the epoxide ring in combination with different substituents. It can be shown that the electron-withdrawing properties of the substituents cause an elongation of the C-C bonds in the epoxide rings and the loss of electron density can be measured by an analysis of critical points, atomic charges, and the source function. The different strengths of the substituents are reflected in these properties. Covalent and electrostatic contributions to the intermolecular interactions and thus the lattice energies are depicted on different molecular surfaces.