Cycloaddition of a chiral nitrone to allylic motifs: an access to enantiopure sugar-based amino acids displaying a stable glycosidic bond and to 4(S)-4-hydroxy-l-ornithine

Novel enantiopure isoxazolidine and C-alkyl imine oxide derivatives as potential hypoglycemic agents: Design, synthesis, dual inhibitors of α-amylase and α-glucosidase, ADMET and molecular docking study

In an effort to explore a new class of antidiabetic inhibitors, a new series of isoxazolidine and C-alkyl imine oxide derivatives scaffolds were designed, synthesized and fully characterized. The newly synthesized analogues were evaluated for their human pancreatic α-amylase (HPA) and human lysosomal acid-α-glucosidase (HLAG) inhibitory activities and have shown a higher potency than acarbose. The compounds 7b (23.1 ± 1.1 μM) and 7a (36.3 ± 1.6 μM) were identified as the potent HPA and HLAG inhibitors with inhibitory effect up to 9 and 21-fold higher than acarbose, respectively. Antihyperglycemic activity results were supported by molecular docking approach of the most potent compounds 7b and 7a showing stronger interactions with the active site of HPA and HLAG as well as by in silico absorption, distribution, metabolism, excretion and toxicity (ADMET) profile suggesting their satisfactory oral druglikeness without toxic effect. Therefore, it can be concluded that both 7b and 7a can be used as effective lead molecules for the development of HPA and HLAG inhibitors for the management of T2DM.

Diastereoselective synthesis of atropisomeric pyrazolyl pyrrolo[3,4-d]isoxazolidines via pyrazolyl nitrone cycloaddition to facially divergent maleimides: intensive NMR and DFT studies

A pyrazolyl nitrone (2) underwent 1,3-dipolar cycloadditions to afford some N-substituted maleimides (3a-o). An atropisomeric character was introduced into the formed cycloadducts by using maleimides that have a restricted rotation around the C-N bond. Also, facial selectivity of both endo and exo cycloaddition was observed where the major atropisomer was one that is formed by attacking the nitrone from the less hindered face of the dipolarophile. On the other hand, maleimides with free rotation around the C-N bond led to endo and exo cycloadducts without atropisomerism. The presence of atropisomerism in the formed cycloadducts was confirmed by extensive NMR studies and DFT calculations.

Characterization of a Citrulline 4-Hydroxylase from Nonribosomal Peptide GE81112 Biosynthesis and Engineering of Its Substrate Specificity for the Chemoenzymatic Synthesis of Enduracididine

The GE81112 tetrapeptides are a small family of unusual nonribosomal peptide congeners with potent inhibitory activity against prokaryotic translation initiation. With the exception of the 3-hydroxy-l-pipecolic acid unit, little is known about the biosynthetic origins of the non-proteinogenic amino acid monomers of the natural product family. Here, we elucidate the biogenesis of the 4-hydroxy-l-citrulline unit and establish the role of an iron- and α-ketoglutarate-dependent enzyme (Fe/αKG) in the pathway. Homology modelling and sequence alignment analysis further facilitate the rational engineering of this enzyme to become a specific 4-arginine hydroxylase. We subsequently demonstrate the utility of this engineered enzyme in the synthesis of a dipeptide fragment of the antibiotic enduracidin. This work highlights the value of applying a bioinformatics-guided approach in the discovery of novel enzymes and engineering of new catalytic activity into existing ones.

Isoxazolidine: A Privileged Scaffold for Organic and Medicinal Chemistry

The isoxazolidine ring represents one of the privileged structures in medicinal chemistry, and there have been an increasing number of studies on isoxazolidine and isoxazolidine-containing compounds. Optimization of the 1,3-dipolar cycloaddition (1,3-DC), original methods including electrophilic or palladium-mediated cyclization of unsaturated hydroxylamine, has been developed to obtain isoxazolidines. Novel reactions involving the isoxazolidine ring have been highlighted to accomplish total synthesis or to obtain bioactive compounds, one of the most significant examples being probably the thermic ring contraction applied to the total synthesis of (±)-Gelsemoxonine. The unique isoxazolidine scaffold also exhibits an impressive potential as a mimic of nucleosides, carbohydrates, PNA, amino acids, and steroid analogs. This review aims to be a comprehensive and general summary of the different isoxazolidine syntheses, their use as starting building blocks for the preparation of natural compounds, and their main biological activities.

Versatile Scope of a Masked Aldehyde Nitrone in 1,3-Dipolar Cycloadditions

A new masked aldehyde-containing nitrone 1 that is easily available through a facile one-step procedure has been developed. It undergoes a [3 + 2]-thermal cycloaddition with a wide range of dipolarophiles, affording isoxazolidine cycloadducts that are suitable for versatile postcycloaddition modifications. The acetal cycloadducts are acid-stable, but allow for acetal hydrolysis under mildly basic conditions. The isoxazolidine ring can be opened via an efficient one-pot procedure to give amine-protected γ-alcohols that can be further converted to furanose derivatives.