A Continuous‐Flow Route to Enantioenriched 3‐Substituted‐3‐Hydroxyoxindoles: Organocatalytic Aldol Reactions of Isatin with Acetone

3-Hydroxy-3-(2-oxopropyl)indolin-2-one, a product of a human-derived Enterocloster strain, is an inhibitor of nitric oxide production

When cultured anaerobically, Enterocloster sp. RD014215 was found to produce 1. Using nuclear magnetic resonance and mass spectroscopy, the planar structure of 1 was determined to be 3-hydroxy-3-(2-oxopropyl)indolin-2-one. The chirality of 1 was implied as S by comparing the optical rotation value of 1 with literature reports of the synthesized compounds. To our knowledge, this work represents the first discovery of the metabolite produced by Enterocloster strain. 1 exhibited inhibition of nitric oxide (NO) production, demonstrating a 50% inhibitory activity (IC50) of 34 µm for NO production by murine macrophage cells subjected to lipopolysaccharide stimulation.

Highly asymmetric aldol reaction of isatins and ketones catalyzed by chiral bifunctional primary-amine organocatalyst on water

Herein, we have reported an environmentally friendly asymmetric aldol reaction between isatins and ketones catalyzed by double-hydrogen-bonded primary amine organocatalysts on water under mild conditions. Enantioenriched 3-hydroxy-2-oxindoles were obtained in high yields (up to 99%) and excellent stereoselectivities (up to 99 : 1 dr and 99% ee) under optimal conditions. Furthermore, the model reaction involving isatin and cyclohexanone was successfully scaled to 10 mmol with no reduction in yield or stereoselectivity. In addition, the catalyst was recovered via simple filtration and was subsequently reused on water, which highlights its good application potential.

The synthesis of pharmacologically important oxindoles via the asymmetric aldol reaction of isatin and the investigation of the organocatalytic activity of new alicyclic β-amino acid derivatives

This work involves the synthesis and subsequent development of a number of novel organocatalysts generated from β-amino acids bearing diendo and diexo norbornene skeletons to improve their catalytic characteristics. The aldol reaction between isatin and acetone selected as the model reaction, was used to test and study enantioselectivities. The potential impact on enantioselectivity control regarding enantiomeric excess (ee%) was probed by varying the reaction parameters, such as additive, solvent, catalyst loading, temperature and substrate range. The corresponding 3-hydroxy-3-alkyl-2-oxindole derivetives were produced by organocatalyst 7 with good enantioselectivity up to 57% ee in the presence of LiOH. Substrate screening was used to investigate a number of substituted isatins with excellent findings up to 99% ee. Another aspect of this effort involved employing high-speed ball mill apparatus to conduct a mechanochemical study to make this model reaction more environmentally benign and sustainable.