N-Hydroxysuccinimide esters (NHS-esters) are important and widely used tools in various areas of chemistry including peptide synthesis, bioconjugate chemistry, functionalized materials and polymers. The usual strategy employed to prepare these active esters generally relies on the coupling reaction with a carboxylic acid and N-hydroxysuccinimide in the presence of a coupling agent. However, more recently, many other efficient strategies have emerged in the literature. This short review covers the literature devoted to the preparation of these valuable N-hydroxysuccinimide esters. 1 Introduction 2 N-Hydroxysuccinimide Coupling Reaction with Activated Carboxylic Acids 3 Carboxylic Acid Coupling Reaction with Activated N-Hydroxysuccinimide 4 Alcohol and Aldehyde Coupling Reaction with N-Hydroxysuccinimide under Oxidizing Conditions 5 Carbonylative Cross-Coupling Reaction 6 Conclusion

A solid phase approach for the preparation of peptides attached to a redox chemical delivery system derived from stable annulated NADH models is reported. The synthesis starts with the grafting on a Merrifield resin of quinoline 4b, precursor of the redox carrier. From the resulting quinoline supported resin 4d, the stepwise SPPS of both octapeptide OP (RPGLLDLK) and octadecaneuropeptide ODN (QATVGDVNTDRPGLLDLK), two neuropeptides exhibiting anorexigenic effects, was successfully achieved by conventional methods. Quaternization of the quinoline moiety prior to cleavage of the modified OP and ODN peptides from the resin, led to the expected quinolinium salt 8a and 8b respectively linked to OP or ODN peptides. Finally, the reduction with NaBH₄ monitored by UV–vis, provided the desired annulated NADH models as peptides carriers with either the OP (11a,b) or ODN (12a,b) moiety.

Despite their side effects, cholinesterase (ChE) inhibitors remain the only approved drugs to treat Alzheimer’s disease patients, along with the N-methyl-d-aspartate (NMDA) receptor antagonist memantine. In the last few years, the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) has also been studied as a promising target for the development of new drugs for this pathology. In this context, and based on our previous characterization of bio-oxidizable prodrugs of potent acetylcholinesterase (AChE) inhibitors, we envisioned a strategy involving the synthesis of a bio-oxidizable prodrug of both ChE and DYRK1A inhibitors. To this end, we fixed our interest on a known potent inhibitor of DYRK1A, namely INDY. The designed prodrug of both ChE and DYRK1A inhibitors was successfully synthesized, connecting both inhibitors by a carbonate link. This prodrug and its corresponding drug were then evaluated as ChEs and DYRK1A inhibitors. Remarkably, in vitro results were in accordance with the starting hypothesis, showing a relative inactivity of the prodrug against DYRK1A and ChEs and a potent inhibition of ChEs by the oxidized form. Molecular docking and kinetic studies of ChE inhibition by the active compound are also discussed in this report.

The DYRK (Dual-specificity tyrosine phosphorylation-regulated kinase) family of protein kinases is involved in the pathogenesis of several neurodegenerative diseases. Among them, the DYRK1A protein kinase is thought to be implicated in Alzheimer’s disease (AD) and Down syndrome, and as such, has emerged as an appealing therapeutic target. DYRKs are a subset of the CMGC (CDK, MAPKK, GSK3 and CLK) group of kinases. Within this group of kinases, the CDC2-like kinases (CLKs), such as CLK1, are closely related to DYRKs and have also sparked great interest as potential therapeutic targets for AD. Based on inhibitors previously described in the literature (namely TG003 and INDY), we report in this work a new class of dihydroquinolines exhibiting inhibitory activities in the nanomolar range on hDYRK1A and hCLK1. Moreover, there is overwhelming evidence that oxidative stress plays an important role in AD. Pleasingly, the most potent dual kinase inhibitor 1p exhibited antioxidant and radical scavenging properties. Finally, drug-likeness and molecular docking studies of this new class of DYRK1A/CLK1 inhibitors are also discussed in this article.

The stereoselective preparation of 1,4-dihydroquinolines possessing a chiral sulfoxide group at C-3 is reported. These novel biomimetic NADH models (R)-1a,b have been shown to be highly enantioselective in the reduction of methyl benzoylformate, producing (R)-methyl mandelate in up to 95% ee. The corresponding quinolinium salts 4a,b have been recovered in good yields. The regenerated models 1a,b could be reused without any significant erosion of the enantioselectivity.