Probing the Mechanism of Allylic Substitution of Morita–Baylis–Hillman Acetates (MBHAs) by using the Silyl Phosphonite Paradigm: Scope and Applications of a Versatile Transformation

Regioconvergent Nucleophilic Substitutions with Morita-Baylis-Hillman Fluorides

Lithium iodide enables regioconvergent C-F bond functionalization of isomeric Morita-Baylis-Hillman fluorides with carbon, sulfur, and nitrogen nucleophiles. The defluorinative carbon-carbon and carbon-heteroatom bond formations give multifunctional compounds in excellent yields and with good to high diastereoselectivities at room temperature. The possibility of catalytic enantioselective allylation is also discussed.

Phosphinic Peptides as Tool Compounds for the Study of Pharmacologically Relevant Zn-Metalloproteases

Phosphinic peptides constitute an important class of bioactive compounds that have found a wide range of applications in the field of biology and pharmacology of Zn-metalloproteases, the largest family of proteases in humans. They are designed to mimic the structure of natural substrates during their proteolysis, thus acting as mechanism-based, transition state analogue inhibitors. A combination of electrostatic interactions between the phosphinic acid group and the Zn cation as well as optimal noncovalent enzyme-ligand interactions can result in both high binding affinity for the desired target and selectivity against other proteases. Due to these unique properties, phosphinic peptides have been mainly employed as tool compounds for (a) the purposes of rational drug design by serving as ligands in X-ray crystal structures of target enzymes and allowing the identification of crucial interactions that govern optimal molecular recognition, and (b) the delineation of biological pathways where Zn-metalloproteases are key regulators. For the latter objective, inhibitors of the phosphinopeptidic type have been used either unmodified or after being transformed to probes of various types, thus expanding the arsenal of functional tools available to researchers. The aim of this review is to summarize all recent research achievements in which phosphinic peptides have played a central role as tool compounds in the understanding of the mechanism and biological functions of Zn-metalloproteases in both health and disease.

Design, Synthesis, and Study of a Novel - Hybrid () as an Antihypertensive Agent

In drug discovery, molecular modification over the lead molecule is often crucial for the development of a drug. Herein, we report the molecular hybridization design of a novel RXPA380-proline hybrid via linking the parent compound, phosphinic peptide RXPA380, with a proline analogue. The presented synthetic route is straightforward and produces the desired product RXPA380-P in moderate yield. The C- and N-domain constructs of the angiotensin-converting enzyme of RXPA380-P appeared to be poor inhibitors of ACE as compared to the parent compound RXPA380.

Magnesium catalyzed [3 + 3] heteroannulation of α-enolic dithioesters with MBH acetate: access to functionalized 3,4-dihydro-2H-thiopyrans

Magnesium catalysis proved to be efficient towards [3 + 3] chemo- and diastereoselective heteroannulation employing racemic Morita-Baylis-Hillman (MBH) acetate as the C3 unit and α-enolic dithioester as the C2S1 unit, leading to highly substituted 3,4-dihydro-2H-thiopyrans in excellent yields. The compatibility with a wide range of functional groups makes this domino formation of C-C and C-S bonds interesting. DFT analyses for the regioselective formation of the intermediate was performed.

The endo-aza-Michael addition in the synthesis of piperidines and pyrrolidines

Intramolecular endo-aza-Michael additions are categorised in various ways.

Late-Stage Diversification of Phosphinic Dehydroalanine Pseudopeptides Based on a Giese-Type Radical C-Alkylation Strategy

A straightforward, late-stage diversification strategy for the installation of side chains on readily accessible unsaturated phosphinopeptidic scaffolds based on a Giese-type addition of alkyl radicals has been investigated. Among different alternatives, the preferred methodology is operationally simple as it can be carried out in an open flask with no need for protection of acidic moieties. Direct application to the synthesis of SPPS-compatible building blocks or to longer peptides is also reported.

Recent developments in the synthesis and applications of phosphinic peptide analogs

Synthetic pseudopeptides that fit well with the active site architecture allow the most effective binding to enzymes, similar to native substrates in high-energy transition states. Phosphinic acid peptide analogs that comprise the tetrahedral phosphorus moiety introduced to replace an internal amide bond exert such an isosteric or isoelectronic resemblance, combined with providing other advantageous features, for example, metal complexing properties. Accordingly, they are capable of inhibiting metal-dependent enzymes involved in biological functions in eukaryotic and prokaryotic cells. These enzymes are associated with notorious human diseases, such as cancer, e.g., matrix metalloproteinases, or are etiological factors of protozoal and bacterial infections, e.g., metalloaminopeptidases. The affinity and selectivity of these compounds can be conveniently adjusted, either by structural modification of dedicated side chains or by backbone elongation to enhance specific interactions with the corresponding binding pockets. Recent approaches to the synthesis of these compounds are illustrated by examples of the preparation of rationally designed structures of inhibitors of particular enzymes. Activity against appealing enzymatic targets is presented, along with the molecular mechanisms of action and therapeutic implications. Innovative aspects of phosphinic peptide application, e.g., as activity-based probes, and ligands of complexes of radioisotopes for nuclear medicine are also outlined.

Enantioselective Michael Reaction of Cyclic β-Ketoesters with Morita-Baylis-Hillman Derivatives Using a Phase-Transfer Catalyst

This study aims to develop a highly enantioselective Michael reaction of cyclic β-ketoesters with Morita-Baylis-Hillman (MBH) derivatives using a phase-transfer catalyst. Cyclic β-ketoesters reacted with MBH derivatives to stereoselectively generate a quaternary carbon center in the presence of cinchona alkaloid-derived bulky ammonium catalyst, and aqueous KOH and Michael adducts bearing an acrylate moiety were obtained in good chemical yields with good enantioselectivity.

Organocatalyzed Decarboxylative Trichloromethylation of Morita-Baylis-Hillman Adducts in Batch and Continuous Flow

Two protocols for the organocatalyzed decarboxylative trichloromethylation of Morita-Baylis-Hillman (MBH) substrates have been developed. Applying sodium trichloroacetate, as the trichloromethyl anion precursor, in combination with an organocatalyst and acetylated MBH-alcohols, the desired trichloromethylated products were obtained in good yields at room temperature in batch. The method was next extrapolated into a two-step continuous flow protocol, starting directly from the MBH alcohols, in combination with tributylamine acting both as base and catalyst. The flow process proved superior to the batch approach, reducing the reaction time from 16 hours to only 20 minutes, with increased yields for all investigated entries. Two examples were also taken to scale-up in flow producing more than 10 grams of both trichloromethylated targets. Finally, substitution of the organocatalyst to (DHQ)₂ PHAL or (DHQD)₂ PHAL induced chiral transfer to the generated stereocenter in the reaction attaining selectivities with nearly 90 % ee.