Regioselective Pyridine to Benzene Edit Inspired by Water-Displacement

Late-stage derivatization of drug-like functional groups can accelerate drug discovery efforts by swiftly exchanging hydrogen-bond donors with acceptors, or by modulating key physicochemical properties like logP, solubility, or polar surface area. A proven derivatization strategy to improve ligand potency is to extend the ligand to displace water molecules that are mediating the interactions with a receptor. Inspired by this application, we developed a method to regioselectively transmute the nitrogen atom from pyridine into carbon bearing an ester, a flexible functional group handle. We applied this method to a variety of substituted pyridines, as well as late-stage transformation of FDA-approved drugs.

Evolution in non-peptide α-helix mimetics on the road to effective protein-protein interaction modulators

Modulation of interactome networks, essentially protein-protein interactions (PPIs), might represent valuable therapeutic approaches to different pathological conditions. Since a high percentage of PPIs are mediated by α-helical structures at the interacting surface, the development of compounds able to reproduce the amino acid side-chain organization of α-helices (e.g. stabilized α-helix peptides and β-derivatives, proteomimetics, and α-helix small-molecule mimetics) focuses the attention of different research groups. This appraisal describes the recent progress in the non-peptide α-helix mimetics field, which has evolved from single-face to multi-face reproducing compounds and from oligomeric to monomeric scaffolds able to bear different substituents in similar spatial dispositions as the side-chains in canonical helices. Grouped by chemical structures, the review contemplates terphenyl-like molecules, oligobenzamides and heterocyclic analogues, benzamide-amino acid conjugates and non-oligomeric small-molecules mimetics, among others, and their effectiveness to stabilize/disrupt therapeutically relevant PPIs. The X-ray structures of a couple of oligomeric peptidomimetics and of some small-molecules complexed with the MDM2 protein, as well as the state of the art on their development in clinical trials, are also remarked. The discovery of a continuously increasing number of new disease-relevant PPIs could offer future opportunities for these and other forthcoming α-helix mimetics.

Conformational preference of bicyclic β-amino acid dipeptides

Bridged bicyclic amino acids have high potential applicability as self-organized, conformationally constrained synthetic building blocks that do not require assistance from hydrogen bond formation. We systematically investigated the intrinsic conformational propensities of dipeptides of bridged bicyclic β-amino acids by means of accelerated molecular dynamics simulation and density functional theory (DFT) calculations in methanol, chloroform, and water. While the main-chain conformation, represented by φ and θ values, is fixed by the nature of the bicyclic ring structure, rotation of the C-terminal carbonyl group (ψ) is also restricted, converging to one or two minima. In endo-type dipeptides, in which the two N- and C-terminal amides are spatially close to each other, the C-terminal amide plane is placed horizontally. In exo-type dipeptides, in which the two amides are on opposite sides of the ring plane, the C-terminal carbonyl group can take two types of positions: either parallel/antiparallel with the N-terminal carbonyl or beneath the bicyclic ring, forcing the amide NHMe moiety to lie outside of the ring. We also examined the cis-trans preference of model bicyclic amides. Although the parent amides exhibit cis-trans equilibrium without any preference, addition of a methyl group on one of the bridgehead positions tips the equilibrium towards trans.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Design, Synthesis, and Conformational Analysis of Oligobenzanilides as Multifacial α-Helix Mimetics

The design, synthesis, and conformational analysis of an oligobenzanilide helix mimetic scaffold capable of simultaneous mimicry of two faces of an α-helix is reported. The synthetic methodology provides access to diverse monomer building blocks amenable to solid-phase assembly in just four synthetic steps. The conformational flexibility of model dimers was investigated using a combination of solid and solution state methodologies supplemented with DFT calculations. The lack of noncovalent constraints allows for significant conformational plasticity in the scaffold, thus permitting it to successfully mimic residues i, i+2, i+4, i+6, i+7, and i+9 of a canonical α-helix.

Multi-Facial, Non-Peptidic α-Helix Mimetics

α-Helices often recognize their target proteins at protein–protein interfaces through more than one recognition face. This review describes the state-of-the-art in the design of non-peptidic α-helix mimetics that reproduce functionality from multiple faces of an α-helix.

Total synthesis of (+)-gelsemine via an organocatalytic Diels-Alder approach

The structurally complex alkaloid gelsemine was previously thought to have no significant biological activities, but a recent study has shown that it has potent and specific antinociception in chronic pain. While this molecule has attracted significant interests from the synthetic community, an efficient synthetic strategy is still the goal of many synthetic chemists. Here we report the asymmetric total synthesis of (+)-gelsemine, including a highly diastereoselective and enantioselective organocatalytic Diels–Alder reaction, an efficient intramolecular trans-annular aldol condensation furnishing the prolidine ring and establishing the configuration of the C20 quaternary carbon stereochemical centre. The entire gelsemine skeleton was constructed through a late-stage intramolecular S_N2 substitution. The enantiomeric excess of this total synthesis is over 99%, and the overall yield is around 5%.

Gelsamine is a naturally occurring alkaloid, whose complex structure makes it an interesting target for total synthesis. Here, the authors report an enantioselective synthesis of (+)-Gelsemine in 5% overall yield, with an enantioselective organocatalytic Diels–Alder reaction as one of the key steps.

α-Helix mimetics: outwards and upwards

α-Helices are common secondary structural elements forming key parts of the large, generally featureless interfacial regions of many therapeutically-relevant protein-protein interactions (PPIs). The rational design of helix mimetics is an appealing small-molecule strategy for the mediation of aberrant PPIs, however the first generation of scaffolds presented a relatively small number of residues on a single recognition surface. Increasingly, helices involved in PPIs are found to have more complex binding modes, utilizing two or three recognition surfaces, or binding with extended points of contact. To address these unmet needs the design and synthesis of new generations of multi-sided, extended, and supersecondary structures are underway.