Stereocontrolled disruption of the Ugi reaction toward the production of chiral piperazinones: substrate scope and process development

Reactivity and Synthetic Applications of Multicomponent Petasis Reactions

The Petasis boron-Mannich reaction, simply referred to as the Petasis reaction, is a powerful multicomponent coupling reaction of a boronic acid, an amine, and a carbonyl derivative. Highly functionalized amines with multiple stereogenic centers can be efficiently accessed via the Petasis reaction with high levels of both diastereoselectivity and enantioselectivity. By drawing attention to examples reported in the past 8 years, this Review demonstrates the breadth of the reactivity and synthetic applications of Petasis reactions in several frontiers: the expansion of the substrate scope in the classic three-component process; nonclassic Petasis reactions with additional components; Petasis-type reactions with noncanonical substrates, mechanism, and products; new asymmetric versions assisted by chiral catalysts; combinations with a secondary or tertiary transformation in a cascade- or sequence-specific manner to access structurally complex, natural-product-like heterocycles; and the synthesis of polyhydroxy alkaloids and biologically interesting molecules.

α-Amino Acids as Synthons in the Ugi-5-Centers-4-Components Reaction: Chemistry and Applications

Since the first reports, the Ugi four-component reaction (U-4CR) has been recognized as a keystone transformation enabling the synthesis of peptide mimetics in a single step and with high atom economy. In recent decades, the U-4CR has been a source of inspiration for many chemists fascinated by the possibility of identifying new efficient organic reactions by simply changing one of the components or by coupling in tandem the multicomponent process with a huge variety of organic transformations. Herein we review the synthetic potentialities, the boundaries, and the applications of the U-4CR involving α-amino acids, where the presence of two functional groups—the amino and the carboxylic acids—allowed a 5-center 4-component Ugi-like reaction, a powerful tool to gain access to drug-like multi-functionalized scaffolds.

Stereoselective Multicomponent Reactions in the Synthesis or Transformations of Epoxides and Aziridines

Small ring heterocycles, such as epoxides and aziridines, are present in several natural products and are also highly versatile building blocks, frequently involved in the synthesis of numerous bioactive products and pharmaceuticals. Because of the potential for increased efficiency and selectivity, along with the advantages of environmentally benign synthetic procedures, multicomponent reactions (MCRs) have been explored in the synthesis and ring opening of these heterocyclic units. In this review, the recent advances in MCRs involving the synthesis and applications of epoxides and aziridines to the preparation of other heterocycles are discussed emphasizing the stereoselectivity of the reactions.

Solid-phase synthesis, cyclization, and site-specific functionalization of aziridine-containing tetrapeptides

Cyclic tetrapeptides comprise a potent and selective class of molecules with a wide range of biological activities, including the phytotoxic activity of tentoxin and the histone deacetylase (HDAC) inhibitory effects of chlamydocin. The incorporation of a functional aziridine group within cyclic peptides enables their conformational control and allows for late-stage and site-selective functionalization of these molecules, thereby creating the potential for covalent protein labeling. This protocol describes the solid-phase synthesis, cyclization, and site-specific structural modification of aziridine-containing tetrapeptides. The linear precursors are assembled by solid-phase peptide synthesis using Fmoc-protected amino acid building blocks, followed by head-to-tail peptide cyclization. Cyclization is performed using a slow reverse-addition method that prevents the formation of undesired higher-order cyclo-oligomeric side products. Site-specific structural modification of the resulting macrocycles is described using sodium azide or thiophenol as representative examples. It requires ∼4 d to prepare peptide macrocycles from their respective Fmoc-protected amino acid starting materials, an improvement upon the 3 weeks required for conventional solution-phase methods. This protocol also addresses important considerations regarding the handling of these compounds, whose electrophilic aziridine functionalities can otherwise be prone to undesired side reactions. With recent developments in aziridine-containing macrocyclic peptide synthesis and the potential for covalent protein labeling, these scaffolds represent a valuable addition to many screening libraries, and we expect that access to these macrocycles will facilitate efforts in drug discovery and molecular probe development.

Synthesis of Chiral Piperazinones Using Amphoteric Aziridine Aldehyde Dimers and Functionalized Isocyanides

We have evaluated a range of functionalized isocyanides in the aziridine aldehyde-driven multicomponent synthesis of piperazinones. High diasteroselectivity for each isocyanide was observed. A theoretical evaluation of the reaction course corroborates the experimental data. Moreover, the reactivity of cis- and trans-configured aziridine aldehyde dimers has been compared. This study further probes the dimer-driven mechanism of cyclization and enables an efficient access to a wide range of chiral piperazinones bearing functionalized side chains.

Mechanistic investigation of aziridine aldehyde-driven peptide macrocyclization: the imidoanhydride pathway

Aziridine aldehydes participate in a multicomponent reaction with α-amino amides and isocyanides to generate reactive imidoanhydride intermediates.

Aziridine aldehyde dimers, peptides, and isocyanides participate in a multicomponent reaction to yield peptide macrocycles. We have investigated the selectivity and kinetics of this process and performed a detailed analysis of its chemoselectivity. While the reactants encompass all of the elements of the traditional Ugi four-component condensation, there is a significant deviation from the previously proposed mechanism. Our results provide evidence for an imidoanhydride pathway in peptide macrocyclization and lend justification for the diastereoselectivity and high effective molarity observed in the reaction.

Solid-Phase Parallel Synthesis of Functionalised Medium-to-Large Cyclic Peptidomimetics through Three-Component Coupling Driven by Aziridine Aldehyde Dimers

The first solid-phase parallel synthesis of macrocyclic peptides using three-component coupling driven by aziridine aldehyde dimers is described. The method supports the synthesis of 9- to 18-membered aziridine-containing macrocycles, which are then functionalized by nucleophilic opening of the aziridine ring. This constitutes a robust approach for the rapid parallel synthesis of macrocyclic peptides.

Efficient isocyanide-less isocyanide-based multicomponent reactions

Isocyanides are the "Jekyll and Hyde" of organic chemistry allowing for extremely interesting transformations that are not only extremely odorous but also noxious. Therefore, an isocyanide-less isocyanide-based multicomponent reaction (IMCR) has been developed, and this protocol is expected to replace many of the old procedures in the future not only in IMCR but in other areas of organic chemistry as well.

Stereoselective synthesis of functionalized 1,2,3,4-tetrahydroisoquinolines (THIQs) via highly diastereoselective Ugi three-component reactions (U3CRs) with chiral 3,4-dihydroisoquinolines (DHIQs)

A highly diastereoselective Ugi three-component reaction (U3CR) of chiral 3,4-dihydroisoquinolines has been developed to synthesize enantiopure 1,2,3,4-tetrahydroisoquinolines (THIQs).