Synthesis of Succinimides via Intramolecular Alder-Ene Reaction of 1,6-Enynes

A novel and convenient method has been developed for the facile synthesis of functionalized succinimide derivatives via intramolecular Alder-ene reaction of 1,6-enynes. This reaction features mild and metal-free reaction conditions, which offers a green and efficient entry to synthetically important succinimide scaffolds. Preliminary mechanistic studies suggest that a diradical intermediate might be involved in this transformation.

One-pot construction of functionalized aziridines and maleimides via a novel pseudo-Knoevenagel cascade reaction

An Ugi, novel pseudo-Knoevenagel, ring expansion cascade reaction was discovered and utilized for the synthesis of aziridinyl succinimides in one-pot. Subsequently, densely functionalized aziridines and maleimides have been designed and synthesized through similar cascade reactions. The target compounds were prepared by means of a mild reaction and a simple operation procedure, which could be applicable to a broad scope of starting materials. This series of novel cascade reactions generates opportunities for the tailored synthesis of a wide range of biologically active scaffolds through tuneable Ugi inputs. Discovery of compound 8i with comparable potency to sorafenib in liver cancer cell lines could provide a new avenue for liver cancer drug discovery.

An organocatalyzed Stetter reaction as a bio-inspired tool for the synthesis of nucleic acid-based bioconjugates

An N-Heterocyclic Carbene (NHC) catalyzed biomimetic Stetter reaction was applied for the first time as a bioconjugation reaction to sensitive nucleoside-type biomolecules to provide original pyrrole linked nucleolipids. A versatile approach allowed the functionalization of thymidine at the three reactive positions (O-5', O-3' and N-3) providing a structural diversity oriented synthesis. This strategy was applied to the synthesis of an original glyconucleolipid amphiphile in the hope that the pyrrole aromatic moiety would induce additional self-assembling properties.

Synthetic Approaches toward Monocyclic 3-Amino-β-lactams

Due to the emerging resistance against classical β-lactam-based antibiotics, a growing number of bacterial infections has become harder to treat. This alarming tendency necessitates continued research on novel antibacterial agents. Many classes of β-lactam antibiotics are characterized by the presence of the 3-aminoazetidin-2-one core, which resembles the natural substrate of the target penicillin-binding proteins. In that respect, this Review summarizes the different synthetic pathways toward this key structure for the development of new antibacterial agents. The most extensively applied methods for 3-amino-β-lactam ring formation are discussed, in addition to a few less common strategies. Moreover, approaches to introduce the 3-amino substituent after ring formation are also covered.

Radical-mediated dehydrative preparation of cyclic imides using (NH4)2S2O8-DMSO: application to the synthesis of vernakalant

Ammonium persulfate–dimethyl sulfoxide (APS–DMSO) has been developed as an efficient and new dehydrating reagent for a convenient one-pot process for the synthesis of miscellaneous cyclic imides in high yields starting from readily available primary amines and cyclic anhydrides. A plausible radical mechanism involving DMSO has been proposed. The application of this facile one-pot imide forming process has been demonstrated for a practical synthesis of vernakalant.

Synthesis of cyclic imides from nitriles and diols using hydrogen transfer as a substrate-activating strategy

An atom-economical and versatile method for the synthesis of cyclic imides from nitriles and diols was developed. The method utilizes a Ru-catalyzed transfer-hydrogenation reaction in which the substrates, diols, and nitriles are simultaneously activated into lactones and amines in a redox-neutral manner to afford the corresponding cyclic imides with evolution of H2 gas as the sole byproduct. This operationally simple and catalytic synthetic method provides a sustainable and easily accessible route to cyclic imides.

NHC-catalyzed intramolecular redox amidation for the synthesis of functionalized lactams

A very efficient NHC-catalyzed lactamization reaction is reported. For most cases, the ring expansion reaction proceeds to cleanly furnish five- and six-membered N-Ts and N-Bn lactams, without the need for further purification. Evidence is presented suggesting a dual role for the stoichiometric base: (1) deprotonation of the triazolium precatalyst and (2) activation of the nitrogen leaving group through hydrogen bonding.

N-Heterocyclic Carbenes as Organic Catalysts

The synthetic utility of azolium salts as catalysts was thought to be limited to the generation of acyl anion equivalents for use in benzoin and Stetter reactions. The discovery, in 2004, of new catalysts, substrates, and reaction manifolds has ignited a new generation of reactions that fall under the general rubrik of N-heterocyclic carbene (NHC) catalyzed reactions. These powerful new processes include the catalytic generation of activated carboxylates for α-functionalized aldehydes, enantioselective annulations via catalytically generated ester enolate equivalents, and the NHC-catalyzed generation of formal homoenolate equivalents. The history of these new reactions and an overview of the reactions, their substrate scope, and mechanistic pathways are summarized in this Chapter.

Design, synthesis and evaluation of β-lactam antigenic peptide hybrids; unusual opening of the β-lactam ring in acidic media

β-Lactam peptides were envisioned as conformational constraints in antigenic peptides (APs). Three different β-lactam tripeptides of varying flexibility were prepared in solution and incorporated in place of the central part of the altered melanoma associated antigenic peptide Leu(27)-Melan-A(26-35) using solid phase synthesis techniques. Upon TFA cleavage from the solid support, an unexpected opening of the β-lactam ring occurred with conservation of the amide bond. After adaptation of the solid phase synthesis strategy, β-lactam peptides were successfully obtained and both opened and closed forms were evaluated for their capacity to bind to the antigen-presenting class-I MHC HLA-A2 protein system. None of the closed β-lactam peptides bound to HLA-A2, but their opened variants were shown to be moderate to good HLA-A2 ligands, one of them being even capable of stimulating a Melan-A-specific T cell line.

NHC-catalyzed ring expansion of oxacycloalkane-2-carboxaldehydes: a versatile synthesis of lactones

Imidazolinium-derived carbenes catalyze the ring-expansion lactonization of oxacycloalkane-2-carboxaldehydes. A variety of functionalized five-, six-, and seven-membered lactones can be formed efficiently under mild reaction conditions. The success of this new method for the construction of lactones is highly influenced by the electronic nature of the carbene catalyst.

I2-Catalyzed enantioselective ring expansion of beta-lactams to gamma-lactams through a novel C3-C4 bond cleavage. Direct entry to protected 3,4-dihydroxypyrrolidin-2-one derivatives

Molecular iodine (10 mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert-butyldimethyl cyanide to afford protected 5-cyano-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a novel C3-C4 bond cleavage of the beta-lactam nucleus.