Studies on the chemistry and reactivity of alpha-substituted ketones in isonitrile-based multicomponent reactions

Ammonium carboxylates in the ammonia-Ugi reaction: one-pot synthesis of α,α-disubstituted amino acid derivatives including unnatural dipeptides

Despite the remarkable developments of the Ugi reaction and its variants, the use of ammonia in the Ugi reaction has long been recognized as impractical and unsuccessful. Indeed, the ammonia-Ugi reaction often requires harsh reaction conditions, such as heating and microwave irradiation, and competes with the Passerini reaction, thereby resulting in low yields. This study describes a robust and practical ammonia-Ugi reaction protocol. Using originally prepared ammonium carboxylates in trifluoroethanol, the ammonia-Ugi reaction proceeded at room temperature in high yields and showed a broad substrate scope, thus synthesizing a variety of α,α-disubstituted amino acid derivatives, including unnatural dipeptides. The reaction required no condensing agents and proceeded without racemization of the chiral stereocenter of α-amino acids. Furthermore, using this protocol, we quickly synthesized a novel dipeptide, D-Leu-Aic-NH-CH2Ph(p-F), which exhibited a potent inhibitory activity against α-chymotrypsin with a Ki value of 0.091 μM.

Two decades of recent advances of Passerini reactions: synthetic and potential pharmaceutical applications

This perspective describes the applications of Passerini reactions in the last two decades from 2000 to 2021 in pharmaceutical applications and synthesis of peptides, natural products, macrocycles, dendrimers, and versatile types of heterocycles.

Chemoselective Hydro(Chloro)pentafluorosulfanylation of Diazo Compounds with Pentafluorosulfanyl Chloride

Pentafluorosulfanyl chloride (SF₅ Cl) is the most prevalent reagent for the incorporation of SF₅ group into organic compounds. However, the preparation of SF₅ Cl often relies on hazardous reagents and specialized apparatus. Herein, we described a safe and practical synthesis of a bench-stable and easy-to-handle solution of SF₅ Cl in n-hexane under gas-reagent-free conditions. The synthetic application of SF₅ Cl was demonstrated through the unprecedented reaction with diazo compounds. The chemoselective hydro- and chloropentafluorosulfanylations of α-diazo carbonyl compounds were developed in the presence of K₃ PO₄ or copper catalyst, respectively. These reactions provide a direct and efficient access to various α-pentafluorosulfanyl carbonyl compounds of high value for potential applications.

Synthesis of Lactams via Isocyanide-Based Multicomponent Reactions

Lactams are very important heterocycles as a result of their presence in a wide range of bioactive molecules, natural products and drugs, and also due their utility as versatile synthetic intermediates. Due to these reasons, numerous efforts have focused on the development of effective and efficient methods for their synthesis. Compared to conventional two-component reactions, multicomponent reactions (MCRs), particularly isocyanide-based MCRs, are widely used for the synthesis of a range of small heterocycles including lactam analogues. Despite their numerous applications in almost every field of chemistry, as yet there is no dedicated review on isocyanide-based multicomponent reactions (IMCRs) concerning the synthesis of lactams. Therefore, this review presents strategies towards the synthesis of α-, β-, γ-, δ- and ε-lactams using IMCRs or IMCRs/post-transformation reactions reported in the literature between 2000 and 2020.

1 Introduction

2 Developments in Lactam Synthesis

2.1 α-Lactams

2.2 β-Lactams

2.3 γ-Lactams

2.3.1 General γ-Lactams

2.3.2 Benzo-Fused γ-Lactams

2.3.3 Spiro γ-Lactams

2.3.4 α,β-Unsaturated γ-Lactams

2.3.5 Polycyclic Fused γ-Lactams

2.4 δ-Lactams

2.5 ε-Lactams

3 Conclusions

First in vivo evaluation of a potential SPECT brain radiotracer for the gonadotropin releasing hormone receptor

OBJECTIVES

In vivo evaluations of a gonadotropin releasing hormone-receptor single photon emission computed tomography radiotracer for non-invasive detection of gonadotropin releasing homone-receptors in brain.

RESULTS

We have used a simple, robust and high-yielding procedure to radiolabel an alpha-halogenated bioactive compound with high radiochemical yield. Literature findings showed similar alpha-halogenated compounds suitable for in vivo evaluations. The compound was found to possess nano molar affinity for the gonadotropin releasing hormone-receptor in a competition dependent inhibition study. Furthermore, liquid chromatography-mass spectrometry analysis in saline, human and rat serum resulted in 46%, 52% and 44% stability after incubation for 1 h respectively. In addition, rat brain single photon emission computed tomography and biodistribution studies gave further insight into the nature of the compound as a radiotracer.

Microwave-assisted facile construction of quinoxalinone and benzimidazopyrazinone derivatives via two paths of post-Ugi cascade reaction

A facile and efficient route to synthesize quinoxalinone and benzimidazopyrazinone was developed via two paths of a post-Ugi cascade reaction. By simply alternating the order of nucleophilic substitution reactions, both heterocycles could be accessed selectively from the same Ugi adduct. Microwave-assisted synthesis protocol provided these compounds with one purification procedure for three steps. These two scaffolds with more possible spaces for further modifications provide great benefit toward combinatorial and medicinal chemistry campaigns.

Multicomponent Cascade Reactions of Unprotected Ketoses and Amino Acids--Access to a Defined Configured Quaternary Stereogenic Center

A highly stereoselective multicomponent cascade reaction of ketones with unprotected amino acids was developed. This operationally simple methodology was expanded to reactions of unprotected ketohexoses and unprotected amino acids. By the careful choice of amino acid and isonitrile, an optional access to all possible enantiomers is given.

Efficient Syntheses of Star-Branched, Multifunctional Mesogens

Star-branched molecular architectures lend themselves to convergent synthesis strategies for creating materials that combine three or more functional modalities, but these approaches require a core moiety with several reactive groups that are orthogonal to one another. The direct synthesis of three-arm, star-branched mesogens has been investigated via the Passerini three-component reaction to demonstrate how multicomponent reactions circumvent the need to identify and synthesize specialized branched core molecules.

Chiral surfactant-type catalyst: enantioselective reduction of long-chain aliphatic ketoesters in water

A series of amphiphilic ligands were designed and synthesized. The rhodium complexes with the ligands were applied to the asymmetric transfer hydrogenation of broad range of long-chained aliphatic ketoesters in neat water. Quantitative conversion and excellent enantioselectivity (up to 99% ee) was observed for α-, β-, γ-, δ- and ε-ketoesters as well as for α- and β-acyloxyketone using chiral surfactant-type catalyst 2. The CH/π interaction and the strong hydrophobic interaction of long aliphatic chains between the catalyst and the substrate in the metallomicelle core played a key role in the catalytic transition state. Synergistic effects between the metal-catalyzed site and the hydrophobic microenvironment of the core in the micelle contributed to high stereoselectivity.

Enhanced reactivity of dendrons in the Passerini three-component reaction

An unexpected substituent effect that accelerates Passerini reactions in THF has enabled the synthesis of three generations of dendrimers.