Squaramide catalyzed enantioselective iodolactonization of allenoic acids

I2/CF3CO2Ag-mediated iodolactonization of various allenoic acids to access versatile 6- to 9-membered ring vinylic iodolactones

Medium-sized lactones are important structural units, but their synthesis remains a great challenge. Herein, we report I2/CF3CO2Ag-mediated iodolactonization of allenoic acids to synthesize various 6- to 9-membered ring vinylic iodolactones in 16-89% yield. This protocol not only develops a new cyclization strategy of allenoic acids, but also provides highly functionalized medium-sized lactones containing alkene and halogen groups.

Arylcyclopropane yet in its infancy: the challenges and recent advances in its functionalization

Electronically unbiased arylcyclopropane functionalization has always been a challenge to organic chemists, and the emergence of donor-acceptor cyclopropanes (DACs) has not only vehemently overshadowed them but still dominates the cyclopropane chemistry. Unlike DACs, the absence of pre-installed functional groups makes it harder for them to activate and participate in a reaction. The field has witnessed considerably slow progress since its inception due to the inherent challenges. There are only a few strategies available to open arylcyclopropanes. Therefore, this work is still in its infancy stage in spite of these materials being one of the earliest known type of cyclopropanes. This review manifests the history, endeavors, and achievements alongside the associated challenges, opportunities, and the need for concerted efforts to accomplish the long-awaited golden age of arylcyclopropanes.

An Overview of Synthetic Methods for the Preparation of Halolactones

Halolactones are used both in chemical synthesis as intermediates as well as in various industries. These compounds may be secondary metabolites of living organisms, although they are mainly obtained by chemical synthesis. The substrates for the synthesis of chloro-, bromo- and iodolactones are often unsaturated carboxylic acids, and sometimes they are unsaturated esters. The article presents a number of different methods for the production of halolactones, both racemic mixtures and enantiomerically enriched compounds.

Catalytic enantioselective iodolactonization reactions

The halolactonization reaction is a useful chemical transformation for the construction of lactones from γ- or δ-substituted alkenoic carboxylic acids or carboxylic esters. Traditionally, the stereoselectivity of these reactions has been controlled by the substrates or the reagents. The substrate-controlled method has been extensively studied and applied in the synthesis of many natural products. However, catalytic, enantioselective iodolactonizations of γ- or δ-substituted alkenoic carboxylic acids have only recently been developed. This review article highlights the advances that have emerged over the last decade.

Structure-Kinetic Profiling of Haloperidol Analogues at the Human Dopamine D2 Receptor

Haloperidol is a typical antipsychotic drug (APD) associated with an increased risk of extrapyramidal side effects (EPSs) and hyperprolactinemia relative to atypical APDs such as clozapine. Both drugs are dopamine D₂ receptor (D₂R) antagonists, with contrasting kinetic profiles. Haloperidol displays fast association/slow dissociation at the D₂R, whereas clozapine exhibits relatively slow association/fast dissociation. Recently, we have provided evidence that slow dissociation from the D₂R predicts hyperprolactinemia, whereas fast association predicts EPS. Unfortunately, clozapine can cause severe side effects independent of its D₂R action. Our results suggest an optimal kinetic profile for D₂R antagonist APDs that avoids EPS. To begin exploring this hypothesis, we conducted a structure-kinetic relationship study of haloperidol and revealed that subtle structural modifications dramatically change binding kinetic rate constants, affording compounds with a clozapine-like kinetic profile. Thus, optimization of these kinetic parameters may allow development of novel APDs based on the haloperidol scaffold with improved side-effect profiles.

Enantioselective Halolactonization Reactions using BINOL-Derived Bifunctional Catalysts: Methodology, Diversification, and Applications

A general protocol is described for inducing enantioselective halolactonizations of unsaturated carboxylic acids using novel bifunctional organic catalysts derived from a chiral binaphthalene scaffold. Bromo- and iodolactonization reactions of diversely substituted, unsaturated carboxylic acids proceed with high degrees of enantioselectivity, regioselectivity, and diastereoselectivity. Notably, these BINOL-derived catalysts are the first to induce the bromo- and iodolactonizations of 5-alkyl-4( Z)-olefinic acids via 5- exo mode cyclizations to give lactones in which new carbon-halogen bonds are created at a stereogenic center with high diastereo- and enantioselectivities. Iodolactonizations of 6-substituted-5( Z)-olefinic acids also occur via 6- exo cyclizations to provide δ-lactones with excellent enantioselectivities. Several notable applications of this halolactonization methodology were developed for desymmetrization, kinetic resolution, and epoxidation of Z-alkenes. The utility of these reactions is demonstrated by their application to a synthesis of precursors of the F-ring subunit of kibdelone C and to the shortest catalytic, enantioselective synthesis of (+)-disparlure reported to date.

Synthesis, Biological Investigation, and Structural Revision of Sielboldianin A

The two ar-bisabol sesquiterpenoids (+)-sielboldianin A (1) and (+)-sielboldianin B (2) were isolated from the stem bark of the plant Fraxinus sielboldiana and belong to a medicinally interesting class of natural products used in traditional Chinese medicine. Herein the total synthesis of the proposed structure of (+)-sielboldianin A (1) is reported using an organocatalyzed enantioselective bromolactonization protocol. X-ray analysis of a key intermediate together with specific rotation values and NOESY data of the synthesized product enabled the revision of the absolute configuration of the natural product (+)-sielboldianin A to (7 R,10 R). Studies on the antioxidant effects using two cell-based assays were conducted. These studies revealed that the enantiomer of 1 exhibited antioxidant effects with IC₅₀ values of 18 ± 3 μM in a cellular lipid peroxidation antioxidant activity assay. Moreover, (-)-1 showed strong protective effects against reactive oxygen species in a cell-based antioxidant activity assay (IC₅₀ = 31 ± 5 μM). In addition, the two ar-sesquiterpenoids (-)-boivinianin B and (-)-gossoronol showed no effect in either assay. No cytotoxic activity in the K562 cancer cell line was observed for the three sesquiterpenoids tested (IC₅₀ > 50 μM).