Copper-Catalyzed [4+2]-Cycloadditions of Isoxazoles with 2-Alkynylbenzaldehydes To Access Distinct α-Carbonylnaphthalene Derivatives: C(3,4)- versus C(4,5)-Regioselectivity at Isoxazoles

Ligand-controlled chemoselectivity in gold-catalyzed cascade cyclization of 1,4-diene-tethered 2-alkynylbenzaldehydes

A synthetic method that relies on the gold(i)-catalyzed cascade annulation of skipped 1,4-diene-tethered 2-alkynylbenzaldehydes for the chemo- and stereoselective assembly polycyclic bridged-pyrrolidines and -azepines is described.

Mild Intermolecular Synthesis of a Cyclopropane-Containing Tricyclic Skeleton: Unusual Reactivity of Isobenzopyryliums

Cyclopropanes embedded in a polycyclic bridged architecture are a versatile structural motif, but such complex frameworks often impose substantial synthetic challenges. Herein we introduce a new approach for the expedient access to such spring-loaded strained systems via an exceptionally mild intermolecular convergent process between the readily available isobenzopyryliums and vinyl boronic acids. Different from the typical conventional approaches, our protocol does not involve the highly active carbenoid intermediates or strong conditions in order to overcome the disfavored kinetic and thermodynamic problems. Instead, the key cyclopropane ring was formed between the well-positioned nucleophile and electrophile in the adduct from the regioselective [4+2] cycloaddition. Thus, this unusual process also represents a new reactivity of the versatile isobenzopyryliums. The choice of a Brønsted acid catalyst with proper acidity is crucial to the high efficiency and selectivity for this multiple bond-forming process. The strained products are precursors to other useful synthetic building blocks.

Organocatalytic Asymmetric Multicomponent Cascade Reaction for the Synthesis of Contiguously Substituted Tetrahydronaphthols

Isobenzopyrylium ions are unique, highly reactive, aromatic intermediates which are largely unexplored in asymmetric catalysis despite their high potential synthetic utility. In this study, an organocatalytic asymmetric multicomponent cascade via dienamine catalysis, involving a cycloaddition, a nucleophilic addition, and a ring-opening reaction, is disclosed. The reaction furnishes chiral tetrahydronaphthols containing four contiguous stereocenters in good to high yield, high diastereoselectivity (up to >20:1), and excellent enantioselectivity (93-98% ee). The obtained products are important synthetic intermediates, and it is demonstrated that they can be used for the generation of frameworks such as octahydrobenzo[h]isoquinoline and [2.2.2]octane scaffolds. Furthermore, mechanistic experiments involving oxygen-18-labeling studies and density functional theory calculations provide a vivid picture of the reaction mechanism. Finally, the bioactivity of 16 representative tetrahydronaphthol compounds has been evaluated in U-2OS cancer cells with some compounds showing a unique profile and a clear morphological change.

Evaluation of genoprotection against malathion induced toxicity by Orthosiphon thymiflorus Sleesen

BACKGROUND

Pesticide toxicity is considered to be one of the significant reason for increased incidence of cancer. Plants are treasure troves of active phytochemical compounds which are used as herbal medicine as well as nutraceuticals.

OBJECTIVE

To evaluate the genoprotective potential of Orthosiphon thymiflorus (Roth) Sleesen, (Lamiaceae) against the toxicity induced by malathion by a battery of four in vivo assays in Swiss albino mice.

MATERIALS AND METHODS

Micronucleus assay was performed for analyzing the micronuclei induction and ratio of polychromatic and normochromatic erythrocytes (PCE/NCE). Anticlastogenic and mito depressive effect of the methanol and hexane extracts of O.thymiflorus were evaluated by chromosome aberration assay. Alkali comet assay was performed to assess double strand DNA repair. DNA damage sensing ability of the bone marrow cells were assessed by γ-H2AX foci formation. Phytochemical screening of hexane and methanol extract was done by GC-MS analysis.

RESULT

O. thymiflorus extracts showed a dose dependant protective effect in all assays. It significantly decreased the frequency of micronuclei and improved PCE/NCE value in post treated groups of animals. Malathion induced clastogenic aberrations were effectively attenuated by methanol and hexane extracts. DNA comet assay showed that malathion induced damage can be protected by O. thymiflorus extracts. Multiple foci formation in γ-H2AX assay confirmed the activation of DNA repair proteins in post treated animals.

CONCLUSION

Genoprotective effect of O. thymiflorus against malathion induced toxicity was confirmed. This study would be helpful to initiate more research including clinical using O. thymiflorus extract against pesticide induced toxicity.

Silver Trifluoromethanesulfonate-Catalyzed Annulation of Propargylic Alcohols with 3-Methyleneisoindolin-1-one

A silver-catalyzed formal [3 + 3] annulation of 3-methyleneisoindolin-1-one with alkynol for the synthesis of 1,5-dihydroindolizin-3(2H)-one derivatives is disclosed. The protocol allows practical synthesis of N-heterocyclic scaffolds with a broad scope of functional groups and could be efficiently scaled up to gram scale, which incarnates a potential application of this methodology. In addition, a range of chlorine anion substitution of alkenes can be constructed by adjusting the structure of the alkynol substrates with the use of TMSCl.

Copper-catalyzed cascade cyclization reaction of 3-aminocyclobutenones with electron-deficient internal alkynes: synthesis of fully substituted indoles

A novel copper-catalyzed cascade cyclization reaction of 3-aminocyclobutenones with electron-deficient internal alkynes has been developed. This reaction provides a new method for the synthesis of fully substituted indoles by formation of four new bonds and two rings in a single step.

Zinc-Catalyzed Asymmetric Formal [4+3] Annulation of Isoxazoles with Enynol Ethers by 6π Electrocyclization: Stereoselective Access to 2H-Azepines

6π electrocyclization has attracted interest in organic synthesis because of its high stereospecificity and atom economy in the construction of versatile 5-7-membered cycles. However, examples of asymmetric 6π electrocyclization are quite scarce, and have to rely on the use of chiral organocatalysts, and been limited to pentadienyl-anion- and triene-type 6π electrocyclizations. Described herein is a zinc-catalyzed formal [4+3] annulation of isoxazoles with 3-en-1-ynol ethers via 6π electrocyclization, leading to the site-selective synthesis of functionalized 2H-azepines and 4H-azepines in good to excellent yields with broad substrate scope. Moreover, this strategy has also been used to produce chiral 2H-azepines with high enantioselectivities (up to 97:3 e.r.). This protocol not only is the first asymmetric heptatrienyl-cation-type 6π electrocyclization, but also is the first asymmetric reaction of isoxazoles with alkynes and the first asymmetric catalysis based on ynol ethers.