Two new phenol compounds from roots of Ardisia crenata.

Two new phenols, ardisiphenol I (1) and ardisiphenol J (2), along with three known compounds (3-5) were isolated and identified from the roots of Ardisia crenata var. bicolor. Their structures were elucidated by means of spectroscopic techniques. Structurally, new compounds 1 and 2 have rare side chain with seven carbons. All compounds were tested for antibacterial activity, and compound 5 showed moderate antibacterial activity against Enterococcus faecalis. This work provided the isolation and structural identification of all the compounds in detail, and shed a new light on its further research.

Enantioselective Synthesis of Bispiro[indanedione-oxindole-cyclopropane]s through Organocatalytic [2+1] Cycloaddition.

A series of compounds featuring a novel bispiro[indanedione-oxindole-cyclopropane] moiety have been synthesized through a squaramide-catalyzed [2+1] cycloaddition reaction. The tandem Michael-alkylation reaction of 2-arylidene-1,3-indanediones with 3-bromooxindoles furnished the cycloadducts in high yields with excellent diastereo- and enantioselectivities. The ammonium ylide in the catalytic process, as a key intermediate, was revealed by the high-resolution mass spectrometry study.

Structural Elucidation and Total Synthesis for the Pair of Unprecedented Polypyridines with Anti-AChE and HIV-1 Protease Activities from Alangium chinense.

Unlike reported pyridine hybrids, 2S (1a) and 2R-alanginenmine A (1b) from Alangium chinense featuring an unprecedented piperidine-bridged polypyridine skeleton represented a pair of alkaloid subtypes with a unique multiple pyridine scaffold. Enlightened by the rare structural characteristics and possible biosynthetic pathway, (±)-alanginenmine A (1) have been achieved in ideal yield by gram-class total synthesis with four steps. In addition, both compounds 1a and 1b exhibited anti-acetylcholinesterase (AChE) and HIV-1 protease activities in the biological activity evaluation. Further, molecular docking was investigated for the mechanism of action between the isolated compounds and HIV-1 protease. The stronger Coulomb interactions and van der Waals interaction, as well as the hydrogen bond interactions of 1a, might be the main cause for its better anti-HIV-1 protease activity than 1b. This work provided a comprehensive research including natural product discovery, bioactivity evaluation, and total synthesis for the new type of leading anti-HIV-1 protease.

Me2(CH2Cl)SiCF3 Facilitated Tandem Synthesis of Oxasilacycles Featuring a Trifluoromethyl Group.

An unprecedented tandem trifluoromethylsilylation/intramolecular SN2 substitution sequence was realized by using bifunctional reagent Me2(CH2Cl)SiCF3, allowing efficient construction of valuable trifluoromethylated oxasilacyclohexanes that are difficult to access by known methods. Initial attempts into developing asymmetric variant reveal that using cinchonine-derived dimeric PTC catalyst could afford chiral oxasilacyclohexanes in up to 92% enantiomeric excess.

Asymmetric Formal (3 + 2) Cyclocondensation of Coumarin-3-Formylpyrazoles as 3-Carbon Partners with 3-Hydroxyoxindoles via Esterification/Michael Addition Sequence.

The first enantioselective formal (3 + 2) cyclocondensation involving α,ß-unsaturated pyrazoleamides as 3-carbon partners was accomplished in a stepwise fashion. The stepwise esterification/Michael addition sequence is promoted by Zn(OTf)2 and quinine-squaramide derivative, respectively. The protocol enables access to spiro-fused pentacyclic spirooxindoles from coumarin-3-formylpyrazoles and 3-hydroxyoxindoles in good to satisfactory overall yields (up to 91%) with excellent dr (all cases >20:1 dr) and high ee values (up to 99%). Mechanistic investigations contributed to shedding light on the enantioselective event of the process.

Organocatalytic enantioselective reactions involving prochiral carbocationic intermediates.

Since the discovery of carbocations in 1901, the past 120 years have witnessed many marvelous advances in the chemistry of carbocations. The state-of-the-art research in this field is to overcome the intrinsic instability and high reactivity of the prochiral carbocationic intermediates to develop catalytic asymmetric reactions. Such transformations enable the facile synthesis of structurally diverse value-added products from readily available starting materials such as alkenes, alcohols, and carbonyl derivatives, and enjoy high and even perfect atom-economy in most cases. Notably, such allows catalytic stereoconvergent synthesis from racemic substrates and can realize regioselectivity in olefin functionalization reactions complementary to radical processes. With the rapid developments in modern asymmetric organocatalysis, a variety of highly enantioselective protocols evolving prochiral carbocationic intermediates have been achieved by employing three strategies, namely chiral ion-pairing, chiral nucleophile, or chiral carbenium ion strategy. This feature article aims to summarize the exciting advances in this emerging area and briefly showcase the possible mechanisms. The advantages and limitations of each strategy are presented as well as their synthetic applications in the synthesis of natural products or bioactive compounds.

Organocatalytic Asymmetric Cyclopropanation of 3-Acylcoumarins with 3-Halooxindoles: Access to Spirooxindole-cyclopropa[c]coumarin Compounds.

A highly diastereo- and enantioselective cyclopropanation reaction of 3-acylcoumarins with 3-halooxindoles catalyzed by an organocatalyst through a [2 + 1] Michael/intramolecular cyclization process was developed. This scenario provides a facile strategy to access spirooxindole-cyclopropa[c]coumarin compounds bearing three continuous stereocenters, including two vicinal quaternary all-carbon stereocenters with high to excellent diastereo- and enantioselectivities. The HRMS study revealed the vital importance of the ammonium ylide intermediate in the catalytic process.

Coumarin-3-formylpyrazoles as 3-carbon synthons in cyclocondensation for the synthesis of spiro-fused pentacyclic spirooxindoles.

Coumarin-3-formylpyrazoles have been synthesized and applied as 3-carbon synthons in reaction with 3-hydroxyoxindoles by using DABCO as the catalyst. A range of structurally diverse spiro-fused pentacyclic spirooxindoles, bearing a spirooxindole-γ-lactone and a 3,4-dihydrocoumarin substructure, could be smoothly obtained in good to excellent yields (up to 99%) with excellent diastereoselectivities (all cases >20 : 1 dr). The asymmetric version of this tandem reaction was preliminarily investigated by using chiral organocatalysts.

Highly enantioselective sequential vinylogous aldol reaction/transesterification of methyl-substituted olefinic butyrolactones with isatins for the construction of chiral spirocyclic oxindole-dihydropyranones.

A highly stereoselective sequential vinylogous aldol reaction/transesterification of methyl-substituted olefinic butyrolactones and isatins was developed. With this developed protocol, a series of chiral spirocyclic oxindole-dihydropyranones were obtained in good to excellent yields (73-99%) and enantioselectivities (71-97% ee).

Organocatalytic Asymmetric Dearomatization of 3-Nitroindoles and 3-Nitrobenzothiophenes via Thiol-Triggered Diastereo- and Enantioselective Double Michael Addition Reaction.

Organocatalytic asymmetric dearomatization of 3-nitroindoles and 3-nitrobenzothiophenes by reaction with ethyl 4-mercapto-2-butenoate has been developed. A range of chiral tetrahydrothiopheneindolines and tetrahydrothiophenebenzothiophenes bearing three contiguous stereocenters are obtained in high yields with good diastereoselectivities and excellent enantioselectivities. This is the first example of thiol-triggered catalytic asymmetric dearomatization of 3-nitroindoles and 3-nitrobenzothiophenes.

Xylastriasan A, a new cytochalasan from the fungus Xylaria striata.

Xylastriasan A (1), a new cytochalasan alkaloid with a rare 5/6/6/5/6 pentacyclic skeleton, and ergosterol (2) were isolated from the ethanol extract of fruiting bodies of the fungus Xylaria striata. Their structures were determined by analysis of their spectroscopic data. Compound 1 exhibited weak cytotoxic activity against HEPG2, B16 and A549 cell lines with IC50 values of 93.61, 85.61 and 91.58 µM, respectively. Ergosterol (2) potentiated pentobarbital-induced sleep by not only increasing the number of falling asleep and prolonging sleeping time but also reducing sleep latency at a dosage of 5 mg/kg.