Catalytic asymmetric cycloadditions of ambident Pd‐containing dipolar species with nucleophilic dipolarophiles, namely, inverse‐electron‐demand cycloadditions, are challenging and underdeveloped. ...Possibly, the inherent linear selectivity of Pd‐catalyzed intermolecular allylations and the lack of efficient chiral ligands are responsible for this limitation. Herein, two cycloadditions of such intermediates with deconjugated butenolides and azlactones were accomplished by using a novel chiral hybrid P,S‐ligand and hydrogen bonding. By doing so, highly functionalized, optically active dihydroquinol‐2‐ones were produced with generally high reaction efficiencies and selectivities. Preliminary DFT calculations were performed to explain the high enantio‐ and diastereoselectivities.
By popular demand: With the help of chiral P,S‐ligands and hydrogen‐bonding interactions, inverse‐electron‐demand asymmetric 4+2 cycloadditions were accomplished for the first time. A variety of optically active, highly functionalized hydroquinolin‐2‐ones were produced in good yields with excellent stereocontrol from readily available starting materials.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Many in vitro studies have shown that tea catechins had vevarious health beneficial effects. However, inconsistent results between in vitro and in vivo studies or between laboratory tests and ...epidemical studies are observed. Low bioavailability of tea catechins was an important factor leading to these inconsistencies. Research advances in bioavailability studies involving absorption and metabolic biotransformation of tea catechins were reviewed in the present paper. Related techniques for improving their bioavailability such as nanostructure-based drug delivery system, molecular modification, and co-administration of catechins with other bioactives were also discussed.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Chiral catalysts tolerating photochemical reactions are in great demand for the vast development of visible‐light‐induced asymmetric synthesis. Now, chiral octahedral complexes based on ...earth‐abundant metal and chiral N4 ligands are reported. One well‐defined chiral CoII‐complex is shown to be an efficient catalyst in the visible‐light‐induced conjugated addition of enones by alkyl and acyl radicals, providing synthetically valued chiral ketones and 1,4‐dicarbonyls in 47–>99 % yields with up to 97:3 e.r.
Chiral octahedral complexes were prepared from earth‐abundant cobalt and chiral N4 ligands. One structurally well‐defined cobalt complex was an efficient chiral catalyst in visible‐light‐induced radical conjugated additions. Synthetically valued chiral ketones and 1,4‐dicarbonyls were afforded in 47–>99 % yields (46 examples) with up to 97:3 e.r.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Catalytic asymmetric cycloadditions via transition-metal-containing dipolar intermediates are a powerful tool for synthesizing chiral heterocycles. However, within the field of palladium catalysis, ...compared with the well-developed normal electron-demand cycloadditions with electrophilic dipolarophiles, a general strategy for inverse electron-demand ones with nucleophilic dipolarophiles remains elusive, due to the inherent linear selectivity in the key palladium-catalyzed intermolecular allylations. Herein, based on the switched regioselectivity of iridium-catalyzed allylations, we achieved two asymmetric 4+2 cycloadditions of vinyl aminoalcohols with aldehydes and β,γ-unsaturated ketones through synergetic iridium and amine catalysis. The activation of vinyl aminoalcohols by iridium catalysts and carbonyls by amine catalysts provide a foundation for the subsequent asymmetric 4+2 cycloadditions of the resulting iridium-containing 1,4-dipoles and (di)enamine dipolarophiles. The former provides a straightforward route to a diverse set of enantio-enriched hydroquinolines bearing chiral quaternary stereocenters, and the later represent an enantio- and diastereodivergent synthesis of chiral hydroquinolines.
The first radical alkoxycarboxylation of aryldiazonium salts using CO gas through visible‐light‐induced photoredox catalysis (16 W blue LEDs) has been developed. This reaction is entirely metal‐free, ...is carried out at room temperature with a low loading of an organic dye as a photocatalyst (0.5 mol %), and provides a wide range of arylcarboxylic acid esters in high yields. Importantly, this photocatalytic system can be successfully extended to other carboxylation reactions.
All lit up: The radical alkoxycarboxylation of aryldiazonium salts using CO gas was accomplished through visible‐light‐induced photoredox catalysis. The reaction is metal‐free, and proceeds at room temperature with a low loading of organic photocatalyst. A wide range of esters were conveniently synthesized in moderate to good yields. Importantly, this strategy can be further applied to other carboxylation reactions.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The problem which is concerned with filter-based neural control for switched uncertain nonlinear systems with incomplete measurement is studied in this paper. Filters are used to estimate unknown ...states, while neural networks approximate unknown functions. Data loss, saturation and other problems often occur during data transmission. An appropriate control law is designed by a backstepping method to solve this problem. Through using the average dwell time, it is proved that the switching system tends to be stable in a certain time. The analysis of probabilistic stability is also carried out to ensure that the system can achieve uniformly ultimately boundedness. Finally, the effectiveness of the previous design is proved by simulation.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Recently, emotion classification from EEG data has attracted much attention with the rapid development of dry electrode techniques, machine learning algorithms, and various real-world applications of ...brain–computer interface for normal people. Until now, however, researchers had little understanding of the details of relationship between different emotional states and various EEG features. To improve the accuracy of EEG-based emotion classification and visualize the changes of emotional states with time, this paper systematically compares three kinds of existing EEG features for emotion classification, introduces an efficient feature smoothing method for removing the noise unrelated to emotion task, and proposes a simple approach to tracking the trajectory of emotion changes with manifold learning. To examine the effectiveness of these methods introduced in this paper, we design a movie induction experiment that spontaneously leads subjects to real emotional states and collect an EEG data set of six subjects. From experimental results on our EEG data set, we found that (a) power spectrum feature is superior to other two kinds of features; (b) a linear dynamic system based feature smoothing method can significantly improve emotion classification accuracy; and (c) the trajectory of emotion changes can be visualized by reducing subject-independent features with manifold learning.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Great achievements in the asymmetric cyclization reactions of sulfur ylides have been reached by using chiral sulfides; however, this method usually suffers from the high loading of chiral sulfides. ...Over the past decade, new catalysis technologies beyond chiral sulfide-based catalysis have been gradually applied to the cyclizations of sulfur ylides. These technologies, including organocatalysis, organometallic catalysis and photocatalysis, can avoid the use of stoichiometric chiral pools and enable the development of new cyclization reactions of sulfur ylides. In this tutorial review, recent advances in this rapidly developing field will be highlighted with particular emphases on the catalytic mechanism and the development of new reactions, new reagents and new concepts.
This Tutorial Review highlighted recent achievements on the catalytic cyclization reactions of sulfur ylide reagents, especially the asymmetric processes avoiding the use of structurally complex chiral sulfides.
Chemical ubiquitination is an effective approach for accessing structurally defined, atypical ubiquitin (Ub) chains that are difficult to prepare by other techniques. Herein, we describe a strategy ...that uses a readily accessible premade isopeptide‐linked 76‐mer (isoUb), which has an N‐terminal Cys and a C‐terminal hydrazide, as the key building block to assemble atypical Ub chains in a modular fashion. This method avoids the use of auxiliary‐modified Lys and instead employs the canonical and therefore more robust Cys‐based native chemical ligation technique. The efficiency and capacity of this isoUb‐based strategy is exemplified by the cost‐effective synthesis of several linkage‐ and length‐defined atypical Ub chains, including K27‐linked tetra‐Ub and K11/K48‐branched tri‐, tetra‐, penta‐, and hexa‐Ubs.
All together now: Chemical protein synthesis enabled the generation of homogeneous atypical ubiquitin (Ub) chains that are difficult to prepare by other approaches. A ligation method mediated by an isopeptide‐linked Ub isomer was developed to assemble the Ub chains. In this approach, a premade isopeptide‐linked 76‐mer (isoUb) bearing an N‐terminal Cys and a C‐terminal hydrazide is the key building block.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
(–)-Epigallocatechin-3-O-gallate (EGCG), the most abundant component of catechins in tea (Camellia sinensis (L.) O. Kuntze), plays a role against viruses through inhibiting virus invasiveness, ...restraining gene expression and replication. In this paper, the antiviral effects of EGCG on various viruses, including DNA virus, RNA virus, coronavirus, enterovirus and arbovirus, were reviewed. Meanwhile, the antiviral effects of the EGCG epi-isomer counterpart (+)-gallocatechin-3-O-gallate (GCG) were also discussed.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
PDF
