Syntheses of Tetracyclic Indoline Derivatives Via Gold(I)-Catalyzed Hydroamination/Cycloisomerization Cascade of 2-Ethynyltryptamides.

A gold(I)-catalyzed hydroamination/cycloisomerization cascade reaction was developed to yield indolizino[8,7-b]indole and indolo[2,3-a]-quinolizine derivatives from 2-ethynyltryptamides. The optimal conditions were determined by condition screening, and the functional group tolerances of these reactions were explored based on synthetic substrates. An insight into the explanation on the selectivity of the ring closure was obtained by density functional theory calculations. A plausible mechanism for the cascade reactions was proposed. Derivatization of the indolizino[8,7-b]indole and total synthesis of nauclefidine demonstrated the practicality of this strategy.

Gold(I)-Catalyzed Substitution-Controlled Syntheses of Spiro[indoline-3,3'-pyrrolidine] and Spiro[indoline-3,3'-piperidine] Derivatives.

Spiro[indoline-3,3'-pyrrolidine] and spiro[indoline-3,3'-piperidine] derivatives were synthesized in a substitution-controlled manner under the catalysis of cationic gold(I) species in the presence of Hantzsch ester (HEH). The optimal reaction condition was determined by screening, and the functional group tolerances of these two pathways were examined by readily synthetic substrates. The endo and exo selectivities of these cyclizations were elucidated by density functional theory calculations, and a plausible mechanism for these transformations was proposed.

Phosphine-Functionalized Syndiotactic Polystyrenes: Synthesis and Application to Immobilization of Transition Metal Nanoparticle Catalysts.

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of high performance materials, but studies toward this goal have met with only limited success to date. The coordination polymerization of diphenylphosphinostyrene (p-StPPh2 and o-StPPh2 ) and its copolymerization with styrene (St) by (C5 Me4 SiMe3 )Sc(CH2 C6 H4 NMe2 -o)2 have been achieved for the first time to afford a new series of phosphine functionalized syndiotactic polystyrene. By the design of the polymer structure, the copolymer of o-StPPh2 and St (poly(o-StPPh2 -alt-St)-b-sPS) containing o-StPPh2 and St atactic alternating copolymer block and syndiotactic polystyrene block (sPS) showed excellent thermal stability and chemical resistance. The simple combination of the triphenylphosphine and syndiotactic polystyrene realized the stable immobilization of metal nanoparticles to afford highly robust metal@poly(o-StPPh2 -alt-St)-b-sPS nanocatalysts at high temperature and various atmospheres. The Cu@poly(o-StPPh2 -alt-St)-b-sPS catalyst can serve as a highly efficient heterogeneous catalyst for the synthesis of quinoline derivatives by acceptorless dehydrogenative coupling of o-aminobenzylalcohol with ketones.

The modulatory effect of polyphenols from green tea, oolong tea and black tea on human intestinal microbiota in vitro.

In the present study, polyphenols from green tea (GTP), oolong tea (OTP) and black tea (BTP) were prepared by extraction with hot water and polyamide column chromatography. In antioxidant assay in vitro, each tea polyphenols exhibited potential activity; the intestinal absorption of GTP, OTP and BTP was investigated individually by Caco-2 transwell system, and each sample was poorly transported, illustrating a low transport rate for tea polyphenols through cell monolayers. The effects of GTP, OTP and BTP on human intestinal microbiota were also evaluated, and each sample induced the proliferation of certain beneficial bacteria and inhibited Bacteroides-Prevotella and Clostridium histolyticum. Moreover, the short-chain fatty acids (SCFA) produced in cultures with tea polyphenols were relatively higher. Together, these results suggested GTP, OTP and BTP may modulate the intestinal flora and generate SCFA, and contribute to the improvements of human health.

Asymmetric Total Synthesis of Neobraclactone C.

Asymmetric total synthesis of neobraclactone C was finished for the first time using the convergent synthetic strategy in 22 steps in the longest linear sequence from known materials. The key steps include a steric hindrance/hydrogen bond dual-controlled Heck arylation of α,ß-unsaturated ketone to construct hemiketal and cis-alkenyl in one step and a CeCl3-catalyzed tricycle formation.

Competitive control of endoglucanase gene engXCA expression in the plant pathogen Xanthomonas campestris by the global transcriptional regulators HpaR1 and Clp.

Transcriptional regulators are key players in pathways that allow bacteria to alter gene expression in response to environmental conditions. However, work to understand how such transcriptional regulatory networks interact in bacterial plant pathogens is limited. Here, in the phytopathogen Xanthomonas campestris, we demonstrate that the global transcriptional regulator HpaR1 influences many of the same genes as another global regulator Clp, including the engXCA gene that encodes extracellular endoglucanase. We demonstrate that HpaR1 facilitates the binding of RNA polymerase to the engXCA promoter. In addition, we show that HpaR1 binds directly to the engXCA promoter. Furthermore, our in vitro tests characterize two binding sites for Clp within the engXCA promoter. Interestingly, one of these sites overlaps with the HpaR1 binding site. Mobility shift assays reveal that HpaR1 has greater affinity for binding to the engXCA promoter. This observation is supported by promoter activity assays, which show that the engXCA expression level is lower when both HpaR1 and Clp are present together, rather than alone. The data also reveal that HpaR1 and Clp activate engXCA gene expression by binding directly to its promoter. This transcriptional activation is modulated as both regulators compete to bind to overlapping sites on the engXCA promoter. Bioinformatics analysis suggests that this mechanism may be used broadly in Xanthomonas campestris pv. campestris (Xcc) and is probably widespread in Xanthomonads and, potentially, other bacteria. Taken together, these data support a novel mechanism of competitive activation by two global regulators of virulence gene expression in Xcc which is probably widespread in Xanthomonads and, potentially, other bacteria.