Stereoselective synthesis of pseudopeptide microbial agent AI-77-B

[structure: see text]. An efficient and highly stereoselective synthesis of the gastroprotective natural product AI-77-B is described. The stereocenters of the hydroxy amino acid moiety were generated by an ester-derived titanium-enolate-mediated syn-aldol reaction, a Curtius rearrangement, and application of Dondoni's aldehyde homologation. Condensation with the dihydroisocoumarin fragment and subsequent deprotecting transformations furnished optically active AI-77-B.     

(Studies on AI-77s,microbial products with pharmacological activity) structures and the chemical nature of AI-77s

The structures of a novel gastroprotective substance AI-77-B and its analogues AI-77-C, D, F and G, which are produced by Bacillus pumilus, are described. Five of the asymmetric centers of AI-77-B have S absolute stereochemistry confirmed by X-ray in combination with chemical studies.     

Studies on AI-77s,microbial products with gastroprotective activity. Structures and the chemical nature of AI-77s

The structures and the chemical nature of a novel gastroprotective substance AI-77-B (1) and its analogues AI-77-C (2), D (3), F (4) and G (5), which are produced by Bacillus pumilus AI-77, are described. The structure of 1 was confirmed to be 6-[[1(S)-(3(S), 4-dihydro-8-hydroxy-1-oxo-1H-2-benzopyran-3-yl)-3-methylbutyl]amino]-4(S),5(S)-dihydroxy-6-oxo-3(S)-aminohexanoic acid by X-ray in combination with chemical studies and the structures of 2, 3, 4 and 5 were determined by chemical syntheses from 1 and spectral analyses.     

Ab initio QM/MM molecular dynamics study on the excited-state hydrogen transfer of 7-azaindole in water solution

Ab initio molecular dynamics (AIMD) simulations for the excited-state hydrogen transfer (ESHT) reaction of 7-azaindole (7AI-(H2O)n; n = 1, 2) clusters in the gas phase and in water are presented. The effective fragment potential (EFP) is employed to model the surrounding water molecules. The AIMD simulations for 7AI-H2O and 7AI-(H2O)2 clusters show an asynchronous hydrogen transfer at t approximately 50 fs after the photoexcitation. While the ESHT mechanism for 7AI-H2O in water does not change appreciably compared with that in the gas phase, the AIMD simulations on 7AI-(H2O)2 in water solution exhibit two different mechanisms. Since the tautomer form is lower in energy compared to the normal form in the S1 state, 7AI and (H2O) n fragments separate from each other after the ESHT. With the use of the results of the AIMD trajectories, the minimum energy conical intersection point in the tautomer region has also been located.     

Stereoselective synthesis of the hydroxy amino acid moiety of Al-77-B,a gastroprotective substance from Bacillus pumilus Al-77

The hydroxy amino acid moiety of Al-77-B (1) has been prepared as its protected form 2 from the (R)-glyceric acid derivative 3 in an efficiently stereoselective manner through the direct C-acylation using diphenyl phosphorazidate and the hydroxy-directed hydrogenation.     

Synthesis,Photoisomerization, Antioxidant Activity,and Lipid-Lowering Effect of Ferulic Acid and Feruloyl Amides

The Ugi four-component reaction employing naturally occurred ferulic acid (FA) is proposed as a convenient method to synthesize feruloyl tertiary amides. Applying this strategy, a peptoid-like derivative of ferulic acid (FEF77) containing 2 additional hydroxy-substituted aryl groups, has been synthesized. The influence of the configuration of the double bond of ferulic acid and feruloyl amide on the antioxidant activity has been investigated thanks to light-mediated isomerization studies. At the cellular level, both FA, trans and cis isomers of FEF77 were able to protect human endothelial cord vein (HECV) cells from the oxidative damage induced by exposure to hydrogen peroxide, as measured by cell viability and ROS production assays. Moreover, in steatotic FaO rat hepatoma cells, an in vitro model resembling non-alcoholic fatty liver disease (NAFLD), the molecules exhibited a lipid-lowering effect, which, along with the antioxidant properties, points to consider feruloyl amides for further investigations in a therapeutic perspective.     

A chemoenzymatic and enantioselective total synthesis of the resorcylic acid lactone L-783,290, the trans-isomer of L-783,277

The structure, 5, assigned to the resorcylic acid lactone L-783,290 has been prepared for the first time and in a modular fashion using a Heck reaction to link the readily available fragments 8 and 14. Chemoenzymatic methods were used to prepare the latter fragment, in enantiopure form, from chlorobenzene.     

Fe3O4(001)-B表面水煤气变换反应机理第一性原理研究

采用自旋极化的密度泛函理论方法系统地研究了Fe_3O_4(001)-B表面水煤气变换的反应机理,计算了整个反应历程。结果表明,对于Fe_3O_4(001)-B表面上的水煤气变换反应,氧化还原、联合和再生三种反应路径共存,但氧化还原和联合机理的有效能垒较低,因而更占优势。对于生成H_2的基元反应,其活性受表面H浓度和催化剂表面O缺陷浓度影响;较高的表面H浓度和O缺陷浓度均有利于H_2生成。这些结果有助于进一步认识铁氧催化剂上的水煤气变换反应机理。     

An efficient and solvent-free one-pot synthesis of dihydropyrimidinones under microwave irradiation

An efficient synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives using formic acid as catalyst, from aldehydes,β-ketoester and urea(thiourea) without solvent under the irradiation of microwave is described. Compared with the classical Biginelli reaction, this new method has the advantage of good yields (77-94% for aromatic aldehydes) and short reaction time (3-8 min).     

手性磷酸在不对称反应中的应用

手性磷酸催化剂因其在不对称催化反应中表现出的高效、高对映选择性而受到人们越来越多的关注.含1,1'-联二萘酚(BINOL)骨架的手性磷酸类催化剂已被广泛用于亚胺的不对称氢转移、Friedel-Crafts反应和Mannich反应等许多重要的有机合成反应.手性磷酸具有同时提供质子和接受质子的双功能作用,因此可以同时活化两个反应底物.含BINOL骨架的手性磷酸可以通过改变BINOL骨架3,3'-位上的取代基调控空间位阻和手性磷酸的酸性,因此可以调节反应的对映选择性.为了合理地设计新的手性磷酸催化剂,扩大其应用范围,最近人们对手性磷酸不对称催化反应机理进行了初步的理论计算研究并取得了显著进展.综述了手性磷酸在不对称反应中的部分研究工作,尤其是理论研究领域的最新成果.     

An unexpected switch in the modulation of AI-2-based quorum sensing discovered through synthetic 4,5-dihydroxy-2,3-pentanedione analogues

Quorum sensing (QS) has traditionally referred to a mechanism of communication within a species of bacteria. However, emerging research implicates QS in interspecies communication and competition, and such systems have been proposed in a wide variety of bacteria. The AI-2-based QS system represents the most studied of these proposed interspecies systems, and has been proposed to regulate diverse functions such as bioluminescence, expression of virulence factors, and biofilm formation. As such, the development of modulatory compounds, both agonists and antagonists, is of great interest for the treatment of bacterial infections and the study of unknown AI-2-based QS systems. Toward this end, we have designed and synthesized a panel of 4,5-dihydroxy-2,3-pentanedione/AI-2 analogues and evaluated their effects on the AI-2 QS of various bacteria. The panel of compounds exhibited differential effects in the bacterial cell lines examined, providing a platform for the development of broad-spectrum modulators of AI-2-based QS.     

Synthesis of Substituted 2-Azolyl-1-pyridylethan-1-ols

Through the reaction of (2-aryloxiran-2-yl)pyridines with triazole or imidazole a series of novel 2-azolyl-1-pyridylethan-1-ols has been synthesized with different positioning of the nitrogen atom in the pyridine fragment for pharmacological and agrochemical screening. The compounds prepared showed high fungicidal activity.     

Synthesis of an advanced intermediate enroute to thiomarinol antibiotics

A stereoselective synthesis of the C1-C14 fragment of thiomarinols is disclosed. The key steps include the stereoselective preparation of an allylic sulfide via a chloro sulfide by 1,2-asymmetric induction, ring-closing metathesis reaction, Kirmse-Doyle reaction for the preparation of a γ,δ-unsaturated ester, Nozaki-Hiyama-Kishi coupling and Julia-Kocienski olefination reaction. Substrate controlled asymmetric induction has been advantageously employed for the creation of stereogenic centers. Noyori transfer hydrogenation and asymmetric hydrogenation reactions have been utilized for the creation of carbinol stereocenters.     

新型超支化聚芳酰胺的合成及表征

以3，5—二硝基苯甲酰氯和对氨基苯甲酸为原料，经两步反应合成了新型AB2型单体4—(3，5-二氨基苯甲酰氨基)苯甲酸。在溶液中通过自缩聚反应合成了新型超支化聚芳酰胺，将其活性端氨基与酰氯反应，经原位改性合成了五种封端的超支化聚芳酰胺，并利用IR、^1HNMR、DSC及TG等方法对所合成的六种新型超支化聚合物的结构和性能进行了表征与测试。     

Isolation of Bacillus stearothermophilus constituent that suppresses mouse mixed leukocyte reaction in vitro.

A novel immunosuppressant, Fr.5-B, has been isolated from the debris of Bacillus stearothermophilus UK563 autolysate. Fr.5-B suppressed mouse mixed leukocyte reaction at doses ranging from 10(-4) to 1 microgram/ml, but not proliferation stimulated by concanavalin A and lipopolysaccharide.     

Quantum-Chemical Study of Yb@C 60 , Yb@B 2 C 58 , and Gd@B 3 C 57 Molecules

Using the DFT PBE0/SDD method, the structural parameters of the Yb@η2-C60, Yb@η6-C60, Yb@η6-B2C58, and Gd@η6-B3C57 molecules, of corresponding anions (1,4-B2C58)2–, (1,3,5-B3C57)3–, and free radicals BkC60–k were calculated. Ytterbium is coordinated by the degraded C=C bond in the Yb@η2-C60 molecule and by the 1,4-diboratacyclohexa-1,3,5-triene fragment, in Yb@η6-B2C58. Symmetric substitution of three atoms of the cyclohexa-1,3,5-triene fragment leads to the formation of cyclopropane fragment, three 1,4-diboratacycloocta-1,3,5,7-tetraene fragments, and three boratacyclobutane fragments. The dipole moment μ(Yb@C60) is directed from the cavity center to Yb; the dipole moment μ(Gd@η6-B3C57) is greater and has the opposite direction (from B3 to Gd). The populations of the 4f-shells of the Yb and Gd atoms are conserved. The binding energy of the endoatom in Ln@BkC60–k is significantly higher than that in Yb@C60.     

The first example of trimethylsilyl methylenenitronate reacting with aldehydes under an apparent Mukaiyama nitro-aldol reaction

Trimethylsilyl methylenenitronate reacts with both aliphatic and aromatic aldehydes in the presence of catalytic amounts of scandium(III) triflate to form the Henry reaction products in low (25%) to good yields (77%). This is the first example of this silyl nitronate undergoing a nitro-aldol reaction under an acid environment.     

A biomimetic approach to the synthesis of a mycolic acid motif

A new method for the stereoselective synthesis of the (R,R)-β-hydroxy-α-alkyl fatty acid fragment of mycolic acids, via an asymmetric anti-aldol reaction is reported. The ‘mycolic acid motif’ fragment was prepared in three steps and >98% ee.     

Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide,an Isoprene-Derived Criegee Intermediate,with Formic Acid: Experiment and Theory

Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity is not well understood. This study identifies the functionalized hydroperoxide species, 1-hydroperoxy-2-methylallyl formate (HPMAF), generated from the reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr = 13.3 hPa). Electronic structure calculations indicate the reaction proceeds via an energetically favorable 1,4-addition mechanism. The formation of HPMAF is observed by the rapid appearance of a fragment ion at m/z 99, consistent with the proposed mechanism and characteristic loss of HO₂ upon photoionization of functional hydroperoxides. The identification of HPMAF is confirmed by comparison of the appearance energy of the fragment ion with theoretical predictions of its photoionization threshold. The results are compared to analogous studies on the reaction of formic acid with methyl vinyl ketone oxide (MVK-oxide), the other four-carbon Criegee intermediate in isoprene ozonolysis.     

Retro-Friedel-Crafts-Type Acidic Ring-Opening of Triptycenes: A New Synthetic Approach to Acenes

The triptycene scaffold has been ring-opened by using a retro-Friedel-Crafts-type reaction under acidic conditions to give its corresponding anthrone product. 9-Hydroxytriptycenes and unsubstituted triptycene undergo ring-opening reaction under strongly acidic conditions, such as with TfOH. An investigation of the substitution effect has revealed that the electron-donating group on the arene moiety allows the reaction to proceed in the presence of a weaker acid, such as TFA. In addition, the reaction has been successfully applied toward the synthesis of tetracene.