α-FACTOR-DIRECTED SYNTHESIS AND SECRETION OF β-SUBUNIT OF HUMAN CHORIOGONADOTROPIN (β-hCG)IN YEAST S. cerevisiae

A couple of sbuttle vectors (pYNA and pYNB), containing a sequence coding for the leader regionof the α-factor precursor (α-factor leader sequence) and the origin of 2μm circle, were constructed. ThecDNA for the β-hCG (145aa) was fused in phase to the 3'-end of the α-factor leader sequence andtransformed into the yeast Saccharomyces cercvisiae. The yeast cells carrying this hybrid gene synthesizedand secreted a protein with the immunoactivity of β-hCG in an amount of 45μg per liter of culture. Thepreliminary characterization of this protein is also reported in this paper.     

Surface engineering of carbon dots for highly sensitive α-glucosidase assay and inhibition evaluation

Monitoring α-glucosidase(α-Glu) activity is of great significance for the early diagnosis of type Ⅱ diabetes. Here the blue fluorescent carbon dots(CDs) were integrated with two different recognizing molecules, β-cyclodextrin and phenylboronic acid, for assembling a multifunctional CDs(mCDs) nanoplatform for sensitively analyzing α-Glu and its inhibitors. The hydrolyzed product of 4-nitrophenyl-α-D-glucopyranoside(α-Glu substrate), p-nitrophenol, could efficiently quench the fluorescence of mCDs...     

WAXD STUDY OF POLYMORPHOUS ISOTACTICPOLYPROPYLENE BY COMPUTER PEAK-RESOLUTION METHOD

Polymorphous i-PP containing a and βphases were studied by WAXD and computer peak-resolution method (CPRM). The asymmetric Gaussian-Cauchy functions (a-GC) were adoptedto fit the profiles of both amorphous and crystalline peaks. For the crystalline peaks, the fitting resultsof a-GC are better than the symmetric-GC; for the amorphous peaks, they are better than polynomialand exponential functions, etc. Using the retarded least-square procedure (RLSP) on microcom-puter the results of peak-resolution are rather satisfatory. For the polymorphous samples containingαand βphases, the relations between phase-state, crystallinity, crystalline size, the ratio of α,βrelativecontent and the crystallization temperature T_c were studied by CPRM. The ratio of α,βrelativecontents obtained by CPRM and Turner-Jones eq. have been carefully compared. There are manyimprovements in this work. A simple estimation method of WAXD peak areas, both for amorphousand crystalline peaki, is suggested.     

THE COURSE OF THE POLYPEPTIDE CHAIN OF TRICHOSANTHIN MOLECULE

The course of the polypeptide chain of Trichosanthin has been determined from the electron density map at 4 resolution. The structure belongs to α+β type. It contains eight α-helices (39% of total residues) and four β-sheets (32% of total residues) which are made up of thirteen β-strands. The α-helices are relatively in the centre of the molecule and surrounded by β-sheets. This is the characteristic feature of Trichosanthin structure. This kind of structural arrangement has not been reported before. The transformation matrix and translation vector, which superpose two molecules in one asymmetric unit, were obtained. The root mean square error is 1.31 for this superposition.     

XPS study of potassium-promoted molybdenum carbides for mixed alcohols synthesis via CO hydrogenation

The X-ray photoelectron spectroscopy (XPS) was used to investigate the surface characteristic of potassium-promoted or un-promoted both β-Mo_2C and α-MoC_(1-x) pretreated by syngas at different temperatures, and the promotional effect of potassium on the catalytic performance was also studied. XPS results revealed that the content of surface Mo and its valence distribution between β-Mo_2C and α-MoC_(1-x) were quite different. Promoted by potassium, the remarkable changes were observed for surface composition and valence of Mo distribution over β-Mo_2C. Potassium had strong electronic effect on β-Mo_2C, which led to a higher Mo~(4+) content. On the contrary, potassium had little electronic effect on α-MoC_(1-x), and K-Mo interaction was weak. Therefore, Mo~0 and Mo~(2+) became the dominant species on the catalyst surface, and the Mo~(4+) content showed almost no increase as the pretreatment temperature enhanced. In terms of catalytic performance of molybdenum carbides, the increase in Mo~0 most likely explained the increase in hydrocarbon selectivity, yet Mo~(4+) might be responsible for the alcohols synthesis.     

Two new triterpenoids from Psidium guajava

Two new triterpenoids,named as 2 α,3 β,23-trihydroxylurs-12,20(30)-dien-28-oic acid β-D-glucopyranoside(1),and 2 α,3 β,6 β,20 β,23,30-hexahydroxyurs-12-en-28-oic acid(2),together with four known triterpenoids were isolated from the leaves of Psidium guajava L.Their structures were elucidated on the basis of mass and spectral evidence.     

HPLC Determination of Neurotoxin β-N-oxalyl-L-α,β -diaminopropionic acid and Its α -Isomer in Lathyrus sativus by Precolumn Derivatization with 1-Fluoro-2,4-dinitrobenzene

A rapid and simple method is presented for determining β-N-oxalyl-α,β-diaminopropionic acid (β-ODAP) and its much less toxic α-isomer (α-ODAP) in Lathyrus sativus. Seed and foliage extracts of Lathyrus sativus were treated with 1-fluoro-2,4-dinitrobenzene (FDNB) and a reversed-phase high-performance liquid chromatographic method for the separation of the derivatives in the pmol range is reported.     

Preparation and Characterization of Chromium ( Ⅲ )-Containing α-and β-Tungstosilicates( Ⅱ )

Two new compounds of A- type α-and β-K4.5H2.5[SiW9Cr3(OH2)3O37]·xH2O were synthesized. The two kinds of isomers of α-and β-SiW12-xCrx(x=2, 3) were identified by Second-derivative IR spectroscopy and cyclic voltammetry. The numbers of electrons involved in reductions were obtained by controlled potential electrolyses of the isomers.     

β-PHASE CRYSTALLIZATION OF ISOTACTIC POLYPROPYLENE

Effects of cooling rate and crystallization and melt temperatures on the melting curves of predomi-nately β-phase isotactic polypropylene (IPP) were investigated by using DSC instrument. Experimental re-sults indicate that the magnitude of βmelting endctherm increases with decreasing cooling rate and withincreasing crystallization temperature. The temperature of melt has no effect on the β-phase crystallizationof IPP below 300℃, but a further increase of the melt temperature will destroy the β-phase nuclei,then the β-phase crystals will not be produced upon cooling. The linear growth rates of α- and β-phasespherulites were determined as a function of temperature between 123 and 140℃. It was found that thegrowth rate of βspherulites is higher than that of αspherulites below 140℃. Studies of the kinetics ofβ-phase crystallization of IPP were also made using a DSC instrument. The results obtained do not fitthe usual Avrami equation. But it can be described by kinetic theory of imcomplete spher     

Two New Cycloartane Triterpenes from The Leaves of Quercus valiabilis Blume

Two new cycloartane triterpenes were separated from the leaves of Quercus valiabilis Blume. The structures were identified as 4 α ,14 α-dimethyl-9 β,19-cycloergost-3 α-yl-24-oneand 4 α, 14 α -dimethyl-9 β,19-cycloergost-24(24‘‘ )-en-3 α -yl-acetate.     

Theoretical Study Of β2,3‐Peptide Models

Conformational features of α,β‐disubstituted β^2,3‐dipeptide models have been studied with quantum mechanics method. Geometries were optimized with the HF/6‐31G** method, and energies were evaluated with the B3LYP/6‐31G** method. Solvent effect was evaluated with the SCIPCM method. For (2S,3S)‐β^2,3‐dipeptide model 1 , a six‐membered‐ring hydrogen bonded structure is most stable. However, the conformation corresponding to the formation of the 14‐helix is only about 1.7 kcal/mol less stable in methanol solution, indicating that the 14‐helix is favored if a (2S,3S)‐β^2,3‐polypeptide contains more than 5 residues. On the other hand, the conformation corresponding to the formation of β‐sheet is most stable for (2R,3S)‐β^2,3‐dipeptide model 2 , suggesting that this type of β‐peptides is intrinsically favored for the formation of β‐sheet secondary structure.     

Solid‐state conformations of linear depsipeptide amides with an alternating sequence of α,α‐disubstituted α‐amino acid and α‐hydroxy acid

Depsipeptides and cyclodepsipeptides are analogues of the corresponding peptides in which one or more amide groups are replaced by ester functions. Reports of crystal structures of linear depsipeptides are rare. The crystal structures and conformational analyses of four depsipeptides with an alternating sequence of an α,α‐disubstituted α‐amino acid and an α‐hydroxy acid are reported. The molecules in the linear hexadepsipeptide amide in (S)‐Pms‐Acp‐(S)‐Pms‐Acp‐(S)‐Pms‐Acp‐NMe₂ acetonitrile solvate, C₄₇H₅₈N₄O₉·C₂H₃N, ( 3b ), as well as in the related linear tetradepsipeptide amide (S)‐Pms‐Aib‐(S)‐Pms‐Aib‐NMe₂, C₂₈H₃₇N₃O₆, ( 5a ), the diastereoisomeric mixture (S,R)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe₂/(R,S)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe₂ (1:1), C₃₂H₄₁N₃O₆, ( 5b ), and (R,S)‐Mns‐Acp‐(S,R)‐Mns‐Acp‐NMe₂, C₃₀H₃₇N₃O₆, ( 5c ) (Pms is phenyllactic acid, Acp is 1‐aminocyclopentanecarboxylic acid and Mns is mandelic acid), generally adopt a β‐turn conformation in the solid state, which is stabilized by intramolecular N—H…O hydrogen bonds. Whereas β‐turns of type I (or I′) are formed in the cases of ( 3b ), ( 5a ) and ( 5b ), which contain phenyllactic acid, the torsion angles for ( 5c ), which incorporates mandelic acid, indicate a β‐turn in between type I and type III. Intermolecular N—H…O and O—H…O hydrogen bonds link the molecules of ( 3a ) and ( 5b ) into extended chains, and those of ( 5a ) and ( 5c ) into two‐dimensional networks.     

Synthesis of β‐Substituted γ‐Aminobutyric Acid Derivatives through Enantioselective Photoredox Catalysis

β‐Substituted chiral γ‐aminobutyric acids feature important biological activities and are valuable intermediates for the synthesis of pharmaceuticals. Herein, an efficient catalytic enantioselective approach for the synthesis of β‐substituted γ‐aminobutyric acid derivatives through visible‐light‐induced photocatalyst‐free asymmetric radical conjugate additions is reported. Various β‐substituted γ‐aminobutyric acid analogues, including previously inaccessible derivatives containing fluorinated quaternary stereocenters, were obtained in good yields (42–89 %) and with excellent enantioselectivity (90–97 % ee). Synthetically valuable applications were demonstrated by providing straightforward synthetic access to the pharmaceuticals or related bioactive compounds (S)‐pregabalin, (R)‐baclofen, (R)‐rolipram, and (S)‐nebracetam.     

5-雄烯-3β, 7α, 17β-三醇和5-雄烯-3β, 7β, 17β-三醇的合成

以5-雄烯二醇为原料,用微生物转化的方法合成了两个重要的神经甾体5-雄烯-3β, 7α, 17β-三醇和5-雄烯-3β, 7β, 17β-三醇。所用菌种总枝毛霉为我们自己筛选,并首次应用于5-雄烯-3β, 7α, 17β-三醇和5-雄烯-3β, 7β, 17β-三醇的合成中。     

SmI2－Mediated Addition Reaction of α－Halomethylsulfones to Carbonyl Compounds. A Convenient Synthesis of β－Hydroxysulfones

Due to the chemoselective dehalogenation by SmI2, the addition of a-halomethylsulfones to carbonyl compounds afforded ,β-hydroxysulfones. Those reactions with α-bromomethylsulfones gave the products in moderate to good yields. The SmI2-mediated addition of gem-dihalomethylsulfones to ketones also afforded α-halo-β-hydroxysulfones in moderate yields.     

Phosphoryl group differentiating α‐amino acids from β‐ and γ‐amino acids in prebiotic peptide formation

In recent years β‐amino acids have increased their importance enormously in defining secondary structures of β‐peptides. Interest in β‐amino acids raises the question: Why and how did nature choose α‐amino acids for the central role in life? In this article we present experimental results of MS and ³¹P NMR methods on the chemical behavior of N‐phosphorylated α‐alanine, β‐alanine, and γ‐amino butyric acid in different solvents. N‐Phosphoryl α‐alanine can self‐assemble to N‐phosphopeptides either in water or in organic solvents, while no assembly was observed for β‐ or γ‐amino acids. An intramolecular carboxylic–phosphoric mixed anhydride (IMCPA) is the key structure responsible for their chemical behaviors. Relative energies and solvent effects of three isomers of IMCPA derived from α‐alanine (2a–c), with five‐membered ring, and five isomers of IMCPA derived from β‐alanine (4a–e), with six‐membered ring, were calculated with density functional theory at the B3LYP/6‐31G** level. The lower relative energy (3.2 kcal/mol in water) of 2b and lower energy barrier for its formation (16.7 kcal/mol in water) are responsible for the peptide formation from N‐phosphoryl α‐alanine. Both experimental and theoretical studies indicate that the structural difference among α‐, β‐, and γ‐amino acids can be recognized by formation of IMCPA after N‐phosphorylation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 232–241, 2003     

Synthesis of Optically Active β-Alkyl-α-methylene-γ-butyro- lactones from Enantioselective Biotransformation of Nitriles, an Unusual Inversion of Enantioselectivity

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Reaction of Grignard Reagents with Diethyl Perfluoroacyl (1-Cyanoethyl)phosphonates. Synthesis of Perfluoroalkylated α,β-Unsaturated Nitriles with Predominant Z-Selectivity

ＩｎｔｒｏｄｕｃｔｉｏｎＲｅｃｅｎｔｌｙｍｕｃｈａｔｔｅｎｔｉｏｎｈａｓｂｅｅｎｄｅｖｏｔｅｄｔｏｔｈｅｓｙｎｔｈｅｓｉｓｏｆα ,β ｕｎｓａｔｕｒａｔｅｄｎｉｔｒｉｌｅｓｓｉｎｃｅｔｈｅｙａｒｅｉｍ ｐｏｒｔａｎｔｓｔｒｕｃｔｕｒａｌｆｅａｔｕｒｅｏｆｓｅｖｅｒａｌｎａｔｕｒａｌｌｙｏｃｃｕｒｒｉｎｇｂｉ ｏｌｏｇｉｃａｌｌｙａｃｔｉｖｅｃｏｍｐｏｕｎｄｓ .1,2 Ｔｈｅｉｎｔｒｏｄｕｃｔｉｏｎｏｆｆｌｕｏ ｒｉｎｅｏｒｔｒｉｆｌｕｏｒｏｍｅｔｈｙｌｇｒｏｕｐｉｎｔｏｂｉｏｌｏｇｉｃａｌｌｙａｃｔｉｖ…     

胆甾-4α-甲基-8-烯-3β，7α-二醇二乙酸酯的结构与性质研究

Lophenol, cholest-4α-methyl-7-en-3β-ol (1), obtained from Dracaena cochinchinensis (Lour.) S. C. Chen, was structurally modified. It was acetylated to protect 3β-hydroxyl group, and then oxidised by selenium dioxide in acetic acid to give cholest-4a-methyl-8-en-3β, Ta-diol diacetate (3). This compound 3 is unstable in chloroform solution or when heated and easily converted to a diene compound, cholest-4a-methyl-7,14-dien-3β-ol acetate (4). The structures of 3 and 4 were elucidated by means of IR, ^1H NMR, ^13C NMR and MS, and the absolute configuration of 3 was established by X-ray crystallography. The property of 3 was also discussed in this paper. Both 3 and 4 are new compounds and were reported for the first time.     

Tandem Reaction of Deprotonation-Oxidation-Wittig Reaction: Stereoselective Synthesis of (E)-α,β-Unsaturated Enoates

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