Intercedenol A and B, Two New Triterpenoids from the Sea Cucumber Mensamaria intercedens

Two new triterpenoids named intercedenol A and B were isolated from the acid hydrolysate of the crude glycoside fraction. The structures were elucidated by ESI-MS and NMR spectrum.     

Homology modelling of the human adenosine A2B receptor based on X-ray structures of bovine rhodopsin, the β2-adrenergic receptor and the human adenosine A2A receptor

A three-dimensional model of the human adenosine A_2B receptor was generated by means of homology modelling, using the crystal structures of bovine rhodopsin, the β₂-adrenergic receptor, and the human adenosine A_2A receptor as templates. In order to compare the three resulting models, the binding modes of the adenosine A_2B receptor antagonists theophylline, ZM241385, MRS1706, and PSB601 were investigated. The A_2A-based model was much better able to stabilize the ligands in the binding site than the other models reflecting the high degree of similarity between A_2A and A_2B receptors: while the A_2B receptor shares about 21% of the residues with rhodopsin, and 31% with the β₂-adrenergic receptor, it is 56% identical to the adenosine A_2A receptor. The A_2A-based model was used for further studies. The model included the transmembrane domains, the extracellular and the intracellular hydrophilic loops as well as the terminal domains. In order to validate the usefulness of this model, a docking analysis of several selective and nonselective agonists and antagonists was carried out including a study of binding affinities and selectivities of these ligands with respect to the adenosine A_2A and A_2B receptors. A common binding site is proposed for antagonists and agonists based on homology modelling combined with site-directed mutagenesis and a comparison between experimental and calculated affinity data. The new, validated A_2B receptor model may serve as a basis for developing more potent and selective drugs.     

A model for the enzyme-catalyzed,coenzyme B12-dependent interconversion of β-methylaspartate with glutamate

A novel rearrangement promoted by vitamin B_12s of diethyl 1-keto-2-bromomethyl-2-methylsuccinate 10 to diethyl 4-methyl-2-ketoglutarate 11 has been discovered. This can serve as a partial model for the coenzyme B₁₂ dependent enzyme catalyzed interconversion of β-methylaspartate and glutamate. The Schiff base corresponding to 10 does not react with vitamin B_12s , but it does rearrange readily under free radical conditions when treated with tri-n-butyltin hydride.     

还原型胰岛素A,B链相互作用的研究

用CD谱研究了厌氧条件下还原型胰岛素A,B链的相互作用。 结果表明,S-磺酸型胰岛素A,B链间及在过量DTT存在下的还原型胰岛素A,B链间基本无相互作用,分离链及混合链均表现为接近无序结构。而按巯基与磺酸基比为1.2和0.6加入DTT时,胰岛素入B链间存在相互作用,并导致α螺旋含量增加。在按巯基与磺酸基比为0.6加入DTT时,近紫外CD谱表明存在着二硫键的极快形成过程,而按巯基与磺酸基比为1.2加入DTT时,巯基基本不氧化,表明有序二级结构的增加与巯基氧化无直接关系,而仅为二条肽链间相互作用的表现。对按不同巯基与磺酸基比加入DTT时,DTT与S-磺酸型胰岛素链上的巯基交换存在二种方式,以及小环关闭的胰岛素A链对胰岛素链间的相互作用并无促进作用的可能性进行了讨论。     

B → A Conformational Transition of DNA under the Influence of a Copper Thiolate,the Copper-cysteine: Biophysical,Spectroscopic and Gel Electrophoresis Studies

The interaction of calf-thymus DNA with copper(II)-cysteine (Cucys) was monitored by various biophysical methods. The interaction ratio was determined by the u.v.-spectrophotometric method, which was found to be 0.14. As the DNA 260 nm band remained insensitive followed by interaction with copper(II)-cysteine, the interaction ratio and the binding constant were determined by monitoring the 248 nm copper-cysteine charge-transfer (CT) band. Visible d–d spectra of Cucys proved that copper remained in the copper(II) state after interaction with DNA. The CD and thin film i.r. spectral studies revealed that there occurred B→A conformational transition of DNA when it was bound by copper-cysteine. Gel electrophoresis study confirmed the binding pattern.     

Dracaenoside A and B, New C-22 Steroidal Lactone Glycosides from the Stem of Dracaena cochinchinensis

Two new C-22 steroidal lactone glycosides, named dracaenoside A and B were isolated from the methanol extract of the fresh stem of Dracaena cochinchinensis. Their structures were established as (20S)3β,14α,16β-trihydroxy pregn-5-ene-22-carboxylic acid (22,16)-lactone 3-O-α-L-rhamnopyranosyl (1→2)[ α-L-rhamnopyranosyl (l→4)]-β-D-glucopyranoside and (20S)3β, 14α,16β-trihydroxy pregn-5-ene-22-carboxylic acid (22,16)-lactone 3-O-α-L-rhamnopyranosyl (1→2)[β-D-glucopyranosyl(1→3)]-β-D-glucopyranoside by means of 2D NMR spectral and chemical methods. It is the first time that steroidal lactone glycosides were isolated from the genus Dracaena.     

A rapid formal synthesis of the macrolide (−)-A26771B

(−)-A26771B, a novel 16-membered macrolide with antibiotic activity, has been formally synthesized. In the synthesis ruthenium catalyzed ring-closing olefin metathesis (RCM) was used as a key reaction to construct the lactone ring.     

ELECTRONIC SPECTRA OF HYPOCRELLIN A, B AND THEIR DERIVATIVES

In this paper, the electronic spectra of hypocrellin A and B (HA and HB) are studied in detail. It has been proved that their three visible absorption bands come respectively from the ππ transition of their conjugated systems and intramolecular proton transfer. In dilute solutions, their fluorescence spectra consist of the fluorescence peak of the neutral monomolecule and that of the zwitter-ions that are formed through proton transfer of excited states. In concentrated solution, the longer wavelength emission band is composed of the overlapped fluorescence peaks of zwitter-ions and excimers. The fluorescence spectra of the crystalline hypocrellin A and B consist of the fluorescence peaks of zwitter-ions and excimers and the fluorescence of neutral monomolecules could not be observed. Their relative intensities are closely related to the excitation wavelength.     

五脂酮A, B和Butyryl Binankadsurin A的分离与结构

从采自广西柳州地区融水县的一种南五味子(Kadsurasp.)种子中分得三个已知化合物---binankadsurinA(1),acetylbinankadsurinA(2),angeloylbinankadsurinA(3)及三个新化合物---五脂酮(schisanlignone)A(4),B(5),butyrylbinankadsurinA(6)。它们的结构由光谱分析和化学转化而阐明。1系首次从自然界分得。在抗癌药理筛选中,4与5在体外都对白血病P-388细胞有抑制作用。其IC~5~0分别为10和40μg/mL。     

FOUR NEW GLYCOSIDES, LIGUROBUSTOSIDES A, B, C AND D FROM LIGUSTRUM ROBUSTUM

ＦＯＵＲＮＥＷＧＬＹＣＯＳＩＤＥＳ，ＬＩＧＵＲＯＢＵＳＴＯＳＩＤＥＳＡ，Ｂ，ＣＡＮＤＤＦＲＯＭＬＩＧＵＳＴＲＵＭＲＯＢＵＳＴＵＭ￥ＪｕｎＴＩＡＮ；ＨｏｎｇＪｉｅＺＨＡＮＧａｎｄＨａｎＤｏｎｇＳＵＮ．（Ｌａｂｏｒａｔｏｒｙｏｆｐｈｙｔｏｃｈｅｍｉｓｔｒ...     

M2B5 or M2B4? A Reinvestigation of the Mo/B and W/B System

The literature states different compositions (M/B = 1:2 vs. 2:5) and structures for diborides of molybdenum and tungsten. Using X‐ray and neutron powder diffraction as well as energy and wavelength dispersive electron microprobe analysis, the Mo/B and W/B systems were now reinvestigated. Molybdenum diboride crystallizes as a stoichiometric compound Mo₂B₄ (formerly described as Mo₂B₅) in space group (No. 166, a, b = 3.01375(2) Å, c = 20.9541(3) Å), and as a non‐stoichiometric compound MoB_2?x (formerly described as MoB₂) in P6/mmm (No. 191, a, b = 3.043(2) Å, c = 3.067(2) Å), whereas stoichiometric tungsten diboride W₂B₄ (formerly described as W₂B₅) is found to crystallize in space group P6₃/mmc (No. 194, a, b = 2.9864(4) Å, c = 13.896(2) Å). These results seem to be supported by DFT calculations which show the instability of a hypothetic W₂B₅.     

Analysis of the vibronic structure of the 1A1g → 1B3g, 1B2u transition in biphenyl -h10 and -d10

The absorption spectra of biphenyl-h₁₀ and -d₁₀ crystals in the region of the ¹A_1g → 1B_3g, ¹B_2u transitions are interpreted in terms of vibronic coupling of the two closely spaced electronic states by six b_1u vibrations.     

266nm激光激励的SO2(X1A1,A1A2,B1B1)体系的态间转移研究

用YAG四倍频激光把SO₂分子从电子基态X¹A₁激励到电子激发态A¹A₂和B¹B₁的高振动耦合区, 获得了320～380um范围内SO₂(B¹B₁→X¹A₁)的激光诱导荧光色散谱, 并给出初步标识;提出一个三能态模型来处理266nm激光激励的SO₂(X¹A₁, A¹A₂, B¹B₁)体系的态间转移, 并获得了A态和B态在高振动能区的耦合系数ξ及耦合达到动态平衡的弛豫时间τ, 发现二者反映的是被研究体系的固有特性, 与提出的模型吻合.     

TAXAYUNTIN A,B,C AND D----FOUR NEW TETRACYCLIC TAXANES FROM TAXUS YUNNANENSIS

Four new taxane diterpenoids were isolated fromthe bark of Taxus yunnanensis.Their structures wereelucidated as the new skeleton with 5/7/6/4 membered ringsby spectral analysis and 2D NMR shift correlationexperiments.     

Hydramicromelins A,B和C母核的对映选择性合成

Hydramicromelins A~C是具有独特化学结构和生物活性的香豆素类化合物.以本实验室发展的[2,3]-Meisenheimer重排为关键反应,以L-苯甘氨醇为起始原料,经过Wittig反应,[2,3]-Meisenheimer重排,环氧化,双羟化等7~8步反应,高收率、高对映选择性地制备出Hydramicromelins A,B和C的母核或其对映体.     

TEUPERNIN A,B AND C,THREE ENT-CLERODANE DITERPENOIDS FROM TEUCRIUM PERNYI FRANCH

Three furanoid ent-clerodane diterpenoids,teupernin A,B and Chave been isolated from the acetone extract of Teucrium pernyi Franch.Theirstructures were established by spectroscopic means(UV,IR,MS,~1H NMR,~(13)CNMR,H-H COSY,C-H COSY and NOE)and by comparison with related compounds.     

鸭血纤维蛋白A,B肽的纯化及一级结构

本文证明鸭血纤维蛋白 A,B肽经 Dowex 50w×2离子交换树脂及DEAE-Se-pharos,CL-6B纯化后,用手工 Edman氨基酸顺序降解法测得A肽的一级结构为十五肽:Pyr~1)·Asp·Gly·Lys·Ser·Ser·Phe·Gln·Lys·Glu·Gly·Gly·Gly·Val·Ayg.B肽的一级结构为十八肽:Pyr·Ala·Ser·Thr·Asp·Tyr~2)·Asp·Asp·Glu·Asp·Glu·Ser·Thr·Val.Pro·Glu·Ala·Arg.