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1.
Complementary regioselective esterification of non-reducing oligosaccharides catalyzed by different hydrolases 总被引:1,自引:0,他引:1
The enzymatic transesterification of several tri- and tetrasaccharides with vinyl laurate is described. The lipases from Candida antarctica B (Novozym 435) and Thermomyces lanuginosus (Lipozyme TL IM) and the alkaline protease from Bacillus licheniformis (subtilisin Carlsberg) have been used with each carbohydrate to obtain different regioisomers. By using the sugars in their amorphous form, complete solubility is achieved in the reaction media (tert-butanol/pyridine mixtures for the lipases and pyridine for the protease) and high isolated yields of the corresponding monoesters are obtained. Good to excellent regioselectivity is observed for all the enzymes, showing a final complementary picture respect to the primary hydroxyls of the oligosaccharides studied. 相似文献
2.
细菌内毒素(LPS)是革兰氏阳性阴性菌细胞外膜层的主要成分,由其引起的革兰氏阴性杆菌脓度症和休克是导致战创伤病人死亡的主要原因之一。而从类脂A(LipidA)的结构出发,以非肽类物质拮抗内毒素受体CD-14为治疗手段的研究在国外刚刚起步。2-乙酰氨基-3,4,6-三乙酰葡萄糖是合成LipidA结构类似物的重要中间体[1,2]。它的合成一般是通过氨基葡萄糖五乙酸酯的选择性水解[3-6]脱去一个乙酰基得到。氨基葡萄糖五乙酸酯是通过氨基葡萄糖的乙酰化反应得到的,由于氨基葡萄糖不稳定,一般是用氨基葡萄糖的盐酸盐作为起始原料。由于… 相似文献
3.
4.
Zhaoqiang Lu Lin Cheng Jun Li Kai Zhang Song Yi Jingui Qin 《Journal of polymer science. Part A, Polymer chemistry》2004,42(4):925-932
The synthesis and structural characterization of a series of novel, fluorinated poly(phthalazinone ether)s containing perfluorophenylene moieties are described. The monomers, 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a – 2d ), were conveniently and efficiently synthesized from phenols and phthalic anhydride in two steps via 2‐(4′‐hydroxybenzoyl)benzoic acids, which were first obtained by the Friedel–Crafts reaction in good yields and with high stereoselectivity and were then converted into 2a – 2d by fusion with hydrazine. All the polymers were prepared by nucleophilic aromatic substitution (SNAr) polycondensation between the compounds perfluorobiphenyl and 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a ‐ 2d ). The resulting fluorinated polymers were readily soluble in common organic solvents (e.g., CHCl3, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N‐methylpyrrolidone, etc.) at room temperature. Their weight‐average molecular weights and the polydispersities ranged from (7.96–18.25) × 103 to 1.31–2.71, respectively. Their glass‐transition temperatures varied from 213 to 263 °C. They were all stable up to 390 °C both in air and in argon. The 5% weight‐loss temperatures of these polymers in air and argon ranged from 393–487 to 437–509 °C, respectively. Wide‐angle X‐ray diffraction studies indicated they were all amorphous and could be attributed to the presence of kink nonplanar moiety, phenyl phthalazinone along the polymer backbone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 925–932, 2004 相似文献
5.
Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2-Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method. 相似文献
6.
Rikuhei Tanikaga Yoshimasa MatsumotoMaki Sakaguchi Yohei KoyamaKentaro Ono 《Tetrahedron letters》2003,44(35):6781-6783
Lipase-mediated acetylations of trans- and cis-2-substituted cyclohexanols gave the corresponding (1R)-cyclohexyl acetates and (1S)-cyclohexanols in high yields and ee, but c-4-tert-butyl-c-2-ethenyl-r-1-cyclohexanol was unreactive owing to the steric interaction between the axial OH group and the axial H atoms at the 3- and 5-positions. In the cis-isomer the OH group occupies an equatorial position to bind to the lipase, and less bulky axial alkenyl and alkynyl groups might not so much prevent acetylations than an alkyl group. 相似文献
7.
8.
Krayushkin M. M. Shirinian V. Z. Belen"kii L. I. Shadronov A. Yu. Vorontsova L. G. Starikova Z. A. 《Russian Chemical Bulletin》2002,51(8):1510-1514
The conditions for acylation of 2,5-dimethylthiophene with squaric acid dichloride were optimized, and 3,4-bis(2,5-dimethylthiophen-3-yl)cyclobut-3-ene-1,2-dione was obtained in good yield. X-ray diffraction analysis demonstrated that the by-product has the structure of 1a,1b-dichloro-5-(2,5-dimethylthiophen-3-yl)-3-hydroxy-4,5a-dimethyl-1b,4a,5,5a-tetrahydro-1aH-1-thiacyclopropa[a]pentalen-2-one. 相似文献
9.
Byeong Hyo Kim Rongbi HanFengyu Piao Young Moo JunWoonphil Baik Byung Min Lee 《Tetrahedron letters》2003,44(1):77-79
N-Arylacetamides were prepared in excellent yields from nitroarenes in the presence of acetic anhydride, acetic acid and indium by a one-pot procedure. 相似文献
10.
Acylation of 6-(1-fluorovinyl)-6-methyl- and 6-(2,2,3,3-tetrafluorocyclobutyl)-4,5-diazaspiro[2.4]hept-4-enes with acetyl chloride proceeds as electrophilic addition to the N(5) atom and is accompanied by opening of the cyclopropane ring to give 1-acetyl-3-(2-chloroethyl)-5-(1-fluorovinyl)-5-methyl- and 1-acetyl-3-(2-chloroethyl)-5-(2,2,3,3-tetrafluorocyclobutyl)-4,5-dihydropyrazoles, respectively. Under the same conditions, acylation of 6-(2,3,3-trifluorocyclobut-1-enyl)-4,5-diazaspiro[2.4]hept-4-ene is not regioselective. The (2-chloroethyl) pyrazolines obtained undergo dehydrochlorination into vinylpyrazolines in the presence of an excess of MeONa in MeOH. The reaction of 4-acetyl-6-(2,3,3-trifluorocyclobut-1-enyl)-4,5-diazaspiro[2.4]hept-5-ene with MeONa results in selective replacement of the F atom at the double bond by a methoxy group.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 419–422, February, 2005. 相似文献