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11.
3-O-Acetyl-1,2-O-isopropylidene--D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene--D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy--D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene--L-talofuranose (6) was also prepared stereoselectively from2 b
via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene--D-allofuranose (4 a) and --L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
12.
13.
Transmission electron microscopy of freeze fractured and replicated samples (TEM) and polarizing light microscopy (PLM) are
used to investigate the defect structures of the thermotropic and lyotropic mesophases of the non-steroidal antiinflammatory
drug fenoprofen sodium and of the thermotropic mesophase of the nonionic surfactant sucrose oleate (O1570). All mesophases
have a layered, smectic structure. The thermotropic liquid crystal of feno-profen sodium is an interdigitated smectic A phase
(smectic Ad) having the highest viscosity of the investigated samples. The thermotropic mesophase of the sugar ester is also
of the type smectic A, likely to be of subtype smectic A2 (bilayered smectic structure). The lyotropic mesophase is of lamellar
liquid crystalline nature and has a much lower viscosity than the thermotropic mesophases. In the PLM the lyotropic fenoprofen
mesophase has a strong tendency to form a pseudoisotropic texture, indicating a strong tendency to form undisturbed layered
structures. Other textures exhibited in the PLM are fan-shaped texture and maltese-cross texture. Confocal domains, cylinders,
pits and peaks as well as screw dislocations are found in great number in the TEM. However, no greater regions of undisturbed
lamellar arrangement in the lyotropic mesophase could be detected. The only texture of the thermotropic fenoprofen mesophase
visible in the PLM is the fan-shaped texture, indicating confocal domains as predominant structural elements. However, no
confocal domains (tori or Dupin cyclides) are found in the TEM. In the PLM the sugar–ester mesophase exhibited a fan-shaped
texture, maltese crosses and oily streaks as dominant textures. In the TEM only a few +π and −π disclinations and imperfect
confocal domains could be detected. The discrepancies in the appearance of defect structures and textures between the mesophases
as well as the discrepancies in the findings in the PLM and in the TEM investigations are caused by the different sample preparation
and the different viscosities of the mesophases.
Received: 28 May 1997 Accepted: 2 September 1997 相似文献
14.
Ana Montero 《Tetrahedron letters》2005,46(3):401-405
A stereocontrolled synthesis of an unsaturated sugar bearing two amino groups (one of them masked as an azide), using an Overman rearrangement as key step, is described. This scaffold is used to prepare two peptides having aromatic fragments, which have shown activity as calpain inhibitors. 相似文献
15.
Takashi Hayashita Akiyo Yamauchi Ai-Jun Tong Jong Chan Lee Bradley D. Smith Norio Teramae 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(1-2):87-94
The design and function of novel supramolecular fluoroionophore/cyclodextrin (CyD) complex sensors for ion and molecule recognition in water are reviewed. For the crown ether fluoroionophore/-CyD complex, the dimerization of the fluoroionophore inside the -CyD is found to be selectively promoted by alkali metal ion binding, thereby resulting in metal-ion-selective pyrene dimer emission in water. This supramolecular function is successfully utilized in the design of a podand fluoroionophore/-CyD complex for sensing toxic lead ion in water. The boronic acid fluoroionophore/-CyD complex binds sugars and produces increased fluorescence emission in water. The response mechanism appears to be due to the suppression of the photoinduced electron transfer (PET) from pyrene donor to trigonal phenylboronic acid acceptor. This is a novel emission function provided by the boronic acid fluoroionophore/-CyD complex sensors in water. 相似文献
16.
《Tetrahedron》2004,60(3):529-534
Cyclodextrin glucosyltransferase (CGTase) from Thermoanaerobacter sp. was covalently immobilized on Eupergit C and used for the synthesis of maltooligosyl fructofuranosides employing soluble starch as donor and sucrose as acceptor. Using a weight ratio starch-sucrose of 1:2, the conversion of starch into acceptor products catalyzed by soluble and immobilized CGTases was higher than 80% in 48 h. Under these conditions, the reaction was selective for the formation of maltosyl fructofuranoside. 相似文献
17.
18.
衍生化毛细管气相色谱法测定糖尿病大鼠眼球晶体中糖醇含量 总被引:4,自引:0,他引:4
建立了大鼠眼球晶体中糖醇化合物包括葡萄糖、肌醇、山梨醇同时测定的毛细管气相色谱分析方法。通过改进用甘露糖为内标,先加入5%盐酸羟胺.吡啶溶液进行肟化反应,再加入醋酸酐溶液进行乙酰化反应,将糖醇化合物转化成相应的糖腈乙酰醇化合物,经SE-30毛细管柱色谱分离,氢火焰离子化检测器检测。葡萄糖、肌醇、山梨醇的回收率均在93%以上,其检出限分别为0.40、0.26和0.30mg/L。比较测定了正常对照组、糖尿病对照组、某中药复方治疗组的大鼠眼球晶体中各单糖的含量。 相似文献
19.
研究了水质、滤膜、溶液浓度、糖液pH值、混浊度的变化与白砂糖色值的关系。研究结果表明,溶液的pH变化影响最严重。不调整糖液pH与用HCl或NaOH调整糖液pH对比所得白砂糖色值的结果是满意的。标准偏差112~186,相对标准偏差116%~225%,调pH使结果偏高,导致产生系统误差。因此:测定白砂糖色值不宜调整糖液的pH。 相似文献
20.
The influence of newly synthesized N-alkanoyl-N-methyllactitolamines (decanoyl [C10MELA], lauoroyl [C12MELA] and miristoyl [C14MELA]) on the thermotropic phase transition of phosphatidylcholine bilayer was compared with common sugar-based surfactants N-dodecyl-β-d-glucopyranoside [C12G1] and decanoyl-N-methyl glucamide [MEGA-10]. The results indicate that CnMELA are very active at the membrane surface and disturb the phospholipid bilayer structure less than commercially used MEGA-10 and C12G1. 相似文献