共查询到20条相似文献,搜索用时 31 毫秒
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(+)-(1S, 3S, 6S, 8S)-and (?)-(1R, 3R, 6R, 8R)-4, 9-Twistadiene: Synthesis and Absolute Configuration A synthesis and the determination of the absolute configuration of (+)-(1S, 3S, 6S, 8S)- and (?)-(1R, 3R, 6R, 8R)-4, 9-twistadiene ((+)- and (?)- 4 , respectively) is described. Their chiroptical properties are compared with those of saturated twistane ((+)- and (?)- 5 ) as well as with those of the unsaturated and saturated 2, 7-dioxatwistane analogs (+)- and (?)- 9 , and (+)- and (?)- 10 , respectively, which also are compounds of known absolute configurations. 相似文献
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[reaction: see text] (-)-(6S,7S,8S,9R,10S,2'S)-Membrenone-A and (-)-(6S,7S,8S,9R,10S)-membrenone-B were prepared in 11 steps (3% and 2.4% overall yield, respectively). Key steps included a tin(II)-mediated aldol followed by a syn selective reduction, giving the C7-C9 stereocenters, a second chain extending aldol coupling, and a p-TsOH-promoted cyclization/dehydration giving the common gamma-dihydropyrone precursor. We have thus established that synthetic (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A, (-)-(6S,7S,8S,9R,10S)-membrenone-B, and (-)-(6S,7S,8S,9R,10S)-membrenone-C are the enantiomers of the natural products. 相似文献
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Total asymmetric synthesis of two components of Panax ginseng showing antitumor activity, i.e., (3R,9R,10R)- and (3S,9R,10R)-Panaxytriol and of both enantiomers of Falcarinol was accomplished. Due to the fact that the synthetic strategy was based on enantioconvergent biotransformations, the occurrence of any undesired stereoisomer was entirely avoided. The absolute configuration of naturally occurring Panaxytriol was confirmed to be (3R,9R,10R) on the basis of optical rotation values. It was shown that enzyme-triggered cascade reactions represent a valuable tool for the synthesis of natural products. 相似文献
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A method is described for the qualitative and quantitative determination of configurational isomers of zeaxanthin (=3,3′ -dihydroxy-β, β -carotene) and lutein (=3,3′ -dihydroxy-α -cartotene). It is based on the reaction of these zeaxathin and lutein isomers with (S)-(+)-α-(1-naphthyl) ethyl isocyanate to afford diastereomeric dicarbamates, which are analyzed by HPLC. 相似文献
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Mohamed Abdou Christoph Kratky Georg Uray 《Monatshefte für Chemie / Chemical Monthly》1990,121(12):1039-1043
Summary The crystal structure of (–)-diphenylethanediammonium-(R,R)-tartrate was determined. From this structure determination, the (S,S) configuration was assigned to the (–)-diphenylethanediamine. The asymmetric unit of the crystal structure contains two units of the title compound plus one molecule of ethanol and one water molecule, which form an intricate network of 19 hydrogen bonds.
Die Kristallstruktur von (S,S)-Diphenylethandiammonium-(R,R)-tartrat
Zusammenfassung Es wurde die Kristallstruktur von (–)-Diphenylethandiammonium-(R,R)-tartrat bestimmt. Aus dieser Strukturbestimmung ergab sich die Zuordnung der (S,S)-Konfiguration zum (–)-Diphenylethandiamin. Die asymmetrische Einheit der Kristallstruktur besteht aus zwei Formeleinheiten der Titelverbindung sowie einem Molekül Ethanol und einem Wassermolekül, welche ein komplexes Netzwerk von insgesamt 19 Wasserstoffbrücken bilden.相似文献
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Ahmed Kamal M. Shaheer Malik Shaik Azeeza Shaik Bajee Ahmad Ali Shaik 《Tetrahedron: Asymmetry》2009,20(11):1267-1271
An enantioselective synthesis of (R)-, (S)-turmerone and (7S,9R)-bisacumol is described. The enantiomerically pure key intermediates, a substituted butanoate ester and acid are utilized in the synthesis of both enantiomers of turmerone. The lipase catalyzed resolution studies of the acetate of bisacumol have been exploited towards the total synthesis of the naturally occurring cytotoxic sesquiterpene, (7S,9R)-bisacumol with high diastereoselectivity (94% de). 相似文献
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A method is described for the qualitative and quantitative determination of configurational isomers of astaxanthin. It is based on the esterification of astaxanthin with (—)-camphanic acid chloride and analysis of the corresponding diesters by HPLC. 相似文献
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以手性四氢吡咯片段3a和3b为起始原料, 采用汇聚式合成策略, 完成氮杂Solamin类似物(threo-trans-erythro)的两个对应的光学异构体2a(15S,16S, 19S,20R, 34S)和2b(15R,16R,19R,20S, 34S)的不对称合成. 化合物的结构以及四氢吡咯片段的立体构型均通过NMR波谱解析的方法得到确证. 这两个非对映异构体具有相近的体外抗肿瘤活性. 相似文献
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