The stereospecific synthesis of methyl α-C-mannobioside: a potential inhibitor of M. tuberculosis binding to human macrophages
摘要:
The synthesis of the C-glycoside analogue of the mycobacteria capping disaccharide, Man alpha 1-2Man, employing a glycosyl organosamarium is described.
通过变温1 H NMR 光谱研究了 CD 2 Cl 2中 (1,3-二苯基烯丙基) 二甲基锍离子的烯丙基重排动力学,该重排通过中间体 1,3-二苯基烯丙基阳离子进行。在低温下,三个烯丙基质子产生 AMX 系统,两个非对映体S-甲基基团以不同的频率共振。在较高温度下,观察到烯丙基质子的 AX 2系统和S-甲基基团的单一信号。所得汇率常数为 (364 ± 2) s –1在 25°C,对应于 C-S 键的异裂速率,用于探索线性自由能关系 log k het (25°C) = s f ( N f + E f ),它描述了由电离参数E f和溶剂相关的离核剂特定参数N f和s f引起的异裂速率。观察到的速率常数证实了先前的结论,即两组不同的N f和s f相同的nucleofuge 可能存在参数。了解反向成键反应是在活化下还是在扩散控制下发生对于选择适当的核逸散性参数集至关重要。
Kinetics of the reactions of nine symmetrically substituted 1,3-diarylallyl cations with different nucleophiles were studied photometrically in dichloromethane, acetonitrile, and DMSO solutions. The second-order rateconstants k2 were found to follow the correlation log k2 = sN(N + E). The electrophilicity parameters E of the title cations were derived, using the known values of sN and N of the nucleophilic
The present invention relates to a method for the enzymatic hydroamination of C—C double bonds catalyzed by enzymes structurally and/or functionally related to phenylalanine ammonia lyase (PAL) isolated from microorganisms of
Petroselinum crispum, Rhodoturula glutinis
and/or functional active derivatives thereof.
Laser Flash, Laser-Drop, and Lamp Photolysis of 1,3-Dichloro-1,3-diphenylpropane. One- <i>versus</i> Two-Photon Reaction Pathways
作者:Miguel Angel Miranda、Julia Pérez-Prieto、Enrique Font-Sanchis、Klára Kónya、J. C. Scaiano
DOI:10.1021/jo9704772
日期:1997.8.1
Low intensity irradiation of 1,3-dichloro-1,3-diphenylpropane (1) in cyclohexane leads to the formation of 3-chloro-1,3-diphenylpropyl radical (2) through homolytic C-CI bond cleavage. Radical 2 gives rise to final products typical of free radical reactions. Neither 1,2-diphenylcyclopropanes (6) nor 3-cyclohexyl-1,3-diphenylpropene (20) are obtained under these conditions. Nevertheless, high intensity laser irradiation of the initially formed monoradical 2 leads to the 1,3-diphenylpropenyl radical (3) detected with nanosecond techniques. This intermediate is completely trapped by the cyclohexyl radicals generated in the medium to yield 20. Photolysis of 1 with the laser-drop technique leads to the cyclopropanes 6 as major photoproducts.
The synthesis of the C-glycoside analogue of the disaccharide Man(alpha 1-->2)Man has been achieved in a highly stereoselective and efficient manner employing an approach which closely parallels O-glycoside synthesis. The key step included the samarium diiodide reduction of mannosyl pyridylsulfone 18 in the presence of the C2-formyl branched mannoside derivative 17a to furnish the C-disaccharide derivative 19a in high yield. An intramolecular formyl group transfer reaction by means of 5-exo radical cyclization and concomitant fragmentation yielded aldehyde 17a stereospecifically. We also present a potentially viable alternative for the deoxygenation of sterically encumbered secondary alcohols. Attempts to extend this procedure to the synthesis of the C-trisaccharide of Man(alpha 1-->2)Man(alpha 1-->2)Man were frustrated by the inability of the disaccharide, pyridylsulfone derivative 43, to undergo coupling with carbonyl substrates upon treatment with SmI2, possibly owing to the sterically bulky C2 substituent.