A trans-product is isolated and characterized under traditional hydroboration–oxidation conditions using Δ5-steroids as substrates. Experimental and theoretical studies indicate that the trans-species occurs via a retro-hydroboration mechanism.
Potassium borohydride reductions of immobilised ketosteroids
作者:Josie C Briggs、Philip Hodge、Zhengpu Zhang
DOI:10.1016/s0040-4020(97)00011-2
日期:1997.3
insoluble supports (powdered polyethylene, microporous 2% crosslinked polystyrene beads, macroporous highly crosslinked polystyrene beads, silica gel and alumina) can be reduced using aqueous potassiumborohydride. The use of phase transfer catalysts generally raises yields. In the case of 6-ketosteriods the supported reactions often follow a stereochemical course significantly different from that of
H-Atom Abstraction vs Addition: Accounting for the Diverse Product Distribution in the Autoxidation of Cholesterol and Its Esters
作者:Zosia A. M. Zielinski、Derek A. Pratt
DOI:10.1021/jacs.8b11524
日期:2019.2.20
serious implications for how these oxysterols are used as biomarkers. The resolution and quantification of all autoxidationproducts by LC-MS/MS was greatly enabled by the synthesis of a new isotopically labeled cholesterol standard and corresponding selected autoxidationproducts. The autoxidation of cholesteryl acetate was also investigated as a model for the cholesterol esters which abound in vivo. Although
我们最近表示,胆固醇的自由基介导的氧化(自氧化)会产生比以前认为的更复杂的氢过氧化物产物混合物。除了主要产物胆固醇 7-氢过氧化物的差向异构体之外,在良好的 H 原子供体存在下,还形成了区域异构 4-和 6-氢过氧化物中的每一种的差向异构体,就像 5α-氢过氧化物一样。在此,我们通过报告竞争性过氧自由基加成到胆固醇产生的产物来完成这个故事,立体异构的胆固醇-5,6-环氧化物占氧化产物的 12%,以及胆固醇氢过氧化物的亲电脱水产物, 4-、6- 和 7- 酮胆固醇。而且,我们询问了在良好的 H 原子供体存在的情况下,它们的分布和相对于 H 原子提取产物的丰度如何变化,这对如何将这些氧甾醇用作生物标志物具有重要意义。LC-MS/MS 对所有自氧化产物的分辨率和定量在很大程度上得益于合成新的同位素标记胆固醇标准品和相应的选定自氧化产物。还研究了胆固醇乙酸酯的自氧化作为体内大量胆固醇酯的模型。尽管
Potassium borohydride reductions of ketones absorbed into polymer supports: stereochemical effects
作者:Josie C. Briggs、Philip Hodge
DOI:10.1039/c39880000310
日期:——
The proportions of 6α-alcohol obtained from aqueous potassium borohydride reductions of 3β-hydroxy-5α-cholestan-6-one (1) absorbed into various polymers varied from 0 to 90% depending on the polymer used and whether or not a phase transfer catalyst was added; some other ketones show similar stereochemical effects, the greatest effects probably arising when the substrates are adsorbed to the inner surfaces
Structural Studies by Exciton Coupled Circular Dichroism over a Large Distance: Porphyrin Derivatives of Steroids, Dimeric Steroids, and Brevetoxin B
作者:Stefan Matile、Nina Berova、Koji Nakanishi、Jörg Fleischhauer、Robert W. Woody
DOI:10.1021/ja960126p
日期:1996.6.5
scope and limitations of porphyrin chromophores for structural studies by the exciton coupled circulardichroic (CD) method. A distance dependency of the porphyrin coupling was investigated in the range between 10 and 50 A. Over short interchromophoric distances, significant changes in the conformational distribution introduced by the bulky porphyrin chromophores were observed. Over longer distances
本研究(参见参考文献 1)通过激子耦合圆二向色 (CD) 方法描述了卟啉发色团用于结构研究的范围和局限性。在 10 到 50 A 的范围内研究了卟啉偶联的距离依赖性。在较短的发色团间距离上,观察到由庞大的卟啉发色团引入的构象分布的显着变化。在更长的距离内,卟啉显示出大约。与常用发色团相比,灵敏度提高了 10 倍,并通过比较指定了相互作用的卟啉过渡时刻的有效方向。二聚体类固醇和短毒素 B 末端的卟啉在高达 50 A 的发色团间距离内表现出激子耦合。