来自皱念珠菌的脂肪酶对α-取代的手性酸(例如2-芳基丙酸)显示出高对映选择性。为了了解皱纹念珠菌脂肪酶(CRL)如何区分手性酸的对映异构体,我们确定了与CRL共价连接的过渡态类似物的X射线晶体结构。CRL对2-甲氧基-2-苯乙酸甲酯,1-甲酯具有中等的对映选择性(E = 23),有利于(S)-对映异构体。我们合成了膦酸酯(R C,R P S P)‐3,与CRL反应后,它模拟了(S的水解的过渡态)1-甲酯,快速反应的对映异构体。该复合物的X射线晶体结构显示出脂肪酶疏水通道中苯环的催化生产取向。Phe345拥挤了基板立体中心附近的区域。慢反应对映异构体的计算机建模检查了相应的慢反应对映异构体的四个可能构象:三个构象,相对于快速反应对映异构体,两个立体中心的取代基已被交换;一个构象具有伞状反转取向。这些取向中的每一个都破坏催化组氨酸的取向,但是破坏的分子基础在每种情况下都不同,这表明高对映选择性需要多种机理。
Photolysis of Triarylmethylphosphonic Acids and Their Esters
作者:Min Shi、Yoshiki Okamoto、Setsuo Takamuku
DOI:10.1246/bcsj.63.453
日期:1990.2
Upon UV-irradiation in an alkaline alcohol solution, some triarylmethylphosphonic acids underwent C–P bond cleavage to give triarylmethanes and alkyl dihydrogenphosphates, while, in an acidic or a neutral alcohol solution, they afforded biaryls. Their dimethyl esters gave also biaryls and dimethyl [alkoxy(aryl)methyl]phosphonates, which were derived from the insertion of (dialkoxyphosphinyl)arylcarbenes
Use of the Wadsworth–Emmons reaction for preparing hindered vinyl ethers and related 1,2-dioxetanes
作者:Carl A. Roeschlaub、Peter G. Sammes
DOI:10.1039/b002101f
日期:——
Arylaldehyde acetals can be reacted with trimethyl phosphite to produce the corresponding dimethyl α-methoxybenzylphosphonates, themselves used in a WadsworthâEmmons reaction with adamantanone to produce hindered methyl vinyl ethers. These vinyl ethers are useful in the preparation of chemiluminescent 1,2-dioxetanes. The scope of the reaction has been explored.
A Flexible Enantioselective Total Synthesis of Diospongins A and B and Their Enantiomers Using Catalytic Hetero-Diels−Alder/Rh-Catalyzed 1,4-Addition and Asymmetric Transfer Hydrogenation Reactions as Key Steps
A unified enantioselective route to totalsynthesis of diospongins A and B and their enantiomers has been developed employing achiral starting materials. All three stereocenters were introduced by means of catalytic reactions.
Synopsis. Upon UV irradiation in methanol,diaryl triphenylmethylphosponate underwent three types of elimination of two aryl groups to give biaryls: the first is an α,α-elimination of two phenyl groups from a triphenylmethyl group which leads to formation of the corresponding carbene intermidiate; the second is an elimination of two aryl groups from a diaryl ester group to afford biaryl; the third is an elimination of phenyl and aryl groups from both moieties to give arylbenzene.