Nandy Jyoti Prokosh, Prabhakaran E N, Kumar S Kiran, Kunwar A C, Iqbal Javed
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India, and Indian Institute of Chemical Technology, Hyderabad 500 007, India.
J Org Chem. 2003 Mar 7;68(5):1679-92. doi: 10.1021/jo020352j.
A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereoselectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d6, and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction.
本文描述了一种由聚苯胺负载的钴（II）双水杨醛缩乙二胺（PASCOS）催化的新型N-肉桂酰基肽的化学和非对映选择性需氧环氧化反应。在这些环氧化反应中，N-肉桂酰基脯氨酸衍生的肽1表现出高π-面选择性。1中这种非对映选择性的起源归因于：（i）N-肉桂酰基脯氨酸酰胺在CDCl3、DMSO-d6和CH3CN介质中主要以反式旋转异构体存在的倾向；（ii）由于分子内氢键的存在，这些肽以有序结构（γ-和β-转角）存在。对1d和1f进行的广泛溶液核磁共振和分子动力学模拟研究表明，高π-面选择性的起源是由于明确的γ-和β-转角，这导致在环氧化反应过渡态中肉桂酰双键的一面受到阻碍。
