Nonplanar Tertiary Amides in Rigid Chiral Tricyclic Dilactams. Peptide Group Distortions and Vibrational Optical Activity

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• 作者：Mark茅ta Pazderkov谩 ; V谩clav Profant ; Jana Hoda膷ov谩 ; Jaroslav 艩ebest铆k ; Tom谩拧 Pazderka ; Pavl铆na Novotn谩 ; Marie Urbanov谩 ; Martin 艩afa艡铆k ; Milo拧 Bud臎拧铆nsk媒 ; Milo拧 Tich媒 ; Lucie Bedn谩rov谩 ; Vladim铆r Baumruk ; Petr Malo艌
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：August 22, 2013
• 年：2013
• 卷：117
• 期：33
• 页码：9626-9642
• 全文大小：631K
• 年卷期：v.117,no.33(August 22, 2013)
• ISSN：1520-5207

文摘

We investigate amide nonplanarity in vibrational optical activity (VOA) spectra of tricyclic spirodilactams 5,8-diazatricyclo[6,3,0,0^1,5]undecan-4,9-dione (I) and its 6,6鈥?7,7鈥?tetradeuterio derivative (II). These rigid molecules constrain amide groups to nonplanar geometries with twisted pyramidal arrangements of bonds to amide nitrogen atoms. We have collected a full range vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra including signals of C鈥揌 and C鈥揇 stretching vibrations. We report normal-mode analysis and a comparison of calculated to experimental VCD and ROA. The data provide band-to-band assignment and offer a possibility to evaluate roles of constrained nonplanar tertiary amide groups and rigid chiral skeletons. Nonplanarity shows as single-signed VCD and ROA amide I signals, prevailing the couplets expected to arise from the amide鈥揳mide interaction. Amide鈥揳mide coupling dominates amide II (mainly C鈥测€揘 stretching, modified in tertiary amides by the absence of a N鈥揌 bond) transitions (strong couplet in VCD, no significant ROA) probably due to the close proximity of amide nitrogen atoms. At lower wavenumbers, ROA spectra exhibit another likely manifestation of amide nonplanarity, showing signals of amide V (未_oop(N鈥揅) at 570 cm^鈥?) and amide VI (未_oop(C鈥测晲O) at 700 cm^鈥? and 650 cm^鈥?) vibrations.