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

0396265 - ÚOCHB 2014 RIV US eng J - Journal Article
Pazderková, Markéta - Profant, V. - Hodačová, J. - Šebestík, Jaroslav - Pazderka, T. - Novotná, P. - Urbanová, M. - Šafařík, Martin - Buděšínský, Miloš - Tichý, Miloš - Bednárová, Lucie - Baumruk, V. - Maloň, Petr
Nonplanar Tertiary Amides in Rigid Chiral Tricyclic Dilactams. Peptide Group Distortions and Vibrational Optical Activity.
Journal of Physical Chemistry B. Roč. 117, č. 33 (2013), s. 9626-9642. ISSN 1520-6106. E-ISSN 1520-5207
R&D Projects: GA ČR GAP205/10/1276
Institutional support: RVO:61388963
Keywords : spirodilactams * amide bond * vibrational circular dichroism * non-planarity * Raman optical activity
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.377, year: 2013

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',7,7'-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 fill range vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra including signals of C-H and C-D 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-amide interaction. Amide-amide coupling dominates amide II (mainly C'-N stretching, modified in tertiary amides by the absence of a N-H 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 (delta(oop)(N-C) at similar to 570 cm(-1)) and amide VI (delta(oop)(C'=O) at similar to 700 cm(-1) and similar to 650 cm(-1)) vibrations.
Permanent Link: http://hdl.handle.net/11104/0224146