title: Nonplanar tertiary amides in rigid chiral tricyclic dilactams. Peptide group distortions and vibrational optical activity.
abstract: 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 full 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 (δ(oop)(N-C) at ~570 cm(-1)) and amide VI (δ(oop)(C'═O) at ~700 cm(-1) and ~650 cm(-1)) vibrations.
authors.affiliation: Institute of Organic Chemistry and Biochemistry AS CR, Prague 6, Czech Republic.
authors.forename: Markéta
authors.initials: M
authors.lastname: Pazderková
authors.forename: Václav
authors.initials: V
authors.lastname: Profant
authors.forename: Jana
authors.initials: J
authors.lastname: Hodačová
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Sebestík
authors.forename: Tomáš
authors.initials: T
authors.lastname: Pazderka
authors.forename: Pavlína
authors.initials: P
authors.lastname: Novotná
authors.forename: Marie
authors.initials: M
authors.lastname: Urbanová
authors.forename: Martin
authors.initials: M
authors.lastname: Safařík
authors.forename: Miloš
authors.initials: M
authors.lastname: Buděšínský
authors.forename: Miloš
authors.initials: M
authors.lastname: Tichý
authors.forename: Lucie
authors.initials: L
authors.lastname: Bednárová
authors.forename: Vladimír
authors.initials: V
authors.lastname: Baumruk
authors.forename: Petr
authors.initials: P
authors.lastname: Maloň
mesh_terms: D000577:Amides / Q000737:chemistry*; D002942:Circular Dichroism; D007769:Lactams / Q000737:chemistry*; D009904:Optical Rotation; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D013237:Stereoisomerism; D014732:Vibration
chemical_list: D000577:Amides; D007769:Lactams; D010455:Peptides