Further monoterpene chromane esters from Peperomia obtusifolia: VCD determination of the absolute configuration of a new diastereomeric mixture

A reinvestigation of the monoterpene chromane ester enriched fraction from Peperomia obtusifolia using chiral chromatography led to the identification of a minor peak, which was elucidated by NMR and HRMS as fenchyl-3,4-dihydro-5- hydroxy-2,7-dimethyl-8-(3″-methyl-2″-butenyl)-2-(4′-methyl- 1′,3′-pentadienyl)-2H-1-benzopyran-6-carboxylate, the same structure assigned to two other fenchyl esters described previously, pointing out a stereoisomeric relationship among them. Further NMR analysis revealed that it was actually a mixture of two compounds, whose absolute configurations were determined by VCD measurements. Although, almost no vibrational transitions could be assigned to the chiral chromane, the experimental VCD spectrum was largely opposite to that obtained for the average experimental VCD [(2S,1‴R,2‴R,4‴S + 2R,1‴R,2‴R,4‴S)/2] for fenchol derivatives. These results allowed us to assign the putative compounds as a racemic mixture of the chiral chromane esterified with the monoterpene (1S,2S,4R)-fenchol, which had not been identified in our early work.Fil: Batista Junior, João Marcos. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Batista, Andrea N. L.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Kato, Massuo J.. Universidade de Sao Paulo; BrasilFil: Bolzani, Vanderlan S.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: López, Silvia Noelí. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; ArgentinaFil: Nafie, Laurence A.. Syracuse University; Estados UnidosFil: Furlan, Maysa. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi

VIBRATIONAL CIRCULAR DICHROISM OF (S,S)-OXIRANE−2,3−2H2-2,3-^{2}H_{2} AND (S,S)-CYCLOPROPANE−1,2−2H2-1,2- ^{2}H_{2} IN THE GAS PHASE AND SOLUTION

Author Institution: Department of Chemistry, Syracuse UniversityVibrational circular dichroism (VCD) spectra of two simple chiral three-membered ring molecules, (S,S)-oxirane-2,3-$^{2}H_{2}$ and (S,S)-cyclopropane-1,2-$^{2}H_{2}$ have been obtained for samples in the gas phase and in $C_{2}Cl_{4}$ and $CS_{2}$ solution. Due to electric dipole moment contributions from oxirane ring stretches, the A-symmetry modes are more intense than the B-symmetry modes in the mid-infrared region of (S,S)-oxirane-$2,3- ^{2}H_{2}$, whereas the mid-infrared B-symmetry are more intense in (S,S)-cyclopropane-$1,2-{^{2}H}_{2}$. The signs and relative intensities of the VCD bands in both molecules can be understood in terms of chiral perturbation, due to the deuterium substitution, of the parent achiral oxirane or cyclopropane vibrations. This perturbation mixes modes of the parent molecule that involve linear charge oscillation along an axis with modes that involve angular charge oscillation about that same axis. Comparisons will be made of the observed rotational strengths with recent published VCD intensity calculations using various theoretical approaches."

CONFORMATIONAL STUDY OF 1,2-AMINO ALCOHOLS BY VIBRATIONAL CIRCULAR DICHROISM

Author Institution: Department of Chemistry, Syracuse UniversityVibrational circular dichroism spectra of $(S-(+)-1-amino-2-propanol$ and (S)-(+)-2-amino-1-propanol in tetrachloroethylene solvent have been obtained in the OH- and NH-stretching regions. In dilute solution, absorption bands corresponding to free OH and NH and to both OH--N and NH--O hydrogen-bonded species are observed. No VCD intensity is observed for the ``free'' OH or NH stretches. Negative VCD bands for $v(NH_{2})$asym and $v(NH_{2})$sym are observed for NH--O conformations in both compounds. Only (S)-(+)-1-amino-2-propanol exhibits an intense negative OH-stretching VCD band for the OH--N species; no VCD corresponding to v(OH) is observed for (S)-(+)-2-amino-1-propanol. An interpretation of the VCD spectra based on the ring current mechanism will be presented that identifies the most abundant solution conformations in these amino alcohols

VIBRATIONAL CIRCULAR DICHROISM AND RAMAN OPTICAL ACTIVITY IN EPHEDRINE MOLECULES

Author Institution: Department of Chemistry, Syracuse University; Department of Chemistry, Syracuse UniversityThe vibrational circular dichroism (VCD) spectra in the OH-, NH- and CH-stretching regions, and the dual circular polarization $(DCP_{I}$) Raman optical activity (ROA) spectra in the 800-1700 $cm^{-1}$ region of (1S,2R)-ephedrine, (1S,2R)-norephedrine, (1S,2S)-pseudoephedrine, and (1S,2S)-norpseudoephedrine will be presented. The hydrogen stretching absorption spectra of the free base molecules in dilute $C_{2}Cl_{4}$ solution reflect differences in intramolecular hydrogen bonding among these amino alcohol drug molecules. The corresponding VCD features, which uniquely characterize each stereoisomer, will be correlated with the rotameric populations deduced from NMR studies. The Raman spectra, obtained for aqueous solutions of the hydrochloride salts, are nearly identical for the four ephedrines. In contrast, the ROA spectra are quite different. Several ROA features can be identified that serve as configurational markers."