Use Of Chiral Shift Reagent Research Articles

Absolute Configuration of In Situ Crystallized (+)-γ-Decalactone

Knowledge about the absolute configuration of small bioactive organic molecules is essential in pharmaceutical research because enantiomers can exhibit considerably different effects on living organisms. X-ray crystallography enables chemists to determine the absolute configuration of an enantiopure compound due to anomalous dispersion. Here, we present the determination of the absolute configuration of the flavoring agent (+)-γ-decalactone, which is liquid under ambient conditions. Single crystals were grown from the liquid in a glass capillary by in situ cryo-crystallization. Diffraction data collection was performed using Cu-Kα radiation. The absolute configuration was confirmed. The molecule consists of a linear aliphatic non-polar backbone and a polar lactone head. In the solid state, layers of polar and non-polar sections of the molecule alternating along the c-axis of the unit cell are observed. In favorable cases, this method of absolute configuration determination of pure liquid (bioactive) agents or liquid products from asymmetric catalysis is a convenient alternative to conventional methods of absolute structure determination, such as optical rotatory dispersion, vibrational circular dichroism, ultraviolet-visible spectroscopy, use of chiral shift reagents in proton NMR and Coulomb explosion imaging.

Differentiation of meso isomers from racemic mixtures with the combined use of chiral shift reagents and two‐dimensional heteronuclear correlation NMR spectroscopy

AbstractIn the presence of chiral shift reagents the enantiotopic nuclei of a pair of enantiomers become diastereotopic and have the potential to give resolved NMR signals. Similarly, the enantiotopic nuclei within a meso isomer become diastereotopic in the presence of a chiral shift reagent and may give resolved NMR signals. However, the diastereotopic nuclei of a meso isomer mixed with a chiral shift reagent, unlike those of a racemic mixture, are located in the same molecule. Their intramolecular character can be established experimentally by detection of spin‐spin splitting between them or to a common third nucleus. Comparison of the correlation peaks in a two‐dimensional, heteronuclear, multiple‐quantum correlation (HMQC) spectrum with those of a heteronuclear multiple‐bond correlation (HMBC) spectrum is an effective means of detection of coupling to a third nucleus. Two‐dimensional NMR spectroscopy was used to identify the meso form of di‐(trans‐2‐aminocyclohexyl)amine.

ChemInform Abstract: RECOGNITION OF ATROPISOMERISM AND THERMALLY LABILE PROCHIRALITY, AND MEASUREMENT OF BARRIERS TO ROTATION IN SULFINES (THIONE OXIDES) BY THE USE OF CHIRAL SHIFT REAGENTS

AbstractChirale Verschiebungsreagenzien wie z.B. Yt‐optishift II werden zum Nachweis der Atropisomerie in Sulfinen mit stark gehinderter Rotation um die CSO‐Aryl‐Bindung wie z.B. in (I) eingesetzt.

Recognition of atropisomerism and thermally labile prochirality, and measurement of barriers to rotation in sulfines (thione oxides) by the use of chiral shift reagents

AbstractThe sulfines 1–9 in which the o‐positions of the aryl ring A are substituted by methyl groups, have a high rotational barrier about the aryl A to sulfine bond (bond α). Due to this α‐barrier, sulfines 1 and 2 exist as a pair of rotational enantiomers (atropisomerism). The symmetrically substituted sulfines 3,4,7,8 and 9 possess a prochiral centre, viz. the mesityl‐CSO part, provided rotation about bond α is restricted. With rapid rotation about bond α this prochirality disappears (thermally labile prochirality). Chiral lanthanide shift reagents are employed to uncover these chiral properties. The atropisomerism in the sulfines 1 and 2 and the thermally labile prochirality in the sulfines 3,4, 7, 8 and 9 are demonstrated by use of chiral shift reagent. Moreover, chiral shift reagents are successfully used to determine the α‐barrier in the sulfines 3, 4 and 9.