Structural and Stereochemical Studies of a Tetralin Norsesquiterpenoid from Ligularia kangtingensis

Abstract

A chiral tetralin norsesquiterpenoid, ligukangtinol, was isolated from the plant Ligularia kangtingensis. Its planar structure was determined by extensive analysis of spectroscopic data (MS, IR, and NMR), and (1S,3R) absolute configuration of the tetralin ring was established by TDDFT-ECD calculations of the solution conformers. Conformational analysis and ECD calculations proved that the semiempirical helicity rules of 6-hydroxytetralins correlating the 1 L b Cotton effect and P/M helicity of the fused carbocyclic ring correctly predicts the absolute configuration and thus can be used for the configurational assignment of related substituted tetralin derivatives. Chirality 00:000-000, 2014.

Atropoisomerism in Biflavones: The Absolute Configuration of (−)-Agathisflavone via Chiroptical Spectroscopy

“…The simultaneous use of more than one of these methods is known to be necessary to provide reliable assignment of stereostructures. , Since the interpretation of chiroptical spectra using empirical or semiempirical methods may give inaccurate results, the currently prevailing trend relies on the use of calculated spectra using reliable quantum chemical methods. Accordingly, the ACs of several chiral natural products and small molecules have been determined by chiroptical spectroscopic methods over the past several years. − …”

Enantioselective High‐Throughput Assay Showcased for the Identification of (R)‐ as well as (S)‐Selective Unspecific Peroxygenases for C−H Oxidation

“…When trying to rationalize stereoselectivity on a structural level, it should be emphasized that 4 a has a C 2 ‐axis of symmetry and displays helicity; [38] thus, there are several binding modes, which can lead to the enantiomers of α‐ 4 b and β‐ 4 b (Figure 5).…”

“…Superimposing enantiocomplementary GdiUPO-II and AaeUPO (wt) demonstrated how introducing steric congestion in the active side, that is, replacing Ala73 and Ala77 of AaeUPO by Leu118 and Leu122 as in GdiUPO-II, forces 4 a to adopt an alternative binding mode, which ultimately led to a switch in stereopreference (Figure 4D). We also observed distinct docking When trying to rationalize stereoselectivity on a structural level, it should be emphasized that 4 a has a C 2 -axis of symmetry and displays helicity; [38] thus, there are several binding modes, which can lead to the enantiomers of α-4 b and β-4 b (Figure 5).…”

Absolute Configuration of (−)-Centratherin, a Sesquiterpenoid Lactone, Defined by Means of Chiroptical Spectroscopy

“…Therefore, the current trend relies on the evaluation of the experimental spectra with reference to those predicted using reliable quantum chemical methods. The popularity of this approach is reflected in the determination of ACs of several chiral natural products by means of chiroptical spectroscopy methods over the past several years. − …”