Assignment of Absolute Configuration of a New Hepatoprotective Schiartane-Type Nortriterpenoid Using X-Ray Diffraction

Chemical constituents from the roots of Kadsura coccinea with their protein tyrosine phosphatase 1B and acetylcholinesterase inhibitory activities

Kadsura coccinea (Lem.) A. C. Smith has been used as a tonic, decongestant, and digestive agent. The roots are also employed in traditional medicine to treat chronic enteritis, acute gastritis, duodenal ulcers, rheumatic pain in bone, and traumatic injuries. In the present study, we have described the biological evaluation of constituents from the roots of K. coccinea with PTP1B and AChE inhibitory activities for the first time in literature. A new compound (1), kadcoccilactone T, and 24 known ones (2‒25) were isolated and identified using spectroscopic methods. All the isolates were examined for PTP1B and AChE inhibitory activities. Compounds 4 and 8 expressed strong PTP1B inhibition with IC₅₀ values of 1.57 ± 0.11 and 3.99 ± 1.08 μM, respectively. Apparently, these compounds were further studied for PTP1B enzyme kinetic analysis. The result indicated that compounds 4 and 8 exhibited mixed-type inhibition with the Κ_i values of 4.97 and 3.26 µM, respectively.

Integrated X-Ray, NMR, ECD, and Computational Approaches to Assign the Stereochemistry of Nortriterpenoids

Highly oxygenated nortriterpenoids are the principle bioactive chemical constituents isolated from plants of the genera Schisandra and Kadsura. The stereochemistry of these molecules remains a highly challenging problem to solve. To establish the stereochemistry and develop a general nuclear magnetic resonance-electric circular dichroism-computational approach to solve these complex metabolites, we reviewed the published methods to solve the stereochemistry of these triterpenoids. A key goal of this review is to provide a protocol to solve the problems hampering the assignment of the relative absolute configurations of other members of this natural product class.

Schincalactones A and B, Two 5/5/6/11/3 Fused Schinortriterpenoids with a 13-Membered Carbon Ring System from Schisandra incarnata

Two novel schinortriterpenoids (SNTs), schincalactones A (1) and B (2), featuring a unique 5/5/6/11/3 ring system, together with schincalide B (3), were isolated from Schisandra incarnata. Their structures were elucidated by detailed spectroscopic analysis, and the absolute configurations of 1 and 3 were confirmed by single-crystal X-ray diffraction. Compounds 1 and 2 possess a 13-membered carbon ring and are the first examples in the SNT family. Plausible biosynthetic pathways of 1-3 were postulated.

Assignment of the absolute configuration of hepatoprotective highly oxygenated triterpenoids using X-ray, ECD, NMR J-based configurational analysis and HSQC overlay experiments

BACKGROUND

The plants of the genus Kadsura are widely distributed in China, South Korea, and Japan. Their roots and stems are traditionally used to treat blood diseases and pain. The main bioactive constituents of Kadsura longipedunculata comprise highly oxygenated triterpenoids. Schiartane-type nortriterpenoids showed anti-HIV, anti-HBV, and cytotoxic bioactivities. For such compounds, the absolute configuration influences the bioactivities, and hence its unambiguous determination is essential. In this work, the absolute configurations of three highly oxygenated schiartane-type nortriterpenoids were unequivocally assigned using X-ray, ECD, and J-based configuration analysis and HSQC overlay data.

METHODS

The ethanol extract of Kadsura longipedunculata Finet et Gagnep was purified by column chromatography using silica, Sephadex LH-20, and ODS as substrates. To help assign the absolute configuration of schiartane-type nortriterpenoids, X-ray diffraction analysis, ECD experiment compared to ab initio computed data, DP4+ analysis, HSQC overlay, NOESY, and J-based configuration analysis were carried out. Hetero- and homo-nuclear coupling constants were extracted from HETLOC experiments.

RESULTS

Three new highly oxygenated triterpenoids, micrandilactone I (1), micrandilactone J (2), and 22,23-di-epi-micrandilactone J (3) were isolated. Their 2D structures were solved using NMR and HRESIMS data and their absolute configurations were elucidated using X-ray diffraction analysis, ECD experimental results compared to ab initio computed spectra, HSQC overlay, DP4+, NOESY, and J-based configuration analysis. Micrandilactone I (1) and 22,23-di-epi-micrandilactone J (3) showed moderate hepatoprotective activity against APAP-induced toxicity in HepG2 cells with cell survival rates of 53.0 and 50.2%, respectively, at 10μM (bicyclol, 49.0%), while micrandilactone J (2) was inactive.

GENERAL SIGNIFICANCE

This is the first comprehensive stereochemical assignment of a non-crystalline schiartane-type nortriterpenoid like 3. This general protocol may contribute towards solving the problems hampering the assignment of the absolute configurations of other members of this class of nortriterpenoids.