Three Sesquiterpenoid Dimers from Chloranthus japonicus : Absolute Configuration of Chlorahololide A and Related Compounds

Chemistry and bioactivity of lindenane sesquiterpenoids and their oligomers

Covering: 1925 to July 2023Among the sesquiterpenoids with rich structural diversity and potential bioactivities, lindenane sesquiterpenoids (LSs) possess a characteristic cis, trans-3,5,6-carbocyclic skeleton and mainly exist as monomers and diverse oligomers in plants from the Lindera genus and Chloranthaceae family. Since the first identification of lindeneol from Lindera strychnifolia in 1925, 354 natural LSs and their oligomers with anti-inflammatory, antitumor, and anti-infective activities have been discovered. Structurally, two-thirds of LSs exist as oligomers with interesting skeletons through diverse polymeric patterns, especially Diels-Alder [4 + 2] cycloaddition. Fascinated by their diverse bioactivities and intriguing polycyclic architectures, synthetic chemists have engaged in the total synthesis of natural LSs in recent decades. In this review, the research achievements related to LSs from 1925 to July of 2023 are systematically and comprehensively summarized, focusing on the classification of their structures, chemical synthesis, and bioactivities, which will be helpful for further research on LSs and their oligomers.

Lindenane sesquiterpenoid dimers from Chloranthus japonicus improve LDL uptake by regulating PCSK9 and LDLR

UPLC-TOF-MS/MDF directed phytochemical research of Chloranthus japonicus led to the isolation of 46 lindenane sesquiterpenoid dimers, which included 13 new analogs. Their structures with absolute configurations were elucidated by analysis of spectroscopic data. Fourteen compounds with ester chains significantly decreased PCSK9 protein level in medium of HepG2 cells, especially for compounds 14 and 29 (5 µM) with inhibition rates of 69.0% and 72.8%, respectively. Compound 14 in HepG2 cells was evaluated via DiI-LDL uptake assays and found to increase LDL uptake by upregulating LDLR mRNA and protein level. Meanwhile, 14 decreased the secretion of PCSK9 protein in medium and downregulated intracellular PCSK9 protein and mRNA level. The discovery of these natural small molecule compounds provides a novel structure basis for design PCSK9 regulators, making them a promising lead for development of new lipid-lowering agents.

Lindenane sesquiterpenoid monomers and oligomers: Chemistry and pharmacological activities

Lindenane sesquiterpenoid monomers and oligomers, characterized by a sterically congested cyclopentane and an unusual trans-5/6 ring junction, are mainly found in Chloranthaceae species and the genus Lindera Thunb (Lauraceae). Numerous studies have shown that lindenane sesquiterpenoid monomers and oligomers exhibit a broad range of biological activities, such as cytotoxicity, anti-inflammation, neuroprotection, antifungal, and anti-malarial activities. This review covers publications from the first identification of lindeneol in 1925-2023 and classifies the lindenane sesquiterpenoid derivatives into sesquiterpenoid monomers, sesquiterpenoid-monoterpene conjugates, sesquiterpenoid homodimers, sesquiterpenoid heterodimers, and trimeric sesquiterpenoids. In addition, their biological activities are summarized. This review will establish a scientific basis and provide guidance for utilizing this unique class of natural products as potential lead compounds to develop their application in treating diseases corresponding to inflammation, cancer, and plasmodium.

ECD exciton chirality method today: a modern tool for determining absolute configurations

The application of the exciton chirality method (ECM) to interpret electronic circular dichroism (ECD) spectra is a well‐established and still popular approach to assign the absolute configuration (AC) of natural products, chiral organic compounds, and organometallic species. The method applies to compounds containing at least two chromophores with electric dipole allowed transitions (e.g., π–π* transitions). The exciton chirality rule correlates the sign of an exciton couplet (two ECD bands with opposite sign and similar intensity) with the overall molecular stereochemistry, including the AC. A correct application of the ECM requires three main prerequisites: (a) the knowledge of the molecular conformation, (b) the knowledge of the directions of the electric transition moments (TDMs), and (c) the assumption that the exciton coupling mechanism must be the major source of the observed ECD signals. All these prerequisites can be easily verified by means of quantum‐mechanical (QM) calculations. In the present review, we shortly introduce the general principles that underpin the use of the ECM for configurational assignments and survey its applications, both classic ones and some reported in the recent literature. Based on these examples, we will stress the advantages of the ECM but also the key requisites for its correct application. Additionally, we will discuss the dependence of the couplet sign on geometrical parameters (angles α,β,γ between TDMs), which can be helpful for discerning the sign of exciton chirality in ambiguous situations. Finally, we will present a molecular orbital (MO) description of the exciton coupling phenomenon.

Naturally occurring [4 + 2] type terpenoid dimers: sources, bioactivities and total syntheses

This review article highlights recent progress on their sources, bioactivities, biosynthetic hypotheses and total chemical syntheses of naturally occurring [4 + 2] type terpenoid dimers.

Natural disesquiterpenoids: an update

This review highlights the progress on the isolation, bioactivity, biogenesis and total synthesis of dimeric sesquiterpenoids since 2010.

Survey of bacteria associated with western corn rootworm life stages reveals no difference between insects reared in different soils

Western corn rootworm (Diabrotica virgifera virgifera LeConte) is a serious pest of maize (Zea mays L.) in North America and parts of Europe. With most of its life cycle spent in the soil feeding on maize root tissues, this insect is likely to encounter and interact with a wide range of soil and rhizosphere microbes. Our knowledge of the role of microbes in pest management and plant health remains woefully incomplete, yet that knowledge could play an important role in effective pest management strategies. For this study, insects were reared on maize in soils from different locations. Insects from two different laboratory colonies (a diapausing and a non-diapausing colony) were sampled at each life stage to determine the possible core bacteriome. Additionally, soil was sampled at each life stage and resulting bacteria were identified to determine the possible contribution of soil to the rootworm bacteriome, if any. We analyzed the V4 hypervariable region of bacterial 16S rRNA genes with Illumina MiSeq to survey the different species of bacteria associated with the insects and the soils. The bacterial community associated with insects was significantly different from that in the soil. Some differences appear to exist between insects from non-diapausing and diapausing colonies while no significant differences in community composition existed between the insects reared on different soils. Despite differences in the bacteria present in immature stages and in male and female adults, there is a possible core bacteriome of approximately 16 operational taxonomic units (i.e., present across all life stages). This research may provide insights into Bt resistance development, improved nutrition in artificial rearing systems, and new management strategies.

Chloraserrtone A, a Sesquiterpenoid Dimer from Chloranthus serratus

Chloraserrtone A (1), a new sesquiterpenoid dimer with two lindenane-type sesquiterpenoid monomers bridged by two six-membered rings, was obtained from Chloranthus serratus. A combination of UV, IR, NMR, HRESIMS, and X-ray diffraction data were used to elucidate the structure of 1. Compound 1 represents the first lindenane-type sesquiterpenoid dimer with extremely unique C-15-C-15', C-4-C-6', and C-6-C-11' linkages to form two six-membered rings between the monomeric units. A plausible biosynthesis toward chloraserrtone A is proposed. This new compound (1), together with the known lindenane dimers (2-11), were assessed for their inhibitory effects on lipopolysaccharide-induced NO production in RAW264.7 cells. Compound 6 showed activity with an IC₅₀ value of 3.7 μM.

Applications of OR/ECD/VCD to the structure elucidation of natural products

OR, ECD and VCD are powerful methods to determine the absolute configuration of natural products either applied independently or in combination.

For a Correct Application of the CD Exciton Chirality Method: The Case of Laucysteinamide A

The circular dichroism (CD) exciton chirality method (ECM) is a very popular approach for assigning the absolute configuration (AC) of natural products, thanks to its immediacy and ease of application. The sign of an exciton couplet (two electronic CD bands with opposite sign and similar intensity) can be directly correlated with the molecular stereochemistry, including the AC. However, a correct application of the ECM necessitates several prerequisites: knowledge of the molecular conformation; knowledge of transition moment direction; and preeminence of the exciton coupling mechanism with respect to other sources of CD signals. In recent years, by using quantum-chemical CD calculations, we have demonstrated that some previous applications of ECM were wrong or based on incorrect assumptions. In a recent publication of this journal (Mar. Drugs, 2017, 15(4), 121), the ECM was employed to assign the AC of a marine metabolite, laucysteinamide A. This is a further case of incorrect application of the method, where none of the aforementioned prerequisites is fully met. Using this example, we will discuss the criteria required for a correct application of the ECM.

Chiroptical and vibrational spectroscopic study of genuine and counterfeit medicines containing tadalafil

The production and distribution of counterfeit pharmaceuticals present a serious problem worldwide. This is true especially in case of phosphodiesterase type 5 inhibitors for treating erectile dysfunction, where consumers often prefer buying them anonymously from unverified sources. In this study, genuine and counterfeit Cialis® 20 mg tablets were analyzed by electronic circular dichroism, vibrational circular dichroism, and infrared spectroscopy. The characteristic spectral patterns were identified by comparison with the spectra of tadalafil standard as an active pharmaceutical ingredient, and its presence was confirmed in all samples. The amount of tadalafil, however, was markedly lower in the case of counterfeit tablet as the observed band intensities were considerably lower. No other significant differences between the genuine and counterfeit tablets were revealed. Ab initio density functional theory calculations provided a detailed description of the stable conformers of tadalafil in a solution and enabled thorough interpretation of the experimental spectra.