Synthetic studies toward lindenane-type dimers via Diels-Alder reaction

Naturally Occurring [4+2] Type Terpenoid Dimers Assembled through Unmatched-electron-demand Cycloaddition

Terpenoid dimers of the [4+2] type, which are naturally occurring compounds biosynthetically derived from the [4+2] cycloaddition of two precursors, have garnered considerable attention due to their complex molecular structures, diverse biological activities, and intriguing biosynthetic pathways. We have previously summarized the advancements in three types of [4+2] terpenoid dimers. In this review, we will focus on the lesser-explored class of [4+2] terpenoid dimers which assembled from two electron-deficient precursors via the unmatched-electron-demand Diels-Alder reaction (UMEDDA). We will summarize their sources, biological activities, proposed biosynthesis, and chemical syntheses. Finally, a summary and outlook for this fascinating class of compounds will be presented.

Terpenoids of plants from Chloranthaceae family: chemistry, bioactivity, and synthesis

Covering: 1976 to December 2023Chloranthaceae is comprised of four extant genera (Chloranthus, Sarcandra, Hedyosmum, and Ascarina), totaling about 80 species, many of which have been widely used as herbal medicines for diverse medical purposes. Chloranthaceae plants represent a rich source of structurally interesting and diverse secondary metabolites, with sesquiterpenoids and diterpenoids being the predominant structural types. Lindenane sesquiterpenoids and their oligomers, chemotaxonomical markers of the family Chloranthaceae, have shown a wide spectrum of bioactivities, attracting significant attention from organic chemists and pharmacologists. Recent achievements also demonstrated the research value of two unique structural types in this plant family, sesquiterpenoid-monoterpenoid heterodimers and meroterpenoids. This review systematically summarizes 682 structurally characterized terpenoids from 22 Chloranthaceae plants and their key biological activities as well as the chemical synthesis of selected terpenoids.

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.

Total Synthesis and Prediction of Ulodione Natural Products Guided by DFT Calculations

A biomimetic synthetic strategy has resulted in a two-step total synthesis of (±)-ulodione A and the prediction of two potential natural products, (±)-ulodiones C and D. This work was guided by computational investigations into the selectivity of a proposed biosynthetic Diels-Alder dimerization, which was then utilized in the chemical synthesis. This work highlights how biosynthetic considerations can both guide the design of efficient synthetic strategies and lead to the anticipation of new natural products.

Asymmetric Total Synthesis of Shizukaol J, Trichloranoid C and Trishizukaol A

The asymmetric total synthesis of three lindenane sesquiterpenoid oligomers, shizukaol J, trichloranoid C and trishizukaol A, has been accomplished concisely in 15, 16 and 18 longest linear steps, respectively. The expeditious construction of molecular architectures was facilitated by Nelson's catalytic asymmetric ketene-aldehyde cycloaddition, a sequence of allylic alkylation/reduction/acidic cyclization to forge a lactone, and a double aldol condensation cascade to construct the 5/6 bicyclic system. Diastereoselective nucleophilic substitution promoted by a phase transfer catalyst constructed the C₁₁ quaternary stereogenic center, thus prompting synthetic efficacy toward shizukaol J. The synthesis of trichloranoid C and trishizukaol A was achieved after a cascade involving furanyl diene formation and a Diels-Alder reaction, as well as a one-pot sequence involving furan oxidation and global deprotection. Furthermore, our biological evaluation revealed that two compounds exhibited unexpected toxicity against tumor cell lines.

The anti-inflammatory activity by suppressing the TRAF6/MAPKs pathway of trishizukaol a from Sarcandra glabra

BACKGROUND

Sarcandra glabra (Thunb.) Makino (Chloranthaceae) is abundant and shows important clinical effects. Traditionally, S.glabra is used to treat diseases involving inflammation, such as bone fracture and joint swelling. Lindenane-type sesquiterpenoids and dimers are the major anti-inflammatory components in S. glabra. Trishizukaol A (TSA), is an abundant lindenane sesquiterpenoid trimer in S.glabra, but its anti-inflammatory activities and mechanisms are poorly understood.

PURPOSE

The study was undertaken to unveil the inhibition of inflammation and mechanism of TSA in RAW 264.7 macrophages stimulated by lipopolysaccharide (LPS).

METHODS

Griess reagent and ELISA were utilized to measure nitric oxide (NO) production and inflammatory cytokines, respectively. Signal proteins such as JNK, nuclear factor E2-related factor 2 (Nrf2) and tumor necrosis factor receptor-associated factor 6 (TRAF6) were quantitatively evaluated in western blot experiments. Flow cytometry was used to determine the concentration of reactive oxygen species (ROS). More importantly, Drug Affinity Responsive Target Stability (DARTS) assay and molecular docking were conducted to investigate the potential targets of TSA.

RESULTS

TSA effectively reduced the NO production (half-maximal inhibitory concentration (IC50) at 12.53 ± 0.31 μM). In addition, TSA restrained the expression of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), and it could up-regulate the levels of interleukin-10 (IL-10). TSA also decreased ROS levels by enhancing the levels of Nrf2 protein and its related target genes. Meanwhile, TSA regulated the nuclear translocation of nuclear factor-κB (NF-κB) by suppressing the MAPKs signaling pathway. Importantly, TSA may suppress the inflammation through the TRAF6/MAPKs pathway.

CONCLUSION

TSA suppressed the inflammatory mechanism mediated by the TRAF6/MAPKs pathway. Our research first revealed the anti-inflammatory effect of a lindenane sesquiterpenoid trimer, providing a therapeutic drug candidate for inflammatory diseases. Furthermore, the lindenane-type sesquiterpenoid trimers may be among the main anti-inflammatory components in S. glabra.

Biomimetic Approaches to the Synthesis of Natural Disesquiterpenoids: An Update

Natural disesquiterpenoids represent a small group of secondary metabolites characterized by complex molecular scaffolds and interesting pharmacological profiles. In the last decade, more than 400 new disesquiterpenoids have been discovered and fully characterized, pointing out once more the "magic touch" of nature in the design of new compounds. The perfect blend of complex and unique architectures and biological activity has made sesquiterpene dimers an attractive and challenging synthetic target, inspiring organic chemists to find new and biomimetic approaches to replicate the efficiency and the selectivity of natural processes under laboratory conditions. In this work, we present a review covering the literature from 2010 to 2020 reporting all the efforts made in the total synthesis of complex natural disesquiterpenoids.

Natural disesquiterpenoids: an update

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

A unified strategy toward total syntheses of lindenane sesquiterpenoid [4 + 2] dimers

The dimeric lindenane sesquiterpenoids are mainly isolated from the plants of Chloranthaceae family. Structurally, they have a crowded molecular scaffold decorated with more than 11 stereogenic centers. Here we report divergent syntheses of eight dimeric lindenane sesquiterpenoids, shizukaols A, C, D, I, chlorajaponilide C, multistalide B, sarcandrolide J and sarglabolide I. In particular, we present a unified dimerization strategy utilizing a base-mediated thermal [4 + 2] cycloaddition between a common furyl diene, generated in situ, and various types of dienophiles. Accordingly, all the three types of lindenane [4 + 2] dimers with versatile biological activities are accessible, which would stimulate future probing of their pharmaceutical potential.

Recent advances in the synthesis of oxaspirolactones and their application in the total synthesis of related natural products

Oxaspirolactones are ubiquitous structural motifs found in natural products and synthetic molecules with a diverse biochemical and physicochemical profile, and represent a valuable target in natural product chemistry and medicinal chemistry.