C13-Norisoprenoid megastigmanes: Biosynthesis, classification, natural sources, biological activities, and structure-activity relationship - A comprehensive review

C13-Norisoprenoid megastigmanes are a currently expanding class of secondary metabolites originating from the oxidative degradation of carotenoids such as lutein and neoxanthin. These metabolites have been isolated either in free, glycosidically bound forms or as acylated derivatives from a wide diversity of the plant kingdom. The classification of megastigmanes depends on the diversity of the oxygenation positions and the biogenetic origin. These compounds play a crucial role in imparting wine with its characteristic variant flavors, and they are potentially important flavoring agents for the food and pharmaceutical industries. Striking examples for the class are the unusually potent fragrances β-ionone, β-damascenone, and megastigmatrienone. The literature highlighted several compounds that need further development and optimization for drug discovery programs of hepatoprotective, anti-inflammatory, antioxidant, cytotoxic, anti-melanogenic, and cholesterol and triglycerides metabolism-promoting drugs. This comprehensive review focuses on classification, biosynthesis, distribution in natural sources, and chemical structures, the studied biological activities, as well as the structure-activity relationship of the new natural C13-norisoprenoid megastigmanes. A total of 800 C13-norisoprenoid megastigmanes were covered from the first reported isolation of megastigmanes up to December 2024 and 355 references are cited.

Biotransformation of Glaucic Acid Isolated from the Root of Lindera glauca by the Endophytic Fungi Penicillium Chrysogenum SHJ-07

Glaucic acid isolated from the root of Lindera glauca, was investigated by the biotransformation methods via the endophytic fungi, resulting in the production of five new glausesquiterpenes A-E (1-5), along with a known analogue 6. Their structures were elucidated based on spectroscopic methods and electronic circular dichroism (ECD) calculations. In the bioassays, glausesquiterpene A (1) showed good inhibitory activity of NO production in LPS-activated RAW 264.7 macrophages with an IC50 value of 20.1 μM than positive control (Indomethacin, IC50 24.1 μM). Further in vitro studies demonstrated that glausesquiterpene A significantly suppressed the protein expression of iNOS and COX-2 at the concentration of 25.0 μM.

Combination of microbial and chemical synthesis for the sustainable production of β-elemene, a promising plant-extracted anticancer compound

Beta-elemene, a class of sesquiterpene derived from the Chinese medicinal herb Curcuma wenyujin, is widely used in clinical medicine due to its broad-spectrum antitumor activity. However, the unsustainable plant extraction prompted the search for environmentally friendly strategies for β-elemene production. In this study, we designed a Yarrowia lipolytica cell factory that can continuously produce germacrene A, which is further converted into β-elemene with 100% yield through a Cope rearrangement reaction by shifting the temperature to 250°C. First, the productivity of four plant-derived germacrene A synthases was evaluated. After that, the metabolic flux of the precursor to germacrene A was maximized by optimizing the endogenous mevalonate pathway, inhibiting the competing squalene pathway, and expressing germacrene A synthase gene in multiple copies. Finally, the most promising strain achieved the highest β-elemene titer reported to date with 5.08 g/L. This sustainable and green method has the potential for industrial β-elemene production.

Eugenilones A-N: sesquiterpenoids from the fruits of Eugenia uniflora

(+) and (-)-Eugenilones A-K, 11 pairs of undescribed enantiomeric sesquiterpenoids, together with three undescribed biogenetically related members eugenilones L-N, were discovered from the fruits of Eugenia uniflora Linn. (Myrtaceae). Structurally, eugenilones A-D were four caged sesquiterpenoids featuring 9,10-dioxatricyclo [6.2.2.0^2,7]dodecane, 11-oxatricyclo [5.3.1.0^3,8]undecane, and tricyclo [4.4.0.0^2,8]decane cores, respectively. Eugenilones E-K were eudesmane-type sesquiterpenoids, while eugenilones L-N were epoxy germacrane-type sesquiterpenoids. Notably, eugenilones A-K were efficiently resolved by chiral HPLC to give 11 pairs of optically pure enantiomers. The structures and absolute configurations of eugenilones A-N were determined through spectroscopic analyses, X-ray crystallography, and ECD calculations. The putative biosynthetic pathways for these undescribed isolates were proposed. Moreover, eugenilones A and E exhibited significant anti-inflammatory effects by inhibiting LPS-stimulated NO overproduction in RAW264.7 cells (IC₅₀ values of 4.89 ± 0.37 μM and 20.89 ± 1.49 μM, respectively) and TNF-α-induced NF-κB activation in HEK293 cells (IC₅₀ values of 10.97 ± 1.03 μM and 28.63 ± 1.59 μM, respectively).

Four New Highly Oxygenated Eremophilane Sesquiterpenes from an Endophytic Fungus Boeremia exigua Isolated from Fritillaria hupehensis

Four new eremophilane-type sesquiterpenes, boeremialanes A–D (1–4) were obtained from solid substrate cultures of Boeremia exigua (Didymellaceae), an endophytic fungus isolated from Fritillaria hupehensis (Liliaceae). Boeremialanes A–C (1–3) are highly oxygenated eremophilanes with a benzoate unit attached at the C-13 position and are rarely found in nature. Their structures and absolute configurations were determined by extensive spectroscopic methods, electronic circular dichroism (ECD), and nuclear magnetic resonance (NMR) calculations with DP4+ analysis. Boeremialane D (4) potently inhibited nitric oxide production in lipopolysaccharide-treated RAW264.7 macrophages with an IC₅₀ of 8.62 μM and was more potent than the positive control, pyrrolidinedithiocarbamate (IC₅₀ = 23.1 μM).

Two New Eudesmane Sesquiterpenoids from the Flowers of Chrysanthemum indicum

The flowers of Chrysanthemum indicum, i.e. Ye-ju-hua recorded in the Chinese Pharmacopoeia, has been widely used in China as an important heat-clearing and detoxifying herb for the treatment of inflammation, headache, and vertigo. A phytochemical investigation of this herb has led to the isolation of two new eudesmane sesquiterpenoids, 7-epi-eudesm-4(15),11(13)-diene-1β,3β-diol (1) and 7-epi-1β-hydroxy-β-eudesmol (2). The molecular structures of these new sesquiterpenoids were established based on the comprehensive spectroscopic analyses, including NMR, MS, and IR, and comparing with the literatures.

Enhanced structural diversity in terpenoid biosynthesis: enzymes, substrates and cofactors

The enormous diversity of terpenes found in nature is generated by enzymes known as terpene synthases, or cyclases. Some are also known for their ability to convert a single substrate into multiple products. This review comprises monoterpene and sesquiterpene synthases that are multiproduct in nature along with the regulation factors that can alter the product specificity of multiproduct terpene synthases without genetic mutations. Variations in specific assay conditions with focus on shifts in product specificity based on change in metal cofactors, assay pH and substrate geometry are described. Alterations in these simple cellular conditions provide the organism with enhanced chemodiversity without investing into new enzymatic architecture. This versatility to modulate product diversity grants organisms, especially immobile ones like plants with access to an enhanced defensive repertoire by simply altering cofactors, pH level and substrate geometry.

Total Synthesis of Highly Oxygenated Bisabolane Sesquiterpene Isolated from Ligularia lankongensis: Relative and Absolute Configurations of the Natural Product

The relative and absolute configurations of an oxygenated bisabolane natural product, isolated from Ligularia lankongensis, were determined by synthesis. All four possible stereoisomers and their tiglate analogues were synthesized from R-(-)-carvone, and their ¹H and ¹³C NMR spectra were compared to establish the 6R,8S,10S configuration. The stereoselective synthesis of the natural product was also achieved, featuring Brown allylation, vanadium-catalyzed epoxidation, and the Mitsunobu reaction.

Bisabolane Sesquiterpenoids from the Plant Endophytic Fungus Paraconiothyrium brasiliense

Brasilamides E-J (1-6), the bisabolane sesquiterpenoids with the 3-cyclohexylfuran (1 and 2) and 3-cyclohexylfuranone (3-6) skeletons, were isolated from the scale-up fermentation cultures of the plant endophytic fungus Paraconiothynium brasiliense Verkley. Although brasilamide E (1) is a known metabolite, its structure elucidation has yet to be described. The structures of 1-6 were elucidated primarily by NMR experiments. Compounds 3-6 were found to be racemic, and 3 was further separated into enantiomers 3a and 3b on a chiral HPLC column. The absolute configurations of 3a and 3b were assigned by electronic circular dichroism calculations. Compound 1 selectively inhibited the proliferation of the breast (MCF-7) and gastric (MGC) cancer cell lines, with IC50 values of 8.4 and 14.7 μM, respectively. Initial mechanistic investigation revealed that compound 1 inhibited the expression of a key energy metabolic enzyme, hexokinase II (HK2), in MCF-7 cells, which resulted in dysfunction of glucose metabolism and ATP depletion and eventually inhibited the proliferation of the breast cancer cells.

Biological activity of natural sesquiterpenoids containing a gem-dimethylcyclopropane unit

The biological activity of sesquiterpenes containing the gem-dimethylcyclopropane unit is described.

Heterocyclic terpenes: linear furano- and pyrroloterpenoids

This review of furano- and pyrroloterpenoids covers the literature, 180 articles in all, published from January 2006 to December 2013.

Cadinane sesquiterpenes from the mushroom Lyophyllum transforme

Two rare cadinane-type sesquiterpenes, lyophyllone A (1) and lyophyllanetriol A (2), were isolated from the mushroom Lyophyllum transforme. The structures were elucidated on the basis of exhaustive NMR techniques, together with MS, UV-Vis and molecular modelling. The absolute configuration of lyophyllone A was determined by ab initio theoretical CD calculation performed by Density Functional Theory (DFT) using the B3PW91/6-31G(d,p) basis set. The experimental CD were found to be in good agreement with the corresponding population-weighted theoretical CD spectra, allowing for the determination of the absolute stereochemistry of the compound.

Natural sesquiterpenoids

This review covers the isolation, structural determination, synthesis and chemical and microbiological transformations of natural sesquiterpenoids. The literature from January to December 2012 is reviewed, and 471 references are cited.

Guanacastane-type diterpenoids from Coprinus radians

Thirteen diterpenoids, named radianspenes A-M (1-13), including three lactams radianspenes J (10), K (11) and L (12) and one dimer radianspene M (13), were isolated from fermentation products of the higher fungal strain Coprinus radians M65. All these compounds possessing guanacastane skeleton were evaluated for antitumor activity using MDA-MB-435 cell line. Radianspene C exhibited inhibitory activity with IC(50) of 0.91 μM.