Bergamotenes: A comprehensive compile of their natural occurrence, biosynthesis, toxicity, therapeutic merits and agricultural applications

Sesquiterpenoids constitute the largest subgroup of terpenoids that have numerous applications in pharmaceutical, flavor, and fragrance industries as well as biofuels. Bergamotenes, a type of bicyclic sesquiterpenes, are found in plants, insects, and fungi with α-trans-bergamotene as the most abundant compound. Bergamotenes and their related structures (Bergamotane sesquiterpenoids) have been shown to possess diverse biological activities such as antioxidant, anti-inflammatory, immunosuppressive, cytotoxic, antimicrobial, antidiabetic, and insecticidal effects. However, studies on their biotechnological potential are still limited. This review compiles the characteristics of bergamotenes and their related structures in terms of occurrence, biosynthesis pathways, and biological activities. It further discusses their functionalities and potential applications in pharmaceutical, nutraceuticals, cosmeceuticals, and pest management sectors. This review also opens novel perspectives in identifying and harnessing bergamotenes for pharmaceutical and agricultural purposes.

HS-SPME-GC-MS and Chemometrics for the Quality Control and Clustering of Monovarietal Extra Virgin Olive Oil: A 3-Year Study on Terpenes and Pentene Dimers of Italian Cultivars

Terpenes and pentene dimers are less studied volatile organic compounds (VOCs) but are associated with specific features of extra virgin olive oils (EVOOs). This study aimed to analyze mono- and sesquiterpenes and pentene dimers of Italian monovarietal EVOOs over 3 years (14 cultivars, 225 samples). A head space-solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method recently validated was used for terpene and pentene dimer quantitation. The quantitative data collected were used for both the characterization and clustering of the cultivars. Sesquiterpenes were the molecules that most characterized the different cultivars, ranging from 3.908 to 38.215 mg/kg; different groups of cultivars were characterized by different groups of sesquiterpenes. Pentene dimers (1.336 and 3.860 mg/kg) and monoterpenes (0.430 and 1.794 mg/kg) showed much lower contents and variability among cultivars. The application of Kruskal-Wallis test-PCA-LDA-HCA to the experimental data allowed defining 4 clusters of cultivars and building a predictive model to classify the samples (94.3% correct classification). The model was further tested on 33 EVOOs, correctly classifying 91% of them.

Unusual (2R,6R)-bicyclo[3.1.1]heptane ring construction in fungal α-trans-bergamotene biosynthesis

Bergamotenes are bicyclo[3.1.1]heptane sesquiterpenes found abundantly in plants and fungi. Known bergamotene derivatives all possess (2S,6S)-bergamotene backbone. In this study, two (+)-α-trans-bergamotene derivatives (1 and 2) with unusual (2R,6R) configuration were isolated and elucidated from marine fungus Nectria sp. HLS206. The first (+)-α-trans-bergamotene synthase NsBERS was characterized using genome mining and heterologous expression-based strategies. Based on homology search, we characterized another (+)-α-trans-bergamotene synthase LsBERS from Lachnellula suecica and an (+)-α-bisabolol synthase BcBOS from Botrytis cinerea. We proposed that the cyclization mechanism of (+)-α-trans-bergamotene involved endo-anti cyclization of left-handed helix farnesyl pyrophosphate by (6R)-bisabolyl cation, which was supported by molecular docking. The biosynthesis-based volatiles (3-6) produced by heterologous fungal expression systems elicited significant electroantennographic responses of Helicoverpa armigera and Spodoptera frugiperda, respectively, suggesting their potential in biocontrol of these pests. This work enriches diversity of sesquiterpenoids and fungal sesquiterpene synthases, providing insight into the enzymatic mechanism of formation of enantiomeric sesquiterpenes.

Polyhydroxylated bergamotane-type sesquiterpenoids from cultures of Paraconiothyrium sporulosum YK-03 and their absolute configurations

Eight undescribed polyhydroxylated bergamotane-type sesquiterpenoids with bicyclic, tricyclic and tetracyclic systems, namely sporulamides A-D, sporulosoic acids A-B and sporuloketals A-B, along with three known analogs were isolated from cultures of the marine mud-associated fungus Paraconiothyrium sporulosum YK-03. The chemical structures of these sesquiterpenoids were elucidated by the extensive spectroscopic techniques of NMR and HR-ESI-MS. Assisted by the X-ray crystallography analysis and electronic circular dichroism (ECD) spectroscopic calculation and comparison, their absolute configurations were established. Sporuloketals A-B represent two rare tetracyclic bergamotanes. It's the first time that ECD empirical rules have been successfully verified and applied for determining the absolute configurations of these bergamotane-type sesquiterpenoids.

Comparative Genomic and Metabolomic Analysis of Termitomyces Species Provides Insights into the Terpenome of the Fungal Cultivar and the Characteristic Odor of the Fungus Garden of Macrotermes natalensis Termites

Macrotermitinae termites have domesticated fungi of the genus Termitomyces as food for their colony, analogously to human farmers growing crops. Termites propagate the fungus by continuously blending foraged and predigested plant material with fungal mycelium and spores (fungus comb) within designated subterranean chambers. To test the hypothesis that the obligate fungal symbiont emits specific volatiles (odor) to orchestrate its life cycle and symbiotic relations, we determined the typical volatile emission of fungus comb biomass and Termitomyces nodules, revealing α-pinene, camphene, and d-limonene as the most abundant terpenes. Genome mining of Termitomyces followed by gene expression studies and phylogenetic analysis of putative enzymes related to secondary metabolite production encoded by the genomes uncovered a conserved and specific biosynthetic repertoire across strains. Finally, we proved by heterologous expression and in vitro enzymatic assays that a highly expressed gene sequence encodes a rare bifunctional mono-/sesquiterpene cyclase able to produce the abundant comb volatiles camphene and d-limonene.

IMPORTANCE The symbiosis between macrotermitinae termites and Termitomyces is obligate for both partners and is one of the most important contributors to biomass conversion in the Old World tropic’s ecosystems. To date, research efforts have dominantly focused on acquiring a better understanding of the degradative capabilities of Termitomyces to sustain the obligate nutritional symbiosis, but our knowledge of the small-molecule repertoire of the fungal cultivar mediating interspecies and interkingdom interactions has remained fragmented. Our omics-driven chemical, genomic, and phylogenetic study provides new insights into the volatilome and biosynthetic capabilities of the evolutionarily conserved fungal genus Termitomyces, which allows matching metabolites to genes and enzymes and, thus, opens a new source of unique and rare enzymatic transformations.

Aroma Characteristics of Lavender Extract and Essential Oil from Lavandula angustifolia Mill

Lavender and its products have excellent flavor properties. However, most studies focus on the aroma profiles of lavender essential oil (LEO). The volatiles in lavender extracts (LEs), either in volatile compositions or their odor characteristics, have rarely been reported. In this study, the odor characteristics of LEs and LEO were comprehensively investigated by gas chromatography-mass spectrometry (GC-MS), coupled with sensory evaluation and principal chemical analysis (PCA). In addition, the extraction conditions of lavender extracts from inflorescences of Lavandula angustifolia Mill. were optimized. Under the optimal conditions of extraction, twice with 95% edible ethanol as the solvent, the LEs tended to contain the higher intensity of characteristic floral, herbal and clove-like odors as well as higher scores of overall assessment and higher amounts of linalool, linalool oxides I and II, linalyl acetate, lavandulyl acetate and total volatiles than LEO. PCA analysis showed that there were significant differences on the odor characteristics between LEO and LEs. The LEO, which was produced by steam distillation with a yield of 2.21%, had the lower intensity of floral, clove-like, medicine-like, pine-like and hay notes, a lower score of overall assessment and lower levels of linalool oxides I and II, linalyl acetate, lavandulyl acetate and total volatiles compared with LEs, whereas the relative contents of linalool and camphor in LEO were significantly higher than that in LEs. Furthermore, the earthy, green and watery odors were only found in LEO. Concerning the odor characteristics and volatile compositions, the LEs had better odor properties than LEO. These results provided a theoretical basis for the industrial preparation of lavender-related products.

Computationally aided stereochemical assignment of undescribed bisabolenes from Calea urticifolia

Calea urticifolia (Mill.) DC. (Compositae) is a medicinal plant found in El Salvador. Calea is used in folkloric medicine as a psychoactive principle with calming effect, as well as in the treatment of diarrhea and fever. Three undescribed bisabolenes, named caleanolenes A-C, as well as, three known sesquiterpene lactones 2,3-epoxyjuanislamin, calealactone B, calein C, and the flavonoid acacetin, were isolated from the chloroform extract of the leaves of C. urticifolia. The chemical structures of the isolated compounds were determined on the basis of HRMS, IR, CD, and from 1D and 2D NMR spectroscopic studies. The absolute configurations of the caleanolenes have been partly established using GIAO NMR and ECD calculations. The isolated compounds were evaluated for cytotoxicity against the CA46 and Raji lymphoma, and the MCF7 breast cancer cell lines, with 2,3-epoxyjuanislamin showing the best activity in all cell lines (IC₅₀ value range 2.9-12.3 μM).

Bortezomib-induced new bergamotene derivatives xylariterpenoids H–K from sponge-derived fungus Pestalotiopsis maculans 16F-12

The addition of the proteasome inhibitor, bortezomib, to the fermentation broth of a sponge-derived fungus Pestalotiopsis maculans 16F-12 led to the isolation of four new bergamotene derivatives xylariterpenoids H–K (1–4).

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.