Vulgarisin A, a New Diterpenoid with a Rare 5/6/4/5 Ring Skeleton from the Chinese Medicinal Plant Prunella vulgaris

[2 + 2]-Cycloaddition-derived cyclobutane natural products: structural diversity, sources, bioactivities, and biomimetic syntheses

This review summarizes the structural diversity, bioactivities, and biomimetic synthesis of [2 + 2]-type cyclobutane natural products, along with discussion of their biosynthesis, stereochemical analysis, racemic occurrence, and biomimetic synthesis.

Unprecedented diterpene skeletons isolated from vascular plants in the last twenty years (2001-2021)

Every year there are hundreds of reports about the isolation of undescribed terpenoids based on novel functionalizations of known carbocyclic skeletons series. However, on some occasions the compounds obtained have a carbocyclic skeleton that does not correspond with the series established, in these peculiar opportunities, in addition to finding an undescribed natural product, is obtained an unprecedented carbocyclic skeleton, whose biogenesis must necessarily involve other additional steps that explain its formation. This review accounts for the reports of seventy-nine unprecedented diterpene skeletons (corresponding to one-hundred-three undescribed diterpenoids) isolated from vascular plants in the last two decades. According to the genus, Euphorbia and Salvia are the most prolific in reports of unprecedented diterpene skeletons with a total of twenty, and nine skeletons, respectively. If the findings are expressed in terms of the family, Euphorbiaceae and Lamiaceae have the highest number of reports of undescribed diterpene skeletons, with twenty-seven and twenty-two, respectively. Finally, fifty-three skeletons are derived from higher diterpenoids (2-12, 68, 69, 86, 104-109, 158-161, 186, 189, 222, 250-255, 285-298, 403-404, 415, 416, and 436), twenty are derived from lower diterpenoids (135, 136, 192-194, 225-229, 363-370, 397, and 425), and six (96, 97, 147, 148, 205, and 206) are derived from skeletons whose biogenesis has not yet been established, or at least, cannot be formally included within the groups mentioned above. This article comprehensively highlights the hypothetical biosynthetic pathway for each of the one-hundred-three undescribed compounds with unprecedented diterpene skeletons and summarizes their most significant biological activities.

Vulgarisin-type diterpenoids from self-heal (Prunella vulgaris) and their neuroprotective effects against ischemia/reperfusion (I/R) via a mitochondria-related pathway

Self-heal (Prunella vulgaris L.) is a perennial edible plant that is widely distributed across the world and is traditionally consumed as a food additive in soft drink beverages. In this study, to explore the functional components of P. vulgaris, an investigation of its ethanol extracts has been conducted by our group. As a result, twelve (1-12) vulgarisin-type diterpenoids with a special 5/6/4/5-fused ring skeleton, including six new ones (1-6), were obtained. Their structures including the absolute configuration were elucidated based on comprehensive spectroscopic evidence, ECD calculations, as well as single-crystal X-ray diffraction analyses. All the isolates were tested for neuroprotective effects against ischemia/reperfusion (I/R) on primary neuron cells through the oxygen and glucose deprivation and reperfusion (OGD/R) induced injury model. The results showed that all twelve vulgarisin-type diterpenoids possess promising neuroprotective activity at a concentration of 10 μM. Among them, compound 3 can significantly suppress cell apoptosis by regulating Bax/Bcl-2 protein expression and inhibiting cleaved caspase-3 and caspase-9 expression with a western blotting assay. Further research revealed that compound 3 could improve mitochondrial function by inhibiting mitochondrial cytochrome c release, reducing ROS levels, and maintaining the membrane potential. This work firstly reports vulgarisin-type diterpenoids possessing neuroprotective activity. These findings also suggest that daily consumption of P. vulgaris might prevent cerebral disorders via a mitochondria-related pathway.

Silver and gold nanoparticles induced differential antimicrobial potential in calli cultures of Prunella vulgaris

Background

Prunella vulgaris is medicinally important plant containing high-valued chemical metabolites like Prunellin which belong to family Lamiaceae and it is also known as self-heal. In this research, calli culture were exposed to differential ratios of gold (Au) and silver (Ag) nanoparticles (1:1, 1:2, 1:3, 2:1 and 3:1) along with naphthalene acetic acid (2.0 mg NAA) to investigate its antimicrobial potential. A well diffusion method was used for antimicrobial properties.

Results

Here, two concentrations (1 and 2 mg/6 µl) of all treated calli cultures and wild plants were used against Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Bacillus atrophaeus, Bacillus subtilis, Agrobacterium tumefaciens, Erwinia caratovora and Candida albicans. Dimethyl sulfoxide (DMSO) and antibiotics were used as negative and positive controls. Here, the calli exposed to gold (Au) nanoparticles (NPs) and 2.0 mg naphthalene acetic acid (NAA) displayed the highest activity (25.7 mm) against Salmonella typhi than other extracts, which was considered the most susceptible species, while Agrobacterium tumefaciens and Candida albicans was the most resistance species. A possible mechanism of calli induced nanoparticles was also investigated for cytoplasmic leakage.

Conclusion

From the above data it is concluded that Prunella vulgaris is medicinally important plant for the development of anti-microbial drugs using nanotechnology and applicable in various pharmaceutical research.

Non-targeted analysis of vulgarisins by using collisional dissociation mass spectrometry for the discovery of analogues from Prunella vulgaris

Vulgarisins are members of diterpenoids with rare 5/6/4/5 ring skeleton from Prunella vulgaris Linn. (P. vulgaris). Their molecular scaffolds comprise different hydroxylation and degree of esterification. Vulgarisins have attracted many attentions in the fields of food and medicine for their potent bioactivities. Firstly, four reference compounds were analyzed by higher-energy collisional dissociation mass spectrometry (HCD MS/MS) and the fragmentation patterns for molecular scaffold were summarized. And then, a high-performance liquid chromatography/electrospray ionization/high-resolution mass spectrometry (HPLC-ESI-HR-MS) method was adopted to investigate the P. vulgaris extracts. Finally, the proposed analysis results were successfully applied to facilitate the discovery of the vulgarisins analogues from P. vulgaris. For the four reference compounds, the sodium adduct was the predominate ion in full scan. A specific fragmentation pathway of [M+Na]⁺ ions leads to produce diagnostic ions of vulgarisins at m/z 325 under HCD, which was formed through consecutive-side chains lost. Twenty-three diterpenoids, including 18 vulgarisins analogues, were identified or tentatively characterized in the botanical extracts of P. vulgaris based on their elemental constituents and characteristic fragment ion profiles. Two new vulgarisins analogues in the plant were isolated and their structures were illustrated based on extensive spectroscopic analysis using ¹D and ²D nuclear magnetic resonance (NMR) spectroscopy. The HCD MS/MS method, including the profiles of the diagnostic ions induced by characteristic fragmentation, is an effective technique for the discovery of vulgarisins analogues in P. vulgaris. The expected fragmentation pattern knowledge will also facilitate the analysis of other natural products.

Crystal structure of (1aS,1a 1 S,2S)-4a-butoxy-1a,1a 1,2,4a,5,6-hexahydro-1H-cyclobuta[de]naphthalen-2-yl-4-nitrobenzoate, C22H25NO5

C22H25NO5, monoclinic, P21/c (no. 14), a = 15.7241(13) Å, b = 7.0223(5) Å, c = 18.4613(14) Å, β = 100.329(4)°, V = 2005.4(3) Å3, Z = 4, R gt (F) = 0.0495, wR ref (F 2) = 0.1564, T = 296(2) K.

Crystal structure of (4aS,5S,6aS,6a1S, 10aS)-4a,5,6a,6a 1,9,10-hexahydro-7H-4,5-methanocyclobuta[4,5]naphtho[8a,1-b]pyran-6(2H)-one, C15H16O2

C15H16O2, triclinic, P1̄ (no. 2), a = 5.6034(7) Å, b = 8.7105(11) Å, c = 12.5661(16) Å, α = 92.790(7)°, β = 100.516(7)°, γ = 106.105(6)°, V = 576.15(13) Å3, Z = 2, R gt(F) = 0.0476, wR ref(F 2) = 0.1348, T = 296.15 K.

Promiscuous terpene synthases from Prunella vulgaris highlight the importance of substrate and compartment switching in terpene synthase evolution

The mint family (Lamiaceae) is well documented as a rich source of terpene natural products. More than 200 diterpene skeletons have been reported from mints, but biosynthetic pathways are known for just a few of these. We crossreferenced chemotaxonomic data with publicly available transcriptomes to select common selfheal (Prunella vulgaris) and its highly unusual vulgarisin diterpenoids as a case study for exploring the origins of diterpene skeletal diversity in Lamiaceae. Four terpene synthases (TPS) from the TPS-a subfamily, including two localised to the plastid, were cloned and functionally characterised. Previous examples of TPS-a enzymes from Lamiaceae were cytosolic and reported to act on the 15-carbon farnesyl diphosphate. Plastidial TPS-a enzymes using the 20-carbon geranylgeranyl diphosphate are known from other plant families, having apparently arisen independently in each family. All four new enzymes were found to be active on multiple prenyl-diphosphate substrates with different chain lengths and stereochemistries. One of the new enzymes catalysed the cyclisation of geranylgeranyl diphosphate into 11-hydroxy vulgarisane, the likely biosynthetic precursor of the vulgarisins. We uncovered the pathway to a rare diterpene skeleton. Our results support an emerging paradigm of substrate and compartment switching as important aspects of TPS evolution and diversification.

The complete chloroplast genome of the common self-heal, Prunella vulgaris (Lamiaceae)

Prunella vulgaris L. is an important medicinal herb widely used in China and western countries. Its natural distribution occurs in various habitats throughout northern hemisphere. In present study, we assembled and characterized its whole chloroplast (cp) genome based on Illumina pair-end sequencing data. The complete chloroplast genome size is 156,132 bp. It contained 134 genes, including 89 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. 8 gene species had two copies. The overall GC content of this genome was 37.9%. A further phylogenomic analysis of Lamiaceae, including 29 taxa, was conducted for the placement of P. vulgaris.

Unusual Anti-allergic Diterpenoids from the Marine Sponge Hippospongia lachne

Hipposponlachnins A (1) and B (2), possessing an unprecedented tetracyclo [9.3.0.0^2,8.0^3,7] tetradecane ring system, and the probable biogenetic precursor [3, (1R*,2E,4R*,7E,10S*,11S*,12R*)-10, 18-diacetoxydolabella-2,7-dien-6-one] of 1‒2 were isolated from the South China Sea marine sponge Hippospongia lachne. The structures of the novel compounds were determined using integrated spectroscopic methods in combination with single-crystal X-ray diffraction analysis. Compounds 1‒2 showed potent inhibitory activity on the release of β-hexosaminidase, a biomarker for degranulation, as well as the production of pro-inflammatory cytokine IL-4 and lipid mediator LTB₄ in DNP-IgE-stimulated RBL-2H3 cells.

Chemoenzymatic Total Syntheses of the Enantiomers of the Protoilludanes 8-Deoxydihydrotsugicoline and Radudiol

Chemoenzymatic and stereoselective total syntheses of the non-natural enantiomeric forms of the recently isolated protoilludane natural products 8-deoxydihydrotsugicoline (1) and radudiol (2) (viz. ent-1 and ent-2, respectively) are reported. The key steps involve the Diels-Alder cycloaddition of cyclopent-2-en-1-one to the acetonide derived from enantiomerically pure and enzymatically derived cis-1,2-dihydrocatechol 3, elaboration of the resulting adduct to the tricyclic ketone 12, and a photochemically promoted rearrangement of this last compound to the octahydro-1H-cyclobuta[e]indenone 13.

Phytochemistry and pharmacological activities of the genus Prunella

Prunella is a genus of perennial herbaceous plants in the Labiatae family. There are approximately 15 species worldwide, distributed widely in the temperate regions and tropical mountains of Europe and Asia. In the genus Prunella, P. vulgaris is the most studied, following a several thousand-year history as a traditional antipyretic and antidotal Chinese herb. Furthermore, since ancient times, P. vulgaris has been widely used as a cool tea ingredient and consumed as a vegetable. The genus Prunella contains triterpenoids and their saponins, phenolic acids, sterols and associated glycosides, flavonoids, organic acids, volatile oil and saccharides. Modern pharmacological studies have revealed that Prunella possess antiviral, antibacterial, anti-inflammatory, immunoregulatory, anti-oxidative, anti-tumor, antihypertensive and hypoglycemic functions. The active components related to these functions are mainly triterpenoids, phenolic acids, flavonoids and polysaccharides. This review mainly summarizes recent advances in traditional usage, chemical components and pharmacological functions.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial as opposed to marine sources and includes, labdanes, clerodanes, pimaranes, abietanes, kauranes, gibberellins, cembranes and their cyclization products. The literature from January to December, 2014 is reviewed.

Design and synthesis of analogues of natural products

In this article strategies for the design and synthesis of natural product analogues are summarized and illustrated with some selected examples.