Semisynthesis and biological evaluation of abietane-type diterpenes. Revision of the structure of rosmaquinone

A Validated HPLC-UV-ESI-IT-MS Method for the Quantification of Carnosol in Lepechinia mutica, a Medicinal Plant Endemic to Ecuador

The diphenolic diterpene carnosol was isolated from several species of the family Lamiaceae, including Lepechinia mutica, a medicinal plant endemic to Ecuador. The compound has exhibited high antioxidant, anti-inflammatory, antimicrobial, neuroprotective, and antifungal properties, as well as promising cytotoxicity against prostate, breast, skin, leukemia, and human colon cancer cell lines. In this paper, we developed and validated a simple, accurate, and reliable analytical HPLC-UV-ESI-IT-MS method, carried out on a C18 column, which is potentially suitable to quantify carnosol in plant extracts. The procedure complied with the established ICH validation parameters of analytical range (linearity in the range of 0.19-5.64 μg/g dried leaves; REAVERGE = 4.9%; R2 = 0.99907), analysis repeatability (RSD = 2.8-3.6%), intermediate precision (RSD = 1.9-3.6%), accuracy (estimated as % carnosol recovery in the range of 81 to 108%), and robustness. Finally, the LOD (0.04 µg/mg) and LOQ (0.19 μg/mg) values of carnosol/dried leaves were determined. Using this validated method, the content of carnosol in L. mutica was estimated to be 0.81 ± 0.04 mg/g of dried leaves (0.081%).

The dichloromethane extract of Callicarpa longissima rich in diterpenoid phenols exerts anti-inflammatory effect via inhibiting the TLR4/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Callicarpa longissima is a typical Yao ethnomedicine that has been used to treat arthritis in China. Our previous study found that the dichloromethane extract (DCME) of C. longissima showed anti-inflammatory activity in vitro. However, the anti-inflammatory mechanism and detailed chemical composition of DCME remain unclear, which lead to the original interest of this study.

AIM OF THE STUDY

The study aimed to evaluate the anti-inflammatory properties of the DCME from C. longissima and further explore the accurate chemical components responsible for this active extract.

MATERIALS AND METHODS

The anti-inflammatory activity of DCME in vivo was tested with carrageenan-induced mice paw edema model. Its anti-inflammatory mechanism was explored with LPS-stimulated RAW264.7 macrophages model. The compounds in DCME were isolated by repeated column chromatography and their structures were identified on the basis of nuclear magnetic resonance spectroscopy. The anti-inflammatory activities of the isolates in vitro were also tested by suppressing releases of inflammatory mediators (NO, IL-6 and TNF-α) in RAW264.7 macrophages model. In addition, the molecular docking analysis, which evaluated the potential interaction between the compounds and Toll-like receptor 4 (TLR4) and nuclear factor κB (NF-κB), was performed.

RESULTS

DCME effectively alleviated the mice paw edema induced by carrageenan. In LPS-stimulated RAW264.7 cells, DCME significantly decreased the production of interleukin (IL)-6 and tumor necrosis factor α (TNF-α) via inhibiting their mRNA transcription, down-regulated the expression of TLR4 and myeloid differentiation factor 88, inhibited the phosphorylation of alpha inhibitor of NF-κB (IκBα), NF-κB p65, and degradation of IκBα. Twelve diterpenoid phenols were identified from DCME, and they not only showed different inhibitory effects on the production of NO, IL-6 and TNF-α in LPS-stimulated RAW264.7 cells, but also could bind to TLR4 and NF-κB as analyzed by molecular docking.

CONCLUSIONS

Taken together, DCME from C. longissima could inhibit inflammatory response both in vitro and in vivo, which is mainly attributed to the synergistic effect of abundant diterpenoid phenols through inhibiting the TLR4/NF-κB signaling pathway, and might be a promising agent for the treatment of inflammatory diseases.

Nine-dimensional bioprofiles of Tunisian sages (Salvia officinalis, S. aegyptiaca and S. verbenaca) by high-performance thin-layer chromatography - effect-directed analyses

Ethyl acetate extracts of Tunisian Salvia aegyptiaca and S. verbenaca aerial parts and S. officinalis leaves were examined via bioanalytical profiling using high-performance thin-layer chromatography (HPTLC) combined with nine bioactivity assays, namely antibacterial (Aliivibrio fischeri, Bacillus subtilis, and Rhodococcus fascians), antifungal (Bipolaris sorokiniana, and Fusarium avenaceum), radical scavenging (DPPH•), and enzyme inhibitory (α-glucosidase, acetylcholinesterase, and lipase) ones. The screening, using toluene - ethyl acetate - methanol 6:3:0.5 (V/V/V) as a mobile phase, revealed five bioactive zones (a-e) that were analyzed by HPTLC-electrospray ionization-mass spectrometry (ESI-MS). Zones b and c, observed exclusively in S. officinalis, were active in all assays except α-glucosidase, and only c inhibited F. avenaceum. Compounds in these zones were identified by HPLC-high resolution tandem MS (LC-HRMS/MS) as rosmanol/epi-rosmanol and methyl carnosate, respectively. In the bioactive zones a and e, corosolic/maslinic acid and ursolic/oleanolic acid isomer pairs were present, which could be identified in all three Salvia species after their HPTLC separation using pre-chromatographic derivatization with iodine and MS detection. The triterpenes inhibited B. subtilis and R. fascians bacteria and α-glucosidase enzyme. Linoleic and linolenic acids were detected in zone d, which showed strong lipase inhibition in all three sage species.

Salvia officinalis L.: Antitrypanosomal Activity and Active Constituents against Trypanosoma brucei rhodesiense

As part of our studies on antiprotozoal activity of approved herbal medicinal products, we previously found that a commercial tincture from Salvia officinalis L. (common Sage, Lamiaceae) possesses high activity against Trypanosoma brucei rhodesiense (Tbr), causative agent of East African Human Trypanosomiasis. We have now investigated in detail the antitrypanosomal constituents of this preparation. A variety of fractions were tested for antitrypanosomal activity and analyzed by UHPLC/+ESI QqTOF MS. The resulting data were used to generate a partial least squares (PLS) regression model that highlighted eight particular constituents that were likely to account for the major part of the bioactivity. These compounds were then purified and identified and their activity against the pathogen tested. All identified compounds (one flavonoid and eight diterpenes) displayed significant activity against Tbr, in some cases higher than that of the total tincture. From the overall results, it can be concluded that the antitrypanosomal activity of S. officinalis L. is, for the major part, caused by abietane-type diterpenes of the rosmanol/rosmaquinone group.

Phytochemical Study of the Ecuadorian Species Lepechinia mutica (Benth.) Epling and High Antifungal Activity of Carnosol against Pyricularia oryzae

The plant Lepechinia mutica (Benth.) Epling (family Lamiaceae) is endemic to Ecuador. In the present study, we report some major non-volatile secondary metabolites from the leaves and the chemistry of the essential oil distilled from the flowers. The main identified compounds were carnosol, viridiflorol, ursolic acid, oleanolic acid, chrysothol, and 5-hydroxy-4′,7-dimethoxy flavone. Their structures were determined by X-ray diffraction and NMR and MS techniques. The essential oil showed a chemical composition similar to that distilled from the leaves, but with some qualitative and quantitative differences regarding several minor compounds. The main constituents (>4%) were: δ-3-carene (24.23%), eudesm-7(11)-en-4-ol (13.02%), thujopsan-2-α-ol (11.90%), β-pinene (7.96%), valerianol (5.19%), and co-eluting limonene and β-phellandrene (4.47%). The volatile fraction was also submitted to enantioselective analysis on a β-cyclodextrin column, obtaining the separation and identification of the enantiomers for α-thujene, β-pinene, sabinene, α-phellandrene, limonene and β-phellandrene. Furthermore, the anti-fungal activity of non-volatile secondary metabolites was tested in vitro, with carnosol resulting in being very active against the “blast disease” caused by the fungus Pyricularia oryzae.

Catalytic [1,3] O-to-C Rearrangement: Rapid Access to Bridged Bicyclic Systems

A catalytic [1,3] O-to-C rearrangement from enyne-ethers was developed for the rapid synthesis of diverse bridged bicyclic systems. In this reaction, a vinyl oxonium intermediate, generated in situ from enyne-ether, was the precursor for the [1,3] O-to-C rearrangement. This versatile protocol represents the first example of catalytic [1,3] O-to-C rearrangement based on ring-expansion strategy, enabling efficient access to bridged bicyclic scaffolds.

Biomimetic syntheses of C23 terpenoids: structural revision of salyunnanin A and confirmation of hassanane

Salyunnanin A and hassanane, two C₂₃ terpenoids, were achieved from (+)-carnosic acid in 6 and 5 steps, respectively.

Dimeric Abietane Diterpenoids and Sesquiterpenoid Lactones from Teucrium viscidum

A new abietane diterpenoid, teuvisone (2), a pair of new dimeric abietane diterpenoid stereoisomers, biteuvisones A (3) and B (4), and three new sesquiterpenoid lactones, teuvislactones A-C (6, 7, and 10), were isolated from the whole plants of Teucrium viscidum, along with four known terpenoids (1, 5, 8, and 9). The structures of the new compounds were elucidated by spectroscopic analysis, and the absolute configurations of 5-10 were determined by electronic circular dichroism analysis. The isolated compounds were evaluated for their cytotoxic effects against five human cancer cell lines and for their α-glucosidase inhibitory effects.

Biotransformation of diterpenes

Structural modification of the diterpenes to enhance their pharmaceutical relevance can be efficiently carried out by the application of biotransformational under mild reaction.

Synthesis of Diterpenoid Rosmic Acid Derivatives

The partial synthesis of derivatives of the antimicrobial diterpenoid rosmic acid from the abundant diterpenoid car-nosol is described. The key step involved the cleavage of ring C of rosmanol with lead tetraacetate or 7- O-methylrosmanol with mCPBA. Three analogues of rosmic acid, 11,12-seco-8,13-abietadien-12,7:20,6β-dilacton-11-oic acid methyl ester, 7α- O-methyl-11,12-seco-11,12-epoxy-11,12-dioxo-8,13-abietadien-20,6β-olide, its dimethyl ester, and the known methylgaldosol and rosmaquinone were obtained.

Phenolic diterpenes from rosemary suppress cAMP responsiveness of gluconeogenic gene promoters

The cAMP/protein kinase A/cAMP response element (CRE)-binding protein pathway is important for various physiological aspects including regulation of gluconeogenic gene expression. Rosemary, a well-known herb, has been reported to decrease blood glucose levels. We found that methanol extracts of rosemary suppressed forskolin (FSK)-stimulated luciferase expression under the control of CRE, as well as the promoters for cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) and glucose-6-phosphatase (G6Pase) catalytic subunit genes in human hepatoma HepG2 cells. Three abietane-type diterpenes and two flavonoids were isolated from the rosemary extracts. Among these, 7-O-methylrosmanol (1) and royleanonic acid (3) effectively suppressed FSK-induced luciferase expression under the control of the CRE, PEPCK-C and G6Pase gene promoters. PEPCK-C and G6Pase, which play a key role in the homeostatic regulation of blood glucose levels, are important for managing type II diabetes mellitus. Therefore, the ability of rosemary and its components to suppress cAMP responsiveness of the PEPCK-C or G6Pase gene may contribute to its antihyperglycemic activity.

Rapid access to ketones related to oleanolic and ursolic acids

We describe in this article a process with which to obtain different ketones related to oleanolic and ursolic acids from a natural source, Salvia canariensis L., with minimal use of chromatography columns. Amongst the isolated compounds was 12α-bromo-3-oxo-olean-13, 28-olide (3), which was fully characterised, including a characterisation of its molecular configuration by X-ray crystallographic analysis by 1 and 2-dimensional NMR techniques.

Gastroprotective effect of carnosic acid gamma-lactone derivatives

Carnosic acid (1) has been shown to possess gastroprotective activity in vitro and in vivo. However, little is known of the gastroprotective effect or cytotoxicity of carnosic acid gamma-lactone (3). To determine structure-activity relationships, a series of 17 esters of 3 were prepared including aliphatic, aromatic, and heterocyclic derivatives. Also, two units of 3 were coupled with succinic and phthalic acid as linkers. The compounds were assessed for their gastroprotective effect in the HCl/EtOH-induced gastric lesions model in mice and for cytotoxicity in human lung fibroblasts, human adenocarcinoma AGS cells, and Hep G2 hepatocellular carcinoma cells. At a single oral dose of 40 mg/kg, the gastroprotective effect increased moderately with the length of the alkyl chain. The best effects were observed for the butyrate (9) and chloroacetate (6) derivatives. Activity of fatty acid esters increased with chain length but decreased with unsaturation. The best gastroprotective effect, with lowest cytotoxicity, was found for the palmitate (11) and oleate (12) derivatives.