A lupeol derivative and other isolates with antiplasmodial activity from the stem root of Rauvolfia mannii Stapf. (Apocynaceae).

Rauvolfia mannii is a plant from western and eastern areas of African continent and is widely used in folk medicine for the treatment of various diseases including malaria. Herein, one previously undescribed acylated triterpene (1), together with five already published natural products (2-6) were removed from its roots. The chemical structures of these compounds were determined by spectroscopic and spectrometric means (NMR, HRESIMS, IR and UV). In addition to the isolated triterpenoids, components 5 and 6 are also newly reported from the genus Rauvolfia. Moreover, some constituents were further tested against the chloroquine-sensitive strain of P. falciparum (3D7). It has been found that 3 and 4 showed a moderate antiplasmodial activity with IC50 values of 46.25 and 39.79 µM respectively.

Chemical fingerprinting of the Brazilian medicinal plant Calea pinnatifida (R. Br.) Less. (Asteraceae) collected at different altitudes.

Calea pinnatifida (R. Br.) Less. is a plant of Brazilian folk medicine. We evaluated the influence of environmental factors on the chemical profile of C. pinnatifida collected during the winter season. C. pinnatifida leaves, alongside soil samples, were collected from two sites of different altitude. Plant samples were sequentially extracted, while soil samples were subject to compositional analysis. Plant extracts were compared using HPTLC-UV, using chemometric analyses to compare samplings harvested at both altitudes. Two marker metabolites, calein A (1) and acetylportentol (2), were isolated from samples collected at the respective altitudes. The differing metabolic profiles observed may be a result of the influence of environmental factors.

Inhibitory Effects of Secondary Metabolites from the Lichen Stereocaulon evolutum on Protein Tyrosine Phosphatase 1B.

Protein tyrosine phosphatase 1B plays a significant role in type 2 diabetes mellitus and other diseases and is therefore considered a new drug target. Within this study, an acetone extract from the lichen Stereocaulon evolutum was identified to possess strong protein tyrosine phosphatase 1B inhibition in a cell-free assay (IC50 of 11.8 µg/mL). Fractionation of this bioactive extract led to the isolation of seven known molecules belonging to the depsidones and the related diphenylethers and one new natural product, i.e., 3-butyl-3,7-dihydroxy-5-methoxy-1(3H)-isobenzofurane. The isolated compounds were evaluated for their inhibition of protein tyrosine phosphatase 1B. Two depsidones, lobaric acid and norlobaric acid, and the diphenylether anhydrosakisacaulon A potently inhibited protein tyrosine phosphatase 1B with IC50 values of 12.9, 15.1, and 16.1 µM, respectively, which is in the range of the protein tyrosine phosphatase 1B inhibitory activity of the positive control ursolic acid (IC50 of 14.4 µM). Molecular simulations performed on the eight compounds showed that i) a contact between the molecule and the four main regions of the protein is required for inhibitory activity, ii) the relative rigidity of the depsidones lobaric acid and norlobaric acid and the reactivity related to hydrogen bond donors or acceptors, which interact with protein tyrosine phosphatase 1B key amino acids, are involved in the bioactivity on protein tyrosine phosphatase 1B, iii) the cycle opening observed for diphenylethers decreased the inhibition, except for anhydrosakisacaulon A where its double bond on C-8 offsets this loss of activity, iv) the function present at C-8 is a determinant for the inhibitory effect on protein tyrosine phosphatase 1B, and v) the more hydrogen bonds with Arg221 there are, the more anchorage is favored.

Salazinic Acid-Derived Depsidones and Diphenylethers with α-Glucosidase Inhibitory Activity from the Lichen Parmotrema dilatatum.

Three new depsidones, parmosidones F - G (1 - 2), and 8'-O-methylsalazinic acid (3), and 3 new diphenylethers, parmetherines A - C (4 - 6), together with 2 known congeners were isolated from the whole thalli of Parmotrema dilatatum, a foliose chlorolichen. Their structures were unambiguously determined by extensive spectroscopic analyses and comparison with literature data. The isolated polyphenolics were assayed for their α-glucosidase inhibitory activities. Newly reported benzylated depsidones 1: and 2: in particular inhibited α-glucosidase with IC50 values of 2.2 and 4.3 µM, respectively, and are thus more potent than the positive control, acarbose.

Eumitrins C-E: Structurally diverse xanthone dimers from the vietnamese lichen Usnea baileyi.

Three new xanthone dimers, eumitrins C - E (1-3), along with a new depsidone, 3'-O-demethylcryptostictinolide (4) were isolated from the acetone extract of the whole thallus of the lichen Usnea baileyi collected in Vietnam. Their structures were unambiguously established by spectroscopic analyses (HRESIMS, 1D and 2D NMR), as well as comparison to literature data. The absolute configurations of 1-3 were elucidated through electronic circular dichroism (ECD) analyses. The absolute configuration of 2 was validated by comparison between experimental and TDDFT-calculated ECD spectra while that of 3 was based on DFT-NMR calculations and subsequent DP4 probability score. The antiparasitic activities against Plasmodium falciparum as well as the cytotoxic activity against seven cell lines were determined for the new compounds 1-3, and led from null to mild bioactivities.

Specialized Metabolites of the Lichen Vulpicida pinastri Act as Photoprotective Agents.

The extreme resiliency of lichens to UV radiations makes them an interesting model to find new photoprotective agents acting as UV-blockers and antioxidant. In this research, using a new in vitro method designed to overcome the shortage of material associated to many studies dealing with natural products, we show that the three major compounds isolated from the lichen Vulpicida pinastri, vulpinic acid, pinastric acid and usnic acid, were UV blocker agents. Antioxidant assays evidenced superoxide anion scavenging activity. Combination of the most promising compounds against UVB and UVB radiations, usnic acid, vulpinic acid and pinastric acid, increased the photoprotective activity. At the same time, they were found not cytotoxic on keratinocyte cell lines and photostable in the UVA and UVB ranges. Thus, lichens represent an attractive source to find good candidate ingredients as photoprotective agents. Additionally, the uncommon scalemic usnic acid mixture in this Vulpicida species was proven through electronic circular dichroism calculation.

NMR reassignment of stictic acid isolated from a Sumatran lichen Stereocaulon montagneanum (Stereocaulaceae) with superoxide anion scavenging activities.

The phytochemical study of Stereocaulon montagneanum harvested in Sumatra (Indonesia) led to the isolation of 11 known compounds including two metabolites not previously described in the genus Stereocaulon, peristictic acid (8) and menegazziaic acid (10). The complete 1H and 13C NMR spectral assignments of stictic acid derivatives are reported with some revisions. Five depsidones belonging to the stictic acid chemosyndrome were superoxide anion scavengers as potent as ascorbic acid and with no toxicity on two human cell lines.

Minor Pyranonaphthoquinones from the Apothecia of the Lichen Ophioparma ventosa.

Four new quinonoid naphthopyranones, ophioparmin (1), 4-methoxyhaemoventosins (2a and 2b), and 4-hydroxyhaemoventosin (3), together with anhydrofusarubin lactone (4) and haemoventosin (5) were isolated from the fruiting bodies of Ophioparma ventosa, a crustose lichen. Their structures were determined by spectroscopic analyses, and the absolute configurations of 1 and 2 were elucidated through experimental and calculated electronic circular dichroism analyses. Compounds 1, 2, and 5 exhibited moderate to strong antioxidant activities. The main pigment haemoventosin exhibited significant cytotoxicity toward a panel of nine cell lines.