Tridepsides as potential bioactives: a review on their chemistry and the global distribution of their lichenic and non-lichenic natural sources

Tridepsides, as fully oxidized polyketides, have been known to exist in lichens for more than a century. Recent studies have showed that these possible defensive lichenochemicals possess various biological activities. Also, a candidate biosynthetic gene cluster was recently reported for gyrophoric acid (GA), an important tridepside. The present study focused on biosynthesis, natural sources, biological activities, and bioanalytical methods of tridepside molecules. Our survey shows that, so far, lichenic tridepsides have been reported from 37 families, 111 genera, and 526 species of lichen. Because many of their species contain tridepsides, the families Parmeliaceae, Lobariaceae, and Peltigeraceae can be considered critical lichenic sources of tridepsides. Furthermore, several species of Hypotrachyna in Parmeliaceae family showed lichenic tridepsides, suggesting that this genus is a viable source of tridepsides. This research also explored tridepsides from non-lichenic sources, such as non-lichenized fungi, lichenicolous fungi, endophytes, parasites, and liverworts, which offer substantial potential as biotechnological sources to produce tridepsides, which are produced in small amounts in lichen thalli. Two lichenic tridepsides have also been detected in non-lichenic sources: GA and tenuiorin (TE). Additionally, no significant correlation was found between tridepside biosynthesis and geographical distribution patterns for several potentially tridepside-producing lichens. We further showed that GA is the most studied tridepside with various reported biological activities, including anticancer, wound healing, photoprotection, anti-aging, antioxidant, cardiovascular effect, DNA interaction, anti-diabetes, anti-Alzheimer’s, anti-bacterial, and antifungal. Last but not least, this study provides an overview of some bioanalytical methods used to analyze tridepsides over the past few years

Antiviral activity of carrageenans from marine red algae

Three carrageenan representatives of each structural type: λ- and ι –family (Gigartina acicularis), ι-family (Euchema denticulatum) and κ –family (Kappaphycus cottonii) have been tested for their in vitro antiviral activity. The carrageenans proved to be potent inhibitors of herpes human virus type 1 (HHV-1) and Poliovirus. The best results were obtained with carrageenans from Gigartina acicularis and Euchema denticulatum, which are more sulfated than those from Kappaphycus cottonii. The selective index values (CC50 /ID50 ) ranged from more than 22 to more than 545 for HHV-1 and more than 6.6 to more than 32 for Poliovirus. No citotoxic effects were observed. At 0.75 mg/ml, none of the carrageenans tested showed a virucidal activity against HHV-1 or Poliovirus. Carrageenans from Euchema denticulatum (ι- family) and Gigartina acicularis (λ- and ι –family) exerted their antiviral effect via, in part, by a lower inhibition of the virus attachment and by the interference in a subsequent stage of the virus replicative cycle. The κ-carrageenan from Kappaphycus cottonii exerted its antiviral effect mainly by a lower inhibition of the virus attachment. In cultures treated with carrageenans from Euchema denticulatum (ι-family) and Gigartina acicularis (λ- and ι –family), the HHV-1 viral DNA synthesis had a reduction of threefold and twofold with 0.75 mg/ml, respectively.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Stictic acid derivatives from the lichen Usnea articulata and their antioxidant activities

Two new β-orcinol depsidones, 1 and 2, together with 13 known compounds were isolated from the lichen Usnea articulata. The structures of 1 and 2 were elucidated by spectroscopic analyses and those of known compounds by comparison of their spectroscopi

Isolation, semi-synthesis, free-radicals scavenging, and advanced glycation end products formation inhibitory constituents from Parmotrema tinctorum

International audienc

Chemical diversity of five coastal Roccella species from mainland France, the Scattered Islands, and São Tomé and Príncipe

International audienceRoccella species constitute interesting models to address questions regarding lichen metabolite diversity across taxonomic, ecological and geographic gradients. Indeed, owing to their wide distribution, their taxonomic diversity and the narrow ecological niche they occupy, Roccella species are good candidates to study the drivers of lichen chemistry. This study focuses on the chemical profiling of five species: R. applanata, R. belangeriana, R. fuciformis, R. montagnei and R. phycopsis. These five species were sampled in a rather narrow longitudinal range (W1°51' to E47°17') covering the Eastern Atlantic and Western Indian Ocean areas along an extended latitudinal range (N48°49' to S22°23'). High Pressure Liquid Chromatography (HPLC) analysis followed by mass spectrometry of 31 Roccella thalli revealed a number of interesting patterns through a multivariate (PCA) analysis, including the first detailed chemical profiles for two species from the Scattered Islands: R. applanata and R. belangeriana. Metabolite segregation amongst all studied Roccella species, including R. montagnei and R. belangeriana, gave some insight into the taxonomy of the latter two species, which we interpret as separate species. An additional analysis focusing on R. montagnei samples revealed chemical differences along both a latitudinal and ecological gradient (from Europa to São Tomé and Príncipe). Three mass spectra databases were built to dereplicate the ions, which gave an overview of the factors that could drive quantitative and qualitative metabolite composition in lichens. Additionally, several new Roccella species records are reported for the Scattered Islands as well as São Tomé and Príncipe

Synthesis of Novel Cyclic Nitrones withgem-Difluoroalkyl Side Chains Through Cascade Reactions

International audienceNew five-membered cyclic nitrones withgem-difluoroalkyl groups in gamma-position have been prepared by a 3-step sequence starting from propargylic alcohols. This domino process involves a base-mediated isomerization reaction to enones, which are trapped in situ by nitroalkane anions. In a final step, starting from these key precursors, a reduction-cyclization process affords the target molecules. Mono- and bicyclic nitrones have been prepared by this route which allows, as well, the synthesis of nitrones with functional groups in terminal position of the side chain

A chemotaxonomic study of the Xanthoparmelia pulla group in Algeria

International audienceThe Xanthoparmelia pulla group is well represented in Algeria from coastal to desert areas. As it is difficult to recognize the species without chemical data, we undertook a study of specimens collected in Algeria using chromatography (TLC and HPLC), mass spectrometry and fluorimetry. Our results confirm the presence of six species, two of which are represented by two chemotypes. We report two diphenyl ethers (beta-collatolic and beta-alectoronic acids) for the first time in X. glabrans. We also provide a key to these taxa based on chemical data, and employ a new test combining UV and K reactions

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

International audienceProtein 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 was identified to possess strong protein tyrosine phosphatase 1B inhibition in a cell-free assay (IC 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()-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 IC 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 (IC 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