Béatrice Legouin

Lichenic extracts and metabolites as UV filters

Three lichen extracts and ten lichenic compounds have been screened for their photoprotective activities. The determination of their Sun Protection Factor (SPF) and Protection Factor-UVA (PF-UVA) values was done in vitro. Among them, a Lasallia pustulata extract and gyrophoric acid exhibited SPF values over 5, which is better than Homosalate (SPF≈4). Their photoprotective properties are only slightly modified after a 2-hours period of irradiation. Salazinic acid and L. pustulata presented characteristics of a UVA booster like the butyl-methoxydibenzoylmethane (Avobenzone) (PF-UVA≈2 vs. 2.8 for Avobenzone). Salazinic acid was a better anion superoxide scavenger than ascorbic acid and none of them exhibited a photosensitizing cytotoxicity by exposing them on HaCaT cells to UVA radiations (photo-irritancy factor PIF<5).

Matrix-Free UV-Laser Desorption Ionization Mass Spectrometry as a Versatile Approach for Accelerating Dereplication Studies on Lichens.

The present study examined the suitability of laser desorption/ionization time-of-flight mass spectrometry (LDI-MS) for the rapid chemical fingerprinting of lichen extracts. Lichens are known to produce a wide array of secondary metabolites. Most of these compounds are unique to the symbiotic condition but some can be found in many species. Therefore, dereplication, that is, the rapid identification of known compounds within a complex mixture is crucial in the search for novel natural products. Over the past decade, significant advances were made in analytical techniques and profiling methods specifically adapted to crude lichen extracts, but LDI-MS has never been applied in this context. However, most classes of lichen metabolites have UV chromophores, which are quite similar to commercial matrix molecules used in matrix-assisted laser desorption ionization (MALDI). It is consequently postulated that these molecules could be directly detectable by matrix-free LDI-MS. The present study evaluated the versatility of this technique by investigating the LDI properties of a vast array of single lichen metabolites as well as lichen extracts of known chemical composition. Results from the LDI experiments were compared with those obtained by direct ESI-MS detection as well as LC-ESI-MS. It was shown that LDI ionization leads to strong molecular ion formation with little fragmentation, thus, facilitating straightforward spectra interpretation and representing a valuable alternative to time-consuming LC-MS analysis.

Novel chiral molecular tweezer from (+)-usnic acid.

A new chiral molecular tweezer was synthesized with (1R,2R)-1,2-diaminocyclohexane as spacer and two molecules of (+)-usnic acid as pincers. The ability of this molecular tweezer to bind 2,4,7-trinitrofluorenone was studied. A charge-transfer complex was formed in which TNF was sandwiched between the two usnic acid units with pi-pi-stacked aromatic interactions.

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.

Spatial mapping of lichen specialized metabolites using LDI-MSI: chemical ecology issues for Ophioparma ventosa.

Imaging mass spectrometry techniques have become a powerful strategy to assess the spatial distribution of metabolites in biological systems. Based on auto-ionisability of lichen metabolites using LDI-MS, we herein image the distribution of major secondary metabolites (specialized metabolites) from the lichen Ophioparma ventosa by LDI-MSI (Mass Spectrometry Imaging). Such technologies offer tremendous opportunities to discuss the role of natural products through spatial mapping, their distribution patterns being consistent with previous chemical ecology reports. A special attention was dedicated to miriquidic acid, an unexpected molecule we first reported in Ophioparma ventosa. The analytical strategy presented herein offers new perspectives to access the sharp distribution of lichen metabolites from regular razor blade-sectioned slices.

Existence of two basic sites in triazolo-1,4-diazepines: determination of two pKa values for a model compound in water

By a UV/VIS spectrophotometric study in the pH range –1.6 to 10.1 and by a polarographic study of a water soluble model compound, the occurrence of two basic sites in water has been ascertained for triazolo-1,4-diazepines. The pKa values found for this model were –0.24 and +1.81. Owing to the overlapping of the two pKa values, microforms exist simultaneously. Corresponding ionization microconstant values have been tentatively assigned.

Synthesis of 5-Formyl and 5-Acyl-1,2-dithiole-3-ones

The preparation of new 5-formyl-, 5-acetyl- and 5-propionyl-1,2-dithiole-3-ones by oxidation of the corresponding 1,2-dithiole-3-thiones with mercuric acetate is described.

pKa Values of the Opened Form of a Thieno-1,2,4-triazolo-1,4-diazepine in Water

The pK a values of the freely water-soluble opened form of a thieno-1,2,4-triazolo-1,4-diazepine, namely 2-(3-amino- methyl-5-methyl-1,2,4-triazolo)-3-(2-chlorobenzoyl)- [2,3-c]thienopiperidine, were determined. pH measurements were made in the range 1 < pH < 10. Two of the three pK a values found in this range significantly overlapped; they quantify the ionization of both the aminomethyl residue and the piperidino moiety of the molecule. The third corresponds exclusively to the ionization of the triazolo nucleus. The pK a value of the thienophenone was obtained by UV spectrophotometry using acidity functions. All results were extracted from experimental data by a curve-fitting method.

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.

The 3-thioxo-1,2-dithiol-4-yl group : A versatile one endowed also with a -R electronic effect

The pKa values in an aqueous solution of some 4-aminodithiolethiones, 4-aminodithiolones, 5-phenyl-4-hydroxydithiolethione, and 5-phenyl-4-hydroxydithiolone were determined by UV-VIS spectrophotometry at 298 K. These compounds exhibited unexpectedly very low pKa values in the range of 0–2 for amino derivatives and in the range of 7 for hydroxy derivatives. Electronic structure calculations by ab initio and DFT methods together with an X-ray measurement indicated that these results may be attributed to a markedly negative π charge on the carbon 5 together with a positive π charge on the basic substituent of the carbon 4. As a result, the dithiole nucleus exerts in this case a strong ─R effect. Although they were very low, pK a values of 4-aminodithiolethiones remained still higher than those found with 5-aminodithiolethiones, which were also determined in this work for comparison. The latter were not unexpectedly in the range -3 < pH < −2.