Usnic acid derivatives from Leprocaulon microscopicum

Dibenzofurans and derivatives from lichens and ascomycetes

“…8 Behera et al detected the production of usnic acid from Usnea ghattensis after cell culture. 58 Isousnic acids (16b, 17b), isolated from Cladonia mitis, C. pleurota and Leprocaulon microscopicum, 8,39,59 differ from usnic acid by the inversion of the groupment at C6 and C9 in the ring A. Usimines A-C 30,60 (20a-c), reported in Stereocaulon alpinum and Ramalina terebrata, are unique derivatives possessing nitrogen-bearing side chain presumably derived from glutamic acid. In fact, these latter exist in the more stable enamine form resulting from the rapid tautomerization of the initial formed imine [61][62] .…”

“…For derivatives possessing partially saturated C-ring, a typical mass fragmentation appears with C-ring fission via a retro Diels-Alder fragmentation and homolysis process. 8,59 The fragmentation pattern of other dibenzofurans corresponds to the loss of H 2 O, CO 2 or fragment chain depending on the substitution of the aromatic groups (e.g. fragmentation observed for condidymic acid).…”

Analysis of Lichen Metabolites, a Variety of Approaches

“…Circular dichroism is another option when experimental circular dichroism of the molecule can be compared to either (i) a set of experimental spectra from related compounds, (ii) data from literature or (iii) calculated theoretical curves (Berova et al 2007). Circular dichroism can also grant information regarding conformational features and was applied to a wide array of lichen compounds including aliphatic acids (Bodo and Molho 1980), cycloaliphatic compounds (Huneck and Himmelreich 1995;Polborn et al 1995;Aberhart et al 1970;Huneck and Höfle 1980;Huneck et al 1986;Huneck and Takeda 1992), quinones (Mathey et al 1980), chromones (Huneck 1972), carotenoids (Czeczuga et al 1988), and dibenzofuran-related compounds (Millot et al 2013). …”

Two New Retigerane‐Type Sesterterpenoids from the Lichen Leprocaulon microscopicum

“…The highly complex chemistry shows variable combination of usnic acid, atranorin, rangiformic acid, zeorin and unidentified substances [8]. Our previous study on the chemical composition of L. microscopicum from French Limousin, shows the abundance of dibenzofuran derivatives including (-)-usnic acid, (-)-isousnic acid, (-)-placodiolic acid and (-)-9-O-methylplacodiolic acid [9]. In our continuing study of minor non aromatic secondary metabolites from L. microscopicum, we describe for the first time in this Genus, the isolation and structure elucidation of compounds 1-2, two new sesterterpenoid derivatives.…”

“…The acetone extract was subjected to centrifugation affording a yellow precipitate as well as a residual acetonic fraction. The yellow precipitate afforded (-)-usnic acid [9] and a triterpene which was identified as zeorin on the basis of mass spectral data and by comparison of their 1 H and 13 C NMR spectral data with literature values [10]. The residual acetonic fraction was then submitted to successive MPLC and preparative TLC on silica gel of the apolar fraction yielding compound 1.…”