ChemInform Abstract: Lobarialides A—C, Antifungal Triterpenoids from the Lichen Lobaria kurokawae

Abstract

Three novel fernane-type triterpenoids, lobarialides A -C (1 -3, resp.), together with two known ones were isolated by antifungal bioassay-guided fractionation of the lichen Lobaria kurokawae. Their structures including configurations were established on the basis of extensive spectroscopic analyses, and that of 1 was confirmed by a single-crystal X-ray diffraction analysis. Antifungal tests of the five triterpenoids showed that the activity increased with the increment of the number of COO groups.Introduction. -Lichens, the symbiotic organisms of fungi and algae, are distributed worldwide and can survive in various harsh environmental conditions. They are also resistant to microorganism infection due to the production of large numbers of unique secondary metabolites such as depsides, depsidones, lactones, and dibenzofuran derivatives [1] [2]. Lobaria kurokawa Yoshim is a lichen which has been applied as a folk medicine for the treatment of hypopepsia, malnutritional stagnation, and abdominal distention in South China [3]. Previously, we have obtained six compounds from this species [4]. As a part of our continuous search for antifungal natural products from the bryophytes and lichens [5] [6], a TLC-bioautography screening [5] and the same bioassay-guided phytochemical investigation for the antifungal constituents was conducted and led to the isolation of lobarialides A -C (1 -3, resp.), three new triterpenoids with unprecedented hemiacetal, dilactone, and 25-norfernane structural features, respectively, together with the known retigeric acids A and B (4 and 5, resp.; cf. Scheme) [4]. Herein, we report the isolation, structure elucidation, and antifungal activity of these triterpenoids.

Enfumafungin synthase represents a novel lineage of fungal triterpene cyclases

“…All these metabolites, with the exception of the kolokosides, exhibited some degree of antifungal activity. Hence, it is unclear if acetylation at the C-2 position is required for the antifungal activity, because structurally similar unacetylated and unglycosylated fernene-type terpenoids, for example, retigeric acid B, the lobarialides and polytolypin also are antifungal (Gamble et al, 1995;Sun et al, 2009;Wang et al, 2009). However, with the exception of retigeric B (Chang et al, 2012), the modes of action of these metabolites have not been determined, and other inhibitory mechanisms may be involved.…”

“…Triterpenoid natural products derived from squalene are cornerstones for diverse biological activities, including anticancer, antibacterial, antiviral and antifungal activities, as well as forming structural steroids, such as cholesterol and ergosterol. Similar fungal‐produced triterpenes, some with antifungal effects, have been described elsewhere, including retigeric acids (Sun et al ., ; Chang et al ., ), lobarialides (Wang et al ., ), polytolypin (Gamble et al ., ), peniciside (Yuan et al ., ), fuscoatroside (=FR207944) (Joshi et al ., ; Kobayashi et al ., ), hyalodendrosides (Bills et al ., ) and the kolokosides (Deyrup et al ., ) (Fig. ).…”