The Rickiols: 20‐, 22‐, and 24‐membered Macrolides from the Ascomycete Hypoxylon rickii

Abstract

In preceding studies the neotropical ascomycete Hypoxylon rickii turned out to be a prolific source of new secondary metabolites, considering that we had obtained terpenoids with five different scaffolds along with a series of terphenyls. From the mycelial extracts of a 70 L scale fermentation of this strain we additionally isolated nine new macrolides (1-9) by RP-HPLC. The planar structures were elucidated by NMR spectroscopy complemented by HR-ESIMS. The relative configurations were assigned by J-based configuration analyses and confirmed by Kishi's Universal Database. Subsequently, the absolute configurations were assigned by Mosher's method using the shift analysis of a tetra-MTPA derivative. For rickiol A (1) and E (5) we observed transesterification of 20-membered ring structures to 22-membered isomers rickiol A2 (6) and E2 (7), and to 24-membered isomers rickiol A3 (8) and rickiol E3 (9), respectively. Cytotoxic effects and moderate antibiotic activity against Gram-positive bacteria were observed for 1-8 and 1-6 and 8, respectively. The total synthesis of rickiol E3 (9) established easier access to these compounds.

Discovery of a new species of the Hypoxylon rubiginosum complex from Iran and antagonistic activities of Hypoxylon spp. against the Ash Dieback pathogen, Hymenoscyphus fraxineus, in dual culture

“…The main metabolite of the mono cultural extract of MUCL 54624 was identified by comparison of UV/Vis and MS data as rickiol A (8; Fig. 11E-F), previously described from H. rickii (Surup et al 2018b). Orthosporin (9; Quang et al 2002), daldinone B (10;Stadler et al 2008) was identified by comparison with an internal database in several strains of H. rubiginosum, H. perforatum and H. petriniae (cf.…”

Cytotoxic, antimicrobial and antiviral secondary metabolites produced by the plant pathogenic fungus Cytospora sp. CCTU A309

“…Biological activities of secondary metabolites from a diverse range of microorganisms have been demonstrated in many studies. Many studies have been done on the secondary metabolites of some antagonistic fungi and many antimicrobial compounds have been identified (Helaly et al, 2017;Richter et al, 2016;Surup et al, 2017).…”

Elsinopirins A–D, Decalin Polyketides from the Ascomycete Elsinoё pyri

“…The biological activity of metabolites 1 – 5 was assessed against a broad test panel of bacteria and fungi as well as the cell lines L929 and KB3.1 [ 10 ]. However, no inhibition was observed for the Gram-positive bacteria Bacillus subtilis , Micrococcus luteus , Mycobacterium sp., Staphylococcus aureus , the Gram-negative bacteria Chromobacterium violaceum , Escherichia coli , Pseudomonas aeruginosa , the filamentous fungus Mucor hiemalis , and the yeasts Candida albicans , Pichia anomala , Rhodotorula glutinis , and Schizosaccharomyces pombe up to 66 µg/mL.…”