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 70â 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 rickiolâ Aâ (1) and Eâ (5) we observed transesterification of 20-membered ring structures to 22-membered isomers rickiolâ A2â (6) and E2â (7), and to 24-membered isomers rickiolâ A3â (8) and rickiolâ E3â (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 rickiolâ E3â (9) established easier access to these compounds.