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The Rickiols: 20‐, 22‐, and 24‐membered Macrolides from the Ascomycete Hypoxylon rickii
Author(s) -
Surup Frank,
Kuhnert Eric,
Böhm Andreas,
Pendzialek Tim,
Solga Danny,
Wiebach Vincent,
Engler Hauke,
Berkessel Albrecht,
Stadler Marc,
Kalesse Markus
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201704928
Subject(s) - stereochemistry , mycelium , terpenoid , chemistry , derivative (finance) , absolute configuration , strain (injury) , ring (chemistry) , fermentation , organic chemistry , botany , biology , anatomy , financial economics , economics
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.