TY - JOUR

T1 - Azaphilone Pigments from Hypoxylon rubiginosum and H. texense: Absolute Configuration, Bioactivity, and Biosynthesis

AU - Becker, Kevin

AU - Kuhnert, Eric

AU - Cox, Russell J.

AU - Surup, Frank

N1 - Funding Information: Foremost, the authors would like to thank Marc Stadler for generous support of this work. The authors wish to thank Silke Reinecke for expert assistance in the lab. We are also grateful for the help of Esther Surges for recording the HR‐ESI‐MS spectra, as well as Christel Kakoschke for performing the NMR measurements. K. Becker, E. Kuhnert, and R. J. Cox are grateful for a grant from the Deutsche Forschungsgemeinschaft (DFG CO 1328/4‐1) in the Priority Programme ‘‘Taxon‐Omics: New Approaches for Discovering and Naming Biodiversity’’ (SPP 1991). Open Access funding enabled and organized by Projekt DEAL.

PY - 2021/9/24

Y1 - 2021/9/24

N2 - We report new stromatal azaphilone pigments rubiginosins Z-X from the ascomycete Hypoxylon rubiginosum, as well as rubiginosins Z and W from H. texense, which were isolated along with known monomeric and dimeric congeners. Structures were elucidated using comprehensive HRMS, NMR, and ECD analysis, revealing azaphilones from both fungi to be exclusively C-8(S)-configured. The orsellinic acid (OA)-carrying rubiginosins A, Z and dimeric rutilins A-B exhibited cytotoxicity. Rubiginosins X-W bearing linear polyketide side chains as well as rutilins A-B were antimicrobial. Structures of the differently-substituted azaphilones were linked to two putative biosynthetic gene clusters (BGCs; hraza1/2) in H. rubiginosum, which are proposed to collaboratively synthesize the OA-substituted azaphilones. These share high homology with the azaphilone-forming BGCs hfaza1/2 from H. fragiforme. Comparison of hraza and hfaza suggests that lack of an FAD-dependent monooxygenase and acyltransferase gene in hraza1 prevent formation of C-8(R)-configured fatty acid-substituted azaphilones in H. rubiginosum. The polyketide synthase-derived side chain of rubiginosins C and X-W is not encoded in the respective BGCs, showing that a third BGC is hypothetically involved in their formation. Cross-interaction of three BGCs which are forming a single molecule is unprecedented in fungal natural product biosynthesis.

AB - We report new stromatal azaphilone pigments rubiginosins Z-X from the ascomycete Hypoxylon rubiginosum, as well as rubiginosins Z and W from H. texense, which were isolated along with known monomeric and dimeric congeners. Structures were elucidated using comprehensive HRMS, NMR, and ECD analysis, revealing azaphilones from both fungi to be exclusively C-8(S)-configured. The orsellinic acid (OA)-carrying rubiginosins A, Z and dimeric rutilins A-B exhibited cytotoxicity. Rubiginosins X-W bearing linear polyketide side chains as well as rutilins A-B were antimicrobial. Structures of the differently-substituted azaphilones were linked to two putative biosynthetic gene clusters (BGCs; hraza1/2) in H. rubiginosum, which are proposed to collaboratively synthesize the OA-substituted azaphilones. These share high homology with the azaphilone-forming BGCs hfaza1/2 from H. fragiforme. Comparison of hraza and hfaza suggests that lack of an FAD-dependent monooxygenase and acyltransferase gene in hraza1 prevent formation of C-8(R)-configured fatty acid-substituted azaphilones in H. rubiginosum. The polyketide synthase-derived side chain of rubiginosins C and X-W is not encoded in the respective BGCs, showing that a third BGC is hypothetically involved in their formation. Cross-interaction of three BGCs which are forming a single molecule is unprecedented in fungal natural product biosynthesis.

KW - Biosynthesis

KW - Hypoxylaceae

KW - Pigments

KW - Polyketides

KW - Xylariales

UR - http://www.scopus.com/inward/record.url?scp=85113705570&partnerID=8YFLogxK

U2 - 10.1002/ejoc.202001661

DO - 10.1002/ejoc.202001661

M3 - Article

VL - 2021

SP - 5094

EP - 5103

JO - European Journal of Organic Chemistry

JF - European Journal of Organic Chemistry

SN - 1434-193X

IS - 36

ER -