13C NMR Spectroscopy of Naphtho-γ-pyrones

Article abstract of DOI:10.1002/mrc.1260241006

The 13C NMR spectra of three naphtho-γ-pyrones produced by Aspergillus fonsecaeus (NRRL 67, O 16-1) viz. 5-hydroxy-6,8-dimethoxy-2-methyl-4H-naphtho<2,3-b>pyran-4-one (rubrofusarin B), 2,3-dihydro-2,5-dihydroxy-6,8-dimethoxy-2-methyl-4H-naphtho<2,3-b>pyran-4-one (fonsecin B) and 2,3-dihydro-2,5,8-trihydroxy-6-methoxy-2-methyl-4H-naphtho<2,3-b>pyran-4-one (fonsecin), have been determined.Assignments of the carbon resonances were carried out from chemical shifts, long-range carbon-hydrogen couplings and hydrogen-deuterium exchange information.Carbon shift assignments previouly reported for fonsecin have been revised.The C-4 and C-5 signals show that the angle of twist of the carbonyl group with the aryl ring system is larger in fonsecin than in fonsecin B, indicating the occurrence of different preferred conformations in the dihydropyrone ring of these compounds.