Isolation of 6,7-iso-Felinone A: A Configurational Reinvestigation of Related Fungal Metabolites

An azaphilone, 6,7-iso-felinone A (2), was isolated from Diaporthales sp. KT3922 along with the known felinone A (1). While compound 2 exhibited weak Cotton effects, its naphthoate derivative (2a) displayed pronounced Cotton effects, enabling the determination of its absolute configuration through electronic circular dichroism (ECD) spectral analysis. Interestingly, the spectroscopically derived relative structure of compound 2 proved identical to previously reported hypoillexidiol (3) and xylariphilone (4). However, substantial differences in ¹H nuclear magnetic resonance data among these compounds warranted structural reinvestigation of the entire series, including the structurally related fungal metabolites, fusaraisochromenone (5) and aspergillusone C (6). Comparative analysis revealed identical relative configurations of compounds 1, 3, 4, and 5. Furthermore, compounds 1 and 3 were determined to have an identical absolute configuration, whereas the absolute configuration of compound 4 remained inconclusive due to a significant mismatch in its ECD spectral profile compared to compound 1. Compound 5 was identified as the enantiomer of compounds 1 and 3. Additionally, we discussed the stereochemistry of the 6,7-cis-diol isomer, aspergillusone C (6).