Isolation of 6,7-<i>iso</i>-Felinone A: A Configurational Reinvestigation of Related Fungal Metabolites

An azaphilone, 6,7-<i>iso</i>-felinone A (<b>2</b>), was isolated from <i>Diaporthales</i> sp. KT3922 along with the known felinone A (<b>1</b>). While compound <b>2</b> exhibited weak Cotton effects, its naphthoate derivative (<b>2a</b>) 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 <b>2</b> proved identical to previously reported hypoillexidiol (<b>3</b>) and xylariphilone (<b>4</b>). 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 (<b>5</b>) and aspergillusone C (<b>6</b>). Comparative analysis revealed identical relative configurations of compounds <b>1</b>, <b>3</b>, <b>4</b>, and <b>5</b>. Furthermore, compounds <b>1</b> and <b>3</b> were determined to have an identical absolute configuration, whereas the absolute configuration of compound <b>4</b> remained inconclusive due to a significant mismatch in its ECD spectral profile compared to compound <b>1</b>. Compound <b>5</b> was identified as the enantiomer of compounds <b>1</b> and <b>3</b>. Additionally, we discussed the stereochemistry of the 6,7-<i>cis</i>-diol isomer, aspergillusone C (<b>6</b>).