Phenylphenalenone-type Phytoalexins from Unripe Buñgulan Banana Fruit.

Fourteen phenylphenalenone-type phytoalexins (1-14), including three new compounds, were isolated from the peel of unripe Musa acuminata [AAA] cv. Buñgulan fruit which had been injured and then inoculated with conidia of Colletotrichum musae. These new phytoalexins were identified as (+)-cis-2,3-dihydro-2,3-dihydroxy-4-(4'-hydroxyphenyl)phenalen-1-one (12), 9-(3',4'-dimethoxyphenyl)-2-methoxyphenalen-1-one (13) and 9-(4'-hydroxyphenyl)-2-methoxyphenalen-1-one (14). The ratios of the relative intensities of the M/M-H ions or M-H2O/M-H2O-H ions in the EI mass spectra were applied to discriminate between 4- and 9-phenylphenalenones. An antifungal test on the phytoalexins showed that a phenolic hydroxyl group was essential for the activity.