Formation of diketopiperazines by Penicillium italicum isolated from oranges

Prolyl-2-(1',1'-dimethylallyl)tryptophyldiketopiperazine and 12,13-dehydroprolyl-2-(1',1'-dimethylallyl)tryptophyldiketopiperazine, known metabolites of Aspergillus ustus, were produced in low yield by Penicillium italicum in liquid culture and on unsterilized orange peel.