Frequentin is a polar neutral metabolite isolated from P. frequentans by Curtis and co-workers at ICI in 1951. Frequentin is a cyclitol-like metabolite bearing a heptadiene chain. Frequentin, the aldehyde analogue of palitantin, exists as the hydroxymethylene in solution. Frequentin has been found in a number of Penicillium species and is a useful metabolite for chemotaxonomy of the genus. Frequentin is a potent antifungal active with minimal toxicity to mammalian cells.