Pentalenic acid has been isolated from many Streptomyces sp. as a co-metabolite of the sesquiterpenoid antibiotic pentalenolactone and related natural products. Pentalenic acid is a shunt metabolite in the biosynthesis of the pentalenolactone family. Pentalenic acid itself is a useful polycyclic skeleton for structural modification. Members of the pentalenolactone family show antitumor, immunosuppressant and antidiabetic effects, but the bioprofile of pentalenic acid is largely unexplored.