Butyrolactone II is a fungal metabolite with antibiotic properties and antioxidant activity. It is known to inhibit 5-lipoxygenase (5-LO) and α-glucosidase, and it also scavenges free radicals. It was first isolated from the fungus Aspergillus terreus.
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Proposal for the biosynthesis of butyrolactone II (13), secoretipolide E (15), retipolide E (16), retipolide C (7), and retipolide A (1).