Dihydroisatropolone C from Streptomyces and Its Implication in Tropolone-Ring Construction for Isatropolone Biosynthesis

Isatropolones/isarubrolones are actinomycete secondary metabolites featuring a tropolone-ring in their structures. From the isatropolone/isarubrolone producer sp. CPCC 204095, 7,12-dihydroisatropolone C (H ITC) is discovered and identified as a mixture of two interchangeable diastereomers differing in the C-6 configuration. As a major metabolite in the mycelial growth period of sp. CPCC 204095, H ITC can be oxidized spontaneously to isatropolone C (ITC), suggesting H ITC is the physiological precursor of ITC. Characterization of H ITC makes us propose dihydrotropolone-ring construction in the biosynthesis of isatropolones.