A new naphthopyrone derivative from Cassia quinquangulata and structural revision of quinquangulin and its glycosides

A novel naphthopyrone derivative, named quinquangulone (1), has been isolat ed from Cassia quinquangulata, along with the known compounds quinquangulin (2) and its two glycosides (3 and 4), rubrofusarin (5) and its two glycosi des (6 and 7), nor-rubrofusarin (8) and its 6-O-glucoside (9), and three st ilbenes (10-12). The structure of quinquangulone was established by spectra l interpretation as 5,8-dihydroxy-8-methoxy-2,9-dimethyl-6-oxo-4H,6H,9H-nap htho-[2,3-b]pyran-4-one. Reinvestigation of the NMR spectra of quinquanguli n led to revision of its structure as 5,6-dihydroxy-8-methoxy-2,9-dimethyl- 4H-naphtho[2,3-b]pyran-4-one (2a). The structures of two quinguangulin glyc osides, 3 and 4, were also revised accordingly. Compound 2a exhibited activ ity against Staphylococcus aureus and methicillin-resistant S. aureus (MIC, 3.125 and 6.25 mug/mL, respectively).