Naquihexcin A, a S‑Bridged Pyrano­naphtho­quinone Dimer Bearing an Unsaturated Hexuronic Acid Moiety from a Sponge-Derived Streptomyces sp. HDN-10-293

S-Bridged pyranonaphthoquinone dimers, naquihexcins A and B (1 and 2), together with a related analogue (−)-BE-52440A (3) were obtained from the culture of a sponge-derived Streptomyces sp. HDN-10-293. Naquihexcin A (1) bears a rare unsaturated hexuronic acid moiety, and (−)-BE-52440A (3) has been discovered from natural resources. Compound 3 showed cytotoxicity against NB4 and HL-60 cells, while 1 could inhibit the proliferation of the adriamycin resistant human breast cancer cell line MCF-7 ADM.