Highly Functionalized Spirobisnaphthalenes from Roussoella sp. KT4147.

Highly functionalized spirobisnaphthalenes, preussomerins N ( 1 ) and O ( 2 ), and simpler compounds, such as 2,3-α-epoxypalmarumycin CP 18 ( 3 ), 3α-hydroxy-CJ-12,372 ( 4 ), and 16 known structurally related congeners, were isolated from a culture broth of Roussoella sp. KT4147. Structural analysis revealed that 1 was a dimer of preussomerin G ( 6 ), connected by a nitrogen atom, and 2 was a derivative of 6 with a macommelin substructure. Preussomerin N ( 1 ) was considered to be biosynthetically derived via the Michael-type 1,4-addition of ammonia to 6 , followed by another Michael addition to another molecule of 6 . Contrarily, 2 was suggested to be derived through an endo -Diels-Alder cycloaddition between a diene derived from the ( E )-enol form of macommelinal via an ene -reaction and dienophile 6 . Compounds 1 and 2 exhibited potent cytotoxicity against COLO-201 human colorectal cancer cells.