| Summary: | Three new bibenzochromenones named phanogracilins A–C (<b>1</b>–<b>3</b>) were isolated from the crinoid <i>Phanogenia gracilis</i>. The structure of <b>1</b> was established using X-ray crystallography as 5,5′,6,6′,8,8′-hexahydroxy-2,2′-dipropyl-4H,4′H-[7,9′-bibenzo[g]chromene]-4,4′-dione. This allowed us to assign reliably 2D NMR signals for compound <b>1</b> and subsequently for its isomer <b>2</b> that differed in the connecting position of two benzochromenone moieties (7,10′ instead of 7,9′), and compound for <b>3</b> that differed in the length of the aliphatic chain of one of the fragments. Compound <b>4</b> was derived from <b>1</b> in alkaline conditions, and its structure was elucidated as 5,5′,6′,8,8′-pentahydroxy-2,2′-dipropyl-4H,4′H-[7,9′-bibenzo[g]chromene]-4,4′,6,9-tetraone. Even though compounds <b>1</b>–<b>4</b> did not contain stereo centers, they possessed notable optical activity due to sterical hindrances, which limited the internal rotation of two benzochromenone fragments around C(7)–C(9′/10′) bonds. Isolated bibenzochromenones <b>1</b>–<b>4</b> were tested for their antiradical, neuroprotective and antimicrobial activities. Compounds <b>1</b>, <b>3</b> and <b>4</b> demonstrated significant antiradical properties towards ABTS radicals higher than the positive control trolox. Compounds <b>1</b> and <b>4</b> exhibited moderate neuroprotective activity, increasing the viability of rotenone-treated Neuro-2a cells at a concentration of 1 µM by 9.8% and 11.8%, respectively. Compounds <b>1</b> and <b>3</b> at concentrations from 25 to 100 μM dose-dependently inhibited the growth of Gram-positive bacteria <i>S. aureus</i> and yeast-like fungi <i>C. albicans</i>, and they also prevented the formation of their biofilms. Compounds <b>2</b> and <b>4</b> exhibited low antimicrobial activity.
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