There is considerable interest in the isolation of potent radical scavenging compounds from natural resources to treat diseases involving oxidative stress. In this report, four new fungal metabolites including one new bisdihydroanthracenone derivative (1, eurorubrin), two new seco-anthraquinone derivatives [3, 2-O-methyl-9-dehydroxyeurotinone and 4, 2-Omethyl- 4-O-(alpha-D-ribofuranosyl)-9-dehydroxyeurotinone], and one new anthraquinone glycoside [6, 3-O-(alpha-D-ribofuranosyl)- questin], were isolated and identified from Eurotium rubrum, an endophytic fungal strain that was isolated from the inner tissue of the stem of the marine mangrove plant Hibiscus tiliaceus. In addition, three known compounds including asperflavin (2), 2-O-methyleurotinone (5), and questin (7) were also isolated and identified. Their structures were elucidated on the basis of spectroscopic analysis. All of the isolated compounds were evaluated for 1,1-diphenyl-2-picrylhydrazyl(DPPH) radical scavenging activity.

anthraquinone, Mangrove plant, Hibiscus tiliaceus, endophytic fungus, Eurotium rubrum, radical scavenging activity

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15
4	aDRibf	103.0	73.8	71.8	88.8	63.2
2	Me	56.4
	Subst	133.6	152.1	100.1	156.4	106.5	136.4	37.5	145.4	122.3	145.7	116.8	158.3	116.8	164.9	21.7


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9	H10	H11	H12	H13	H14	H15
4	aDRibf	5.65	4.20	4.04	4.20	3.66
2	Me	3.76
	Subst	-	-	6.40	-	6.40	-	3.89	-	6.87	-	7.01	-	-	-	2.32


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9	C10/H10	C11/H11	C12/H12	C13/H13	C14/H14	C15/H15
4	aDRibf	103.0/5.65	73.8/4.20	71.8/4.04	88.8/4.20	63.2/3.66
2	Me	56.4/3.76
	Subst			100.1/6.40		106.5/6.40		37.5/3.89		122.3/6.87		116.8/7.01				21.7/2.32

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

COc1cc(O[C@H]2O[C@H](CO)[C@@H](O)[C@H]2O)cc2c1OC(=O)c1c(O)cc(C)cc1C2

418.398 g/mol (C₂₁H₂₂O₉)