To study the metabolites of the mangrove fungus Alternaria sp. R6

the compounds were isolated by silica gel and Sephadex LH-20 column chromatography. Their structures were characterized by spectroscopy. The antifungal activities were investigated using the broth tube dilution method. Ten compounds

including (4R

5R)-4

5-dihydroxy-3-methoxy-5-methyl-cyclohex-2-en-1-one(1)

(4R

5S

6R)-4

5

6-trihydroxy-3-methoxy-5-methyl-cyclohex-2-en-1-one (2)

xylariacyclone B (3)

(4S

5S

6S)-5

6-epoxy-4-hydroxy-3-methoxy-5-methyl-cyclohex-2-en-1-one (4)

LL-C10037α(5)

1- hydroxy-8-(hydroxymethyl)-6-methoxy-3-methyl-9H-xanthen-9-one (6)

8-hydroxy-6- methyl- 1- meth-oxycarbonyl-xanthen-9-one (7)

8-dimethoxy-1

6-dimethoxycarbonyl-xanthen-9-one(8)

ergosterol and ergosterolperoxide

were isolated from the methanol extracts. Among them

the compounds 1

2

3

4

5

6 and 8 were obtained from Alternaria sp. for the first time. The compounds 6 and 8 showed good inhibitory activity against Fusarium graminearum Schw. and Colletotrichum musae (Berk. & M. A. Curtis) Arx. While the compound 2 only showed good inhibitory activity against the latter.