(3R,4S)-3,4,8-Trihydroxy-1,2,3,4-tetrahydronaphthalen-1-one monohydrate from Embellisia eureka

In the title hydrate, C10H10O4·H2O, the six-membered aliphatic ring that is fused to the benzene ring has a sofa shape, with the hydroxy group in the 3-position (that represents the sofa back) of the aliphatic ring occupying a quasi-axial position. The hydroxy group of the aromatic ring is hydrogen-bond donor to the carbonyl O atom; other O—H⋯O hydrogen bonds link the organic molecules and the water molecules into a three-dimensional network.

In the title hydrate, C 10 H 10 O 4 ÁH 2 O, the six-membered aliphatic ring that is fused to the benzene ring has a sofa shape, with the hydroxy group in the 3-position (that represents the sofa back) of the aliphatic ring occupying a quasi-axial position. The hydroxy group of the aromatic ring is hydrogen-bond donor to the carbonyl O atom; other O-HÁ Á ÁO hydrogen bonds link the organic molecules and the water molecules into a three-dimensional network.
Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2010). Hypoxylon mammatum (Borgschulte et al., 1991), Nigrospora sp. (Trisuwan et al., 2008) and Pyrichularia orayzae (Iwasaki et al., 1972). The compound was isolated from Embellisia eureka in this study; the compound was found to crystallize as a monohydrate (Scheme I). In the hydrate, C 10 H 10 O 4 . H 2 O, the six-membered aliphatic ring that is fused to the benzene ring has a soft shape. The C-3 atom represents the sofa back. The hydroxy group of the aliphatic ring occupies a quasi-axial position (Fig. 1). The hydroxy group of the aromatic ring is hydrogen-bond donor to the carbonyl O atom; other O-H···O hydrogen bonds link the organic molecule and water molecule to form a 3D network (Table 1).

Fungal extraction
The fungal strain, Embellisia eureka, was identified by PCR. About 250 ml of ethyl acetate was added into each culture material of the fungus in an Erlenmeyer flask. The ethyl acetate phase was then concentrated under reduced pressure. The residue was diluted in 90% aqueous methanol and further extracted with n-hexane to remove fatty acids and other nonpolar constituents. The remaining 90% methanol phase was evaporated under reduced pressure to yield 3.0 g of crude product.

Isolation protocol of 3,4-dihydro-3,4,8-trihydroxy-1[2H]-naphthalenone
The 90% methanol extract was submitted to vacuum liquid chromatography on a column packed with silica as the stationary phase,. The resulting fraction was submitted two successive fractionations on a Sephadex column packed with Sephadex LH-20 as stationary phase. The mobile phase was the 100% methanol. This gave 113.4 mg of a material that was purified by using the semi-preparative HPLC to give 7.0 mg of the pure compound. Crystals were obtained by slow evaporation of a methanol: water (9:1) solution of the compound.

Refinement
The aromatic and methylene H-atoms were placed in calculated positions (C-H 0.93-0.97 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U(C). The hydroxy and water H-atoms were located in a difference Fourier map, and were refined with a distance restraint of 0.84±0.01 Å; their temperature factors were refined.
The absolute configuration was assumed from published assignments (Trisuwan et al., 2008)