(6S*)-6-[(1S*,2R*)-1,2-Dihydroxypentyl]-4-methoxy-5,6-dihydro-2H-pyran-2-one

The title compound, C11H18O5, was isolated from a liquid culture of Pestalotiopsis sp. In the molecule, the pyran-2-one ring assumes a half-chair conformation. The two terminal C atoms of the pentyl group were refined as disordered over two sets of sites, with refined occupancies of 0.881 (10) and 0.119 (10). In the crystal, molecules are linked via O—H⋯O hydrogen bonds forming a three-dimensional network.


Comment
The title compound was first isolated from an unidentified Penicillium sp. (McGahren et al., 1973). Multiple routes have been reported for the total synthesis (Kirihata et al., 1990;Kirihata et al., 1992a;Masaki et al., 1994) including syntheses creating unnatral stereoisomers (Kirihata et al., 1992b). Closely related products have been reported from other fungi (Kirihata et al., 1996;Lee et al., 1995). The 6-substituted 5,6-dihydropyran-2-one moiety present in the title compound is also found in natural products from several species of plants and fungi (Davies-Coleman & Rivett, 1989). Although many structures with this moiety exhibit bioactivity, it appears that the title compound displays none of the reported activities.
Notably, the gibberellin synergistic activity of the very closely related compound pestalotin is not found (Kimura et al., 1986;Venkatasubbaiah & Van Dyke, 1991). In our lab we observed moderate antifungal activity. Crystal structures for the related natural products, kavain, dihydrokavain and methysticin have been reported (Yoshino & Nowacki, 1972;Engel & Nowacki, 1972a;Engel & Nowacki, 1972b). In the title compound, the atoms of the pyran-2-one assume a halfchair conformation. The conformations of the methoxy and dihydroxypentyl groups are shown in Fig. 1. Carbons 4′ and 5′ are disordered over two sites with occupancies of 0.881 (10):0.119 (10). In the crystal, molecules are linked via O-H···O hydrogen bonds forming a three-dimensional network (see Table 1 and Fig. 2).

Experimental
The title compound was obtained by liquid-liquid extraction (CH 2 Cl 2 /H 2 O) of a culture of an endophytic Pestalotiopsis sp. The CH 2 Cl 2 fraction was evaporated under reduced pressure then purified by chromatography on a silica column with CHCl 3 /CH 3 OH (8/2) as eluent. After pooling common fractions, a crystal was grown by slow evaporation of a MeOH solution.

Refinement
The molecule exhibits orientational disorder at atoms C4 and C5. Hydrogen atoms were located and refined isotropically except those on C4 and C5 which were placed in calculated positions of C-H = 0.98 and 0.99Å and assigned isotropic displacement parameters of U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ), and their coordinates were allowed to ride on their respective carbons using SHELXL97 (Sheldrick, 2008). In the absence of anomalous dispersion effects the Friedel pairs were merged. The absolute configuration is not known.

Figure 1
Molecular structure of the title compound. Displacement ellipsoids are shown at the 50% probability level on nonhydrogen atoms. The disorder is not shown. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.16 e Å −3 Δρ min = −0.18 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.033 (6) Special details Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm that effectively corrects for absorption effects. High redundancy data were used in the scaling program thus the 'multi-scan′ code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size′ command in the SHELXL97<i/> input file. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 >σ(F 2 ) is used only for calculating R-factors(gt) etc and is not relevant to the choice of reflections for refinement. R factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.