Absolute Configurations of Asperlin, a Metabolite of Aspergillus nidulans, and Its Related Compounds

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Abstract
The structures of asperlin (1) C10H12O5 and asperlinol (2) C10H14O6, isolated from Aspergillus nidulans, and a chloro derivative of asperlin (3) C10H13O5Cl have been studied by the X-ray diffraction method. The absolute configuration of 3 has been determined by the Bijvoet method by utilizing the anomalous scattering of chlorine atom for Cu Kα radiation. The present analysis has verified the configurations of the atoms in an αβ-unsaturated δ-lactone ring as suggested by spectroscopy. In each compound, the acetoxyl group occupies a quasi-axial and the three-carbon side chain a quasi-equatorial position on the lactone ring. All the crystals are orthorhombic, space group P212121with Z=4. The cell dimensions are a=26.536, b=5.955, c=6.973 Å for 1, a=25.496, b=7.097, c=6.329 Å for 2, and a=26.050, b=5.899, c=7.548 Å for 3. The structures of 1, 2, and 3 were refined by the block-diagonal least-squares method to R=0.068 for 1084 reflections, R=0.056 for 1127 reflections, and R=0.051 for 831 reflections, respectively.