Absolute configuration of the fungal metabolite spirolaxine

The relative stereochemistry of the four stereocentres of spirolaxine 1, a bioactive 6,5-spiroacetal phthalide secondary metabolite, was determined through single-crystal X-ray analysis. Its absolute configuration was determined by circular dichroism; the experimental spectrum of spirolaxine is in good agreement with that evaluated by means of DeVoe coupled-oscillator calculations.