Crystal structures of the dihydro- and 2α-hydroxydihydro-derivatives of phytuberin

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Abstract
The X-ray crystal structure analyses of two derivatives of the potato stress metabolite phytuberin, are reported. Dihydrophytuberin (III){8-(1-acetoxy-1-methylethyl)-3a,5a-dimethylperhydrofuro[3,2-c]isobenzofuran} has space group P21, a= 9.723(2), b= 10.722(5), c= 8.107(5)Å, β= 101.29(3)°, and its structure was derived by direct methods. Full-matrix least-squares refinement, to R 0.060 for 1 650 reflections, showed a very compact, rigid molecule, with considerable conformational strain within the three-ring system. 2α-Hydroxydihydrophytuberin (II) has two independent molecules in the triclinic P1 cell, a= 10.887(3), b= 10.057(8), c= 8.661(5)Å, α= 111.85(5), β= 89.63(4), γ= 99.43(5)°. This structure was determined from the alignment of the rigid skeletal structure of (III) with small ring fragments in an E map. The final refined structure, R 0.134 for 2 845 measured reflections, shows a pseudo-two-fold screw axis closely relating the two molecules. There are negligible differences in the conformations of the two molecules, and only in the rings adjoining the hydroxy-groups do they differ from (III). The packing arrangements of the two derivatives are quite different. It is suggested that, in (II) there is a hydrogen-bonding scheme spiralling parallel to the a axis; in (III), no such interactions are possible and all intermolecular contacts are at van der Waals distances.

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