Crystal structures of (±)-(1SR,5SR,6SR,7SR,10SR,11SR,13RS,14SR,15SR,16RS)-13-acet-oxy-16-benzyloxy-15-hy-droxy-7-meth-oxy-meth-oxy-3-oxo-11,15,18,18-tetra-methyl-2,4-dioxa-tetra-cyclo[12.3.1.01,5.06,11]octa-decan-10-yl benzoate and its 13-epimer.

The title compounds, C₃₈H₄₈O₁₁ (A and B), are tetra-cyclic benzoates composed of a taxane ring with a fused dioxolane ring as the core skeleton. In compound A, the five-membered dioxolane ring is essentially planar while the two cyclo-hexane rings and the cyclo-octane ring adopt chair and chair-chair forms, respectively, and there are three intra-molecular H⋯H short contacts. The corresponding ring conformations in B are similar; however, one intra-molecular C-H⋯O inter-action and two H⋯H short contacts are observed, and the benzoyl and meth-oxy-methyl groups show orientational disorder. In the crystal of A, a pair of inter-molecular O-H⋯O hydrogen bonds link two mol-ecules into an inversion dimer, and weak inter-molecular C-H⋯O inter-actions connect the dimers, forming a three-dimensional network. In the crystal of B, an inversion dimer is similarly generated by a pair of inter-molecular O-H⋯O hydrogen bonds, and weak inter-molecular C-H⋯O and C-H⋯π inter-actions connect the dimers into a three-dimensional architecture.