Crystal structures of ()-(1SR,5SR,6SR,7SR,10SR,-11SR,13RS,14SR,15SR,16RS)-13-acetoxy-16-benz-yloxy-15-hydroxy-7-methoxymethoxy-3-oxo-11,15,18,18-tetramethyl-2,4-dioxatetracyclo-[12.3.1.0^1,5.0^6,11]octadecan-10-yl benzoate and its 13-epimer

The title compounds, C₃₈H₄₈O₁₁ (A and B), are tetracyclic 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 cyclohexane rings and the cyclooctane ring adopt chair and chair–chair forms, respectively, and there are three intramolecular H H short contacts. The corresponding ring conformations in B are similar; however, one intramolecular C—H O interaction and two H H short contacts are observed, and the benzoyl and methoxymethyl groups show orientational disorder. In the crystal of A, a pair of intermolecular O—H O hydrogen bonds link two molecules into an inversion dimer, and weak intermolecular C—H O interactions connect the dimers, forming a three-dimensional network. In the crystal of B, an inversion dimer is similarly generated by a pair of intermolecular O—H O hydrogen bonds, and weak intermolecular C—H O and C—H π interactions connect the dimers into a three-dimensional architecture.