Crystal structure of 2-debenzoyl, 2-acetoxy paclitaxel (Taxol): conformation of the paclitaxel side-chain.

Crystals of the C2-acetate analog of paclitaxel, grown from a mixture of isopropyl alcohol and methanol, belong to the space group P2(1) with a = 9.058(3), b = 18.306(5), c = 15.043(1) Angstrum, beta = 97.09(1) degrees, Z = 2, V = 2475.1(9)Angstrum3, Dcalc = 1.269 gcm-3 and mu = 0.75 cm-1. The structure was determined by direct methods and refined to R(F) = 0.054 and wR(F) = 0.057 for 605 variables and 3496 observed reflections. The paclitaxel side chain possesses a conformation similar to that observed in the crystal structure of docetaxel (Taxotere). A three dimensional network of hydrogen bonds is formed through solvent molecules and stabilizes the crystal lattice.