Crystal and molecular structure of 3 beta-acetoxy-21-(2-hydroxy-2-methylpropoxy)-cholest-5-en-25-ol, the first "double side chain" cholesterol analogue investigated by X-ray diffraction

The title steroid crystallizes in the monoclinic P2(1) space group with uni t cell dimensions: a = 11.745(2) Angstrom, b = 10.564(2) Angstrom, c = 12.9 79(3) Angstrom, beta = 95.73(3)degrees. Its crystal and molecular structure was determined by X-ray diffraction methods. The A ring has a symmetrical chair conformation. The B ring has a half-chair conformation, with asymmetr y parameter Delta C-2(5,6) = 0.6 degrees. The C ring has an intermediate so fa-half-chair conformation with asymmetry parameters: Delta C-s(9) = 2.3 de grees, Delta C-s(11) = 5.8 degrees, Delta C-2(9,11) = 4.8 degrees, and Delt a C-2(8,9) = 5.6 degrees. Tbe D ring adopts an envelope conformation with a symmetry parameter Delta C-s(T3) = 10.7 degrees. The cholesterol side chain adopts a fully extended conformation with torsion angles -170.6(6)degrees, 167.9(6)degrees, -171.9(6)degrees and 175.6(7)degrees, i.e. it belongs to the most populated conformer A, and with the terminal C26 and C27 methyl gr oups in gauche, trans conformations.