Journal of Lipid Research, Vol 38, 1014-1021, Copyright © 1997 by Lipid Research, Inc.

ARTICLES

X-ray crystal structure of cytotoxic oxidized cholesterols: 7- ketocholesterol and 25-hydroxycholesterol

MP McCourt, K Ashraf, R Miller, CM Weeks, N Li, W Pangborn and DL Dorset
Electron Diffraction Department, Hauptman Woodward Medical Research Institute, USA.

The cytotoxic cholesterol derivative, 7-ketocholesterol, crystallizes in a monoclinic unit cell, space group P2(1) with a = 11.405 A, b = 6.288 A, c = 35.393 A and beta = 92.75 degrees (Z = 4). Its room temperature crystal structure was solved by direct methods, i.e., the minimal principle via the Shake-and-Bake (SnB) algorithm. In contrast to the continuous chain pattern found for the cholesterol monohydrate structure, hydrogen bonding in the 7-ketocholesterol structure is localized to specific sites via one water molecule that forms linkages between two O3 hydroxyl groups and one keto oxygen. The final weighted R factor for 4562 reflections was 0.144. The 25-hydroxycholesterol also crystallizes in a monoclinic unit cell (P2(1)), with a = 10.840 A, b = 14.533 A, c = 16.093 A and beta = 95.91 degrees (Z = 4). The low temperature structure was solved by DIRDIF. In this instance, molecular packing is anti-parallel in layers stabilized by hydrogen bonding networks via both hydroxyl functions, differing both from cholesterol monohydrate and the 7-ketocholesterol. The final weighted R-factor for 6566 reflections was 0.034. Functional differences of the oxysterols therefore, may be expressed by observed variations in the molecular packing and geometry.
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