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Use of conformational differences between identical parts of molecule in the serch of low-energy conformations by the OS method

The overlapping spheres (OS) method for fintidng the low-energy conformations is based on the construction of the central sphere (defined with its radius Rv), centered at the geometrical center of the molecule or molecular framgent. However, there is no a priori criterion for the proper molecular fragmentation and the choice of the central sphere radius. In order to solve that problem, we proposed a topological fragmentation (besed on cluster analysis - Ward's method), but this approach showed less success for the molecules possessing some kind of symmetry. For these molecules we invented a method based on the analysis of conformational diferences between topologically identical parts of molecule. It was applied to three stereoisomes of copper(II) bis-chelates with 1-[N-(tert-butoxycarbonyl)aminog-2-hyddroxymethylcyclopropane-1-carboxylic acid. The newly proposed fragmentation technique gave similar of slightly better results in comparison to the topological and topograplhical fragmentations. In the case of (1-2, 1S, SR)(N-S, 1S, 2R), (N-R, 1S, 2R)(N-S, 1R, 2S), and (N-R, 1S, 2S)(N-S, 1R, 2R) isomers the lowest-energy conformations obtained heve the energy of 1561.9, 1561.0, and 1580.2 kJ mol-1, respectively, which are substantially lower values than those obtained by the other two methods (topological and topograplhical fragmentation), which yielded 1562.9, 1562.6, and 1883.3 kJ mol-1 for the respective isomers. The newly proposed method was also cehcked on copper(II) bis-complex with N, N-diethylalanine, but with less success.

overlapping spheres; cluster analysis; conformational analysis; 1-aminocyclopropane-1-carboxylic acid

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