Determination of a set of parameters for the molecular modelling of phosphorothioate DNA

Phosphorothioate DNAs, have emerged as a new class of potent drugs. They ar e obtained by the replacement of the anionic oxygens of the phophodiester b ackbone by sulphur. A set of parameters has been developed for the FLEX for ce field implemented in JUMNA 10.0 to take into account the influence of su lphur on the structure of the DNA double helix. The consistency of our para meters was tested by modelling a phosphorothioate oligomer namely d(GC)8. d (GC)8. Results, obtained on both R-ps and S-ps diastereoisomers, were compa red to the phosphodiester counterpart and are in agreement with available e xperimental data. Thus, our set of parameters seems suitable for further mo lecular modelling of other phosphorothioate oligomers.