Refined preparation of 1alpha,3-dipyrrolidino-androsta-3,5-diene-17-one, a key intermediate in the exemestane synthesis.

A significant improvement of the patent route for exemestane synthesis has been achieved. The key intermediate 1alpha,3-dipyrrolidino-androsta-3,5-diene-17-one (7) was obtained in a good yield and effectively used without further isolation in the next reaction step. The original analytical method for the identification and quantification of the substrate androsta-1,4-diene-3,17-dione (ADD, 6), intermediate 7 and 1-pyrrolidinoandrosta-1,3,5-triene-17-one (9) impurity in the reaction mixture was applied. Due to the newly developed process, the economical synthesis of the final pharmaceutical product in a large scale was possible. In addition, the complete NMR characteristics of 7 was described for the first time. The experiments were also analyzed with the theoretical quantum mechanical density functional B3LYP calculations for the energy outputs in model reactions. Based on these studies hypothetical routes of key intermediate (7) formation have been suggested. These predictions were consistent with the solutions of kinetic equations fitted to the experimental curves for time-dependence of three components of the reaction mixture.