Practical Synthesis of BILA 2157 BS, a Potent and Orally Active Renin Inhibitor: Use of an Enzyme-Catalyzed Hydrolysis for the Preparation of Homochiral Succinic Acid Derivatives.

We have developed a highly convergent and stereoselective synthesis of BILA 2157 BS, a potent and orally active renin inhibitor. The synthesis proceeds in 15 distinct chemical steps (with several integrated, multistep operations) from aminodiol 4. The key step in the synthesis involves the use of an enantiospecific, enzyme-catalyzed hydrolysis of a substituted succinate diester to provide a homochiral succinic acid derivative in 98% enantiomeric excess (>/=2.5 kg scale). Recycling of the unwanted enantiomer is accomplished through base-catalyzed racemization, leading to an efficient deracemization of the starting racemic diester. The entire sequence proceeds without chromatographic purifications and delivers the product with >97% homogeneity. In addition, compared to the previously reported syntheses of BILA 2157 BS, this approach avoids the use of expensive chiral auxiliaries and cryogenics and, thus, should be amenable to the preparation of large quantities of this peptidomimetic inhibitor.