No abstract

A new synthetic process was developed for (+)-2-((1R,2R,3R,5S)-2-amino-6,6-dimethylbicyclo[3.1.1]hept-3-yl)ethanol, a key intermediate of S-5751. Diastereoselective alkylation of (+)-nopinone with ethyl bromoacetate, formation of O-methyl oxime, and diastereoselective reduction with NaBH 4 -AlCl 3 could be safely carried out. Stereochemistry of the (1R,2R,3R,5S)-6,6-dimethylbicyclo[3.1.1]heptane ring was discussed to achieve high diastereoselectivity on these reactions. For the scale-up, detailed consideration was given to the safety of the NaBH 4 -AlCl 3 reduction.

Semisynthetic endothelin receptor antagonist S-0139 was synthesized in 14 steps from oleanolic acid 2 in a 20% overall yield on a multi-kilogram scale. Our previous synthesis of the oleanane skeleton was modified and improved to give phosphonate 9 as a key intermediate. The side chain on the 27-position was introduced by Horner-Wadsworth-Emmons olefination of phosphonate 9 with aldehyde 5. Aldehyde 5 was prepared in a one-pot reduction-acylation process starting from 5-hydroxy-2-nitrobenzaldehyde. The entire sequence of the synthesis can be done without chromatography and yields S-0139 of high purity.