Revision of the Structure of N,O-Diacetylsolasodine. Unusual Epimerization at the Spiro Carbon Atom during Acetylation of Solasodine

The steroidal alkaloid solasodine (1) undergoes inversion of configuration at the C-22 spiro atom when treated with acetic anhydride pyridine at ambient temperature. The basic solvolysis of the N,O-diacetyl derivative (2) reverses the reaction, yielding the starting solasodine (1). The mechanisms of both processes (acetylation and deacetylation) were studied in terms of possible reaction pathways.