Intramolecular formation of cyclic ether by dehydration of 20(S)-ginsenoside Rg3

Two new conversion ginsenosides having cyclic ether together with ginsenoside Rg5, Rk1, and Rz1 were isolated from dehydration products of 20(S)-ginsenoside Rg3. On the basis of NMR spectroscopic analyses and comparison with spectral data of ginsenoside Rg3 as a starting material, the chemical structures of two new ginsenosides were established as 12β-O-20(S)-ginsenoside Rg3 and 12β-O-20(R)-ginsenoside Rg3. The compounds were named as neoginsenoside L1 and L2 respectively. The conversion mechanism was expected to be accomplished by the formation of a tertiary carbocation or intramolecular nucleophilic displacement. The two new ginsenosides confirmed the existence from red ginseng extract by liquid chromatography.