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

Two new conversion ginsenosides having cyclic ether together with ginsenoside Rg(5), Rk(1), and Rz(1) were isolated from dehydration products of 20(S)-ginsenoside Rg(3). On the basis of NMR spectroscopic analyses and comparison with spectral data of ginsenoside Rg(3) as a starting material, the chemical structures of two new ginsenosides were established as 12 beta-O-20(S)-ginsenoside Rg(3) and 12 beta-O-20(R)-ginsenoside Rg(3). The compounds were named as neoginsenoside L-1 and L-2 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. (C) 2009 Elsevier Ltd. All rights reserved.