2′-, 4′-, and 6′-o-substituted 1,5,9-epideoxyloganic acids from nepeta grandiflora

Abstract

In addition to the known 1,5,9-epideoxyloganic acid and 1,5,9-epideoxyloganin, Nepeta grandiflora has provided four new iridoid glucosides: 6′- O -acetoacetyl-, 2′- O -methyl-, 4′- O -methyl-, and 6′- O -methyl-1,5,9-epideoxyloganic acid. Their structures were proved by 1 H and 13 C-NMR studies. The conformation of the molecules was studied by molecular modelling and 1 H NMR coupling constant analysis. The absolute configurations were supported by CD spectroscopy.