Distribution of iridoids in different populations of Physostegia virginiana and some remarks on iridoids from Avicennia officinalis and Scrophularia ningpoensis

Two subspecies of Physostegia virginiana from seven different origins were investigated for iridoid glycosides. The plant material included the authentic sources of 'deoxyloganic acid', isolated in 1970 by one of the authors. This substance has now been identified as a 2.6:1 mixture of 7-deoxy-8-epiloganic acid and 10-deoxygeniposidic acid. Additionally, we isolated 14 known compounds and three new iridoids: stegioside I from P. virginiana ssp. virginiana (origin Freiburg) and stegiosides II and III from P. virginiana ssp. paemorsa (origin Chicago). The distribution of 16 out of 20 iridoids, previously reported or now isolated from P. virginiana, was determined in all populations. The iridoid patterns were significantly different between the two subspecies. The differences within ssp. virginiana were substantially smaller. The structure of 'avicennioside', previously isolated from Avicennia officinalis, is revised to linarioside. Ningpogenin, previously isolated from Scrophularia ningpoensis, is identical to a compound obtained by partial synthesis from aucubin.