6-O-Isobutyryl-tetrahydrohelenalin from the flowers of Arnica montana.

From the flowers of ARNICA MONTANA L., the helenanolides 6- O-isobutyryl-tetrahydrohelenalin and 2beta-ethoxy-6- O-isobutyryl-2,3-dihydrohelenalin were isolated and their structures established by spectroscopic methods.

[Helenalin- and 11,13-Dihydrohelenalinester from Flowers of Arnica montana.]. / Helenalin- und 11,13-Dihydrohelenalinester aus Blüten von Arnica montana*

From the flowers of ARNICA MONTANA L. 13 helenanolides were isolated and identified. They are shown to be 11,13-dihydrohelenalin ( 1), helenalin ( 2) and their ester derivatives 3-13 (see figure). The natural occurence of 6-O-isobutyryl-, 6-O-tigloyl-, 6-O-isovaleryl- and 6-O-(2-methyl)-butyrylhelenalin (compounds 9, 11, 12, 13) is reported for the first time. The qualitative sesquiterpene lactone composition in flowers of A. MONTANA from different regions was found to be variable.