Absolute configuration of longipinenyl epoxyangelates from three Stevia species

The complete stereostructures of two longipinene derivatives-from three Ste via species, which contain chiral epoxyangelate moieties are assigned as (4 R,5S,7R,9R,10R,11R,2'R,3'R)- and (4R,5S,7R,9R,10R,11R,2'S,3'S)-9-angeloylox y-7-(2',3'-epoxy-2'-methylbutyryloxy)-1-oxolongipin-2-ene. These results fo llow from the preparation of the substances by incorporation of both enanti omers of epoxyangelic acid into 9-angeloyloxy-7-hydroxy-1-oxolongipin-2-ene , followed by comparison of the N-1 NMR data of the prepared esters with th ose of the natural substances. Minimum energy structures for both compounds using molecular mechanics calculations are also reported. (C) 1998 Publish ed by Elsevier Science Ltd. All rights reserved.