Nonpolar and medium polarity fractions from whole plant methanolic extracts of Stevia monardifolia afforded the new 7β-angeloyloxy-8α-isovaleroyloxylongipin-2-en-1-one 1 along with known 7β,8α-diangeloyloxylongipin-2-en-1-one 2 and 7β,8α-diangeloyloxylongipinan-1-one 3. Alkaline hydrolysis of a mixture of 1 and 2 gave 7β,8α-dihydroxylongipin-2-en-1-one 4 which was subjected to a single crystal X-ray diffraction study. The new compound 1, which is the third 7β,8α-dihydroxylongipin-2-en-1-one diester natural product isolated from a Stevia especies, was fully characterized by one-and two-dimensional NMR spectroscopy and its absolute configuration was confirmed as the 4R,5S,7S,8S,10R,11R enantiomer by vibrational circular dichroism (VCD) measurements in comparison to calculation at the B3LYP/DGDZVP level of theory.
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