Abstract
| - A new highly cytotoxic iridoid has very recently been isolated from Prismatomeris tetrandra and shownto have the structure 3, similar to that of the iridoid oruwacin, 2. We report the determination of theabsolute configuration (AC) of the new iridoid, prismatomerin, using vibrational circular dichroism (VCD)spectroscopy. The VCD spectrum of the acetate derivative of 3, 4, is analyzed using the Stephens theoryof VCD and density functional theory (DFT). The AC of the naturally occurring 3 is shown to be1R,5S,8S,9S,10S, identical to that of the naturally occurring iridoid plumericin, 1, also determined usingVCD spectroscopy. The [α]D values of the natural products 3 and 1 are negative and positive, respectively.Since the ACs of 3 and 1 are identical, it follows that the AC of 3 cannot be correctly determined byempirical comparison of the signs of the [α]D values of 3 and 1.
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