Plumeridoid C from the Amazonian traditional medicinal plant Himatanthus sucuuba

The stereochemistry of the iridoid plumeridoid C, C₁₅H₁₈O₇, was established by X-ray single-crystal structure analysis, giving (2′R,3R,4R,4aS,7aR)-methyl 3-hydroxy-4′-[(S)-1-hydroxyethyl]-5′-oxo-3,4,4a,7a-tetrahydro-1H,5′H-spiro[cyclopenta[c]pyran-7,2′-furan]-4-carboxylate. The absolute structure of the title compound was determined on the basis of the Flack x parameter and Bayesian statistics on Bijvoet differences. The hydrogen-bond donor and acceptor functions of the two hydroxy groups are employed in the formation of O—H...O-bonded helical chains.