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Bicyclic Tetrahydro-α-Pyrone Derivatives from Cryptocarya sp. are Artifacts
As a part of the Madagascar International Cooperative Biodiversity Group (ICBG) program, an ethanol extract of the wood of Cryptocarya retusa (Lauraceae) was selected for evaluation as a source of potential antimalarial agents based on its activity against Plasmodium falciparum Dd2. Bioassay-guided fractionation of the extract led to the isolation of a series of new 5,6-dihydro-α-pyrones (1 – 4) and bicyclic tetrahydro-α-pyrone derivatives (5 – 6) with moderate antimalarial activities. The structure elucidation of all compounds was based on NMR spectra, mass spectroscopic data, and chemical derivatization methods. The absolute stereochemistry of all isolated compounds was determined by CD and the Mosher ester method. The tetrahydro-α-pyrone derivatives were shown to be formed by cyclization of 5,6-dihydro-α-pyrones by silica gel and were not detectable in the original extract. They thus are artifacts of the isolation process.