DURING the course of our work on Guttiferae we required maclurin (I). Examination of commercial maclurin extracted from Morus tinctoria* (Moraceae) (we thank the Aldrich Chemical Co. for disclosing their source of maclurin) showed a small amount of impurity which was identified as 1,3,6,7-tetrahydroxyxanthone (IIa) by comparison with an authentic sample using paper chromatography (Whatman No. 1; 60 per cent aqueous acetic acid; RF 0.70). 1,3,5,6-Tetrahydroxyxanthone (IIIa) has a similar RF value but a different colour under ultra-violet light, and the structure of the impurity was therefore confirmed by methylation with dimethyl sulphate. The resulting 1,3,6,7-tetramethoxyxanthone (IIb) was identified by thin-layer chromatography (silica gel by Stahl; benzene–chloroform, 3 : 7; RF 0.35) because under these conditions the isomeric 1,3,5,6-tetramethoxyxanthone (IIIb) has a higher RF (0.42). Authentic xanthones were prepared by unambiguous synthesis1.
Yates, P., and Stout, G. H., J. Amer. Chem. Soc., 80, 1691 (1958). Shah, G. D., and Shah, R. C., J. Sci. Indust. Res., India, 15, B, 630 (1956).
Other conditions for xanthone formation by phenol oxidative coupling are described by Lewis, J. R., and Warrington, B. H., J. Chem. Soc., 5074 (1964).
Wolfrom, M. L., et al., J. Org. Chem., 29, 692 (1964).
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JEFFERSON, A., SCHEINMANN, F. Presence of 1,3,6,7-Tetrahydroxyxanthone in Maclurin from Chlorophora tinctoria (L) Gaud. (Morus tinctoria L) (Moraceae). Nature 207, 1193 (1965). https://doi.org/10.1038/2071193a0
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