Structure elucidation and NMR assignments for curcuminoids from the rhizomes of Curcuma longa

Thirteen curcuminoids (1-13) were isolated from the rhizomes of Curcuma longa. Among them, 1,5-dihydroxy-1,7-bis(4-hydroxyphenyl)-4,6-heptadiene-3-one (1), 1,5-dihydroxy-1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)-4,6-heptadiene-3-one (2), 1,5-dihydroxy-1-(4-hydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-4,6-heptadiene-3-one (3), and 3-hydroxy-1,7-bis-(4-hydroxyphenyl)-6-heptene-1,5-dione (4) are new compounds, and 1-(4-hydroxyphenyl)-7-(3, 4-dihydroxyphenyl)-1, 6-heptadiene-3, 5-dione (5) is isolated from natural sources for the first time. The structures of these compounds were elucidated by extensive spectroscopic analyses, especially 1D and 2D NMR spectroscopy. The C-13 NMR data and complete (1H) and C-13 NMR assignments of some known compounds are reported for the first time. In addition, the errors of H-1 and C-13 assignments reported in the literature were corrected. Copyright (C) 2009 John Wiley & Sons, Ltd.