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 (13)C NMR data and complete (1)H and (13)C NMR assignments of some known compounds are reported for the first time. In addition, the errors of (1)H and (13)C assignments reported in the literature were corrected.