The biosynthetic route of curcumin is uncertain. In 1973, Roughly and Whiting proposed two mechanisms for curcumin biosynthesis. The first mechanism involves a chain extension reaction by cinnamic acid and 5 malonyl-CoA molecules that eventually arylized into a curcuminoid. The second mechanism involves two cinnamate units coupled together by malonyl-CoA. Both use cinnamic acid as their starting point, which is derived from the amino acid phenylalanine.
Plant biosyntheses starting with cinnamic acid is rare compared to the more common p-coumaric acid.[9] Only a few identified compounds, such as anigorufone and pinosylvin, build from cinnamic acid.[10][11]
An experimentally backed route was not presented until 2008. This route follows both Roughley and Whiting mechanisms. However, the labeling data supported the first mechanism model in which 5 malonyl-CoA molecules react with cinnamic acid to form curcumin. However, the sequencing in which the functional groups, the alcohol and the methoxy, introduce themselves onto the curcuminoid seemed to support more strongly the second proposed mechanism.[9] Therefore, the second pathway was accepted.