Experiments in the biosynthesis of curcumin

The biogenesis of natural diarylheptanoids is discussed, with particular reference to curcumin 1,7-bis-(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione, the pigment of Curcuma Ionga rhizome. Methods for the isolation, characterisation, and degradation of curcumin, suitable for biosynthetic work, are reported. In administration of labelled precursors to C. Ionga,1- and 3-14Cphenylalanine were incorporated into curcumin without scrambling of the label. 1- and 2-14C-Acetate and -malonate were also incorporated, and the fractional distribution of label along the heptane chain was determined; the results do not provide satisfactory support for the expected biosynthetic scheme, in which two cinnamate units condense with one malonate unit. Other interpretations are discussed. 3H-4-Hydroxy-3-methoxy-, -4-hydroxy-, and -3,4-dihydroxy-cinnamic acids were prepared, and supplied to C. Ionga with 14Cphenylalanine. The first two cinnamic acids are incorporated into curcumin significantly better than the last, although none was utilised quite as efficiently as phenylalanine.