Figure 1

Proposed biosynthetic pathway from L-Phe to diarylheptanoids and gingerol-related compounds in ginger and turmeric. Enzymes are as follows: PAL = phenylalanine ammonia lyase; C4H = cinnamate 4-hydroxylase; 4CL = 4-coumarate:CoA ligase; CST = p-coumaroyl shikimate transferase; C3´H = p-coumaroyl 5-O-shikimate 3´-hydroxylase; OMT = O-methyltransferase; CCOMT = caffeoyl-CoA O-methyltransferase; SAMS = S-adenosylmethionine synthetase; SAHC = S-adenosylhomocysteine. All conversions have been demonstrated in other species, except for those catalyzed by the polyketide synthases, the reductases, and the hydroxylases and OMTs that would convert bisdemethoxycurcumin via demethoxycurcumin to curcumin (indicated by dashed arrows). The polyketide synthases indicated represent two distinct classes that work in tandem: diketide synthases and curcuminoid/gingerol synthases. Different combinations of these two classes appear to be responsible for production of different compounds in these plants. The large red X and the solid arrows associated with the DKS1 + CURS reactions indicate that formation of curcumin has been demonstrated to proceed directly from feruloyl-CoA, and not through the orthodiol intermediate B. Compounds A and B, therefore, are not likely to be intermediates in the pathway to curcumin but instead are likely to be products of a different pair of PKS enzymes.