Reactions involving phenylpropanoids

Fig. (1). Schematic view of some branches of phenylpropanoid metabolism. Solid arrows indicate enzymatic reactions with the respective enzyme indicated on the right. PAL, phenylalanine ammonia-lyase C4H, cinnamate 4-hydroxylase 4CL, 4-coumarate CoA ligase CHS, chalcone synthase CF1, chalcone flavavone isomerase F3H, flavanone 3-hydroxylase DFR, dihydroflavonol reductase CHR, chalcone reductase. Broken arrows indicate metabolic branches towards several classes of phenylpropanoids, or several subsequent enzymatic steps. In some cases the enzymes indicated are also involved in other reactions, not shown.

Figure 3-4. The general phenylpropanoid pathway. The enzymes involved in this pathway are (a) phenylalanine ammonia lyase (PAL E.C. 4.3.1.5), (b) cinnamic acid 4-hydroxylase (C4H E.C. 1.14.13.11), and (J) 4-coumaric acid CoA ligase (4CL E.C. 6.2.1.12). (a) depicts tyrosine ammonia lyase activity in PAL of graminaceous species. The grey structures in the box represent an older version of the phenylpropanoid pathway in which the ring substitution reactions were thought to occur at the level of the hydroxycinnamic acids and/or hydroxycinnamoyl esters. The enzymes involved in these conversions are (c) coumarate 3-hydroxylase (C3H E.C. 1.14.14.1), (d) caffeate O-methyltransferase (COMT EC 2.1.1.68), (e) ferulate 5-hydroxylase (F5H EC 1.14.13), and (g) caffeoyl-CoA O-methyltransferase (CCoA-OMT EC 2.1.1.104). These enzymes are discussed in more detail in Section 10.

Another method for the syntheses of phenyltetralin-type lignans, a route involving the condensation of two phenylpropanoid-type compounds followed by an intramolecular Diels-Alder reaction (ref. 2a), was found to be applicable to the synthesis of hernandin (15). 

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