Mechanisms naringenin chalcone

Although it has long been thought, based on genetic mutant and biochemical evidence, that aurones are derived from chalcones, the biosynthetic mechanism has only recently been clarified, and some aspects of the enzymatic process still await in vivo proof An mRNA from A. majns, specifically expressed in the petal epidermal cells, has been shown to encode a recombinant protein with aureusidin synthase (AUS) activity.AUS is a variant polyphenol oxidase (PPO) that can catalyze conversion of either 2, 4, 6, 4-etrahydroxychalcone (naringenin chalcone) or 2, 4, 6, 3,4-pentahydroxychalcone to... 

Figure 1. Proposed mechanism for the formation of (A) naringenin chalcone from 4-coumaroyl-CoA and three molecules of malonyUCoA by CHS, (B) triacetic lactone from acetyl-CoA and two molecules of malortyUCoA by 2PS, (C) aloesone from acetyl-CoA and six molecules of malonyUCoA by ALS, (D) 5,7-dihydroxy-2-methylchromone from five molecules of malonyl-CoA by PCS, and (E) SEK4 and SEK4b from eight molecules of malonyl-CoA by OKS. Bis-noryangonin (BNY) and 4-coumaroyltriacetic acid lactone (CTAL) are derailment by-products of the CHS reactions in vitro when the reaction mixtures are acidified before extraction. In A. arborescens PCS and OKS, acetyl-CoA, resulting from decarboxylation of malonyl-CoA, is also accepted as a starter but not so efficiently as in the case ofR. palmatum ALS.

Havanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthocyanidins), flavan-4-ols, and flavan-3,4-diols. They arise from plant secondary metabolism through condensation of phenylalanine derived from the shikimate pathway with malonyl-CoA obtained from citrate that is produced by the tricarboxylic acid cycle, leading to the formation of the key precursor in the flavonoids biosynthesis the naringenin chalcone. The exact nature of the molecular species that undergo polymerization and the mechanism of assembly in proanthocyanidins are still unknown. From a structural point of view, flavanols... 

---