Derivatives of mandelic acid are formed as a result of metabolism of adrenaline and noradrenaline by monoamine oxidase and catechol-O-methyl transferase.
Excerpt from The Kinetics of the Reaction Inactivation of Tyrosinase during its Catalysis of the Aerobic Oxidation of Catechol
Petunidin could form in the exocarp of fruits from delphinidin, with an anthocyanin flavonoid O-methyltransferase (Catechol-O-methyl transferase) catalyzing the B-ring methylation and S-Adenosyl-L-methyl-3H methionine being the methyl group donor.