 The phenylpropanoid pathway starts from the aromatic amino acids L-phenylalanine or L-tyrosine, both products of the Shikimate pathway.When starting from L-phenylalanine, first the amino acid is non-oxidatively deaminated by phenylalanine ammonia lyase (PAL) to make cinnamate, followed by oxidation at the "para" position by cinnamate 4-hydroxylase (C4H) to produce "p"-coumarate.As L-tyrosine is already oxidized at the "para" position, it skips this oxidation and is simply deaminated by tyrosine ammonia lyase (TAL) to arrive at "p"-coumarate.