Figure 3. Dihydrocaffeic acid biosynthesis—proposed simplified pathway (adapted and modified from
[19][20][21][22][23][24]). Explanations: (
a)–(
r)—compounds, A–R—enzymes, i.e., (
a)—D-Erythrose 4-phosphate, (
b)—Phosphoenolpyruvate, (
c)—7-phospho-2-dehydro-3-deoxy-D-arabino-heptonate, (
d)—3-Dehydroquinate, (
e)—3-Dehydroshikimate, (
f)—Shikimate, (
g)—Shikimate-3-phosphate, (
h)—5-
O-(1-carboxyvinyl)-3-phosphoshikimate, (
i)—Chorismate, (
j)—Prephenate, (
k)—L-Arogenate, (
l)—Phenylalanine, (
m)—Tyrosine, (
n)—
trans-Cinnamic acid, (
o)—
p-Coumaric acid, (
p)—Caffeic acid, (
q)—3,4-Dihydroxy-L-phenylalanine (L-Dopa), (
r)—Dihydrocaffeic acid, (
A)—3-deoxy-7-phosphoheptulonate synthase (EC 2.5.1.54), (
B)—3-dehydroquinate synthase (EC 4.2.3.4), (
C)—3-dehydroquinate dehydratase I (EC 4.2.1.10), (
D)—shikimate dehydrogenase (EC 1.1.1.25), (
E)—shikimate kinase (EC 2.7.1.71), (
F)—3-phosphoshikimate 1-carboxyvinyltransferase (EC 2.5.1.19), (
G)—chorismate synthase (EC 4.2.3.5), (
H)—chorismate mutase (EC 5.4.99.5), (
I)—bifunctional aspartate aminotransferase and glutamate/aspartate-prephenate aminotransferase (EC 2.6.1.1, EC 2.6.1.78, EC 2.6.1.79), (
J)—arogenate/prephenate dehydratase (EC 4.2.1.91, EC 4.2.1.51), (
K)—arogenate dehydrogenase (NADP
+) (EC 1.3.1.78), (
L)—phenylalanine ammonia-lyase (EC 4.3.1.24), (
M)—phenylalanine/tyrosine ammonia-lyase (EC 4.3.1.25), (
N)—
trans-cinnamate 4-monooxygenase (EC 1.14.14.91), (
O)—
p-coumarate 3-hydroxylase (EC 1.14.13.-), (
P)—tyrosine 3-monooxygenase (EC 1.14.16.2), (
Q)—3,4-dihydroxy-L-phenylalanine ammonia-lyase (EC 4.3.1.22), and (
R)—double bond reductase (EC 1.3.1.-).