Conversion into protocatechuic acid

Figure 9.7b. Pathways for the enzymatic conversion of aromatic compounds into protocatechuic acid.

The conversion of phenylalanine, a C-6—C-3 precursor, to the C-6—C-1 unit of the Amaryllidaceae alkaloids requires the formal loss of two carbon atoms from the side chain of the amino acid as well as the introduction of at least two oxygenated substituents into the aromatic ring. The results shown in the latter part of Table III emphasize the specificity of the C-6—C-1 precursor. Benzaldehyde, -hydroxybenzal-dehyde, isovanillin, and protocatechuic acid are not incorporated to any appreciable extent into the alkaloids, while cinnamic, -hydroxy-cinnamic and caffeic acids, protocatechuic aldehyde, and 3-hydroxy-4-methoxy-i C-A-methyl-i4( ., enzylamine readily become part of the C-6—C-1 unit. 

Figure 5. The biocatalytic pathway (boxed arrows) created for microbial conversion of D-glucose into cis, cw-muconate from the perspective of the biochemical pathways from which the enzymes were recruited. Conversion of D-glucose into DHS requires transketolase (tkt) from the pentose phosphate pathway and DAHP synthase (aroF, aroG, aroH)y DHQ synthase aroB and DHQ dehydratase aroD) from the common pathway of aromatic amino acid biosynthesis. Conversion of DHS into catechol requires DHS dehydratase (aroZ, enzyme A) from hydroaromatic catabolism, protocatechuate decarboxylase aroY, enzyme B), and catechol 1,2-dioxygenase (caM, enzyme C) from the benzoate branch of the p-ketoadipate pathway. (Adapted and reproduced with permission from ref. 21.)...

---