Synthesis of gallic acid: Cu(2+)-mediated oxidation of 3-dehydroshikimic acid.
With the elaboration of high-yielding, high-titer syntheses of 3-dehydroshikimic acid from glucose using recombinant Escherichia coli, oxidation of this hydroaromatic becomes a potential route for synthesis of gallic acid. Conversion of 3-dehydroshikimic acid into gallic acid likely proceeds via initial enolization of an alpha-hydroxycarbonyl and oxidation of the resulting enediol. 3-Dehydroshikimate enolization in water was catalyzed by inorganic phosphate while Zn(2+) was used to catalyze enolization in acetic acid. Enediol oxidation employed Cu(2+) as either the stoichiometric oxidant or as a catalyst in the presence of a cooxidant. Gallic acid was produced in a yield of 36% when 3-dehydroshikimic acid in phosphate-buffered water reacted for 35 h with H2O2 and catalytic amounts of CuSO(4). 3-Dehydroshikimate-containing, phosphate-buffered culture supernatants reacted with stoichiometric amounts of CuCO(3)Cu(OH)(2) and Cu(x)(H(3-x)(PO4)(2) to give gallic acid in yields of 51% in 5 h and 43% in 12 h, respectively. Solutions of 3-dehydroshikimic acid in acetic acid reacted with stoichiometric amounts of Cu(OAc)(2) to afford a 74% yield of gallic acid in 36 h. Acetic acid solutions of 3-dehydroshikimic acid could also be oxidized by air using catalytic quantities of Cu(OAc)(2). ZnO accelerated these oxidations leading to a 67% yield of gallic acid in 4 h when an acetic acid solution of 3-dehydroshikimic acid was reacted with O(2) and a catalytic amount of Cu(OAc)(2).
Kambourakis
S
S
Department of Chemistry and Department of Chemical Engineering, Michigan State University, East Lansing, Michigan 48824, USA.
Frost
J W
JW
D002384:Catalysis; D003300:Copper; D004926:Escherichia coli / Q000737:chemistry; D005707:Gallic Acid / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010710:Phosphates / Q000737:chemistry; D012765:Shikimic Acid / Q000031:analogs & derivatives* / Q000737:chemistry
D010710:Phosphates; C096387:3-dehydroshikimate; D012765:Shikimic Acid; D005707:Gallic Acid; D003300:Copper