Investigation of the Mechanism of Action of Pyrogallol–Phloroglucinol Transhydroxylase by Using Putative Intermediates

Abstract

Pyrogallol-phloroglucinol transhydroxylase from Pelobacter acidigallici, a molybdopterin-containing enzyme, catalyzes a key reaction in the anaerobic degradation of aromatic compounds. In vitro, the enzymatic reaction requires 1,2,3,5-tetrahydroxybenzene as a cocatalyst and the transhydroxylation occurs without exchange with hydroxy groups from water. To test our previous proposal that the transfer of the hydroxy group occurs via 2,4,6,3',4',5'-hexahydroxydiphenyl ether as an intermediate, we synthesized this compound and investigated its properties. We also describe the synthesis and characterization of 3,4,5,3',4',5'-hexahydroxydiphenyl ether. Both compounds could substitute for the cocatalyst in vitro. This indicates that the diphenyl ethers can intrude into the active site and initiate the catalytic cycle. Recently, the X-ray crystal structure of the transhydroxylase (TH) was published16 and it supports the proposed mechanism of hydroxy-group transfer.

Evaluation of the pharmacophoric motif of the caged Garcinia xanthones

“…This compound was prepared as shown in Scheme 5. Commercially available 1,2,3-trimethoxy-5-methylbenzene ( 37 ) was demethylated with excess BBr 3 to form polyphenol 38 in 59% yield 22. Friedel–Crafts acylation of 38 with 2-fluorobenzoyl chloride ( 28 ) in the presence of AlCl 3 followed by Na 2 CO 3 -induced cyclization of the resulting benzophenone produced xanthone 39 in 69% combined yield.…”

“…Commercially available 1,2,3-trimethoxy-5methylbenzene (37) was demethylated with excess BBr 3 to form polyphenol 38 in 59% yield. 22 Friedel-Crafts acylation of 38 with 2-fluorobenzoyl chloride (28) in the presence of AlCl 3 followed by Na 2 CO 3 -induced cyclization of the resulting benzophenone produced xanthone 39 in 69% combined yield. The Pd(0)catalyzed reverse prenylation with carbonate 10b gave rise to compound 40 which, upon heating, underwent the Claisen/Diels-Alder reaction cascade to form caged xanthone 41 in 85% yield (Scheme 5).…”

The First Total Synthesis of Gravicycle

“…3a3c Under such conditions, good yields via O-arylation are realized only in the case of simple phenols and aryl halides, whereas reactions of 2,6-disubstituted phenols and functionalized aryl halides have resulted in low yields. 5 There are few methods that allow the preparation of highly substituted biaryl ethers under mild conditions.…”

Electrostatic fingerprints of catalytically active amino acids in enzymes

“…Pyrogallol hydroxytransferase, also called transhydroxylase (TH), from the anaerobic bacterium Pelobacter acidigallici (Uniprot P80563; EC 1.97.1.2; PDB http://firstglance.jmol.org/fg.htm?mol=4V4E) is an Mo‐dependent enzyme that catalyzes a net hydroxyl group transfer, converting pyrogallol to phloroglucinol 38 . H144, D174, and Y404 are reported to play general acid/base roles in the mechanism 38,39 . The active site of TH has an especially extensive network of strongly coupled residues; D174 and H144 each have 12 coupling partners with energies of interaction greater than or equal to 1.0 kcal/mol (Table S11).…”