Catechol cleavage

A biomimetic catechol cleavage reaction was carried out on dihydro-caffeic acid derivative 1922 using the iron(III)-catalyzed peracetic acid cleavage process of Pandell.25 This produced the cyclized muconic acid derivative 20 which could be transformed into pyrone 21 by treatment with hydrochloric acid. Bromination followed by azide displacement gave key intermediate 22 which could either be reduced directly to (i)-stizolobic acid 16 or ammonolyzed and then reduced to give ( )-3-(6-carboxy-2-oxo-4-pyridyl)alanine 17 (Scheme 4). 

Assuming that the general methodology in Scheme 62 would be applicable, catechol precursors were required for the C-4 pyridone substituents of 5 and 6. This led (using analogies to the catechol cleavages illustrated in Schemes 4 and 5) to a requirement for boronic acids 178 and 179 for use in the Suzuki cross-coupling step (Scheme 64). 

These enzymes are red in color and contain ferric ion as the sole cofactor. Two types of enzymes have been isolated from various bacteria — pyrocatechases which catalyze catechol cleavage and protocatechuate 3,4-dioxygenases which cleave 3,4-dihydroxybenzoate (protocatechuate). The pyrocatechases have molecular weights in the 60.000-90.000 dalton range9-11) the enzyme from Pseudomonas arvilla (MW 63.000) has two subunits with the molecular form a0Fe9), while the enzyme from Acinetobacter calcoaceticus (MW 85.000) is a dimer of the form (aFe)210). 

Oxanthrene is cleaved by lithium in THF at 25 °C and the product obtained by quenching the intermediate with carbon dioxide is the carboxylic acid (60) in 56% yield. On heating with lithium in THF for 7 h the main isolated product is catechol. Cleavage of phenoxathiin with lithium in ether occurs at C-5 to give, after carboxylation, product (61), analogous to those obtained from oxanthrene, and the disulfide of this same compound. However, this reaction, when run in THF at 50°C and terminated by carboxylation, produced 2-thiolphenol and phenoxathiin-4,6-dicarboxylic acid, the product of dimetallation <58JA380>. 

Weller and Weser s iron(III)-NTA complex shows catechol cleavage activity [96], converting 3,5-DTBC to 3,5-di-t-butyl-5-carboxymethyl-... 

The oxidation of 3,5-di-t-butyl-o-benzosemiquinone (3,5-DTBSQ) with dioxygen has been investigated with the objective of throwing more light on its possible role in catechol cleavage [123]. The reaction of 0 with NaDBSQ is catalyzed by a number of cobalt (II) and (III)... 

PROTECTION FOR PHENOLS AND CATECHOLS 24. 4-Picolyl Ether ArOCH2-4-pyridyl (Chart 4) Formation /Cleavage ... 

The principal variations on the normal crown synthesis methods were applied in preparing mixed crowns such as those shown in Eq. (3.55) and in forming isomers of the dibinaphthyl-22-crown-6 systems. The latter has been discussed in Sect. 3.5 (see Eq. 3.21) . The binaphthyl unit was prepared to receive a non-naphthyl unit as shown in Eq. (3.57). Binaphthol was allowed to react with the tetrahydropyranyl ether or 2-chloroethoxyethanol. Cleavage of the THP protecting group followed by tosyla-tion of the free hydroxyl afforded a two-armed binaphthyl unit which could serve as an electrophile in the cyclization with catechol. Obviously, the reaction could be accomplished in the opposite direction, beginning with catechol". ... 

Nal, SiCl4, rt, 20-60 min, 78% yield. Cleavage results in subsequent formation of a diiodide, but this is not a general process. For the most part, ketals are cleaved to give the ketone, while catechol methylene acetals return the catechol. ... 

Hughes EJL, RC Bayly (1983) Control of catechol mera-cleavage pathway in Alcaligenes eutrophus. J Bacterial 154 1363-1370. 

FIGURE 9.2 Ring-cleavage pathways for the biodegradation of 3-substituted catechols. 

Sala-Trepat JM, WC Evans (1971) The meta cleavage of catechol by Azotobacter species 4-oxalocrotonatev pathway. Eur J Biochem 20 400-413. 

Carvalho MF, MIM Ferreira, IS Moreira, PML Castro, DB Janssen (2006) Degradation of fluorobenzene by Rhizobiales strain Fll via ortho cleavage of 4-fluorocatechol and catechol. Appl Environ Microbiol 72 7413-7417. 

Strubel V, K-H Engesser, P Fischer, H-J Knackmuss (1991) 3-(2-hydroxyphenyl)catechol as substrate for proximal meta ring cleavage in dibenzofuran degradation by Brevibacterium sp. strain DPO 1361. J Bacterial 173 1932-1937. 

The cleavage of catechols with the incorporation of oxygen is clearly favored in the presence of some of the iron(III) complexes as catalysts. Que and co-workers proposed a substrate activation mechanism for these reactions, wherein the delocalization of the unpaired spin density... 

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