<i>vic</i>-Dihydroxybenzenoid &rarr; 2-Oxopent-4-enoate derivative + Carboxylate<br>1-Amino-2-hydroxybenzenoid &rarr; 2-Amino-2,4-dienoate derivate + Carboxylate<br><br>Comments:<br>This rule handles extradiol (<i>meta</i>) ring cleavage for <i>vic</i>-dihydroxybenzenoids and 1-amino-2-hydroxybenzenoids, including, but not limited to, 2,3-dihydroxybiphenyl derivatives, many PCB congeners (<a href="http://www.ncbi.nlm.nih.gov/sites/entrez?SUBMIT=y&db=PubMed&cmd=search&term=15614564">Pieper, 2005</a>), 3- and 4-substituted chlorocatechols, 2-aminophenol, 2,3-dihydroxy DDT and its derivatives, 3- and 4-substituted alkyl catechols, diphenylether derivatives, and aromatized intermediates of steroid degradation (<i>e.g.</i>, testosterone). It includes extradiol ring cleavage of <i>vic</i>-dihydroxybenzenoids (bt0008) and distal ring cleavage of 1-amino-2-hydroxybenzenoids (bt0041) to form 2-hydroxymuconate semialdehyde and 2-aminomuconate semialdehyde derivatives, respectively. 2-Aminomuconate semialdehyde derivatives undergoes hydrolytic deamination (bt0032) to form the 2-hydroxymuconate semialdehyde product. 3-Carboxyl catechols, such as 2,3-dihydroxy-<i>p</i>-cumate, undergo decarboxylation of the 3-carboxy group following meta cleavage. Hydrolysis of the C5-C6 bond (bt0040), or oxidation of the aldehyde to a carboxylate (bt0003), followed by decarboxylation (bt0051), produces a 2-amino-2,4-dienoate derivative or an enol product, which quickly tautomerizes to a 2-oxopent-4-enoate derivative. 2,3-Dihydroxybiphenyl derivatives are only cleaved at the side closest to the second phenyl ring. Rings are not cleaved next to the halogenated carbon in 3-halocatechol substrates. If the catechol substrate is not symmetric and its cleavage site preference is unknown, the compound is cleaved on both sides of the <i>vic</i>-dihydroxyl group.