Aromatic compounds, substituted metabolites

Furthermore, it has to be noted that the nitro groups in the NMCs are metabolized by microorganisms and animals such as fish and rats. It is known that aromatic amines (substituted anilines) are acetylated to acetanilides. Some of these compounds possess anti-androgenic properties [351 b, c, d]. It is supposed that some N-acetylated metabolites of NMCs, e.g. 2-methyl-3-nitro-4-methoxy-5-ferf-butyl-acetanilide (metabolite of musk ambrette) and 4-ferf-butyl-2,6-di-methyl-3,5-dinitro-acetanilide (metabolite of musk xylene) are bound to the androgen receptor (AR) and may act as weak anti-andxogens [351 e]. 

Because the half-life of the epoxide intermediate is short, immediate rearrangement or reaction may lead to a single metabolite or a variety of substituted metabolites. The intermediacy of an epoxide intermediate can be inferred by the identification of para-and meta-hydroxylated and dihydrodiol metabolites, although their relative abundances will vary with substitution and steric considerations. Acetanilide, like phenobarbital discussed previously, exemplifies the aromatic compounds that rearrange rapidly following CYP-mediated arene epoxide formation leading to a single metabolite, as shown in Scheme 11.10. 

You are usually advised when making a complex aromatic compound to have any oxygen atoms (directly joined to the benzene ring) already present at the start. In their synthesis of the lichen metabolite dechlorolecideoidin 27, McEwen and Sargent3 chose the fully substituted benzene 29 as precursor for the right hand ring. 

The nature of the substituent in a substituted aromatic compound influences the position of hydroxylation. Thus, o-/7-directing substituents, such as amino groups, result in o- and p-hydroxylated metabolites such as the o- and /7-aminophenols from aniline (figure 4.8). Meta-directing substituents such as nitro groups lead to m- and /7-hydroxylated products, for example nitrobenzene is hydroxylated... 

Most aromatic compounds in plants are derived from shikimic acid metabolism many of these substances are phenols. Compounds derived from this pathway are extensively modified and considered under other classes of plant secondary metabolites. Although many types of secondary compounds are produced from intermediates of the shikimic acid pathway (e.g., certain naphthoquinones and anthraquinones discussed in Chapter 6), most are derived from four aromatic amino acids phenylalanine, tyrosine, anthranilic acid, and tryptophan. Aromatic compounds that arise from the shikimic acid pathway usually can be distinguished from those of other origins by their substitution patterns and by a knowledge of the compounds with which they co-occur. 

The evidence that (- )-shikimic acid plays a central role in aromatic biosynthesis was obtained by Davis with a variety of nutritionally deficient mutants of Escherichia coli. In one group of mutants with a multiple requirement for L-tyrosine, L-phenylalanine, L-tryptophan and p-aminobenzoic acid and a partial requirement for p-hydroxybenzoic acid, (—)-shikimic acid substituted for all the aromatic compounds. The quintuple requirement for aromatic compounds which these mutants displayed arises from the fact that, besides furnishing a metabolic route to the three aromatic a-amino acids, the shikimate pathway also provides in micro-organisms a means of synthesis of other essential metabolites, and in particular, the various isoprenoid quinones involved in electron transport and the folic acid group of co-enzymes. The biosynthesis of both of these groups of compounds is discussed below. In addition the biosynthesis of a range of structurally diverse metabolites, which are derived from intermediates and occasionally end-products of the pathway, is outlined. These metabolites are restricted to certain types of organism and their function, if any, is in the majority of cases obscure. 

Structural alerts or chemical motifs known to be associated with toxicity through either the parent compound or reactive metabolites have also been used to predict potential toxicity from chemical structures. These expert algorithms appear in commercial software programs and in onhne open access sites. For instance, there are seven chemical domains that are used to define and predict the covalent interaction between a chemical and a macromolecule (biological target) that leads to an initiating event at the beginning of an AOP [34]. These include Michael addition, acylation, Schiff base formation, aromatic nucleophilic substitution, unimolecular... 

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