Heteroaromatic compounds, identification

Structure elucidation does not necessarily require the complete analysis of all multiplets in complicated spectra. If the coupling constants are known, the characteristic fine structure of the single multiplet almost always leads to identification of a molecular fragment and, in the case of alkenes and aromatic or heteroaromatic compounds, it may even lead to the elucidation of the complete substitution pattern. 

This technique has been applied to the determination of heteroaromatic compounds, anthropogenic hydrocarbons, polymers, haloaromatic compounds in soils, polyaromatic hydrocarbons, cationic surfactants and polychlorobiphenyls and mixtures of organic compounds in non-saline sediments and bacteria identification in sludges. 

A great deal of research in heterocyclic chemistry concerns the development of strategies for efficient S3mthesis and the discovery of new methods of ring formation, since more than half of the biologically active compounds produced by nature contain a heterocyclic moiety as a fundamental unit in their structure. Also, heteroaromatic compounds are always of great importance for chemists and the identification and confirmation of highly potent and selective bioactive molecules is a decisive step both in academic and pharmaceutical research. 

A qualitative test for aromatic and heteroaromatic compounds is their solubility in concentrated sulfuric acid (Shriner, R. L. Fuson, R. C. and Curtin, D. Y. The Systematic Identification of Organic Compounds Wiley New York, 1956. Another precedent is the H-D exchange of thiophene by dissolving the latter in concentrated D2SO4. 

Qualitative Analysis. High-resolution MS generally can separate and identify the formulas of essentially all heteroaromatic components containing one or more oxygen, sulfur, and nitrogen atoms per molecule, although some difficulties remain in the routine identification of sulfur compounds. The approach used to compensate for the latter difficulty is discussed in the section on quantitative analysis. 

Murphy et al. [39] reported the synthesis of pyrrolidine 7 combinatorial libraries. Starting from polystyrene resin-bound amino acids, the a-amino ester was condensed with aromatic and heteroaromatic aldehydes in neat trimethylorthoformate to afford the resin-bound aryl imine. Pyrrolidine and pyrroline derivatives were obtained through cycloaddition of the 1,3-dipoles azomethine ylides to olefin and acetylene dipolarophiles. A library of 500 compounds was reported. The screening of this library for in vivo inhibition of angiotensin-converting enzyme (ACE) led to the identification of l-(3 -mercapto-2 -(S)-methyl-1 -oxopropyl)-5-phenyl-2,4-pyrrolidinedicarboxy-lic acid 4-methyl ester as a potent ACE inhibitor that incorporates the mer-captoisobutyryl side chain (Fig. 3e). 

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