2-Aminoacetophenone: Versatile Aromatic Compound

2-Aminoacetophenone (2-AA), also known as ortho-aminoacetophenone, is an organic compound characterized by an acetophenone structure with an amino group at the ortho position of the phenyl ring. Its unique chemical architecture, featuring both a nucleophilic amino group and a reactive ketone moiety, makes it a versatile precursor in the synthesis of a wide array of heterocyclic compounds and active pharmaceutical ingredients (APIs). Besides, 2-Aminoacetophenone exhibits diverse biological roles. It is recognized as a pheromone in honeybees, a diagnostic marker for Pseudomonas aeruginosa infections, and a contributor to the atypical aging flavor in white wines. In neuropharmacology, this substance acts as a norepinephrine-dopamine releasing agent.

2-Aminoacetophenone as a potential breath biomarker

Pseudomonas aeruginosa is a Gram negative bacterium that produces a sweet "grape-like" odour during growth. In 1966 Mann identified this compound as 2-aminoacetophenone (2-AA) by thin-layer chromatography. Cox & Parker confirmed 2-AA as the compound responsible for this odour and we have also successfully detected and identified 2-AA in the headspace of in vitro cultures using gas chromatography/mass spectrometry (GC/MS). 2-Aminoacetophenone is a small, volatile aromatic compound with a molecular weight of 135 g/mol. It is an intermediate product in the biosynthesis of quinazolines, which branches from the tryptophan catabolic pathway. 2-Aminoacetophenone is consistently produced by multiple Ps. aeruginosa strains, on all culture media, and is a major metabolite, but the biological significance of this compound is unknown. There is a single report of 2-AA detected in the headspace of Escherichia coli cultures but 2-AA is not known to be produced by other respiratory pathogens. Because of the well described evidence of the production of 2-AA by Ps. aeruginosa and its apparent specificity we thought it may be useful as a volatile biomarker for infection and/or colonisation of the lung. We have therefore undertaken an investigation to determine whether 2-AA is consistently produced by Ps. aeruginosa and other respiratory pathogens during in vitro culture and if 2-AA is detectable in the breath of CF patients colonised with Ps. aeruginosa.[1]

Cultures of 20 clinical strains of Ps. aeruginosa but not other respiratory pathogens had high concentrations of 2-Aminoacetophenone in the head space of in vitro cultures when analysed by GC/MS. 2-AA was stable for 6 hours in deactivated glass sampling bulbs but was not stable in Tedlar® bags. Optimisation of GC/MS allowed detection levels of 2-AA to low pico mol/mol range in breath. The 2-AA was detected in a significantly higher proportion of subjects colonised with Ps. aeruginosa 15/16 (93.7%) than both the healthy controls 5/17 (29%) (p < 0.0002) and CF patients not colonised with Ps. aeruginosa 4/13(30.7%) (p < 0.001). The sensitivity and specificity of the 2-AA breath test compared to isolation of Ps. aeruginosa in sputum and/or BALF was 93.8% (95% CI, 67-99) and 69.2% (95% CI, 38-89) respectively. The peak integration values for 2-Aminoacetophenone analysis in the breath samples were significantly higher in Ps. aeruginosa colonised subjects (median 242, range 0-1243) than the healthy controls (median 0, range 0-161; p < 0.001) and CF. subjects not colonised with Ps. aeruginosa (median 0, range 0-287; p < 0.003) Our results report 2-AA as a promising breath biomarker for the detection of Ps. aeruginosa infections in the cystic fibrosis lung.

2-aminoacetophenone promotes association of pathogenic bacteria with flies

Insects are notorious for transmitting infectious diseases. Diptera in particular are susceptible to colonization by various human pathogens. Houseflies (Musca domestica), for example, often feed on faecal waste and garbage and carry microbes, such as pathogenic Escherichia coli and Pseudomonas aeruginosa, on their outer surface and in their gut. While bacteria contaminate flies by targeting fly habitats and fly food, attraction of flies by the bacteria themselves may aid colonization. For example, bacteria and their products have been shown to attract various Diptera species, including fruit flies, screw-worm flies, apple maggots and mosquitoes. Here we studied the ability of 2-aminoacetophenone (2AA), a secondary metabolite of P.a, to induce the association between bacteria and flies. 2AA is a single benzene ring aromatic compound with a ‘grape-like’ odour that promotes chronic P.a infection phenotypes, including long-term bacterial survival at a stationary phase and a reduction in bacterial virulence in various hosts. We assess the ability of 2AA to attract flies and to facilitate intestinal colonization by P.a upon 2AA ingestion. We find that 2-aminoacetophenone acts both as an odorant attractant and as a facilitator of intestinal colonization in several fly species, including M. domestica, C. capitata and D. melanogaster.[2]

We showed that a P.a strain that produces 2AA versus an isogenic strain that does not produce 2AA attracts more flies (D. melanogaster, M. domestica or C. capitata). Furthermore, we demonstrated that both olfactory organs mediate the fly response to 2AA. Thus, apart from its effect on long-term colonization, 2-Aminoacetophenone may have evolved to attract and colonize flies facilitating bacterial dissemination. It is possible that many fly species can sense and respond to 2AA, but those living in an ecosystem that harbours high concentrations of 2AA-producing bacteria are lured to its source. Apart from 2AA, other odorants can also attract flies to their food source. For example, citrus odours increase oviposition, and yeast fermentation odours act as attractants in drosophilids. Because olfactory neurons in both the fly antennae and maxillary palps can respond to single benzene ring aromatic compounds, such as 2-Aminoacetophenone, we propose that odorant receptors in both organs can sense food odours, including 2AA, and thus control attraction to fly food. The pertinent neuronal circuit and concomitant feeding behaviour might be exploitable for the diversion of harmful flies away from human food and into flytraps.

2-Aminoacetophenone as a potential contributor to boar taint

2-Aminoacetophenone especially attracts immediate attention as a potential boar taint compound, because 2-AAP has already been identified as an off-flavor compound in white wines. Thus, the objective of the presented work was the evaluation of 2-AAP as a potential boar taint compound. After a first qualitative analysis of 2-AAP in backfat samples, a novel SIDA–HS-SPME–GC/MS method was developed to precisely quantitate 2-AAP in backfat samples. Finally, the odor detection threshold of 2-AAP was determined and sensory evaluation of backfat samples spiked with 2-AAP was performed. The major objective of the presented study was to evaluate whether the hepatic skatole metabolite 2-aminoacetophenone is a potential contributor to boar taint, which is an undesired off-flavor in pork. Therefore, backfat samples were screened by HS-SPME–GC/MS revealing a significant accumulation of the hepatic skatole metabolite 2-AAP in boar fat. Subsequently, a stable-isotope dilution assay (SIDA) was elaborated to precisely quantitate 2-AAP in a set of 130 backfat samples. The observed concentrations ranged between 34 ng/g and 1178 ng/g, resulting in a mean value of 100 ng/g. In addition, the odor detection threshold of 2-AAP was evaluated by a trained sensory panel using a single-staircase, triple forced choice paradigm. The determined 2-AAP odor detection threshold is similar to the thresholds of the major boar taint compounds androstenone and skatole. Finally, a sensory evaluation of backfat samples spiked with 2-Aminoacetophenone was performed in a triangle test with untrained testers. Here, the 2-AAP spiked samples were frequently identified as the odd sample independent of their respective androstenone and skatole levels. In conclusion, the hepatic skatole metabolite 2-AAP was identified as a potential contributor to boar taint.[3]

References

[1]Scott-Thomas AJ, Syhre M, Pattemore PK, Epton M, Laing R, Pearson J, Chambers ST. 2-Aminoacetophenone as a potential breath biomarker for Pseudomonas aeruginosa in the cystic fibrosis lung. BMC Pulm Med. 2010 Nov 7;10:56. doi: 10.1186/1471-2466-10-56. PMID: 21054900; PMCID: PMC2989937.

[2]Kapsetaki, SE., Tzelepis, I., Avgousti, K. et al. The bacterial metabolite 2-aminoacetophenone promotes association of pathogenic bacteria with flies. Nat Commun 5, 4401 (2014).

[3]Fischer, J., Gerlach, C., Meier-Dinkel, L., Elsinghorst, P. W., Boeker, P., Schmarr, H.-G., & Wüst, M. (2014). 2-Aminoacetophenone – A hepatic skatole metabolite as a potential contributor to boar taint. Food Research International, 62, 35–42.