Identification of 2-Amino-1,7-dimethylimidazo[4,5-g]quinoxaline:  An Abundant Mutagenic Heterocyclic Aromatic Amine Formed in Cooked Beef

Abstract

A previously unknown isomer of the carcinogenic heterocyclic aromatic amine (HAA) 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (8-MeIQx) was recently discovered in urine of meat-eaters and subsequently detected in cooked ground beef [Holland, R.D. et al. (2004) Chem. Res. Toxicol. 17, 1121 -1136. In this current investigation, the identity of the analyte was determined through comparison of its chromatographic t R by HPLC, and through UV and mass spectral comparisons to the synthesized isomers of 8-MeIQx. Angular tricyclic isomers of 8-MeIQx were excluded as potential structures of the newly discovered HAA, based upon dissimilar t R and product ion mass spectral data. The linear tricyclic isomers 2-amino-1,6-dimethylimidazo[4,5-g]quinoxaline (6-MeIgQx) and 2-amino-1,7-dimethylimidazo[4,5-g]quinoxaline (7-MeIgQx) were postulated as plausible structures. Both compounds were synthesized from 4-fluoro-5-nitro-benzene-1,2-diamine in five steps. The structure of the analyte was proven to be 7-MeIgQx, based upon co-injection of the compound with the synthetic isomers, and corroborated by comparisons of the UV and mass spectral data of the analyte and MeIgQx isomers. 7-MeIgQx induced 348 revertants/μg in the S. typhimurium tester strain YG1024, when liver S-9 homogenate of rats pretreated with polychlorinated biphenyls (PCBs) was used for bioactivation. This newly discovered 7-MeIgQx molecule is one of the most abundant HAAs formed in cooked ground beef patties and pan-fried scrapings. The human health risk of 7-MeIgQx requires investigation.

Food Borne Carcinogens: A Dead End?

“…These findings initiated research into heterocyclic amines (HCAs) and since then several series of mutagenic HCAs have been identified. Some potential and new HCAs have been recently reported in thermally treated food Turesky et al, 2007). HCAs result from the reaction of natural components present in protein rich food at normal cooking conditions.…”

Analytical methods applied to the determination of heterocyclic aromatic amines in foods

“…Analytical sensitivity and selectivity can be optimized by combining different sorbents and eluents, or by coupling different sorbents in tandem [1,5,7,8,11,12,18,24,42,44,45,48,49,[51][52][53][54][55][56]58,. Some methods are based on the HAAs extraction by sample alkalinisation and subsequent extraction with kieselgur [109] or with diatomaceous earth (Extrelut-20) [1,5,8,9,11,41,45,[53][54][55][56]66,67,[69][70][71][72][73][74][77][78][79][80][81][82][83][84][85][86]…”

“…An isomer of 8-MeIQx was discovered in grilled meat and human urine [3]. Recently, the compounds IQ [4,5-b], 7-MeIgQx and 7,9-DiMeIgQx have been identified and quantified in meats cooked under common household conditions [4,5]. In addition, six novel compounds that appear to contain the IQx skeleton have also been detected.…”

“…In addition, six novel compounds that appear to contain the IQx skeleton have also been detected. One of them, 7-MeIgQx, has the same nominal molecular weight as 4-MeIQx and 8-MeIQx [5]. Other four are likely to be isomers of DiMeIQx [4].…”

Analysis of Heterocyclic Amines in Human Urine Using Multiple Solid-Phase Extraction by Liquid Chromatography/Mass Spectrometry

“…Various extraction methods have been used for detecting HCAs in food, including liquid-liquid extraction (LLE), 26,27 supercritical fluid extraction (SFE), 28 and solid phase extraction (SPE), [29][30][31][32] but analysis of HCAs in urine has primarily been performed using SPE methods. SPE sorbents, such as Blue Rayon, 33,34 Blue Cotton, 25,35,36 and Blue Chitin 17,37 offer high selectivity for polycyclic aromatic compounds [38][39][40] and selectively isolate target HCAs from urine.…”