2-Amino-5-nitrothiazole: A Normal Heterocyclic Amine

2-Amino-5-nitrothiazole is defined as a heterocyclic amine that has been utilized in the development of blue dischargeable monoazo dyes, specifically noted for its application in producing colorants such as CI Disperse Blue 339.It is a hypoxic radiosensitizing drug and forms square-planar complex, trans-[PdCl2(ANT)2] with palladium in methanol. 2-Amino-5-nitrothiazole was used as diazo component in the synthesis of monoazo disperse dyes[3]. It was used as matrix during matrix-assisted laser desorption/ionization time-of-flight mass spectrometric study of oligonucleotide and protein.

Bioassay of 2-amino-5-nitrothiazole for possible carcinogenicity

A bioassay of 2-amino-5-nitrothiazole for possible carcinogenicity was conducted by administering the test chemical in feed to Fischer 344 rats and B6C3F1 mice. Groups of 50 rats and 50 mice of each sex were fed 2-amino-5-nitrothiazole at one of the following doses, either 300 or 600 ppm for rats, and either 50 or 100 ppm for mice. The rats were dosed for 110 weeks, followed by 1 week of observation; the mice were dosed for 104 weeks. Matched controls consisted of 50 untreated rats and 50 untreated mice of each sex. All surviving rats were killed at week 111, all surviving mice at week 104. The mean body weights of the groups of rats and mice fed 2-amino-5-nitrothiazole in the diet were slightly lower than those of the controls throughout most of the period of administration. No other clinical signs related to administration of the chemical were noted. There was a dose-related trend in mortality only in the male rats; however, sufficient numbers of rats were at risk in all groups for development of late-appearing tumors. In male rats, there was a significant dose-related trend (P=0.044) in the incidences of malignant lymphomas, lymphocytic leukemias, or undifferentiated leukemias, although the results of direct comparisons of incidences in each of the dosed groups with those in the controls were not significant.[1]

The incidences of chromophobe adenomas of the pituitary which were observed in control groups of rats used in a similar bioassay of another test chemical at the same laboratory were 13/49 (27%) for the males and 26/50 (52%) for the females. Because of the variability in incidences of the tumor among different control groups, the occurrence of chromophobe adenomas of the pituitary in the dosed female rats cannot be clearly associated with the administration of 2-amino-5-nitrothiazole. Also in female rats, there was a higher incidence of endometrial stromal polyps of the uterus in the low-dose group (P=0.023) than in the matched controls (controls 2/50, low-dose 9/49, high-dose 3/50). Since, however, only three high-dose animals had this tumor, the occurrence of uterine tumors in the low-dose group cannot be clearly associated with administration of the test chemical. In the mice, no neoplasms were observed at a statistically significant incidence in the dosed groups when compared with the controls. It is concluded that under the conditions of this bioassay, the occurrence of tumors of the hematopoietic system, i.e., lymphoma and granulocytic leukemia, in dosed male Fischer 344 rats was associated with administration of 2-amino-5-nitrothiazole. 2-Amino-5-nitrothiazole was not carcinogenic in female Fischer 344 rats or in male or female B6C3F1 mice.

Biological Activity of 2-Amino-5-Nitrothiazole Amide Analogues of Nitazoxanide

Nitazoxanide is a broad-spectrum FDA approved drug utilized for the treatment of anaerobic intestinal parasites Giardia lamblia and Cryptosporidium parvum but is efficacious in the treatment of other anaerobic bacteria and parasites residing in the human gut. PFOR is present in all strictly anaerobic bacteria, anaerobic parasites and ε-proteobacteria (Helicobacter pylori and Campylobacter jejuni), while mammals and eubacteria oxidize pyruvate by the NTZ insensitive pyruvate dehydrogenase (PDH). Therefore, PFOR of H. pylori, C. jejuni, and Clostridium difficile is a logical small-molecule drug target and we postulated that modification of the 2-amino-5-nitrothiazole portion of NTZ would potentiate analogue activity. Owing to the structural simplicity of NTZ we postulated that modifications of the benzene ring moiety (tail region) and thiazole (head group) could yield increased antibacterial properties. Previous research in this area has determined that the 2-amino-5-nitrothiazole ring is well suited for activity yet has been problematic to replace or modify to obtain increased activity. In an effort to further test this conclusion, we aimed to synthesize a small library of NTZ-head group analogues based on five simple amide tail region analogues.[2]

Through this study we discovered two unique and active 2-amino-5-nitrothiazole surrogate head groups from a library of 39 analogues. We also identified 2-amino-5-nitrothiazole analogues that displayed better activity than the parent compound NTZ against PFOR utilizing microorganisms. While most of the library members were inactive, head group was discovered to be only slightly less active. A library of 39 analogues was synthesized and assayed for their ability to suppress growth of Helicobacter pylori, Campylobacter jejuni, Clostridium difficile and inhibit NTZ target pyruvate:ferredoxin oxidoreductase (PFOR). Two head groups assayed recapitulated NTZ activity and possessed improved activity over their 2-amino-5-nitrothiazole counterparts, demonstrating that head group modification is a viable route for the synthesis of NTZ-related antibacterial analogues.

References

[1]National Toxicology Program. “Bioassay of 2-amino-5-nitrothiazole for possible carcinogenicity.” National Cancer Institute carcinogenesis technical report series vol. 53 (1978): 1-126.

[2]Ballard TE, Wang X, Olekhnovich I, Koerner T, Seymour C, Hoffman PS, Macdonald TL. Biological activity of modified and exchanged 2-amino-5-nitrothiazole amide analogues of nitazoxanide. Bioorg Med Chem Lett. 2010 Jun 15;20(12):3537-9. doi: 10.1016/j.bmcl.2010.04.126. Epub 2010 May 18. PMID: 20488706; PMCID: PMC2881195.