6-Amino-1H-indazole-7-carboxylic acid

Synthesis

Pyrrolo[2,3-g]indazole-7,8(1H,6H)-dione (Formula 7, the product of Example II, 9.4 g, 50 mmol) was used as a raw material, which was dissolved in 10% aqueous sodium hydroxide solution (100 mL). Subsequently, 10% aqueous hydrogen peroxide solution (17 mL, 50 mmol) was slowly added at 100 °C. The reaction mixture was kept at 100°C for 10 minutes until the release of carbon dioxide gas stopped. Next, the pH of the reaction solution was adjusted with concentrated hydrochloric acid to 4.0-5.5. The resulting 6-amino-1H-indazole-7-carboxylic acid (formula 8) was collected by filtration and washed with cold water, and finally dried under vacuum in the presence of CaCl2 to give 7.71 g of the product in brown powder form in 87% yield with a melting point of 205 °C (decomposition started at 177 °C). The infrared spectrum (KBr) of the product showed characteristic absorption peaks: 1580, 1630, 1660 cm-1 (corresponding to aromatic ring and carbonyl carboxylic acid, respectively). The NMR hydrogen spectrum (100 MHz, DMSO-d6) data were as follows: δ 6.70 (d, 1H, J=9Hz, H-4), ca. 6.80-9.00 (D2O-exchangeable broad peak, 2H, NH2), 7.66 (d, 1H, J=9Hz, H-5), and 7.93 (s, 1H, H-3). The mass spectrum (70 eV) showed molecular ion peaks m/e 177 (100%, M+) and m/e 159 (86%, M+-H2O). Samples recrystallized from methanol failed to yield satisfactory data by elemental analysis.

References

[1] Tetrahedron Letters, 1980, vol. 21, # 32, p. 3029 - 3032
[2] Journal of Organic Chemistry, 1980, vol. 45, # 15, p. 3072 - 3077
[3] Heterocycles, 1981, vol. 15, # 2, p. 1053 - 1059
[4] Patent: US4223143, 1980, A
[5] Patent: WO2007/93402, 2007, A1. Location in patent: Page/Page column 42