Ultraviolet absorption spectra of esters of 4(5)-aminoimidazole-5(4)-carboxylic acid
Abstract Generated abstract
The study examines ultraviolet and visible absorption spectra of 4(5)-nitroimidazole-5(4)-carboxylic acid, selected nitro esters, and a series of esters of 4(5)-aminoimidazole-5(4)-carboxylic acid in base, hydrochloride, picrate, and benzoylated forms. Spectra were recorded with a quartz spectrophotometer in water or alcohol over 220 to 480 nm, and absorption maxima and molar extinction coefficients were tabulated. The results show characteristic shifts in absorption maxima associated with esterification, replacement of the nitro group by an amino group, picrate formation, and benzoylation, with amino ester bases and hydrochlorides absorbing near 270 to 272 nm and picrates displaying additional absorption characteristic of picric acid.
Full Text
ULTRAVIOLET ABSORPTION SPECTRA OF ESTERS OF 4(5)-AMINOIMIDAZOLE-5(4)-CARBOXYLIC ACID
V. R. Koroleva
(Submitted by Professor, Doctor of Chemical Sciences L. P. Kulyzhan)
In an earlier published paper [1], the synthesis of a series of esters of 4(5)-aminoimidazole-5(4)-carboxylic acid, of pharmacological interest, was reported. In order to study the spectral characteristics of the products obtained, we recorded their absorption spectra in the ultraviolet and visible regions of the spectrum.
From the literature data it is known [2] that 4(5)-aminoimidazole-5(4)-carboxylic acid has an absorption maximum at \(\lambda = 260\) m\(\mu\) \((\varepsilon = 9300)\) in alkaline medium \((\mathrm{pH} = 9)\). The ultraviolet absorption spectra of the hydrochloride of the ethyl ester of 4(5)-aminoimidazole-5(4)-carboxylic acid and of some of its derivatives have also been investigated [3]. It was found that the hydrochloride of the ethyl ester of 4(5)-aminoimidazole-5(4)-carboxylic acid has an absorption maximum at \(\lambda = 274\) m\(\mu\) \((\varepsilon = 14400)\). No information was found in the literature on the absorption spectra of other esters of 4(5)-aminoimidazole-5(4)-carboxylic acid.
The starting product for obtaining the esters of 4(5)-aminoimidazole-5(4)-carboxylic acid is 4(5)-nitroimidazole-5(4)-carboxylic acid. The synthesis was carried out according to the following scheme:
\[ \mathrm{ \begin{array}{ccc} \text{HOOC--C--NH} & & \text{ROOC--C--NH} \\ \ \ \ \ \Vert \ \ \ \ \ \ \diagup \mathrm{CH} & \xrightarrow{\mathrm{ROH}} & \ \ \ \ \Vert \ \ \ \ \ \ \diagup \mathrm{CH} \\ \mathrm{O_2N--C--N} & & \mathrm{O_2N--C--N} \end{array} \ \xrightarrow[\{ \mathrm{Fe,Cl} \}]{\mathrm{H_2}}\ \begin{array}{c} \text{ROOC--C--NH} \\ \ \ \ \ \Vert \ \ \ \ \ \ \diagup \mathrm{CH} \\ \mathrm{H_2N--C--N} \end{array} } \]
Since no data were found in the literature on the absorption spectra of the starting 4(5)-nitroimidazole-5(4)-carboxylic acid, a spectroscopic study in the ultraviolet was carried out for this acid and two of its esters.
The absorption spectra were recorded on an SF-4 quartz spectrophotometer in the range 220–480 m\(\mu\). The light sources were a hydrogen lamp and an incandescent lamp with natural cooling. The thickness of the absorbing layer was 1 cm. The working concentration was \(1 \cdot 10^{-4}\) M–\(2.5 \cdot 10^{-5}\) M. Specially purified water and ethyl alcohol were used as solvents. The curves were constructed in a system in which wavelengths \((\lambda)\) in m\(\mu\) were plotted on the abscissa axis, and the logarithms of the molar extinction coefficient \((\varepsilon)\) on the ordinate axis. The results obtained are summarized in Tables 1 and 2.
\[ \begin{array}{c} \mathrm{ROOC{-}C{-}NH}\\[-2pt] \left\| \quad \right. \!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\diagdown \ \mathrm{CH}\\[-2pt] \mathrm{O_2N{-}C{-}N} \end{array} \]
Table 1
| No. | R | \(\lambda_{\max}\), Å | \(\varepsilon_{\max}\) | Solvents |
|---|---|---|---|---|
| 1 | H | 3050 | 10840 | water |
| 2 | \(iso\text{-}\mathrm{C_3H_7}\) | 2220 | 91600 | alcohol |
| 2 | \(iso\text{-}\mathrm{C_3H_7}\) | 2820 | 57480 | alcohol |
| 3 | \(iso\text{-}\mathrm{C_4H_9}\) | 2220 | 69200 | alcohol |
| 3 | \(iso\text{-}\mathrm{C_4H_9}\) | 2820 | 30600 | alcohol |
\[ \begin{array}{c} \mathrm{ROOC{-}C{-}NH}\\[-2pt] \left\| \quad \right. \!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\diagdown \ \mathrm{CH}\\[-2pt] \mathrm{R'HN{-}C{-}N} \end{array} \]
Table 2
| No. | R | R′ | Base \(\lambda_{\max}\), Å | Base \(\varepsilon_{\max}\) | Hydrochlorides \(\lambda_{\max}\), Å | Hydrochlorides \(\varepsilon_{\max}\) | Picrates \(\lambda_{\max}\), Å | Picrates \(\varepsilon_{\max}\) |
|---|---|---|---|---|---|---|---|---|
| 1 | \(\mathrm{CH_3}\) | H | — | — | 2720 | 14100 | 2600 | 17500 |
| 1 | \(\mathrm{CH_3}\) | H | — | — | 2720 | 14100 | 3550–3600 | 13000 |
| 2 | \(\mathrm{C_2H_5}\) | H | 2720 | 12600 | 2720 | 13100 | 2600 | 16800 |
| 2 | \(\mathrm{C_2H_5}\) | H | 2720 | 12600 | 2720 | 13100 | 3550–3600 | 12850 |
| 3 | \(n\text{-}\mathrm{C_3H_7}\) | H | 2720 | 12420 | 2720 | 11470 | 2600 | 25900 |
| 3 | \(n\text{-}\mathrm{C_3H_7}\) | H | 2720 | 12420 | 2720 | 11470 | 3550–3600 | 18920 |
| 4 | \(iso\text{-}\mathrm{C_3H_7}\) | H | 2720 | 12700 | — | — | 2600 | 17280 |
| 4 | \(iso\text{-}\mathrm{C_3H_7}\) | H | 2720 | 12700 | — | — | 3550–3600 | 12900 |
| 5 | \(n\text{-}\mathrm{C_4H_9}\) | H | 2700 | 10250 | 2710 | 11750 | 2600 | 27000 |
| 5 | \(n\text{-}\mathrm{C_4H_9}\) | H | 2700 | 10250 | 2710 | 11750 | 3550–3600 | 21600 |
| 6 | \(iso\text{-}\mathrm{C_4H_9}\) | H | 2720 | 13300 | 2720 | 12300 | 2600 | 27100 |
| 6 | \(iso\text{-}\mathrm{C_4H_9}\) | H | 2720 | 13300 | 2720 | 12300 | 3550–3600 | 19400 |
| 7 | \(iso\text{-}\mathrm{C_5H_{11}}\) | H | — | — | 2710 | 12100 | 2600 | 15500 |
| 7 | \(iso\text{-}\mathrm{C_5H_{11}}\) | H | — | — | 2710 | 12100 | 3550–3600 | 12200 |
| 8* | \(\mathrm{C_2H_5}\) | \(\mathrm{C_6H_5CO}\) | 2320 | 112500 | — | — | — | — |
| 8* | \(\mathrm{C_2H_5}\) | \(\mathrm{C_6H_5CO}\) | 2920 | 104700 | — | — | — | — |
As is seen from the data given in Table 2, the wavelength \(\lambda_{\max}\) for the bases and hydrochlorides of the amino esters fluctuates within the range 2700–2720 Å. As was already mentioned above, for the hydrochloride of the ethyl amino ester the absorption maximum was described at \(\lambda_{\max}=2740\ \mathrm{m\mu}\), with alcohol used as the solvent. We carried out a study
* Solvent: alcohol; for all the other substances the solvent was water.
in an aqueous medium; this may also explain the small difference in the wavelength of the absorption maximum and in the value of the molar extinction coefficient.
As can be seen from Table 1, esterification of 4(5)-nitroimidazole-5(4)-carboxylic acid leads to a hypsochromic effect of 230 Å. At the same time, for this acid and its esters a large difference is observed in the magnitude of the absorption intensity.
As Gillam and Stern [4] indicate, the nitro group itself gives one weak absorption band (\(\varepsilon = 15\)) in the region of 2700–2800 Å.
When the nitro group is replaced by an amino group, a change occurs in the position and magnitude of the absorption maximum. The bases and hydrochlorides of the esters of 4(5)-aminoimidazole-5(4)-carboxylic acid give an absorption maximum at \(\lambda_{\max} = 2700\text{–}2720\) Å, shifting by 100–120 Å relative to the nitro esters and by 330–350 Å relative to 4(5)-nitroimidazole-5(4)-carboxylic acid toward shorter wavelengths.
As was indicated above, 4(5)-aminoimidazole-5(4)-carboxylic acid itself has \(\lambda_{\max} = 260\) mµ (at pH = 9). Esterification leads to a shift of \(\lambda_{\max}\) by 100–120 Å toward longer wavelengths. In this respect it differs from 4(5)-nitroimidazole-5(4)-carboxylic acid, whose esterification leads to a shift of \(\lambda_{\max}\) toward shorter wavelengths.
Introduction of a benzoyl radical into the amino group of the ethyl ester of 4(5)-aminoimidazole-5(4)-carboxylic acid causes the appearance of two absorption maxima at 2320 Å and 2920 Å. Apparently, here the absorption band is shifted by 200 Å toward longer wavelengths in comparison with the ethyl ester of 4(5)-aminoimidazole-5(4)-carboxylic acid, and a new absorption band appears, characteristic of the benzoyl ring.
Picrates of the amino esters give two absorption maxima: at \(\lambda = 2600\) Å, characteristic of the imidazole ring, and at \(\lambda = 3550\text{–}3600\) Å, characteristic of picric acid. At the same time, a shift of the absorption maximum by 100–120 Å is found in comparison with the bases and hydrochlorides. Most probably, this shift is due to the formation of a complex bond between picric acid and the amino ester.
Conclusions
Absorption in the ultraviolet and visible regions of the spectrum has been studied for 4(5)-nitroimidazole-5(4)-carboxylic acid and its esters, as well as for the bases, hydrochlorides, and picrates of esters of 4(5)-aminoimidazole-5(4)-carboxylic acid. Shifts in the wavelength position of the absorption maximum are observed when the nitro group is replaced by an amino group, upon esterification, upon formation of picrates, and upon benzoylation of the amino group.
Literature
- L. P. Kutep and V. R. Koroleva, ZhOKh, XXIX, 2401, 1959.
- G. C. Rabinowitz, J. biol. Chem., 218, 175, 1956.
- H. Badger, J. D. Downer. J. Chem. Soc., 2775, 1949.
- A. Gillam and E. Stern. Electronic Absorption Spectra of Organic Compounds, Inlit, Moscow, 1957.