ON THE DEPENDENCE OF THE PHYSIOLOGICAL ACTIVITY OF ACYL DERIVATIVES OF 4-METHYLAMINOANTIPYRINE ON THEIR HYDROLYSIS RATE

L. A. Shabrova, G. M. Stepnova

(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)

Medicinal preparations containing acyl groups, in the human organism, as a rule, undergo hydrolytic cleavage. The physiological activity of these medicinal preparations in a number of cases depends on the rate of their hydrolysis and on the amount of the active principle thereby liberated. Thus, acetanilide is hydrolyzed in the organism with formation of aniline, which then exhibits an antipyretic effect. An analogous reaction takes place under the same conditions for aspirin, which splits off salicylic acid, and for phenacetin, which gives 4-aminophenol [1].

In order to study the indicated dependence, we obtained a series of acyl derivatives of 4-methylaminoantipyrine [2] and determined the comparative rate of their hydrolysis.

Physiological tests of the compounds obtained were carried out at the Tomsk Medical Institute under the direction of Professor A. S. Saratykov.

Upon hydrolysis of acyl derivatives of 4-methylaminoantipyrine, a carboxylic acid and 4-methylaminoantipyrine are formed. The resulting substances were determined quantitatively by a colorimetric method (hydrolysis was carried out in a medium of 0.1 \(N\) hydrochloric acid) and by an electrical-conductivity method (hydrolysis was carried out in distilled water).

The experiments showed that the hydrolysis rate of acyl derivatives is inversely dependent on the dissociation constant of the acid. Moreover, the hydrolysis rate of acyl derivatives in 0.1 \(N\) hydrochloric acid solution exceeds by a factor of 3–5 the rate of their hydrolysis in a neutral medium.

Substituents in the benzoyl ring of the acyl residue, according to their accelerating influence on the hydrolysis rate, may be arranged in the series

\[ 4-\mathrm{Br} < 4-\mathrm{NO}_2 < \mathrm{H} < 4-\mathrm{NHCOCH}_3 < 4-\mathrm{NH}_2, \]

and according to the influence of the position of the substituents, in the sequence

\[ 2-\mathrm{Br} < 3-\mathrm{Br} < 4-\mathrm{Br} < \mathrm{H};\quad \mathrm{H} < 2-\mathrm{NH}_2 < 3-\mathrm{NH}_2 < 4-\mathrm{NH}_2. \]

Comparison of the hydrolysis rate and physiological activity showed that, as a rule, there exists a direct dependence between the hydrolysis rate of the compounds studied and their antipyretic and anti-inflammatory activity.

Fig. 1. Hydrolysis in 0.1 N HCl of the following antipyramidamides:
1—4-(4′-aminobenzoyl)-methylaminoantipyrine;
2—4-(3′-aminobenzoyl)-methylaminoantipyrine;
3—4-(4′-acetamidobenzoyl)-methylaminoantipyrine;
4—4-(2′-aminobenzoyl)-methylaminoantipyrine;
5—4-benzoylmethylaminoantipyrine;
6—4-(4′-nitrobenzoyl)-methylaminoantipyrine;
7—4-(3′-nitrobenzoyl)-methylaminoantipyrine;
8—4-(4′-bromobenzoyl)-methylaminoantipyrine;
9—4-(3′-bromobenzoyl)-methylaminoantipyrine;
10—4-(2′-bromobenzoyl)-methylaminoantipyrine.

Fig. 2. Hydrolysis in water of the following antipyramidamides:
1—4-(4′-aminobenzoyl)-methylaminoantipyrine;
2—4-(2′-aminobenzoyl)-methylaminoantipyrine;
5—4-benzoylmethylaminoantipyrine;
6—4-(4′-nitrobenzoyl)-methylaminoantipyrine;
7—4-(4′-nitrobenzoyl)-methylaminoantipyrine;
11—4-(2′-oxybenzoyl)-methylaminoantipyrine.

Experimental Part

The hydrolysis of acyl derivatives of 4-methylaminoantipyrine was carried out as follows:

1. A weighed portion of the substance was placed in a flask with a 0.1 \(N\) solution of hydrochloric acid; the flask was fitted with a reflux condenser and placed in a thermostat at a constant temperature \((99^\circ\mathrm{C})\). At definite intervals, 10 ml of solution was withdrawn from the flask, in which the content of 4-methylaminoantipyrine was determined by a colorimetric method. For this purpose, 2 ml of a 5% solution of ferric chloride was added to the sample and the absorption was measured on an FEK-M photoelectric colorimeter. 4-Methylaminoantipyrine with ferric chloride gives a complex colored raspberry-violet.

The concentration of 4-methylaminoantipyrine was found from a calibration curve.

1. A weighed portion of the substance was placed in a flask with water twice distilled over potassium permanganate; the flask was fitted with a reflux condenser and placed in a thermostat \((99^\circ\mathrm{C})\). To determine the concentration of the carboxylic acid formed during hydrolysis, a sample of the solution was poured into a vessel placed in the thermostat for measuring electrical conductivity by the compensation method. The concentration of the acid was found from the electrical conductivity using calibration curves, which had been constructed in advance for each acyl derivative. The standard solutions required for this contained a mixture of the acyl derivative, the carboxylic acid, and methylaminoantipyrine in amounts corresponding to different degrees of hydrolysis of the acyl derivative. For each substance tested, 6 standard solutions were prepared. A GZ-10 audio generator was used as the current source; an EO-7 oscilloscope was used as the null instrument in the bridge diagonal.

The results obtained are presented in Figures 1 and 2.

Conclusions

1. The rate of hydrolysis of 11 acyl derivatives of 4-methylaminoantipyrine was studied by the colorimetric method and by the electrical-conductivity method.

2. It was established that the rate of hydrolysis of these compounds is inversely dependent on the dissociation constant of the acid whose residue is included in the molecule of the acyl derivative of 4-methylaminoantipyrine. The nature and position of substituents in the benzene ring of the acid residue of the acyl derivative have a certain influence on the rate of hydrolysis.

3. It was found that, between the anti-inflammatory and antipyretic activity and the rate of hydrolysis of the compounds studied, there is, in general, a direct relationship.

LITERATURE

1. G. Dyson and P. May. Chemistry of Synthetic Medicinal Substances. Moscow, 122, 1964.

2. L. A. Shabrova, G. M. Stepanova. Zhurn. VKhO, 9(2), 240, 1964.