.Gamma.-Glutamyl-4-Nitroanilide Compounds

9.1 g of 2-nitro-5-aminobenzoic acid (50 millimoles) and 14.2 g of phthaloylglutamic acid anhydride (55 millimoles) were dissolved in 50 ml of absolute dioxane after the addition of 13 ml of tributyl amine. The reaction mixture was refluxed for two hours. After cooling, 100 ml of 2N ammonia was added to the reaction mixture and the tributylamine that separated was extracted with ether. The aqueous solution was concentrated until dry, dissolved in methanol, and adjusted to pH 10 with 80% hydrazine hydrate. The reaction mixture was let stand at room temperature for about 20 hours, during which time a product partially separated which, after filtration and washing with methanol, was discarded. The methanolic filtrate was concentrated until dry and the residual oil was dissolved in about 300 ml of distilled water.

This aqueous solution was chromatographed on a column containing 100 ml of Dowex 1 .times. 2 (50-100 mesh) Formiat-Form, washed with 300 ml distilled water and eluted, graduating with 2 liters of water against 2 liters of 0.5N ammonium carbonate solution. The eluate was collected in 100 ml fractions and tested by thin-layer chromatography (silica gel plates made by Riedel de Haen, No. 37350) in a mixture of butanol, glacial acetic acid and water in a ratio of 50:15:15 (chromatogram development: blue spots in ultraviolet light, or, after spraying with ninhydrin followed by heating, brown spots in the zones containing amino acid). The fractions containing the product glutamic acid-p-nitroanilide-3-carboxylic acid (R.sub.f value 0.25) were collected and concentrated in vacuo until dry. The remaining powder is saturated with abs. ethanol, filtered and dried in vacuo over calcium chloride.

Yield: 7 g .gamma.-glutamyl-p-nitroanilide-3-carboxylic acid, monoammonium salt (58% of theory).

Ultraviolet spectrum:

.lambda. max = 317 nm

.epsilon. = 11.7 [cm.sup.2 /.mu. mole] at 317 nm

2-Nitro-5-aminobenzoic acid was liberated during the enzymatic cleavage. Its ultraviolet spectrum had the following characteristics:

.lambda. max = 380 nm

.epsilon. = 9.4 [cm.sup.2 /.mu. mole] at 405 nm

= 12.75 [cm.sup.2 /.mu. mole] at 380 nm;

c = 9.83 .times. 10.sup.-5 M.

A. performance of the Measurement

Pipette the following into a cell:

0.1 M tris-buffer, 100mM glycylglycine, pH = 8.25: 2.8 ml

130 mM GLUPA-3-carboxylic acid in above buffer: 0.2 ml

Adjust temperature to 25.degree. C. Begin determination by adding:

Human serum: 0.2 ml

Stir, read extinction at 405 nm and simultaneously start the stopwatch. Read again after precisely 1, 2 and 3 minutes.

Determine the average of the extinction differences per minute (.DELTA.E/min) and use in the computation.

B. computation

One international unit (U) is the enzyme activity which will react 1 .mu.mole of substrate in 1 minute at 25.degree. C. The basis is to be 1 ml of body fluid, e.g., serum. For the computation of the enzyme activity per milliliter (A), the following formula generally applies: ##EQU1##

The extinction coefficient .epsilon. of 3-carboxy-4-nitroaniline amounts to 9.4 cm.sup.2 /.mu.mole at 450 nm. The layer thickness (d) of the cell is 1 cm, v is the volume of the serum used (0.2 ml), V is the total of the volumes (3.2 ml). The measurement of the extinction E is performed at intervals of one minute. Consequently,

115 g of aniline-4-nitro-3-sulfonic acid and 150 g of phthaloylglutamic acid anhydride were suspended in 2 liters of absolute dimethylformamide and then heated in the oil bath to 145.degree. C.

After this temperature was reached the mixture was kept at 145.degree. C. for 1 hour and then cooled. The mixture was filtered and the filtrate concentrated in vacuo until dry. The oily residue was dissolved in methanol and adjusted with 80% hydrazine hydroxide to pH 9. After 24 hours the crystals formed were removed by suction filter, washed with a small amount of methanol and discarded.

The filtrate was concentrated until dry and intensely cooled acetone was cautiously added, with cooling. The precipitate that formed was suction filtered, washed well with acetone, and the residue dissolved in water with stirring. The water-insoluble residue was filtered off and the filtrate was adjusted with ammonia to pH 7.5 and concentrated. The ammonium salt of .gamma.-glutamyl-4-nitroanilide-3-sulfonic acid was crystallized out by the addition of acetone. The product crystallized very well in light-yellow druses.

Melting point: 186.degree.-187.degree. C.

Spectrum showed absorption maximum at 290 nm = 4.57 [cm.sup.2 /.mu.mole]

Yield: Approximately 115-120 g; another 15 to 20 g may be obtained from the crystallization mother liquor.

Total yield approx. 135 g, corresponding to 70% of the theory.

The compound is easily soluble at room temperature and achieves about 160% of the reaction rate of .gamma.-glutamyl-p-nitroanilide under the same conditions.

In the enzymatic cleavage of the compound of the invention p-nitroaniline-3-sulfonic acid is liberated. Its ultraviolet spectrum has the following characteristics:

.lambda. max = 380 nm

.epsilon. = 5.45 [cm.sup.2 /.mu. mole] at 405 nm.

= 7.38 [cm.sup.2 /.mu.mole] at 380 nm.

A. performance of the Measurement

Pipette the following into a cell:

0.1 m tris-buffer, 150 mM glycylglycine, pH = 8.5 : 2.8 ml

130 mM GLUPA-3-sulfonic acid in above buffer: 0.2 ml

Adjust temperature to 25.degree. C. Begin determination by the addition of

Human serum: 0.2 ml

Stir, read extinction at 405 nm, and at same time start the stop watch. Repeat the reading after precisely one, two and three minutes.

Compute the average of the extinction differences per minute (.DELTA.E/min) and use this in the computation.

B. computation

One international unit (U) is the enzyme activity which reacts 1 .mu.mole of substrate in 1 minute at 25.degree. C. The basis is 1 ml of body fluid such as serum. For the computation of the enzyme activities per ml (A) the following formula generally applies: ##EQU2##

The extinction coefficient (.epsilon.) of p-nitroaniline-3-sulfonic acid amounts to 5.45 cm.sup.2 /.mu.M at 405 nm under the test conditions. The layer thickness (d) of the cell is 1 cm, v is the volume of the serum used (0.2 ml), V is the sum of the volumes (3.2 ml). The measurement of the extinction E is performed at intervals of one minute. The result is:

It will be understood that the foregoing specification and examples are illustrative but not limitative of the present invention inasmuch as other embodiments within the spirit and scope of the invention will suggest themselves to those skilled in the art.