(R)-α-phenylethylammonium (-)-(1R, 2S)-(1,2-epoxypropyl)phosphonate monohydrate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

March 1995 - May 1995

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Deviations:

yes

Remarks:

(No replicates were conducted and no data available on analytical method, as recommended in the test guideline).

GLP compliance:

yes

Radiolabelling:

not specified

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products:
Preliminary test at 50 ºC at pH 4, 7 and 9. Sampling timers: 2.4, 120 hours
Determination of the reaction order at pH 4 and 55 ºC: sampling time: 0, 2, 3, 5, 8, 23, 25, 26, 47, 52 hours
Determination of the reaction order at pH 4 and 65 ºC: sampling time: 0, 2, 4, 8, 23 hours
Determination of the reaction order at pH 4 and 75 ºC: 0, 1, 2, 3, 4, 6, 8, 23 hours
Determination of the reaction order at pH 7 and 70 ºC: 0, 29, 44, 74, 146 hours
Determination of the reaction order at pH 7 and 80 ºC: 0, 16, 19, 21, 39 hours

Buffers:

- pH: 4
- Type of buffer: C. Erba cod. n. 486281
- pH: 7
- Type of buffer: C. Erba cod. n. 486421
- pH: 9
- Type of buffer: C. Erba cod. n. 486571

Estimation method (if used):

In case of non pseudo-first order the half time (time required for 50% hydrolysis) is graphically estimated.
In case of pseudo-first order, the rate constants k are calculated from the plots of the logarithm of concentration versus time using the expression K = -slope x 2.303. K at 25 ºC is then evaluated by applying the Arrhenius equation.

Details on test conditions:

TEST MEDIUM
- Preparation of test medium: test substance (Fosfomycin PEA salt) in buffer solutions:
pH 4: C.Erba cod. n. 486281
pH 7: C.Erba cod. n. 486421
pH 9: C.Erba cod. n. 486571

OTHER TEST CONDITIONS
- Adjustment of pH: 4, 7 and 9

Number of replicates:

1

Positive controls:

no

Negative controls:

no

Preliminary study:

The test substance can be considered stable at pH 9 (degradation after 120 h = 3.9% < 10%). At this pH no further tests have been carried out.
The hydrolysis reaction order:
- at pH 4 at 55 ºC
- at pH 7 at 70 ºC, in order to have acceptable reaction time (shorter than a week) for > 20% hydrolysis.

Transformation products:

not measured

% Recovery:

22.7

pH:

4

Temp.:

55 °C

Duration:

52 h

% Recovery:

7.1

pH:

4

Temp.:

65 °C

Duration:

23 h

% Recovery:

1.8

pH:

4

Temp.:

75 °C

Duration:

23 h

% Recovery:

26

pH:

7

Temp.:

70 °C

Duration:

146 h

% Recovery:

42.5

pH:

7

Temp.:

80 °C

Duration:

39 h

pH:

4

Temp.:

55 °C

Hydrolysis rate constant:

0.03 h-1

DT50:

23.4 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: correlation coefficient = 0.994

pH:

4

Temp.:

65 °C

Hydrolysis rate constant:

0.791 h-1

DT50:

9.3 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: correlation coefficient = 0.999

pH:

4

Temp.:

75 °C

Hydrolysis rate constant:

0.163 h-1

DT50:

4.2 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: correlation coefficient = 0.999

Key result

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

459.6 h

Type:

other: Arrhenius relationship

pH:

7

Temp.:

70 °C

Hydrolysis rate constant:

0.008 h-1

DT50:

83.1 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: correlation coefficient = 0.999

pH:

7

Temp.:

80 °C

Hydrolysis rate constant:

0.022 h-1

DT50:

31.1 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: correlation coefficient = 0.997

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

15 628 h

Type:

other: Arrhenius relationship

Table 1. Preliminary test

pH of the solution	Degradation (%)
	After 24h	After 120h
4.0	5.1	85.8
7.0	< 1	11.4
9.0	< 1	3.9

 

Table 2. Determination of the reaction order at pH 4 and 55ºC.

Time (h)	Conc. (mg/L)	Degrad. (%)
0	1733.1	0.0
2	1665.6	3.9
4	1590.5	8.2
5	1575.3	9.1
8	1399.3	19.3
23	973.9	43.8
25	890.8	48.6
26	870.1	49.8
47	411.5	76.3
52	393.4	77.3

 

Table 3. Determination of rate of hydrolysis at pH 4 at 65ºC.

Time (h)	Conc. (mg/L)	Degrad. (%)
0	1786.2	0.0
2	1596.4	10.6
4	1342.2	24.7
8	1037.8	44.5
23	323.4	84.4

 

Table 4. Determination of rate of hydrolysis at pH at 75ºC.

Time (h)	Conc. (mg/L)	Degrad. (%)
0	1842.8	0.0
1	1597.0	13.3
2	1273.6	30.7
3	1094.7	42.8
4	920.5	53.0
6	666.0	67.1
8	468.7	77.5
23	43.1	98.2

 

Table 5. Evaluation of rate constant at pH 4 at 25ºC.

Temperature (ºC)	Rate constant (h^-1)		Half-life time (h)
75	1.63 E-1	(exp.)	4.2
65	7.49 E-2	(exp.)	9.3
55	2.96 E-2	(exp.)	23.4
25	1.51 E-3 (4.19 E-7 s^-1)	(calc.)	459.6

 

Table 6. Determination of the reaction order at pH 7 and 70ºC.

Time (h)	Conc. (mg/L)	Degrad. (%)
0	1802.2	0.0
29	1355.8	24.6
44	1220.9	32.1
74	952.7	50.0
146	525.8	74.0

 

Table 7. Determination of rate of hydrolysis at pH 7 at 80ºC.

Time (h)	Conc. (mg/L)	Degrad. (%)
0	1706.2	0.0
16	1235.7	27.4
19	1125.1	33.9
21	1052.8	38.1
39	785.2	57.5

 

Table 8. Evaluation of rate constant at pH 7 and 25ºC.

Temperature (ºC)	Rate constant (h^-1)		Half-life time (h)
80	2.23 E-2	(exp.)	31
70	8.34 E-3	(exp.)	83
25	4.43 E-6 (1.23 E-8 s^-1)	(calc.)	15628

 

Conclusions:

At pH 4 and 25 ºC, the rate constant is 1.51E-03 h-1 (= 4.19E-07 s-1) and a half-life time of 459.6 hours.
At pH 7 and 25 ºC, the rate constant is 4.43E-05 h-1 (= 1.23E-08 s-1) and a half-life time of 15628 hours.

Executive summary:

The hydrolysis study of Fosfomycin PEA salt was carried out according to EU Method C 7.

In a preliminary test, the test substance is considered stable at pH 9 (degradation after 120 h = 3.9% < 10%). At this pH no further tests have been carried out and the hydrolysis reaction orders were 55 ºC at pH 4 and 70 ºC at pH 7, in order to have acceptable reaction time (shorter than a week) for > 20% hydrolysis.

The rate constants and the half-life times were calculated, at pH 4 and 7 (the test substance is stable at pH 9).

The hydrolysis reactions at pH 4 (55, 65 and 75 ºC) and pH 7 (70 and 80 ºC) can be considered a pseudo-first order reactions.

Therefore, the rate constant were calculated by the least square method from the slope.

The evaluation of rate constants at pH 4 and 7 (25 ºC) were estimated through the use of the Arrhenius relationship.

The results of the study were:

At pH 4 and 25 ºC the rate constant is 1.51E-03 h-1 (= 4.19E-07 s-1) and a half-life time of 459.6 hours.

At pH 7 and 25 ºC the rate constant is 4.43E-06 h-1 (= 1.23E-08 s-1) and a half-life time of 15628 hours.

Description of key information

Key study: Test method according to EU Method C.7 with deviations. GLP study.

Key value for chemical safety assessment

Half-life for hydrolysis:

15 628 h

at the temperature of:

25 °C

Additional information

Key study: Test method according to EU Method C.7 with deviations. GLP study. At pH 7 and 25 ºC the rate constant is 4.43E-06 h-1 (= 1.23E-08 s-1) and a half-life time of 15628 hours.