Triisooctyl 2,2',2''-[(octylstannylidyne)tris(thio)]triacetate

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 January 2015 to 17 February 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Reason / purpose for cross-reference:

other: read-across target

Reference

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study conducted on read-across material

Justification for type of information:

Read Across to Octyltin tris(2-ethylhexylmercaptoacetate) (MOTE) (EC Number 248-227-6 and CAS No 27107-89-7) based on structural similarity and hydrolytical behaviour, see attached justification.

Reason / purpose for cross-reference:

read-across source

Conclusions:

It can be concluded that DOTCE is the only tin-containing metabolite of DOTE that is formed under the simulated mammalian gastric environment. No DOTC was formed and detected under the conditions of this study.

Executive summary:

The hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7.

The stability of the test material was investigated at pH 4, 7 and 9 and pH 1.2 using NMR spectroscopy.

The study showed that MOTE is hydrolytically stable at pH 9, 7 and 4. After 5 days of hydrolysis at 50 °C less than 10% MOTE was hydrolysed (t 0.525 °C> 1 year). Amount of hydrolysed MOTE was increased at lower pH values from 1.85 % at pH 9 to 5.33 % at pH 7 and 7.01 % at pH 4. At the simulated gastric conditions (0.1 M HCl/pH 1.2 /37 °C) 75% MOTE was hydrolysed to it’s monochloride (DOTCE). No formation of DOTC was detected under the conditions of the study.

Hydrolysis of MOTE can be monitored by the decrease in the relative intensity of the respective 119Sn-NMR signal at 73.4 ppm and the increase of the DOTCE signal at 33.3 ppm. The sum of both intensities agrees well with MOTE signal intensity of the untreated test material. DOTC could not be identified in any of the hydrolysed MOTE samples and DOTC= 133 ppm using the 119Sn-NMR spectroscopy. Detection limit for DOTC has been experimentally found to be 0.5% w/w. It was shown in that when spiked with DOTC, MOTE signal present in a partially hydrolysed MOTE sample containing DOTCE, disappeared but still no peak characteristic to DOTC was detected. These results provide direct evidence that DOTC readily reacts with MOTE and forms DOTCE. Similar behaviour of MOTE was described in a study focused on the fate of MOTE in a polyvinylchloride (PVC) film. In that study MOTE was also converted to DOTCE due to the exposure to HCl that is formed as a result of the thermal degradation of PVC. No DOTC was detected until all MOTE has been transformed into DOTCE.

TOC analysis has been conducted to ensure completeness of the analysis and recover all organic carbon in aqueous phases including all possible water-soluble organotin substances and their breakdown components. The analyses detected some organic carbon content (from 1.4 to 4.2 % of the total available organic carbon) in the aqueous phases of the experiments. These traces of organic carbon could be attributed to 2-EHTG (a hydrolysed ligand of DOTE) and its breakdown products EH and TGA. 

Therefore, it can be concluded that DOTCE is the only tin-containing metabolite of DOTE that is formed under the simulated mammalian gastric environment. No DOTC was formed and detected under the conditions of this study.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2015

Report date:

2015

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-ethylhexyl 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4-octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate

EC Number:

248-227-6

EC Name:

2-ethylhexyl 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4-octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate

Cas Number:

27107-89-7

Molecular formula:

C38H74O6S3Sn

IUPAC Name:

2-ethylhexyl 10-ethyl-4-({2-[(2-ethylhexyl)oxy]-2-oxoethyl}sulfanyl)-4-octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecan-1-oate

Test material form:

liquid

Details on test material:

- Appearance: pale yellow liquid
- Storage: in original container, at 15 °C to 25°C

Radiolabelling:

not specified

Results and discussion

Any other information on results incl. tables

HYDROLYSIS AT PH 4, 7 AND 9

- Samples of the test material were added to the respective buffer solutions at 50 °C for 5 days (120 h). The 119Sn-NMR spectra of the reaction products show only slight signs of hydrolysis. The NMR peak characteristic to the MOTE molecule at about 70 ppm decreased from 91.8 Mol % in the untreated staring material to a minimal value of 85.7 Mol % in the pH 4 buffer solution. In all cases the degree of hydrolysis was lower than 10 %. Thus, the higher tier testing was not considered for these pH-value buffers.

HYDROLYSIS AT PH 1.2

- A sample of the test material was added to an excess 0.1 M Hydrochloric Acid at 37 °C for 5 days (120 h). The 119Sn-NMR spectrum of the recovered reaction product (Annex 2) showed that MOTE is hydrolysed to MOTEC. Both substances were present in an equilibrium in a 25/75 MOTE/DOTCE mol. % ratio.

- MOTEC, a product of hydrolysis, has been identified based on the 119 Sn-NMR signal.  Pure DOTCE substance was synthesised via two different synthetic routes.

- Besides the MOTE hydrolysis product (DOTCE), the spectrum showed minor peaks corresponding to MOTE hydrolysis component (MOTE was present as an impurity in MOTE), which was MOTE2C at -14.7 ppm.  Other signals appeared at 77.5 ppm (0.6 Mol % attributed to the TOTE that was present as an impurity in MOTE) and 143.4 (1.2 Mo l% / not identified).

No signal corresponding to DOTC (typically present at 133 ppm) was detected.

MASS BALANCE

- For each tested pH value, a 1g (1.3 mmol) sample of the test material was added to the respective buffer solution.  After the required hydrolysis period of 5 days amounts of the hydrolysate were recovered via hexane extraction from the aqueous phase.

- Recovery rates:

pH 4: 100 %

pH 7: 100 %

pH 9: 100 %

pH 1.2: 92 % (The recovered amount was corrected assuming a 75 % reaction with HCl)

- The mass balance showed a high recovery of the initial material of the test material after hydrolysis over the required period (5 days) and the extraction with hexane.  It demonstrates high reliability of the chosen experimental design of the study.

TIER 2 TESTING AT PH 1.2

- Additional 1 g (1.33 mmol) samples of the test material were hydrolysed over 6 different time periods (from 15 seconds to 48 hours) in an excess of 0.1 M Hydrochloric Acid at 37 °C.  The recorded 119Sn-NMR spectra detected DOTCE (? = 32.7 ppm) as the only product of MOTE hydrolysis. MOTE which was present in the sample as impurity hydrolysed to MOTE2C (? = -14.5 ppm).  No DOTC (? = 133 ppm) signal was detected in the hydrolysate.

- Kinetics of the hydrolysis was studied measuring intensities of the NMR-signals for MOTE and MOTEC. The sum of both signal intensities was about the same (within 3 %).  The kinetics of the first and the second test series were nearly identical.

- After 15 seconds of contact with the preheated buffer (an aqueous solution of hydrochloric acid), the test material was worked up immediately.  The 119Sn-NMR showed that the MOTE signal was reduced by about 50 % of its initial signal intensity.  Conversion of MOTE continued during 1 hour of hydrolysis to about 25 % of the initial signal intensity, whereas the DOTCE signal increased proportionally at the same rate.  

- The MOTE concentration then increased slightly to 35 and 41 % after 2 and 8 hours, respectively.  The MOTE signal intensity was then decreased to about 25 % of the initial value after 48 hours of exposure and has not change much after 120 hours.  It may represent an equilibrium state between MOTE and DOTCE, since the same MOTE/DOTCE ratio was measured at 120 hours of exposure during Tier 1 experiments.

MASS BALANCE

- For each tested 1g (1.3 mmol) sample of MOTE, the test material was added to a preheated (to 37 °C) solution of hydrochloric acid.  After completing the respective hydrolysis period, 94 to 100 % of the test material were recovered via the hexane extraction from the aqueous phase.

- The mass balance showed high recovery of the initial amount of the test material. It demonstrates high reliability of the chosen experimental design of the study.

TOC MEASUREMENT

- TOC (NPOC) was used to determine organic carbon content attributed to water-soluble breakdown products of MOTE that might be formed and present in the aqueous phases under the conditions of the experiment after recovering the test material.  

- Results can be seen in Table 1. The table shows a low content of organic carbon remaining in the aqueous phases after completion of the simulated gastric hydrolysis under Tier 2 test conditions (rows from W54-101-A1 to W54-101-F2). The NPOC values range from 81.8 to 239.6 mg/L.  Since the test material contained a total of 57.4 % of organic carbon, these values represent from 1.4 to 4.2 % of the available organic carbon.  Certain organic carbon content values of Tier 1 tests were higher, due to the presence of organic material in the buffer solution (W54-100A) and/or the longer hydrolysis/exposure time (W54-100D). Hydrolysis products that have higher [compared with MOTE (< 0.1 mg/l) and other organotin compounds] water solubility are 2-EHTG (4.73 mg/L) (a ligand of MOTE) and its breakdown products, such as 2-ethylhexanol (0.9 mg/l) and thiogylcolic acid (> 1000 g/L).

Applicant's summary and conclusion

Conclusions:

It can be concluded that DOTCE is the only tin-containing metabolite of DOTE that is formed under the simulated mammalian gastric environment. No DOTC was formed and detected under the conditions of this study.

Executive summary:

The hydrolysis of the test material as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7.

The stability of the test material was investigated at pH 4, 7 and 9 and pH 1.2 using NMR spectroscopy.

The study showed that MOTE is hydrolytically stable at pH 9, 7 and 4. After 5 days of hydrolysis at 50 °C less than 10% MOTE was hydrolysed (t 0.525 °C> 1 year). Amount of hydrolysed MOTE was increased at lower pH values from 1.85 % at pH 9 to 5.33 % at pH 7 and 7.01 % at pH 4. At the simulated gastric conditions (0.1 M HCl/pH 1.2 /37 °C) 75% MOTE was hydrolysed to it’s monochloride (DOTCE). No formation of DOTC was detected under the conditions of the study.

Hydrolysis of MOTE can be monitored by the decrease in the relative intensity of the respective 119Sn-NMR signal at 73.4 ppm and the increase of the DOTCE signal at 33.3 ppm. The sum of both intensities agrees well with MOTE signal intensity of the untreated test material. DOTC could not be identified in any of the hydrolysed MOTE samples and DOTC= 133 ppm using the 119Sn-NMR spectroscopy. Detection limit for DOTC has been experimentally found to be 0.5% w/w. It was shown in that when spiked with DOTC, MOTE signal present in a partially hydrolysed MOTE sample containing DOTCE, disappeared but still no peak characteristic to DOTC was detected. These results provide direct evidence that DOTC readily reacts with MOTE and forms DOTCE. Similar behaviour of MOTE was described in a study focused on the fate of MOTE in a polyvinylchloride (PVC) film. In that study MOTE was also converted to DOTCE due to the exposure to HCl that is formed as a result of the thermal degradation of PVC. No DOTC was detected until all MOTE has been transformed into DOTCE.

TOC analysis has been conducted to ensure completeness of the analysis and recover all organic carbon in aqueous phases including all possible water-soluble organotin substances and their breakdown components. The analyses detected some organic carbon content (from 1.4 to 4.2 % of the total available organic carbon) in the aqueous phases of the experiments. These traces of organic carbon could be attributed to 2-EHTG (a hydrolysed ligand of DOTE) and its breakdown products EH and TGA. 

Therefore, it can be concluded that DOTCE is the only tin-containing metabolite of DOTE that is formed under the simulated mammalian gastric environment. No DOTC was formed and detected under the conditions of this study.