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Conclusion on classification

Ecotoxicological information in the present dossier is based on read-across information from studies with 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite]:

Two study reports (rated as Klimisch 1) on aquatic organisms are available covering two trophic levels: a primary producer (freshwater algae, represented by the model species Pseudokirchneriella subcapitata) and a primary consumer (aquatic invertebrates, represented by the model species Daphnia magna).

 

D. magna was exposed for 48 hours to 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] in a semi-static short-term GLP toxicity study (OECD 202) at the limit of water solubility (loading 100 mg/L nominal). No effect on D. magna was observed. The test concentration was below the LOD (=0.01 mg/L) of the HPLC-UV, although the substance was stirred for 48 hours in the test medium. Therefore, it can be concluded that 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] is not toxic to D. magna up to the limit of water solubility (determined water solubility according to OECD 105, see section 4.8 in the present report).

 

The freshwater algae P. subcapitata was exposed to 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] for 72 hours in a GLP toxicity study (OECD 201) at the limit of water solubility (loading 100 mg/L nominal). No effect on P. subcapitata was observed. The test concentration was below the LOD (=0.01 mg/L) of the HPLC-UV, although the substance was stirred for 48 hours in the test medium. Therefore, it can be concluded that 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] is not toxic to P. subcapitata up to the limit of water solubility. 

 

5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] is considered to be not readily biodegradable based on ThCO2 (Flach 2018), and the estimated log Kow is ≥ 4.

Taking into account that the source substance 5′-O-[bis(4-methoxyphenyl)phenylmethyl]-2′-deoxythymidine, 3′-[2-cyanoethyl N,N-bis(1-methylethyl)phosphoramidite] displays no acute (i.e. Algae and Daphnia acute EC50 > water solubility) or chronic (Algae 72 h-NOEC > water solubility) toxicity in available tests up to the limit of water solubility the substance is considered to be not toxic towards the aquatic environment and is not classified according to the provisions laid down in the CLP Regulation (Regulation (EC) No 1272/2008).

Therefore the target substance 5'-Dimethoxytrityl-N4-benzoyl-2'deoxycytidine-3'-O-b-Cyanoethyl-N,N-diisopropyl- phosphoramidite is as well not classified as toxic to the aquatic environment according to the provisions laid down in the CLP Regulation (Regulation (EC) No 1272/2008).

This information is used in a read-across approach in the assessment of the target substance. For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

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