Reaction Mass of (1R)-1-[(1S)-3,3-dimethylcyclohexyl]ethyl formate and (1R,2S)-2,6,6-trimethylcycloheptyl formate

Endpoint summary

Description of key information

CP Formate is not a skin sensitiser, based on analogue information of CP Acetate and absence of structural features for skin sensitisation.

CP Formate is not expected to be a respiratory sensitiser.

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

In the absence of skin sensitisation study with CP Formate, read across with CP Acetate was used to assess this skin sensitisation of CP Formate. First the executive summary of the source is presented and thereafter the read-across justification.

GPMT with CP Acetate

A GPMT was performed in accordance with OECD TG 406. Fifteen test and fifteen control animals were used. Dose levels for the induction phase were: intradermal 10% v/v in liquid paraffin and 10% v/v in a 50:50 mixture of Freund's complete adjuvant and liquid paraffin, topical application as supplied and challenge application as 10% and 20% v/v in liquid paraffin. In the induction phase, CP Acetate was applied to the dorsal skin on the scapular region (intradermal injection) or the interscapular area (topical application) of the guinea-pigclipped and shaved free of hair. Erythema and oedema were scored 24, 48 and 72 hours after the challenge. In the test animals and controls localised dermal reactions were seen, which were thought to be related to skin irritation rather than sensitisation because the number and frequency of the findings were similar in the treated groups and the test animals. In conclusion, CP Acetate is not considered a sensitiser.

 

CP Formate and its non-sensitising properties using read across from CP Acetate and supporting information

Introduction and hypothesis for the read across

For CP Formate skin sensitisation data are scarce and do not fulfil the regulatory requirements for a decision on the skin sensitisation potential. Therefore, additional information is used in accordance with Article 13 of REACH where it is said that lacking information should be generated whenever possible by means other than vertebrate animal tests, i.e., applying alternative methods such as in vitro tests, SARs, grouping and read-across. The mechanisms of skin sensitisation are well known including the chemical features resulting in a skin sensitising reaction (ECHA’s R.7.3).Therefore, analogue approach and (Q)SAR information are used to assess the potential for sensitisation of CP Formate.

Hypothesis: CP Formate is not expected to have sensitising properties based on analogue information and the absence of structural alerts for skin sensitisation.

Source chemical(s): The information on CP Formate and the analogue information are presented in the data matrix.

Purity / Impurities: CP Formate is a multi-constituent composed of 65-85% 1-(3,3-dimethylcyclohexyl) ethyl formate and 8-18% 2,6,6-trimethylcycloheptyl formate. The major constituent of CP Formate is a formic-ester of ethyl-substituted cyclohexanol. The minor constituent has a similar functional group but a larger ring structure of 7- C atoms (see IUCLID section 1). This similarity in the functional group presents similar reactivity. Furthermore, it is not expected that any impurities present in CP Formate will significantly affect the toxicity, because of their presence < 5%.

Analogue justification

According REACH Annex XI an analogue approach and structural alert information can be used to replace testing when information from different sources provides sufficient evidence to conclude that this substance has or does not have a particular dangerous property. The result derived should be applicable for C&L and/or risk assessment and be presented with adequate and reliable documentation.

For the structural related CP Acetate a well conducted Maximisation test (OECD TG 406, but non-GLP) is available, showing the absence of skin sensitising potential. CP Acetate has one additional methyl group at the alkyl chain of the ester bond. This additional methyl group does not influence the reactivity of the substance and thus its sensitisation potential. Therefore, the information from CP Acetate can be used for CP Formate. Also, other structural analogues show the absence of skin sensitising effects (see data matrix).

In addition, the absence of skin sensitisation will be supported using structural information. The mode of action of skin sensitisation will shortly be explained to show that CP Formate has no structural alerts for causing this effect.

For skin sensitization two main causes for induction are known. Skin sensitisation is caused by covalent binding between the negatively charged skin proteins and the positively charged carbon-atom in the molecular structure due to adjacent electrophilic substructures such as oxygen atoms. This covalent binding between these two is the onset of an immunological reaction as presented in ECHA’s R.7.3.4.1. This onset can also be caused by radicals. Radical formation may be caused by hydroperoxides and peroxides: R-O-OH bonds or R1-O-O-R2 bonds, respectively.

For CP Formate the carbon-ester would be the potential site for attack for proteins in the skin. Due to the limitedly positively charged carbon of this ester, the proteins will not bind (sufficiently) to cause an immunological reaction. This is because of the absence of additional electrophilic activating groups on the alpha or beta position of the ester e.g., no halogens and no double or triple bonds. The OECD Toolbox and Derek Nexus both predict the absence of skin sensitisation for CP Formate. They also predict the absence of hydroperoxide metabolites when using the skin metabolism profiler, which may be another cause for skin sensitisation.

Structural similarities and differences: CP Formate, its constituents and the analogues presented all belong to the cyclic-esters. The key analogue substance is CP Acetate, which has one methyl group extra on the alkyl chain attached to the ester. All analogues have a cyclohexyl ring with short alkyl groups on different positions of the ring. The ester bond is the functional group, and its reactivity is low because there are no electron-withdrawing groups closely attached to this ester (at alpha or a beta position) and no (hydro)peroxide structures are present in the structure or can be formed upon skin metabolism. The structural difference between CP Formate and the CP Acetate is an additional methyl group on the alkyl chain attached to the ester. The last analogue (4-Isopropyl-cyclo-hexyl propionate) has a propyl chain attached to the ester and has a para-substituted iso-propyl group. These methyl groups as such limitedly influence the reactivity of the ester bond because they are not electrophilic. CP Formate and the cyclic-esters all have similar water solubilities and log Kow values indicating that these substances will be absorbed by the skin to a similar extent. The structural-activity relations and the analogue information show that for CP Formate no additional functional groups or additional substituents are present that might influence the reactivity and thus the sensitisation behaviour. In addition, the physico-chemical properties of these substances are similar and also the chemical mechanism considering the non-sensitising potential (ECHA’s R.7.3.4.1).

In summary, CP Acetate Maximisation test and the HRIPT test up to 100%, show a negative response. This information is supported by two other analogues (HRIPT up to 100 %) and information on the absence of structural alerts of CP Formate.

Remaining uncertainties: There are no remaining uncertainties because CP Acetate is a structurally very close analogue with only methyl group extra on the alkyl chain attached to the ester. Also, the information of the other analogues showed negative response up to 100%. In addition, the skin sensitisation mechanisms are well known and are well described by e.g., Aptula and Roberts (as referenced in ECHA’s R7.3.4.1). CP Formate does not contain structural alerts for skin sensitisation. Therefore, there are no remaining uncertainties.

Conclusions per endpoint for C&L, PBT/vPvB and dose descriptor

From analogue information and structural alert information, it can be concluded that CP Formate has no skin sensitising properties. Therefore, CP Formate is not sensitising, and it does not need to be classified and labelled for sensitisation according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.

Data matrix Information on CP Formate and analogues important for assessment of skin sensitising properties.

CHEMICAL NAME	l-Cyclo-citronellene formate (CP Formate)	1-(3,3-Dimethylcyclohexyl)ethyl acetate (CP Acetate)	Cyclohexylmethyl-carbinyl acetate	4-Isopropyl-cyclo-hexyl propionate
	Target	Source	Source	Source
CAS	25225-08-5	25225-10-9	13487-27-9	63449-95-6
Molecular structure#
Molecular weight	184	198	170	198
Physico-chemical properties
Appearance s	Liquid	Liquid	Liquid	Liquid
Vapour pressureat 25˚C (Pa)	13.4	10 (EpiSuite)	33 (EpiSuite)	6 (EpiSuite)
Water solubility at 20˚C(mg/L)	26	7.4 (EpiSuite)	57 (EpiSuite)	6.9 (EpiSuite)
Log Kow	3.8	4.42 (EpiSuite)	3.55 (EpiSuite)	4.46 (EpiSuite)
Skin sensitisation animal tests	Read across	20%-negative OECD TG 406	No data	No data
Skin sensitisation HRIPT*^: Reliability 2	5%-negative 42 subjects	100%-negative 52 subjects	100%-negative 52 subjects	100%-negative 52 subjects

#These structures are visible in the attached read across document at (IUCLID 7.4 Endpoint summary

*Api, A.M., 2002, Sensitization methodology and primary prevention of the Research Institute for Fragrance Materials. Dermatology, 205, 84-87.

^ Politano, V.T. and Api, A.M., 2008, The Research Institute for Fragrance Materials' human repeated insult patch test protocol. Regul. Toxicol. Pharmacol., 52, 35-38.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Respiratory sensitisation can be assessed using human data such as indicated in R7.3.5.2 of the ECHA guidance that indicate respiratory reactions e.g. from consumer experience or occupational exposure. In the absence of such data for CP Formate, the respiratory sensitisation was assessed using the integrated evaluation strategy for respiratory sensitisation data in the ECHA guidance (R7A, Fig. 7.3-2). As CP Formate is not skin sensitising, this substance is unlikely to be a respiratory sensitiser as presented in the REACH guidance: Scheme of R7A, Fig. 7.3 -2.

Justification for classification or non-classification

From the analogue approach and SAR information it can be concluded that CP Formate has no skin sensitising properties. This is based on a close analogue CP Acetate being negative in a Maximisation test up to the maximum achievable concentration of 20% and negative at 100% in a HRIPT test, which is supported by two additional analogues. In addition, the substance does not have structural alerts for skin sensitisation. Therefore CP Formate is not skin sensitising, and it does not need to be classified for skin and respiratory sensitisation according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008 and its amendments.