Reaction mass of 3a,4,5,6,7,7a-hexahydro-4,7-methano-1H-inden-5-yl isobutyrate and 3a,4,5,6,7,7a-hexahydro-4,7-methano-1H-inden-6-yl isobutyrate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

The NOAEL is >= 1000 mg/kg bw, based on read across from Cyclacet which was tested in an OECDTG 421)

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Study duration:

subacute

Quality of whole database:

In addition, to the key study, also information on reproductive organs from a 90-day study is available for Cyclacet. In this study no fertility effects were seen. Also in the 28-day study for Cyclobutanate no effects on the reproductive organs were found. Both studies have been carried out according to OECD guidelines and under GLP. Therefore the quality of the whole database is sufficiently adequate to cover this endpoint.

Additional information

No experimental study on fertility was available for Cyclabute. The endpoint can, however, be fulfilled using data from a Reproscreening study with structural similar substance, Cyclacet, which can be used for read across (its adequacy is documented below). First the reproduction/developmental toxicity screening test according to OECD TG 421 with Cyclacet will be summarised. Thereafter the read across justification is presented.

Cyclacet tested in the Reproductive screening test.

The test material was administered by gavage to three groups, each of ten male and ten female Wistar rats, for up to forty-six consecutive days (including a two week maturation phase, pairing, gestation and early lactation for females), at dose levels of 100, 300 and 1000 mg/kg/day. A control group of ten males and ten females was dosed with vehicle alone (Arachis oil BP). Clinical signs, bodyweight change, dietary intake and water consumption were monitored during the study. Pairing of animals within each dose group was undertaken on a one male: one female basis within each treatment group on Day 15 of the study, with females subsequently being allowed to litter and rear their offspring to Day 5 of lactation. During the lactation phase, daily clinical observations were performed on all surviving offspring, together with litter size and offspring weights and assessment of surface righting reflex. Adult males were terminated on Day 43, and all females and surviving offspring on Day 5 post partum. All animals were subjected to a gross necropsy examination and histopathological evaluation of reproductive tissues was performed. Results: The oral administration of Cyclacet to rats by gavage, for a period of up to forty six consecutive days at dose levels of 100, 300 and 1000 mg/kg/day did not result in any treatment-related reproductive effects. The ‘No Observed Adverse Effect Level’ (NOAEL) for reproductive (fertility and developmental) toxicity was therefore considered to be 1000 mg/kg/day. Based on this result, the read-across NOAEL for Cyclabute was also established to be 1000 mg/kg bw/day. The read across is documented below.

The reproductive toxicity of Cyclabute is assessed using read across from Cyclacet

Introduction and hypothesis for the analogue approach

Cyclabute is an isobutanoic ester attached to a tricyclodecenyl fused ring structure. For this substance no reproductive toxicity (a.o. fertility and developmental toxicity) data are available.

In accordance with Article 13 of REACH, lacking information should be generated whenever possible by means other than vertebrate animal tests, i. e. applying alternative methods, such as in vitro tests, QSARs, grouping and read-across. For assessing the fertility and developmental toxicity of Cyclabute the analogue approach is selected because for one closely related analogue reliable fertility and developmental toxicity information is available from a Reproscreen OECD 421 study, which can be used for read across.

Hypothesis: Cyclabute has similar reproductive and developmental toxicity compared to Cyclacet resulting in a similar NOAEL, based on similarity in chemical structure, bioavailability and Mode of Action. The one ethyl shorter chain length of Cyclacet will not present a significant change in reproductive toxicity. Cyclabute has also similar reproductive toxicity compared to Cyclobutanate, which has a butanoic ester instead of an isobutanoic one.

Available experimental information: The source chemical Cyclacet has been tested in a well conducted Reproscreen (OECD TG 421 under GLP) up to 1000 mg/kg bw (highest dose tested) and the test result receives a reliability of 1. In addition, for Cyclobutanate a 28-day repeated dosed toxicity study (OECD TG 407 under GLP) is available in which no effects were seen on male and female reproductive organs up to 1000 mg/kg bw (highest dose tested) with a reliability of 1.

Target chemical and source chemical(s)

Chemical structures of the target chemical and the source chemicals are shown in the data matrix as are the physico-chemical properties and toxicological information, thought relevant for reproductive and developmental toxicity. These esters have a tricyclodecenyl fused ring structure with an unsaturated bond in the right ring. On the left ring an ester bond is attached with a short alkyl chain (<C4).

Purity / Impurities

The purity and impurities of the source chemicals do not indicate a reproductive toxic potential. The impurities are all below < 10%. Also the purity and impurities of the target chemical do not indicate reproductive toxicity potential and are below 10%. The unsaturated bond in the right ring can be at the 5-yl or the 6-yl position, which is not thought to make a difference for the reproductive and developmental toxic potential because such a double bond at 5-yl or at 6- yl is not expected to be reactivity as such or influence the stereochemistry.

Analogue approach justification

According to Annex XI 1.5 read across can be used to replace testing when the similarity can be based on a common backbone and a common functional group. When using read across the result derived should be applicable for C&L and/or risk assessment and it should be presented with adequate and reliable documentation.

Analogue selection: Cyclabute has the same backbone and the same ester functional group as its key (Cyclacet) and supporting (Cyclobutanate) analogues and for the key analogue repeated dose and fertility information is available fulfilling this Annex. For the supporting analogue supporting repeated dose toxicity information is available showing the repeated dose effects are the same whether the accompanying ester is acetate or a butanoate.

Structural similarities and differences: The target and the source chemicals all being Cycla-esters, have a tricyclodecenyl fused ring structure with an unsaturated bond in the right ring. On the left ring an ester bond is attached with a short alkyl chain (<C4). The alkyl chain of Cyclabute (C4) is two methyl groups longer than of Cyclacet (C2). These differences between the target and source chemicals are not expected to behave differently compared to the target organs because the alkyl side chains (isobutyl versus acetyl) are not expected to influence significantly the reproductive toxicity of these chemicals.

Toxico-kinetic: Cyclabute has similar toxico-kinetic characteristics compared to Cyclacet (and Cyclobutanate) based on the similarity in chemical structure and physico-chemical properties.

Absorption: The molecular weight of the target chemical is 220, whereas for Cyclacet it is 192. They are both liquids. Their vapour pressures are around 1 Pa. It can be seen that the water solubility of the acetic ester is somewhat higher and the log Kow somewhat lower compared to Cyclabute, which contains an isobutanoic ester instead. These physico-chemical differences are expected to be minimal with respect to absorption, distribution and excretion via all exposure routes.

Metabolisation: the target and the source chemical will both be metabolized into the Cycla-alcohol, which will be glucuronidated thereafter (see toxico-kinetic section). The target will metabolise also into the isobutanoic and the source into acetic acid. This metabolisation is illustrated in the figure below. Isobutanoic and acetic will be further metabolised in innocuous products and acetic acid is a normal constituent of the body and therefore both metabolites are not expected to cause reproductive and developmental toxicity.

Toxico-dynamics: Cyclacet and Cyclabute have the same backbone and functional group and therefore the same reproductive toxicity potential. In addition after metabolisation, the key metabolite is for both substances Cycla-alcohol further supporting the same mode of action.

Similarities in results for toxicological endpoints between the target and the source chemical(s): In the data matrix a summary of the other toxicological data are presented to show that these substances have a low order of toxicity. The source and the target chemicals also show negative results in the common Ames genotoxicity tests and therefore reproductive and developmental toxicity resulting from genotoxicity is not expected.

Uncertainty of the prediction: The prediction of the NOAEL of >=1000 mg/kg bw for the target chemical for reproductive toxicity (both fertility and developmental toxicity) has a high certainty because of close similarity between the target and the source chemicals. The two methyl group difference in the alkyl chain will not have an impact on the reproductive toxicity because the systemic exposure will be to the Cycla-alcohol and the isobutanoic acid. This latter substance will be further metabolised in innocuous products (WHO, 1999) and therefore no reproductive /developmental toxicity is expected for this acid. This is also supported in the reproductive and developmental toxicity information on isobutanoic acid which has been assessed OECD SIDS HPVC framework (OECD, 2003, SIAM 17). The available information from the source chemicals are all of a high quality Reproscreen test (Reliability 1).

Data matrix

The relevant information on physico-chemical properties and toxicological characteristics are presented in the Data Matrix.

Conclusions for hazard

For Cyclabute no reproductive toxicity is available but for a close analogue Cyclacet such information is present and is supported with information from Cyclobutanate. When using read across the result derived should be applicable for C&L and/or risk assessment and be presented with adequate and reliable documentation. For Cyclacet (acetic side chain) a well conducted Reproscreen test is available (Reliability 1) with a NOAEL of >=1000 mg/kg bw for fertility and developmental toxicity. Based on the read-across approach described it can be concluded that Cyclabute also has a NOAEL of >=1000 mg/kg bw for reproductive toxicity

Final conclusion on hazard: Cyclabute has a NOAEL of >=1000 mg/kg bw for reproductive toxicity including fertility and developmental toxicity

Data matrix for the read across to Cyclabute from Cyclacet (key) and Cyclobutanate (supporting) for reproductive and developmental toxicity

Common names	Cyclabute	Cyclacet	Cyclobutanate
Chemical structures
CAS no	93941-73-2 (generic) C14H20O2	54830-99-8 (generic) C12H16O2	113889-23-9 (generic) C14H20O2
EC no	916-331-7	911-369-0	441-420-8
	Target	Source (key)	Source (supporting)
Molecular weight	220	192	220
Physico-chemical data
Physical state	liquid	liquid	liquid
Melting pointoC	< -20	< -20	< -20
Boiling pointoC	273	249	275
Vapour pressure Pa	0.61	2.1	11.2
Water solubility mg/l	16	186	11.5
Log Kow	5.1	3.9	4.48
Human health endpoints
Acute oral tox in mg/kg bw	>10000 (Eq OECD TG 401)	2750 (OECD TG 401)	>2000 (OECD TG 423)
Acute dermal tox in mg/kg bw	> 2000 based on oral LD50 > 2000	>5000 (OECD TG 402)	>2000 (OECD TG 402)
Genotoxicity – Ames test	Negative (OECD TG 471)	Negative (OECD TG 471)	Negative (OECD TG 471)
Genotoxicity – Cytogenicity	Negative (OECD TG 487)	Negative (Read across)	Negative (OECD TG 473)
Genotoxicity – MLA	Negative (Read across from Cyclacet)	Negative (OECD TG 476)	Negative (Read across)
Repeated dose toxicity (mg/kg bw/day)	NOAEL >=1500 (Read across from Cyclacet 90-day study)	NOAEL >=1500 (OECD TG 408)	NOAEL >=1000 (28-day study: OECD TG 407)
Reproductive toxicity Fertility toxicity mg/kg bw Developmental toxicity mg/kg bw	NOAEL >=1000 (Read across from Cyclacet)  NOAEL >=1000 (Read across Cyclacet)	NOAEL >=1000 (OECD TG 421) NOAEL >=1000 (OECD TG 421)	NOAEL >= 1000 (OECD TG 407)  NOAEL >=1000 (Read across Cyclacet)

References:

ECHA, 2010, Cyclacet registration under EC no: 911-369-0; https://echa.europa.eu/nl/registration-dossier/-/registered-dossier/13281

OECD SIDS, 2003, SIDS Initial Assessment Profile of Isobutyric acid and Isobutyric anhydride; http://webnet.oecd.org/HPV/UI/handler.axd?id=26f9f920-1dc6-4e53-b5c4-fdd8b34af201

WHO, 1999, Evaluation of certain food additives, WHO Technical report series 885: http://whqlibdoc.who.int/trs/WHO_TRS_884.pdf     

Effects on developmental toxicity

Description of key information

Reproduction/developmental toxicity screening test (Read across from Cyclacet, OECD 421):
- NOAELdevelopmental: >=1000 mg/kg bw/day
- NOAELmaternal: >= 1000 mg/kg bw/day

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Additional information

No experimental information on developmental toxicity is available for Cyclabute. The experimental study of Cyclacet (OECD TG 421) will be used for read across (its documentation is presented at the fertility section above).

Justification for classification or non-classification

Based on all information available including the absence of effects in a reproduction/developmental toxicity screening study with structural similar substance Cyclacet (read across), Cyclabute does not need to be classified for reproductive/fertility/developmental toxicity according to EU CLP (EC/1272/2008 and its updates).