Elucidation of the upper pathway of alicyclic musk Romandolide® degradation in OECD screening tests with activated sludge

Abstract

The degradation of Romandolide ([1-(3',3'-dimethyl-1'-cyclohexyl)ethoxycarbonyl] methyl propanoate), a synthetic alicyclic musk, by activated sludge inocula was investigated using both the manometric respirometry test OECD 301F and the CO₂ evolution test. In addition to measuring its biodegradability, key steps of the upper part of the metabolic pathway responsible for Romandolide degradation were identified using extracts at different time points of incubation. Early metabolism of Romandolide yielded ester hydrolysis products, including Cyclademol (1-(3,3-dimethylcyclohexyl)ethanol). The principal metabolites after 31 days were identified as 3,3-dimethyl cyclohexanone and 3,3-dimethyl cyclohexyl acetate. Formation of 3,3-dimethyl cyclohexanone from Cyclademol by sludge was confirmed in subsequent experiments using Cyclademol as a substrate, indicating the involvement of an oxygen insertion reminiscent of a Baeyer-Villiger oxidation. Further mineralization of 3,3-dimethyl cyclohexanone was also confirmed in subsequent studies. Three steps were thus required for complete biodegradation of the alicyclic musk: (1) successive ester hydrolyses leading to the formation of Cyclademol with concomitant degradation of the resulting acids, (2) conversion of Cyclademol into 3,3-dimethyl cyclohexanone, and (3) further mineralization via ring cleavage.

An assessment of biodegradability of quaternary carbon–containing fragrance compounds: Comparison of experimental OECD screening test results and in silico prediction data

“…Judging from the compounds that degraded well, biodegradability clearly depends on a different part of the molecule than the quaternary carbon. As we were able to show recently , the initial steps in the pathway of biodegradation of structure IV1 involve modifications of the side chain, that is, successive ester cleavages and transforming the cleavage product into 3,3‐dimethyl cyclohexanone. This is then thought to degrade further by the action of a BVMO as shown previously for unsubstituted cyclohexanone .…”

“…As we were able to show recently , the initial steps in the pathway of biodegradation of structure IV1 involve modifications of the side chain, that is, successive ester cleavages and transforming the cleavage product into 3,3‐dimethyl cyclohexanone. This is then thought to degrade further by the action of a BVMO as shown previously for unsubstituted cyclohexanone . For the other monocyclic structures of Figure that show significant biodegradation, similar metabolites may be formed, allowing further degradation by ring fission between ring carbons distant from the quaternary carbon carrying the geminal dimethyl.…”

“…The experimental result for Romandolide, a synthetic alicyclic musk, is interesting in that depending on the test conditions, a biphasic growth kinetic can be observed . This would indicate the action of 2 independent consecutive pathways rather than 1 complete series of catabolic reactions.…”

Exposure of the population of Catalonia (Spain) to musk fragrances through seafood consumption: Risk assessment

“…Finally, the use of alicyclic Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/envres musks, as well as the investigations focused on their toxicological properties, is still very scarce. Although alicyclic musks have been suggested to biodegrade (Seyfried et al, 2014), more studies are necessary to confirm it.…”

Modeling ready biodegradability of fragrance materials

“…Readers interested in microbial catabolism of fragrance compounds should consult the article on Romandolide biodegradation by Seyfried et al , which itself has many useful references on this topic; and the Eawag.bbd (formerly University of Minnesota Biocatalysis and Biodegradation) database (http://eawag-bbd.ethz.ch/index.html), which has detailed information on several relevant pathways (e.g., camphor, citronellol, p‐cymene, geraniol, limonene, menthol, and alpha‐pinene).…”