Elucidation of the upper pathway of alicyclic musk Romandolide® degradation in OECD screening tests with activated sludge
2014
Seyfried, M. | Boschung, A. | Miffon, F. | Ohleyer, E. | Chaintreau, A.
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 CO₂evolution 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.
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