Article pubs.acs.org/JAFC
Hydrolysis of Chlorantraniliprole and Cyantraniliprole in Various pH Buffer Solutions Ashok K. Sharma,*,† William T. Zimmerman,† Chris Lowrie,‡ and Simon Chapleo‡ †
Stine Haskell Research Center, E. I. DuPont de Nemours and Company Newark, Delaware 19714, United States Charles River Laboratories, Tranent, Edinburgh EH33 2NE, United Kingdom
‡
ABSTRACT: The hydrolysis reactions of [14C]-chlorantraniliprole (CLAP) and cyantraniliprole (CNAP) were investigated in sterile buffer solutions at pH 4, 7, and 9. Both compounds displayed similar degradation reactions. The reactions observed were intramolecular cyclizations and rearrangements instead of the anticipated amide hydrolysis to carboxylic acids. Despite a minor difference in their structures, the degradation rates for the two compounds were substantially different. The reaction rates were examined at multiple temperatures to understand the mechanistic aspects of the underlying transformations. Similarities and differences in the hydrolysis behavior of these compounds in various pH values and temperatures are described. KEYWORDS: chlorantraniliprole, cyantraniliprole, hydrolysis, quinazolinone, anthranilic diamides, cyclodehydration
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Figure 1. Test substances. Arrows indicate locations of 14C.
CLAP were prepared as described previously.6 The corresponding degradates for CNAP were prepared in an analogous manner and were available for identification while this work was in progress. Preparation of Buffers and Test Solutions. A 0.01 M, pH 4, buffer solution was prepared by combining a 0.1 M citric acid solution (33 mL) with 0.1 M sodium citrate solution (17 mL) and then diluting to 500 mL with Milli-Q water. Final pH adjustments were made with sodium hydroxide as necessary. The pH of the buffer solution was verified to be pH 4.0 ± 0.1 before and after sterilization. A 0.1 M, pH 7, buffer solution was prepared by combining a 0.2 M TRIS−maleic acid solution (50 mL) with 0.2 M sodium hydroxide solution (48 mL) and diluting to 200 mL with Milli-Q water. A 0.01 M, pH 7, buffer was subsequently prepared by diluting 100 mL of 0.1 M buffer to 1000 mL with Milli-Q water. The pH of the buffer solution was verified to be 7.0 ± 0.1 before and after sterilization A 0.1 M, pH 9, buffer solution was prepared by combining a 0.05 M borax solution (59 mL) with 0.2 M boric acid solution (50 mL) and diluting to 200 mL with Milli-Q water. A 0.01 M, pH 9, buffer was subsequently prepared by diluting 100 mL of 0.1 M buffer to 1000 mL with Milli-Q water. Final pH adjustments were made with sodium hydroxide as necessary. The pH of the buffer solution was verified to be 9.0 ± 0.1 before and after sterilization. Test solutions were prepared by adding an aliquot (5 mL) of the appropriately labeled compound to a sterile volumetric flask (500 mL capacity), which was made up to volume with filter-sterilized buffer solution to obtain a final concentration of approximately 1.0 μg/mL for CNAP or 0.6 μg/mL for CLAP. The concentration of acetonitrile cosolvent was ≤1% in the test solutions. Nominal test substance concentrations were well below the water solubilities of 14.6 and 1.2 μg/mL for CNAP and CLAP, respectively. All glassware, incubation vessels, and associated equipment were sterilized by autoclaving. Incubation of test solutions was carried out in glass hydrolysis vessels (15 mL capacity) with tightly sealed Teflon-lined crimp caps. After addition of the test substance, all test vessels were placed in a water bath in darkness at the desired temperatures, and the temperature was maintained within ±1 °C. Each test vessel was filled with 12 mL of sterile pH 4, 7, or 9 buffer containing the test substance. At selected time
the pyrazole carbonyl- 14 C (PC-label) was identical in both compounds, whereas the benzamide ring was labeled in the cyano carbon for CNAP (CN-Label) and on the benzamide carbonyl (BC-Label) in CLAP. Synthetic standards of degradates 1, 2, and 3 for
Received: Revised: Accepted: Published:
INTRODUCTION DuPont has recently introduced a new class of insecticides1−4 known as anthranilic diamides. Chlorantraniliprole (CLAP) and cyantraniliprole (CNAP) are two analogous products from this class of compounds. They have minor differences in their structure, yet there is a marked difference in the insects affected by these products. Outstanding mammalian safety along with a broad spectrum of crop uses is leading to extensive applications of these products. Widespread use of these products has also prompted reports on degradation in food commodities5,6 as well as interest from the academic community in further scrutiny of these compounds.7 The hydrolytic stability of these compounds was investigated in sterile buffer solutions under acidic and alkaline conditions at environmentally relevant concentrations to determine the route of degradation of these compounds in water. Hydrolysis under conditions that mimic food processing and sterilization was also investigated for degradations at 90−120 °C for short periods. Whereas we anticipated the formation of free carboxylic acids to prevail in the degradation reactions, the reactions observed showed some unusual cyclization reactions, which are described below.
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MATERIALS AND METHODS
Two 14C-labeled versions of each compound were used in these investigations, and the structures are illustrated in Figure 1. Location of
© 2014 American Chemical Society
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February 7, 2014 April 1, 2014 April 2, 2014 April 2, 2014 dx.doi.org/10.1021/jf500671w | J. Agric. Food Chem. 2014, 62, 3531−3536
Journal of Agricultural and Food Chemistry
Article
intervals, the samples were analyzed directly by liquid scintillation counting (LSC) to determine the total test substance related amounts in each sample to account for mass balance. Applied test substance recovery was quantitative in all reaction samples. For high-temperature reactions, each test vessel was filled, leaving a small headspace to allow for expansion during heat treatment, with ca. 12 mL of sterile buffer containing the test substance. The test vessels were capped and heat-treated at either 90, 100, or 120 °C for short durations (
