Abstract
A series of novel tetramic acid derivatives, 5-sec-butyl-3-(1-substitutedamino)ethylidene-1Hpyrrolidine-2,4-diones 5a-y were synthesized by reaction with aryl amines or alkyl amines under reflux. Each title compound was formed as (5S,6S) and (5R,6S) C-5 epimers, and the structure of 5l was proved by X-ray diffraction analysis. Our preliminary bioassay results show the title compounds to exhibit some herbicidal activities and better antifungal activities than the leading compound tenuazonic acid at 100 mg L –1 in vitro, and the compound 5u displayed excellent herbicidal activity and antifungal activity.
Highlights
Tenuazonic acid, a metabolic toxin from widely differing phytopathogenic fungi,[1] was first isolated from the culture filtrates of Alternaria tenuis.[2]
Chemistry The intermediate 4 was prepared by the reported method, starting from L-isoleucine, through esterification, N-aceto-acetylation and a cyclization reaction as shown in Scheme 1.23 It was noted that during the cyclization, epimerization occurred at the position C-5 to give two epimers (5S, 6S) and (5R, 6S), and the diastereoisomer ratio was related to the sodium methoxide concentration and reaction time.[24]
A series of the compounds 5-sec-butyl-3-(1-substitutedamino)ethylidene-1Hpyrrolidine-2,4-diones 5a-y were synthesized by reacting the compounds 4 with aryl amine or alkyl amine in ethanol under refluxing condition (Scheme 1)
Summary
Tenuazonic acid, a metabolic toxin from widely differing phytopathogenic fungi,[1] was first isolated from the culture filtrates of Alternaria tenuis.[2]. Folkes reported a series of tetramic acid derivatives containing an imide function at the 3-position and found that some of them show excellent potency against plasminogen activator inhibitor-1 Figure 1, B.16. Zhu synthesized 3-[(α-hydroxy-substituted)benzylidene]pyrrolidine-2,4-diones and found them to exhibit good herbicidal activities Figure 1, C.17. Raghunandan reported N-Substituted-3- acetyltetramic acid derivatives displaying antibacterial activities (Figure 1, D).[18]. Some tenuazonic acid analogs such as, reutericyclin, cryptocin, β-cyclopiazonic acid, and melophlin A and B, derived from natural products, have been found and displayed a wide range of biological activities.[19,20,21]. We synthesized twenty-five novel tetramic acid derivatives, 5-sec-butyl-3-(1-substituted-amino)ethylidene-1H-pyrrolidine-2,4-diones, 5a-y, containing (5S,6S) and (5R,6S) C-5 epimers. Some of the compounds were found to exhibit better antifungal activities than tenuazonic acid against five fungi (Fusarium graminearum, Rhizoctonia cerealis, Colletotrichum capsici, Botrytis cinerea and Fusarium moniliforme) at 100 mg L–1 in vitro.
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