5-氧代三酮类化感物质及其衍生物的合成和除草活性
Synthesis and herbicidal activity of allelochemical-derived 5-oxyl-triketones

为评价5-氧代三酮类化感物质AB5046A和AB5046B及其衍生物的除草活性，以均三酚为起始原料合成了天然化合物AB5046A和AB5046B，同时合成了13个2-脂肪酰基和2-芳香甲酰基衍生物，并采用小杯法和平皿法测定了它们及其衍生物对油菜和稗草的生物活性。结果表明：所建立的合成方法仅通过5步反应即可分别以36%和28%的较高收率合成AB5046A和AB5046B，包括：（1）均三酚通过部分氢化还原和酸性离子交换树脂以83%的产率转化为3-乙氧基-5羟基-环己烯酮；（2）通过对羟基氯甲基甲醚保护，以80%的产率得到酮，（3）经3 mol/L HCl去乙基，进一步在4-N，N-二甲基氨基吡啶（DMAP）/二环己基碳二亚胺（DCC）条件下与相应等量羧酸缩合，分别以77%和71%的产率得到二酮，（4）~（5）随后在三甲基碘硅烷/4A分子筛条件下反应，分别以83%和70%的产率完成AB5046A和AB5046B的合成。AB5046A和AB5046B及其衍生物具有明显的除草活性，油菜和稗草表现出白化和褪绿特征，其中在100 μg/mL浓度下，AB5046A和AB5046B对油菜的根长抑制率均为43.9%，对稗草的株高抑制率则为38.6%和53.2%。在合成的13个衍生物中，5-羟基保护的衍生物2-正辛酰基-3-羟基-5-氧甲氧基甲基-2-环己烯酮（TM-6）对油菜和稗草的抑制率分别达到70.2%和62.5%，除草活性较2个天然产物明显提高，可以作为除草剂先导结构进行优化。
To evaluate the herbicidal activity of allelochemicals AB5046A and AB5046B and their derivatives (TM-1-TM-13), natural products AB5046A and AB5046B and their 13 derivatives were synthesized from phloroglucinol as starting material. Then their herbicidal activities against Brassica campestris L. and Echinochloa crusgalli (L.) Beauv. were evaluated in laboratory bioassays. The results showed that a concise synthetic method could be established only by five-step reactions and AB5046A and AB5046B were synthesized in overall yield of 36% and 28%, respectively. The synthetic route included the following steps:directed transformation of phloroglucinol to 3-ethoxy-5-hydroxy-cyclohex-2-enone 2 by using partial reduction reaction and acidic cation exchange resin in 83% yields; the hydroxyl group was protected by using chloromethylmethyl ether (MOMCl) in the presence of N-diisopropylethyl-amine (DIPEA) and 4-N,N-dimethylaminopyridine (DMAP), which afforded ketone 3 in 80% yields. Then, stirring with 3 mol/L HCl afforded diketone 4 in 85% yields. The following condensation reaction of 4 with alkyl acids in the presence of dicyclohexylcarbodiimide (DCC) and DMAP at room temperature afforded (5 and 6) in 77% and 71% yields, respectively, which were treated with trimethylsilyl iodide (TMSI) to produce AB5046A and AB5046B in 83% and 70% yield, respectively. The in vitro bioassay results showed that natural products AB5046A, AB5046B and their derivatives had some herbicidal activity with chlorosis and bleaching symptoms. The herbicidal activities of two natural products AB5046A and AB5046B were 43.9%, 38.6% and 43.9%, 53.2% against B. campestris and E. crusgalli at 100 μg/mL, respectively.Among 13 derivatives, 2-n-octyl acyl-3-hydroxy-5-oxy-methyl-2-cyclohexenone (TM-6) had higher herbicidal activity than two natural products against B. campestris and E. crusgalli at 100 μg/mL with an inhibition rate of 70.2% and 62.5%. The