Síntese e avaliação da atividade inseticida de N-alquil e N-aril amidas

Abstract

A piperina é uma amida isolada dos frutos das espécies de Piper e apresenta atividade inseticida. Este trabalho descreve a síntese de amidas insaturadas a partir do sorbato de potássio, visto que este reagente possui as ligações duplas conjugadas como aparece na estrutura da piperina e também amidas de cadeia saturadas, estas a partir do anidrido hexanóico para posterior comparação da atividade inseticida. Foram preparados vinte e um compostos, um composto intermediário e vinte amidas. Das vinte amidas quatro são inéditas, todos os compostos foram caracterizados por espectroscopias no infravermelho e de ressonância magnética nuclear, análise elementar e espectrometria de massas. As amidas sintetizadas foram: (2E, 4E)-N- (cicloexil)exa-2,4-dienamida [22], (2E, 4E)-N-(benzil)exa-2,4-dienamida [23], (2E, 4E)-N-(2-etilfenil)exa-2,4-dienamida [24], (2E, 4E)-N-(pentil)exa-2,4- dienamida [25], (2E, 4E)-N-(fenil)exa-2,4-dienamida [26], (2E, 4E)-N,N- (difenil)exa-2,4-dienamida [27], (2E, 4E)-N,N-di(propan-2-il)exa-2,4-dienamida [28], (2E, 4E)-N,N-(dietil)exa-2,4-dienamida [29], (2E, 4E)-1-(pirrolidin-1-il)exa- 2,4-dien-1-ona [30], (2E, 4E)-N-(exil)exa-2,4-dienamida [31], (2E, 4E)-1- [32], (piperidin-1-il)exa-2,4-dien-1-ona N-fenilexanamida [33], N- benzilexanamida [34], N-(cicloexil)exanamida [35],1-(pirrolidin-1-il)exan-1-ona [36], N-(pentil)exanamida nitrofenil)exanamida [39], [37], N-(2-etilfenil)exanamida N-(4-clorofenil)exanamida [38], [40], N-(3- N-(3- clorofenil)exanamida [41]. A atividade inseticida das amidas sintetizadas foi avaliada sobre Diaphania hyalinata e Solenopsis saevissima. As amidas que apresentaram maior taxa de mortalidade sobre Diaphania hyalinata foram [38], [32] e [22] apresentando taxas de 85,00%, 96,5% e 100,0%, respectivamente, sendo maior do que o apresentado pela piperina que foi de 88,3%. A piperina não apresentou atividade frente à Solenopsis saevissima, no entanto, os compostos [28], [29], [30], [31], [32], [36] e [37] apresentaram taxa de mortalidade igual a 100%. Dos compostos inéditos [24], [25], [31] e [41], para xviii Diaphania hyalinata apenas o [31] apresentou alta toxicidade com uma taxa de mortalidade de 78,33%, enquanto que os compostos [24], [25] e [41] apresentaram taxa de mortalidade igual a 51,67%, 53,33% e 40,00% respectivamente. Já para a Solenopsis saevissima os compostos [25], [31] e [41] apresentaram alta toxicidade com uma taxa de mortalidade igual a 85,00%, 100,00% e 96,67% respectivamente e o composto [24] 53,33%. Comparando-se as amidas que possuem ligação dupla conjugada com as amidas que não possuem essas ligações observa-se que tanto para os insetos das espécies Diaphania hyalinata quanto para Solenopsis saevissima essa diferença estrutural não afetou a toxicidade dos compostos.Piperine is an amide found in fruits of Piper species presenting insecticide activity. The synthesis of unsaturated amides is described in this work from potassium sorbate as it has the conjugated double bonds as in piperine. Saturated amides were prepared from hexanoic anhydride and the insecticidal activity was compared with the unsaturated amides. A total of 21 compounds were prepared, where 4 of them are novel. The amides were purified and characterized by infrared spectroscopy and nuclear magnetic resonance, elemental analysis and mass spectrometry. The amides prepared were: (2E,4E)-N-cyclohexylhexa-2,4-dienamide [22], (2E,4E)-N-benzylhexa- 2,4-dienamide [23], (2E,4E)-N-(2-phenylethyl)hexa-2,4-dienamide [24], (2E,4E)-N-pentylhexa-2,4-dienamide [25], (2E,4E)-N-phenylhexa-2,4- dienamide [26], (2E,4E)-N,N-diphenylhexa-2,4-dienamide [27], (2E,4E)-N,Ndi( propan-2-yl)hexa-2,4-dienamide [28], (2E,4E)-N,N-diethylhexa-2,4- dienamide [29], (2E,4E)-1-(pyrrolidin-1-yl)hexa-2,4-dien-1-one [30], (2E,4E)-Nhexylhexa- 2,4-dienamide [31], (2E,4E)-1-(piperidin-1-yl)hexa-2,4-dien-1-one [32], N-phenylhexanamide [33], N-benzylhexanamide [34], Ncyclohexylhexanamide [35], 1-(pyrrolidin-1-yl)hexan-1-one [36], Npentylhexanamide [37], N-(2-phenylethyl)hexanamide [38], N-(3- nitrophenyl)hexanamide [39], N-(4-chlorophenyl)hexanamide [40], N-(3- chlorophenyl)hexanamide [41]. The insecticidal activity of the amides was evaluated against Diaphania hyalinata and Solenopsis saevíssima. The amides which presented the highest mortality rates against Diaphania hyalinata were [38], [32], and [22], showing rates of 85.00%, 96.5% and 100.0% respectively. The mortality rates presented by these amides were higher than piperine s, which was of 88.3%. Piperine has not presented activity against Solenopsis saevíssima, however compounds [28], [29], [30], [31], [32], [36], and [37] presented mortality rate of 100%. The novel amides [24], [25], [31], and [41] presented mortality rates of 51.67%, 53.33%, 78.33%, and 40.00% against Diaphania hyalinata respectively. Therefore from the novel amides only [31] presented high activity and the others presented only moderate activity against Diaphania hyalinata. The novel compounds [25], [31], and [41] presented high toxicity against Solenopsis saevíssima with mortality rates of 85.00%, 100.00%, and 96.67% respectively. While amide [24] presented a moderate activity of 53.33%. Comparing the amides with conjugated double bonds with the amides that don't have these unsaturations, it was observed that as for the Diaphania hyalinata insect species, as for the Solenopsis saevíssima, these structural differences has not affected the compounds toxicity.