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There is an urgent need to replace highly polluting pesticides with environmentally friendly green pesticides of high efficiency and low toxicity, because of the growing concern for quality and safety of agricultural products. To discover new pesticides with diverse chemical structures from natural products, a series of rhein derivatives 3a-9b were designed, synthesized, and evaluated for their antifungal activity and insecticidal activity. The bioassay showed that some compounds exhibited moderate antifungal activity against Rhizoctonia solani, but lower activity against the other five pathogens. Surprisingly, most compounds displayed potent insecticidal activity against Spodoptera litura and Tetranychus cinnabarinus at a concentration of 2 μmol/mL. In particular, compounds 3a, 5a and 3 b exhibited potent insecticidal activities against S. litura at 72 h, with mortality rates of 100%, 100% and 92.1%, respectively, which were equivalent to that of the insecticide fipronil (100%). Their structure-activity relationships were also discussed. The findings of this experiment provide helpful research ideas for the development of these rhein derivatives as novel natural product-based pesticides in crop protection. [ABSTRACT FROM AUTHOR]

To develop new phenazine carboxylic acid derivatives with better phloem mobility, five novel 7-amino acid substituted phenazine-1-carboxylic acids were synthesised by introducing amino acids into PCA at the 7-position. The phloem mobility experiments in Ricinus communis seedlings showed that retaining the carboxyl group of PCA and conjugating amino acids to its phenazine ring can also endow PCA with phloem mobility. Comparing our previous research, we found the amino acids substituted at 7-position on phenazine ring of PCA could clearly enhance the phloem mobility of PCA than that of amino acids conjugated with carboxyl group. Especially, the phloem transport concentration of the compound 7-L-isoleucine substituted PCA (7d) was 21 times higher than PCA-L-isoleucine conjugate (8d). These data suggest that the introduction of amino acids at different structural sites on the phenazine ring could effectively enhance the phloem mobility of PCA and it is worth a further study. [ABSTRACT FROM AUTHOR]

A series of novel hydrocarbylidene nitrohydrazinecarboximidamides were designed and synthesized using an insecticidal natural product Galegine as a lead compound. The bioassay results show that the target compounds exhibited moderate to good insecticidal activities against Hyalopterus pruni Geoffroy at a concentration of 200 mg/L, and most compounds show excellet insecticidal activities against Aphis gossypii Glover. In particular, compounds IIc-01, IIc-03, IIe-02 and IIf-01 show the equal activities to a commercial pesticide Imidacloprid with their LC50 values are 0.21 mg/L, 0.27 mg/L, 0.12 mg/L and 0.24 mg/L, respectively, and compounds IIc-02 and IIe-05 show 10 times insecticidal activities as much as Imidacloprid with their LC50 values both are 0.02 mg/L. Structure–activity relationship and 3D-QSAR analyses indicate that the introduction of fluorine atom is useful for increasing the insecticidal activity of target compounds. [ABSTRACT FROM AUTHOR]

Phenazine-1-carboxylic acid (PCA) as a natural product which has significant inhibition effects against many soil-borne fungal phytopathogens in agricultural application and has been registered in China as the fungicide against rice sheath blight. In order to find new higher fungicidal activities lead compounds and develop new eco-friendly agrochemicals, we introduced substructure piperazines which also have high biological activity into PCA, designed and synthesized a series of phenazine-1-carboxylic piperazine derivatives, and their structures were confirmed by 1H NMR and HRMS. Most compounds exhibited certain in vitro fungicidal activities. In particular, Compounds 5r exhibited the activity against all the tested pathogenic fungi, such as Rhizoctonia solani, Alternaria solani, Fusarium oxysporum, Fusarium graminearum, Pyricularia oryzac Cavgra, with the EC50 value of 24.6μM, 42.9μM, 73.7μM, 73.8μM, 34.2μM, respectively, more potent activities than PCA (33.2μM, 81.5μM, 186.5μM, 176.4μM, 37.3μM). This result provided a highly active lead compound for the further structure optimization design. [ABSTRACT FROM AUTHOR]

Taking natural product phenazine-1-carboxamide (PCN) as a lead compound, a series of novel phenazine-1-carboxylic acid diamide derivatives were designed and synthesised. Their structures were confirmed by 1H-NMR and HRMS. The bioassays showed that some of the target compounds exhibited promising in vitro fungicidal activities, and exhibited excellent and selective herbicidal activities. Particularly, compounds c, h, o and s displayed root length inhibition activities against barnyard grass with the rate of more than 80%. Compound c exhibited the best activity among all the target compounds against barnyard grass stalk length with the IC50 value of 0.158 mmol/L, and compound o exhibited the best and wide spectrum inhibition against barnyard grass root length and rape in both root length and stalk length herbicidal activities with its IC50 values of 0.067, 0.048 and 0.059 mmol/L respectively. The analysis of preliminary Structure-Activity Relationships provides the theoretical basis for further design of phenazine-1-carboxylic acid. [ABSTRACT FROM AUTHOR]

Rubrolides are natural butyrolactones isolated from the tunicate Ritterella rubra , shows antibacterial, antiviral and plant photosynthesis inhibitory activities. In this study, a facile total synthetic method for preparing the rubrolides from benzaldehyde by a Darzens reaction, aldol reaction and vinylogous aldol condensation in five steps is presented. Three natural rubrolides (E, C and F) were synthesised in the total yields of 25-40%. The bioassay results indicate that rubrolides E, C and F exhibit some herbicidal inhibitory effect against rapeseed, in particular, rubrolide F shows the best herbicidal activities against rapeseed root with the growth inhibitory rate of 72.8%. At greenhouse treatment concentrations of 100 and 500 mg/L, rubrolide F show a positive dose-toxicity correlation towards abutilon plants. Collectively, facile total Synthesis strategy provided the base for further bioactivities study of rubrolides family. Rubrolide F may be act as inhibitor of photosynthesis, and this could be lead structure of new herbicide.