Synthesis And Herbicidal Activity Of 2-substituted Benzothiazole Derivatives

Benzothiazole(BTA) and its derivatives bear a variety of biological activity and have been widely used in agriculture, medicinal chemistry and industry. Our laboratory occasionally synthesized a novel N, O-acetal compound: N-(methoxymethyl)-4-methyl-benzothiazol-2-amine, which exhibitedstrong herbicidal activity. To best understand the relationship between structure and activity, more2-substituted benzothiazole N,O-acetal analogues were synthesized and evaluated for their herbicidal activities. The results were as follows.1. Benzothiazol-2-amine derivatives(A01~A10,B01~B07, B09~B11) and Nalkoxyalkoxy benzothiazole derivatives(C01~C21, D01~D12) had been prepared by N, O acetalization or acylation and etherification of 2-amino-4-methyl-benzothiazole andthese compounds were a total of 53.Their structures were elucidated based on 1H-NMRand ESI-MS.2. The Seed germinationand shoot length inhibitory activityagainst Amaranthus retroflexus of all compounds were testedwith the plate method, as well as inhibition concentration(IC50) of highly active compounds. The results indicated that most Nmethoxymethyl-benzothiazol-2-amine derivatives(A series) exhibited good seed germination inhibitory activity. Compounds A02, A05, A06 and A08 exhibited stronggermination and growthinhibitory activityagainst A. retroflexus. The50% inhibition concentrationsof them were 22.465、28.499、22.428 and 22.397μg/m L, respectively.The compounds of N, N- bis methoxymethyl benzothiazol-2-amine(B series) and N- alkoxy-alkyl thiazole amide(C, D series) had no seed germination inhibitory activity against A. retroflexus.Some of them, such as B11,C01, C02 and D01 exhibited moderate growth inhibitory activity.3. The growth inhibitory activityof compounds against wheat was investigated bywheat without endosperm method. The results indicated thatmostcompounds in A seriesexhibited good growth inhibitory activity. The effect of compounds A05, A06 and A08 is more obvious and the wheat growth inhibition ratewith the concentration of 50μg/m L was 87.9%, 85.2% and 65.7%, respectively. B series compounds had no inhibitory activity.The inhibitory activity of the compounds in C and D series was very different, and the amide substituents and the group of N-methoxymethyl have a greater impact on the activity of compounds.When the amide substituents werealkyl, compounds had a good activity.The growth inhibition ratesof C01 and C04 against wheat with the concentration of 50μg/m L were 72.5% and 83.2%, respectively. However, when the amide substituents were aromatic ring or heterocyclic, compoundsdidn’t have inhibitory activity.The inhibitory activity of compounds in the D series was significantly reducedwith the lengthening of N-methoxymethyl alkyl chain. The inhibitory activity of compoundswere preferable when the substituent was ethyl(D01 or D04), and the activities were weak of compounds with pentyl as substituent(D09 or D10).4. The fresh weight inhibitory activity of compounds against Setaria viridis and A. retroflexus was investigated by sand cultivation method. The trend of inhibitory activity was similar to the result performed by wheat without endosperm method. Compounds A05, A06, A08, C01, C04 and D04 showed better inhibitory activity, wherein C04 with the obviously bleaching effect against S. viridis. The fresh weight inhibitory activity of compounds A05, A06, A08, C01, C04 and D04 were measured using the same method against a variety of weeds to identify the herbicidal spectrum. The inhibitory activities were strongagainst A. retroflexus, Chenopodium album, S.viridis, Poa annua and Digitaria sanguinalis, and weakagainst Brachypodium distachyon, Avena fatua, Secale cereal, Bromus japonicas and Echinochloa crus-galli. The compoundsdidn’t exhibit obvious selectivity to monocotyledonous plants and dicotyledonous plants. Except S. viridis, compound C04 didn’t exhibit bleaching effect against other weeds.