Neonicotinoid insecticides induce salicylate-associated plant defense responses.

Neonicotinoid insecticides control crop pests based on their action as agonists at the insect nicotinic acetylcholine receptor, which accepts chloropyridinyl- and chlorothiazolyl-analogs almost equally well. In some cases, these compounds have also been reported to enhance plant vigor and (a)biotic stress tolerance, independent of their insecticidal function. However, this mode of action has not been defined. Using Arabidopsis thaliana, we show that the neonicotinoid compounds, imidacloprid (IMI) and clothianidin (CLO), via their 6-chloropyridinyl-3-carboxylic acid and 2-chlorothiazolyl-5-carboxylic acid metabolites, respectively, induce salicylic acid (SA)-associated plant responses. SA is a phytohormone best known for its role in plant defense against pathogens and as an inducer of systemic acquired resistance; however, it can also modulate abiotic stress responses. These neonicotinoids effect a similar global transcriptional response to that of SA, including genes involved in (a)biotic stress response. Furthermore, similar to SA, IMI and CLO induce systemic acquired resistance, resulting in reduced growth of a powdery mildew pathogen. The action of CLO induces the endogenous synthesis of SA via the SA biosynthetic enzyme ICS1, with ICS1 required for CLO-induced accumulation of SA, expression of the SA marker PR1, and fully enhanced resistance to powdery mildew. In contrast, the action of IMI does not induce endogenous synthesis of SA. Instead, IMI is further bioactivated to 6-chloro-2-hydroxypyridinyl-3-carboxylic acid, which is shown here to be a potent inducer of PR1 and inhibitor of SA-sensitive enzymes. Thus, via different mechanisms, these chloropyridinyl- and chlorothiazolyl-neonicotinoids induce SA responses associated with enhanced stress tolerance.

S-Arachidonoyl-2-thioglycerol synthesis and use for fluorimetric and colorimetric assays of monoacylglycerol lipase.

We report the first synthesis of 2-thioglycerol and S-arachidonoyl-2-thioglycerol (the thioester analog of the endocannabinoid 2-arachidonoylglycerol) in an eight or nine step procedure with a yield of approximately 25% and establish the use of this substrate for maleimide-based fluorescent and dithiobis(2-nitrobenzoic acid)-based colorimetric assays of human recombinant monoacylglycerol (MAG) lipase (hMAGL) and human brain membrane MAG hydrolase activity. Inhibitor structure-activity relationships observed here for hMAGL and 2-ATG correlate well (r(2)=0.93, n=9) with earlier findings for mouse brain MAG hydrolase with non-thiol substrates.

Pt-catalyzed cyclization/migration of propargylic alcohols for the synthesis of 3(2H)-furanones, pyrrolones, indolizines, and indolizinones.

Several heterocycles such as furanones, pyrrolones, and indolizines, which are of pharmacological importance, are easily accessed via the Pt(II)-catalyzed heterocyclization/1,2-migration of propargylic ketols or hydroxy imine derivatives. This method sidesteps the challenges of traditional heteroaromatic oxygenation strategies such as regioselectivity and functional group tolerance in the syntheses of these heterocycles.

Pt(II)-catalyzed synthesis of 1,2-dihydropyridines from aziridinyl propargylic esters.

Pt(II)-catalyzed cycloisomerization of aziridinyl propargylic esters affords 1,2-dihydropyridines with regiodefined installation of substituents. A mild conversion of the 1,2-dihydropyridines to the corresponding substituted pyridines as well as chirality retention from the aziridinyl propargylic ester substrates have been demonstrated.

Pt-catalyzed cyclization/1,2-migration for the synthesis of indolizines, pyrrolones, and indolizinones.

Indolizine, pyrrolone, and indolizinone heterocycles are easily accessed via the Pt(II)-catalyzed cycloisomerization or a tandem cyclization/1,2-migration of pyridine propargylic alcohols and derivatives. This method provides an efficient synthesis of highly functionalized heterocycles from readily available substrates. [reaction: see text]