Adaptation mechanism and tolerance of Rhodopseudomonas palustris PSB-S under pyrazosulfuron-ethyl stress.

BACKGROUND: Pyrazosulfuron-ethyl is a long lasting herbicide in the agro-ecosystem and its residue is toxic to crops and other non-target organisms. A better understanding of molecular basis in pyrazosulfuron-ethyl tolerant organisms will shed light on the adaptive mechanisms to this herbicide. RESULTS: Pyrazosulfuron-ethyl inhibited biomass production in Rhodopseudomonas palustris PSB-S, altered cell morphology, suppressed flagella formation, and reduced pigment biosynthesis through significant suppression of carotenoids biosynthesis. A total of 1127 protein spots were detected in the two-dimensional gel electrophoresis. Among them, 72 spots representing 56 different proteins were found to be differently expressed using MALDI-TOF/TOF-MS, including 26 up- and 30 down-regulated proteins in the pyrazosulfuron-ethyl-treated PSB-S cells. The up-regulated proteins were involved predominantly in oxidative stress or energy generation pathways, while most of the down-regulated proteins were involved in the biomass biosynthesis pathway. The protein expression profiles suggested that the elongation factor G, cell division protein FtsZ, and proteins associated with the ABC transporters were crucial for R. palustris PSB-S tolerance against pyrazosulfuron-ethyl. CONCLUSION: Up-regulated proteins, including elongation factor G, cell division FtsZ, ATP synthase, and superoxide dismutase, and down-regulated proteins, including ALS III and ABC transporters, as well as some unknown proteins might play roles in R. palustris PSB-S adaptation to pyrazosulfuron-ethyl induced stresses. Functional validations of these candidate proteins should help to develope transgenic crops resistant to pyrazosulfuron-ethyl.

Dinuclear zinc complex catalyzed asymmetric methylation and alkynylation of aromatic aldehydes.

A general AzePhenol dinuclear zinc catalytic system has been successfully developed and introduced into the asymmetric addition of dimethylzinc and alkynylzinc to aromatic aldehydes. In this system, an azetidine derived chiral ligand has proven to be an effective enantioselective promoter. Under the optimal reaction conditions, a series of chiral 1-hydroxyethyl (up to 99% ee) and secondary propargylic alcohols (up to 96% ee) were generated with good yields and enantioselectivities. Additionally, this novel catalytic system showed good functional group compatibility. Remarkably, the substituent's electronic nature alone is not sufficient to allow for exclusive enantioselectivity, an additional substituent's location also had an effect. We proposed that the formation of a stable and structural rigid transition state by the chelation of ortho substituted benzaldehydes to the zinc atom was responsible for the observed higher enantioselectivity. The possible catalytic cycles of both transformations accounting for the stereoselectivity were described accordingly.

Desilylation-Activated Propargylic Transformation: Enantioselective Copper-Catalyzed [3+2] Cycloaddition of Propargylic Esters with ß-Naphthol or Phenol Derivatives.

A copper-catalyzed asymmetric [3+2] cycloaddition of 3-trimethylsilylpropargylic esters with either ß-naphthols or electron-rich phenols has been realized and proceeds by a desilylation-activated process. Under the catalysis of Cu(OAc)2⋅H2O in combination with a structurally optimized ketimine P,N,N-ligand, a wide range of optically active 1,2-dihydronaphtho[2,1-b]furans or 2,3-dihydrobenzofurans were obtained in good yields and with high enantioselectivities (up to 96 % ee). This represents the first desilylation-activated catalytic asymmetric propargylic transformation.

Highly diastereo- and enantioselective copper-catalyzed propargylic alkylation of acyclic ketone enamines for the construction of two vicinal stereocenters.

The first highly diastereo- and enantioselective propargylic alkylation of acyclic ketone enamines to form vicinal tertiary stereocenters has been reported by employing copper catalysis in combination with a bulky and structurally rigid tridentate ketimine P,N,N-ligand.

Enantioselective synthesis of highly functionalized dihydrofurans through copper-catalyzed asymmetric formal [3+2] cycloaddition of ß-ketoesters with propargylic esters.

An enantioselective synthesis of highly functionalized dihydrofurans through a copper-catalyzed asymmetric [3+2] cycloaddition of ß-ketoesters with propargylic esters has been developed. With a combination of Cu(OTf)2 and a chiral tridentate P,N,N ligand as the catalyst, a variety of 2,3-dihydrofurans bearing an exocyclic double bond at the 2 position were obtained in good chemical yields and with good to high enantioselectivities. The exocyclic double bond can be hydrogenated in a highly diastereoselective fashion to give unusual cis-2,3-dihydrofuran derivatives, thus further enhancing the scope of this transformation.

Enantioselective copper-catalyzed decarboxylative propargylic alkylation of propargyl ß-ketoesters with a chiral ketimine P,N,N-ligand.

The first enantioselective copper-catalyzed decarboxylative propargylic alkylation has been developed. Treatment of propargyl ß-ketoesters with a catalyst, prepared in situ from [Cu(CH3 CN)4 BF4 ] and a newly developed chiral tridentate ketimine P,N,N-ligand under mild reaction conditions, generates ß-ethynyl ketones in good yields and with high enantioselectivities without requiring the pregeneration of ketone enolates. This new process provides facile access to a range of chiral ß-ethynyl ketones in a highly enantioenriched form.