Han-Xun Wei

Bacterial volatiles promote growth in Arabidopsis

Several chemical changes in soil are associated with plant growth-promoting rhizobacteria (PGPR). Some bacterial strains directly regulate plant physiology by mimicking synthesis of plant hormones, whereas others increase mineral and nitrogen availability in the soil as a way to augment growth. Identification of bacterial chemical messengers that trigger growth promotion has been limited in part by the understanding of how plants respond to external stimuli. With an increasing appreciation of how volatile organic compounds signal plants and serve in plant defense, investigations into the role of volatile components in plant–bacterial systems now can follow. Here, we present chemical and plant-growth data showing that some PGPR release a blend of volatile components that promote growth of Arabidopsis thaliana. In particular, the volatile components 2,3-butanediol and acetoin were released exclusively from two bacterial strains that trigger the greatest level of growth promotion. Furthermore, pharmacological applications of 2,3-butanediol enhanced plant growth whereas bacterial mutants blocked in 2,3-butanediol and acetoin synthesis were devoid in this growth-promotion capacity. The demonstration that PGPR strains release different volatile blends and that plant growth is stimulated by differences in these volatile blends establishes an additional function for volatile organic compounds as signaling molecules mediating plant–microbe interactions.

A Novel Electrophilic Diamination Reaction of Alkenes

A three-component electrophilic reaction transforms olefins into imidazoline and diamine derivatives. Rhodium(II) heptafluorobutyrate dimer (2 mol %) was utilized as the catalyst and N,N-dichloro-p-toluenesulfonamide (TsNCl2 ) and acetonitrile as the nitrogen sources. Modest to good yields (45-82 %) and high regio- and stereoselectivity were achieved.

A Plasma Membrane Protein from Zea mays Binds with the Herbivore Elicitor Volicitin

Volicitin (17-hydroxylinolenoyl-l-Gln) present in the regurgitant of Spodoptera exigua (beet armyworm caterpillars) activates the emission of volatile organic compounds (VOCs) when in contact with damaged Zea mays cv Delprim (maize) leaves. VOC emissions in turn serve as a signaling defense for the plant by attracting female parasitic wasps that prey on herbivore larvae. A tritiated form of volicitin was synthesized and shown to induce volatiles in the same fashion as the biological form. [3H]-l-volicitin rapidly, reversibly, and saturably bound to enriched plasma membrane fractions isolated from Z. mays leaves with an apparent Kd of 1.3 nM and a Hill coefficient of 1.07. Analog studies showed that the l-Gln and hydroxy moieties of volicitin play an important role in binding. Treatment of plants with methyl jasmonate (MeJA) increased the total binding of [3H]-l-volicitin to the enriched plasma membrane more than threefold, suggesting that MeJA activates transcription of the gene encoding the binding protein. S. exigua feeding also increased total binding fourfold. Cycloheximide pretreatment of plants significantly decreased binding of radiolabeled volicitin to the enriched plasma membrane. These data provide the first experimental evidence that initiation of plant defenses in response to herbivore damage can be mediated by a binding protein–ligand interaction.

TiCl4-Mediated Baylis–Hillman and aldol reactions without the direct use of a Lewis base

TiCl4-Mediated Baylis–Hillman and aldol reactions were developed without the direct use of a Lewis base. These processes involve the conjugate addition of TiCl4 to α,β-unsaturated substrates followed by carbonyl coupling. Baylis–Hillman olefins were obtained when α,β-unsaturated ketones were employed as the substrates, whereas β-halogenated aldol products were generated with an α,β-unsaturated N-acyl benzoxalinone as the Michael-type acceptor.

The first transition metal–ligand complex-catalyzed regioselective and stereoselective aminohalogenation of cinnamic esters

Abstract Transition metal–ligand complex-catalyzed regio- and stereoselective aminohalogenation of cinnamic esters has been developed using p-TsNCl2 as the nitrogen and chlorine sources. Dichloro-(1,10-phenanthroline)-palladium (II) as the catalyst can be handled very conveniently due to its property of less hygroscopic as compared with other aminohalogenation catalysts. The reaction is suggested to proceed through the mechanism involving N-tosyl N-chloro aziridinium intermediate. Eight examples are presented with modest to good yields (56–82%) and excellent stereoselectivity (>10:1).

Unexpected copper-catalyzed aminohalogenation reaction of olefins using N-halo-N-metallo-sulfonamide as the nitrogen and halogen sources

N-Chloro-N-sodium-sulfonamide was found to react with olefins in the presence of copper catalyst to give vicinal haloamine derivatives instead of aziridines. The resulting regio and stereochemistry indicates that this unexpected reaction could proceed through the formation of unprecedented N-chloro-N-copper-2-nitrobenzenesulfonyl aziridinium intermediates, which can increase the successful chance to render the asymmetric version of the aminohalogenation reaction. In addition, this finding provides a more convenient protocol by the use of solely pure NsNClNa for the aminohalogenation reaction as compared to the mixed nitrogen and chlorine sources consisting of NsNCl2 and NsNHNa as previously reported by us. Two new simple olefin substrates, trans-stilbene and styrene, were also found to be effective for this new reaction system.

Highly Stereoselective α-Hydroxyalkylation/Chlorination of α,β-Acetylenic Ketones—An Efficient Approach to β-Halogeno Baylis–Hillman Adducts

Abstract A highly stereoselective method for the synthesis of (E)-β-halogeno Baylis–Hillman adducts has been developed. The new method involves a tandem α-hydroxyalkylation/β-chlorination of α,β-acetylenic ketones by using TiCl4 as the chlorine source for α,β-conjugate addition, and concurrently as the Lewis acid promoter for the carbonyl addition. The new system tolerates a broad scope of reactants in which aliphatic and aromatic α-acetylenic ketones can be subjected to the conjugate addition. Both aliphatic and aromatic aldehydes can also be employed as electrophilic acceptors. Good yields (61–88%) and high E/Z stereoselectivity have been obtained for the nine examples which were examined, only in one case was E/Z selectivity of 17/1 observed and the two individual isomers are separable via flash column chromatography.

α,β-Differentiated tandem diamination of cinnamic esters using N,N-dichloro-2-nitrobenzenesulfonamide and acetonitrile as the nitrogen sources

Tandem diamination of cinnamic esters provides a new approach to anti alkyl Nα-(2-Ns), Nβ-Ac diaminophenylpropionates. The new reaction proceeds to completion within 3 hours at room temperature using N,N-dichloro-2-nitrobenzenesulfonamide (2-NsNCl2) as the nitrogen source in acetonitrile, which is also involved in the reaction process. Seven diamine derivatives have been obtained with good yields and stereoselectivity.

A new stereospecific synthesis of unusual (Z)-β-branched Baylis-Hillman adducts

Abstract A new method has been developed for the stereospecific synthesis of unusual ( Z )- β -branched Baylis-Hillman adducts with high Z E selectivity (>99 %) in modest to good yields. The process involves successful formation of anionic β-substituted [α-(alkoxycarbonyl)vinyl]aluminum intermediates and their coupling with aldehydes and ketones catalyzed by n -Bu 2 BOTf at −78 °C.

New catalytic diamination of alkenes provides a novel access to 1-p-toluenesulfonyl-3-trichloromethyl-4,5-imidazolines

Non-oxidative catalytic diamination reaction of α,β-unsaturated esters and ketones with N,N-dichloro-p-toluenesulfonamide and acetonitrile has been established for the synthesis of 1-p-toluenesulfonyl-3-trichloromethyl-4,5-imidazoline derivatives. Rhodium(II) acetate dimer was found to be superior to rhodium(II) heptafluorobutyrate as the catalyst for this reaction which was carried out at 55°C. Six examples were examined with chemical yields of 57–77%.