Cross-Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes.

Alkynes are among the most fundamentally important organic compounds and are widely used in synthetic chemistry, biochemistry, and materials science. Thus, the development of an efficient and sustainable method for the preparation of alkynes has been a central concern in organic synthesis. Cross-dehydrogenative coupling utilizing E-H and Z-H bonds in two different molecules can avoid the need for prefunctionalization of starting materials and has become one of the most straightforward methods for the construction of E-Z chemical bonds. This Review summarizes recent progress in the preparation of internal alkynes by cross-dehydrogenative coupling with terminal alkynes.

Catalytic sp3C-CN Bond Cleavage: Ni-Mediated Phosphorylation of Alkylnitriles.

A direct phosphorylation of the sp3C-CN bond catalyzed by a nickel catalyst is disclosed. A wide range of primary nitriles readily coupled with secondary phosphine oxides to produce the corresponding phosphorylated products in high yields. As a key step, this new method was applied to the synthesis of anticancer drug Combretastatin-A4, significantly shortening its synthetic path.

Direct C-OH/P(O)-H dehydration coupling forming phosphine oxides.

A t-BuONa-mediated C-OH/P(O)-H cross dehydration coupling to produce alkylphosphine oxides is developed. This reaction employed readily available alcohols and P(O)-H compounds as the starting materials, providing an efficient alternative method for constructing sp3 C-P bonds. A reasonable reaction path involving dehydration and subsequent regio-selective hydrophosphorylation of the resulting alkenes was proposed.

Transition-Metal-Catalyzed Three-Component Difunctionalizations of Alkenes.

Three-component reactions can directly convert three reactants into the desired products in one pot and thus greatly shorten the synthetic path. Recently, transition-metal catalysis has been applied in the difunctionalization of alkenes and remarkable progress has been achieved to facilitate the construction of a wide range of functional molecules with high atom- and step-economic efficiency. This Focus Review highlights recent advances in this field.

Efficient and selective hydrogenation of C-O bonds with a simple sodium formate catalyzed by nickel.

A Ni-catalyzed hydrogenation of C-O compounds with sodium formate is developed. Various esters, i.e. aryl, alkenyl, benzyl pivalates, and even the aryl ethers, were efficiently reduced with a loading of nickel catalysts down to 0.5 mol%. Reactive functional groups such as C-C double bonds, carbonyl, CN, MeS and halogen groups are tolerable. This reaction can be used for the modification of complex molecules and carried out at a large scale.

Silver-Free Direct Synthesis of Alkynylphosphine Oxides via spC-H/P(O)-H Dehydrogenative Coupling Catalyzed by Palladium.

A silver-free palladium-catalyzed dehydrogenative phosphorylation of terminal alkynes with hydrogen phosphine oxides has been developed. Both aromatic and aliphatic terminal alkynes including those bearing functional groups coupled readily with hydrogen phosphine oxides, producing the corresponding value-added alkynylphosphine oxides in good to excellent yields. This reaction could be easily conducted at gram scales (10 mmol) without any decrease of the reaction efficiency, showing highly potential synthetic value in organic synthesis. A plausible Pd(0)/Pd(II) mechanism is proposed.

t-BuOK-mediated reductive addition of P(O)-H compounds to terminal alkynes forming ß-arylphosphine oxides.

A novel and efficient t-BuOK-mediated reductive addition of P(O)-H compounds to terminal alkynes was developed. A variety of ß-arylphosphine oxides including the valuable ß-heteroarylphosphine oxides were produced in moderate to high yields under mild reaction conditions. This reaction may proceed via a tandem process involving regio-selective double addition and subsequent transfer hydrogenation.

Dehydrogenative coupling involving P(O)-H bonds: a powerful way for the preparation of phosphoryl compounds.

Because of the unique properties and wide applications, continuing efforts have been devoted to developing simpler and cleaner methods for the synthesis of organophosphorus compounds. Recently, transition metal-catalysed dehydrogenative coupling has been emerging as one of the powerful methodologies for constructing chemical bonds. Herein, we highlight the recent progress in the preparation of organophosphorus compounds via transition metal-catalysed dehydrogenative couplings of P(O)H compounds with Z-H compounds.

Nickel-catalysed P-C bond formation via P-H/C-CN cross coupling reactions.

Nickel-catalysed P-H/C-CN cross coupling reactions take place efficiently under mild reaction conditions affording the corresponding sp(2)C-P bonds. This transformation provides a convenient method for the preparation of arylphosphines and arylphosphine oxides from the readily available P-H compounds and arylnitriles.

Biological activity of the tzs gene of nopaline Agrobacterium tumefaciens GV3101 in plant regeneration and genetic transformation.

Agrobacterium tumefaciens has been widely used in plant genetic transformation. Hormone-encoding genes residing in the T-DNA region have been removed, resulting in disarmed Agrobacterium strains that are used in various transformation experiments. Nopaline Agrobacterium strains, however, carry another hormone gene, trans-zeatin synthesizing (tzs), that codes for trans-zeatin in the virulence region of the tumor-inducing plasmids. We investigated the activity and function of the tzs gene of a nopaline Agrobacterium sp. strain GV3101 in plant in vitro regeneration. Leaf explants of tobacco and Nicotiana benthamiana co-cultured with strain GV3101 exhibited active shoot regeneration in media without added plant growth regulators. On medium without plant growth regulators, transgenic shoots were also induced from explants co-cultured with GV3101 containing a binary vector. Enzyme-linked immunosorbent assay showed that cell-free extracts of Agrobacterium sp. strain GV3101 culture contained the trans-zeatin at 860 ng/liter. Polymerase chain reaction using tzs-specific primers showed that the tzs gene was present in strain GV3101 but not in other Agrobacterium strains. The study showed that the tzs gene in GV3101 was actively expressed, and that trans-zeatin produced in the Agrobacterium strain can promote plant shoot regeneration.

Metschnikowia sinensis sp. nov., Metschnikowia zizyphicola sp. nov. and Metschnikowia shanxiensis sp. nov., novel yeast species from jujube fruit.

Eight yeast strains were isolated from jujube fruit surfaces collected in Shanxi and Shandong Provinces, China. All eight strains produced needle-shaped ascospores under suitable conditions. Three separate groups, representing three novel species in the genus Metschnikowia, were recognized by sequence comparisons of the 26S rDNA D1/D2 domain and internal transcribed spacer (ITS) region. The names Metschnikowia sinensis sp. nov. (type strain XY103(T)=AS 2.3110(T)=CBS 10357(T)), Metschnikowia zizyphicola sp. nov. (type strain XY201(T)=AS 2.3111(T)=CBS 10358(T)) and Metschnikowia shanxiensis sp. nov. (type strain XY801(T)=AS 2.3112(T)=CBS 10359(T)) are proposed for the three novel species. Phylogenetic analysis of the 26S rDNA D1/D2 domain sequence showed that these three novel species are clustered in a clade together with the previously described species Metschnikowia fructicola, Metschnikowia andauensis, Metschnikowia pulcherrima and Metschnikowia chrysoperlae.

Identification of AtENT3 as the main transporter for uridine uptake in Arabidopsis roots.

Previous studies have shown that Arabidopsis equilibrative nucleoside transporters (AtENTs) possess transport activities when produced in yeast cells and are differentially expressed in Arabidopsis organs. Herein, we report further analysis on the nucleoside transport activities and transcriptional patterns of AtENT members. The recombinant proteins of AtENTs 3, 6, and 7, but not those of AtENTs 1, 2, 4, and 8, were found to transport thymidine with high affinity. Contrary to previous suggestion that AtENT1 may not transport uridine, this work showed that recombinant AtENT1 was a pH-dependent and high-affinity transporter of uridine. When grown on MS plates, the AtENT3 knockout plants were more tolerant to the cytotoxic uridine analog 5-fluorouridine than wild-type plants and the knockout plants of AtENT1 or AtENT6. Consistent with this observation, the AtENT3 knockout line exhibited a significantly decreased ability to take up [(3)H]uridine via the roots when compared with wild-type plants and the plants with mutated AtENT1 or AtENT6. This indicates that AtENT3, but not AtENTs 1 and 6, is the main transporter for uridine uptake in Arabidopsis roots. The transcription of AtENTs 1, 3, 4, 6, 7, and 8 was regulated in a complex manner during leaf development and senescence. In contrast, the six AtENT members were coordinately induced during seed germination. This work provides new information on the transport properties of recombinant AtENT proteins and new clues for future studies of the in vivo transport activities and physiological functions of the different ENT proteins in Arabidopsis plants.

Screening of a RAPD marker tightly linked to Co gene in apple and the SCAR marker conversion.

A DNA marker linked to the columnar gene (Co) in apple (Malus domestica) was explored based on the population of 105 progenies of 'Spur Fuji' x 'Telamon' by bulk segregant analysis (BSA) and Random Amplified Polymorphic DNA (RAPD) technique. A total of 300 random primers were screened and a RAPD marker (S1142(682)) closely linked to Co gene (2.86 cM) was identified and then sequenced. Four specific PCR primers (two forward primers and two reverse primers) were designed,and the products of SCAR-PCR indicated that all the four pairs of primers could amplify polymorphic bands between columnar and non-columnar traits, so any of them could serve as the specific SCAR primers. One pair of these specific primers was chosen to amplify each individual in the population, and the result showed that the co-segregation pattern of this SCAR marker and Co gene was the same as that of the RAPD marker. Furthermore, it was found that the nucleotide sequence of the RAPD marker fragment contained an open reading frame (ORF) that could encode 68 deduced amino acid residues at the position of +45 - +251.