Syngenta

About: Syngenta is a company organization based out in Basel, Switzerland. It is known for research contribution in the topics: Population & Gene. The organization has 4724 authors who have published 6036 publications receiving 164311 citations. The organization is also known as: Syngenta & Syngenta AG.

Mapping out the key carbon–carbon bond-forming steps in Mn-catalysed C–H functionalization

Abstract: Detailed understanding of the mechanistic processes that underpin transition metal-catalysed reactions allows for the rational and de novo development of complexes with enhanced activity, efficacy and wider substrate scope. Directly observing bond-cleaving and -forming events underpinning a catalytic reaction is non-trivial as the species that facilitate these steps are frequently short-lived and present at low concentrations. Here, we describe how the photochemical activation of a manganese precatalyst, [Mn(ppy)(CO)4] (ppy = 2-phenylpyridine), results in selective loss of a carbonyl ligand simulating entry into the catalytic cycle for manganese-promoted C–H bond functionalization. Time-resolved infrared spectroscopy (on the ps–ms timescale) allows direct observation of the species responsible for the essential C–C bond formation step and an evaluation of the factors affecting its rate. This mechanistic information prompted the discovery of a new photochemically initiated manganese-promoted coupling of phenylacetylene with 2-phenylpyridine. This study provides unique insight into the mechanistic pathways underpinning catalysis by an Earth-abundant metal, manganese. Although mechanistic understanding can drive new reactivity development, the key bond-forming and -breaking steps in catalytic cycles are often sufficiently fast to elude observation. Here, the authors photochemically produce a key intermediate in Mn-catalysed C–H functionalization, and follow the subsequent steps—spanning processes occurring over seven orders of magnitude in time—using time-resolved infrared spectroscopy.

Biphenyl derivatives and their use as fungicides

Abstract: A fungicidally active compound of formula (I): where Het is a substituted 5-or 6-membered heterocyclic ring; R1 is hydrogen, formyl, CO-C1-4 alkyl, COO-C1-4 alkyl, C1-4 alkoxy(C1-4)alkylene, CO-C1-4 alkylenoxy(C1-4)alkyl, propargyl or allenyl; R2, R3, R4 and R5 are each, independently, hydrogen, halogen, methyl or CF3; each R6 is, independently, halogen, methyl or CF3; R7 is (Z)mC=C(Y1), (Z)mC(Y1)=C(Y2)(Y3) or tri(C1-4)alkylsilyl; X is O or S; Y1, Y2 and Y3 are each, independently, hydrogen, halogen, C1-6 alkyl [optionally substituted by one or more substituents each independently selected from halogen, hydroxy, C1-4 alkoxy, C1-4 haloalkoxy, C1-4 alkylthio, C1-4 haloalkylthio, C1-4 alkylamino, di(C1-4)alkylamino, C1-4 alkoxycarbonyl, C1-4 alkylcarbonyloxy and tri(C1-4)alkylsilyl], C2-4 alkenyl [optionally substituted by one or more substituents each independently selected from halogen], C2-4 alkynyl [optionally substituted by one or more substituents each independently selected from halogen], C3-7 cycloalkyl [optionally substituted by one or more substituents each independently selected from halogen, C1-4 alkyl and C1-4 haloalkyl] or tri(C1~4)alkylsilyl; Z is C1-4 alkylene [optionally substituted by one or more substituents each independently selected from hydroxy, cyano, C1-4 alkoxy, halogen, C1-4 haloalkyl, C1-4 haloalkoxy, C1-4 alkylthio, COOH and COO-C1-4 alkyl]; m is 0 or 1; and n is 0, 1 or 2; the invention also relates to novel intermediates used in the preparation of these compounds, to agrochemical compositions which comprise at least one of the novel compounds as active ingredient and to the use of the active ingredients or compositions in agriculture or horticulture for controlling or preventing infestation of plants by phytopathogenic microorganisms, preferably fungi.

The expression of a maize glutathione S-transferase gene in transgenic wheat confers herbicide tolerance, both in planta and in vitro

Abstract: Maize (Zea mays), in common with a number of other important crop species, has several glutathione S-transferase (GST) isoforms that have been implicated in the detoxification of xenobiotics via glutathione conjugation. A cDNA encoding the maize GST subunit GST-27, under the control of a strong constitutive promoter, was introduced into explants of the wheat (Triticum aestivum L.) lines cv. Florida and L88-31 via particle bombardment, using the phosphinothricin acetyltransferase (pat) gene as a selectable marker. All six independent transgenic wheat lines recovered expressed the GST-27 gene. T1 progeny of these wheat lines were germinated on solid medium containing the chloroacetanilide herbicide alachlor, and tolerance to this herbicide was correlated with GST-27 expression levels. In glasshouse sprays, homozygous T2 plants were resistant not only to alachlor but also to the chloroacetanilide herbicide dimethenamid and the thiocarbamate herbicide EPTC. These additional GST-27 activities, demonstrated via over-expression in a heterologous host, have not been described previously. T2 plants showed no enhanced tolerance to the herbicides atrazine (an s-triazine) or oxyfluorfen (a diphenyl ether). In further experiments, T2 wheat plants were recovered from immature transgenic scutella cultured on medium containing 100 mg/l alachlor, a concentration which killed null segregant and wild-type scutella. These data indicate the potential of the maize GST-27 gene as a selectable marker in wheat transformation.

Arbuscular mycorrhiza in mini‐mycorrhizotrons: first contact of Medicago truncatula roots with Glomus intraradices induces chalcone synthase

Abstract: Summary • The association of plants with arbuscular mycorrhizal (AM) fungi is widespread in nature, but little is known about molecular aspects of this symbiosis. Particularly during the early stages of the AM symbiosis, it is difficult to monitor growth of the two partners, to dissect gene expression patterns and to correlate them with plant, fungal or symbiosis development. • A new system, the ‘mini-mycorrhizotron’, was established to cultivate seedlings of Medicago truncatula in mycorrhizal symbiosis with Glomus intraradices under gnotobiotic conditions. This system allows natural growth of the symbiotic partners and permits the continuous noninvasive observation of the development of plant and fungus under a microscope. • The mini-mycorrhizotron was used to determine the stage of induction of a mycorrhiza-related gene detected by differential display-reverse transcription-PCR, namely a novel chalcone synthase (Mt-chs1). The gene is induced in roots at the stage of the first fungal contact. • The mini-mycorrhizotron allowed identification and cloning of a symbiosis-related gene, and the correlation between its expression and the developmental stage of the symbiosis was established. This provides a useful tool for molecular and developmental studies of the early stages of AM symbioses. Mt-chs1 nucleotide sequence can be found at the Genbank data base (accession no. AJ277211). The following sequences were also used: Glycine maxchs (X52097), chs1 (X54644); chs2 (X65635), chs3 (X53958), chs5 (L07647), chs6 (L03352), chs7 (M98871); Pisum sativumchs (X80007), chs1 (D10661), chs2 (X63334), chs3 (D88261), chs4 (D88260), chs5 (D88262), chs7 (D88263); Medicago sativachs1 (L02901), chsI (X68106), chs2 (L02902), chs4–1 (U01018), chs8 (L02904), chs9 (L02905), 12–1 (U01021); Medicago truncatulachs1, this work (AJ277211); Trifolium subterraneumchs1 (M91193), chs2 (M91194), chs3 (L24515), chs4 (L24516), chs5 (L24517), chs6 (M91195); Phaseolus vulgarischs (X06411) and Vigna unguiculatachs (X74821).