A convenient method for the oxidation of nucleoside phosphites to phosphates

Bis(trimethyl) peroxide serves as an excellent agent for oxidation of nucleoside phosphites to the phosphates. The reaction is conspicuously accelerated by added trimethylsilyl triflate or Nafion-TMS.     

Chiral phosphites derived from carboranes: electronic effect in catalytic asymmetric hydrogenation

A series of new fine-tunable monodentate phosphite and phosphoramidite ligands based on carboranes have been synthesized and used for asymmetric Rh-catalyzed hydrogenation of prochiral olefins with the result of up to 99.8% ee. Dependence of the enantioselectivity on the electron-withdrawing or electron-donating properties of the carboranyl substituent has been studied.     

Simple and rapid procedure for synthesis of deoxynucleoside 3'-2-cyanoethyl-N,N-diisopropyl-amino phosphites

2-Cyanoethyl-bis/N,N-diisopropyl/phosphoamidite can be prepared from PCl3 by a very fast and efficient procedure. Without purification it was used for the phosphitilation of suitably protected deoxynucleosides which after simple purification are obtained with a high yield, in a stable and easy to manage form.     

Potassium phosphites in the protection of common bean plants against anthracnose and biochemical defence responses

The aim of this study was to investigate the effectiveness of potassium phosphites for the control of anthracnose and the mode of action of these products on common bean plants against Colletotrichum lindemuthianum, comparing it with the standard resistance inducer acibenzolar‐S‐methyl. The protection of plants against anthracnose was evaluated in greenhouse after treatment with potassium phosphites (Phosphite A and B, 5.0 ml/L), acibenzolar‐S‐methyl (0.25 g/L), or no treatment (control). Two sprayings of the treatments were performed, respectively, at V4 stage (three trifoliate leaves) and at the R5 stage (flower buds present). The inoculation with C. lindemuthianum was performed 5 days after the first spraying. Phosphite formulations A and B reduced the severity of anthracnose by 68.7% and 55.6%, respectively, and the presence of phosphites in the leaf tissues were detected at concentrations between 1 and 3 mm by 7 days after spraying. These same concentrations of phosphites reduced the mycelial growth of C. lindemuthianum in vitro by 15.0% to 25.7%. In addition, the activities of defence enzymes and the levels of phenolic compounds and lignin were assessed. Phosphite treatments enhanced the activity of various enzymes, including superoxide dismutase, peroxidase, chitinase, and β‐1,3‐glucanase, and increased the lignin and a small increase in the levels of soluble phenolics. This study provides evidence that phosphite treatments control anthracnose by acting directly on C. lindemuthianum and by inducing the production of defence responses.     

Reinvestigation of deoxyribonucleoside phosphorothioites: synthesis and properties of deoxyribonucleoside-3'' dimethyl phosphites.

Further investigation of the synthesis of deoxyribonucleoside-3' (t-butyl) O-(2-cyanoethyl) phosphorothioites as monomer building units for the phosphorothioite approach has led us to conclude that internucleotidic bond formation proceeded via bis(deoxyribonucleoside-3') (2-cyanoethyl) phosphite intermediates, which proved to be activated by iodine, rather than the mechanism previously reported. In connection with this study, deoxyribonucleoside-3' dimethyl phosphites were synthesized and detailed properties of them are also described.     

Environmentally benign beta-stereoselective glycosidations of glycosyl phosphites using a reusable heterogeneous solid acid, montmorillonite K-10

Environmentally benign and stereoselective beta-glycosidations of glycopyranosyl phosphites and alcohols using a reusable heterogeneous solid acid, montmorillonite K-10, as an activator have been developed. By these glycosidations, beta-gluco-, 2-deoxy-beta-gluco-, and beta-mannopyranosides were selectively produced in good to high yields.     

Synthesis of phosphites and phosphates of neuraminic acid and their glycosyl donor properties — convenient synthesis of GM3

The importance and requirements for catalytic activation of sialyl donors are discussed, leading to the acid sensitive phosphite and phosphate moiety, respectively, as leaving group and nitriles as solvent. Therefore, from readily availableN-acetylneuraminic acid, derivative1 with phosphochloridites2a-f and Huenigs' base sialyl phosphites3a-f were prepared and isolated in high yields. Oxidation of3a, c withtert-butyl-hydroperoxide afforded the corresponding phosphates4a, c. As expected, phosphites3 could be activated in acetonitrile by catalytic amounts of TMSOTf; thus, from3a-e as donors and lactose derivatives8A, B as acceptors the ganglioside building blocks9A and9B, respectively, were obtained in good yields. The best results were obtained with diethyl phosphite derivative3a as sialyl donor, which exceeded by far the reults obtained with the corresponding phosphate derivative4a. Trisaccharide9B was transformed into known9A and into the fullyO-acetylated GM₃-trisaccharide10.     

A study of the donor properties of sialyl phosphites having an auxiliary 3-(S)-phenylseleno group

Two phosphite sialyl donors, each having an auxiliary 3-(S)-phenylseleno group, were prepared and evaluated. The phenylseleno group was introduced via a new mode of generating phenylselenenic acid ('PhSeOH'). Although the sialyl donors provided fair yields (32-76%) of the desired sialosides in glycosylations of the reactive acceptor 1,2;3,4-di-O-isopropylidene-alpha-D-galactopyranose, no sialylated products could be obtained with less reactive acceptors. The presence of a 5-N-acetylacetamido group on the phosphite sialyl donor did not appear to improve its sialylating capability. The weak C-Se bond, possibly in combination with a steric hindrance, which disfavors alpha-nitrilium ion formation, seem to explain the unsuccessful sialylations of the less reactive acceptors.     

Rapid glycosylations under extremely mild acidic conditions. Use of ammonium salts to activate glycosyl phosphites via P-protonation

Trifluoromethanesulfonic acid salts of tertiary amines were employed as extremely mild acidic activators for rapid glycosylations. Glycosyl phosphite triesters bearing an acid-labile 4,4′-dimethoxytrityl (DMTr) group for transient protection worked as glycosyl donors effectively in the presence of the activators to afford the corresponding disaccharides in good yields without loss of the DMTr group.     

Kinetics of nucleophilic attack on coordinated organic moieties Part 29. Mechanism of addition of tertiary phosphines and phosphites to the tropylium ring of [M(CO)3(η-C7H7] (M = Cr, Mo, W) cations

Kinetic studies of the addition of a wide range of tertiary phosphines and phosphites to the tropylium ring of the cation [Cr(CO)₃(η⁷-C₇H₇]⁺ (1) reveal the two-term raw, k_obs = k₁[PR₃] + k₋₁. This is consistent with the reversible equilibrium process (i) which is also confirmed from IR and ¹H NMR studies. In the case of the highly basic nucleophiles PBu₃ⁿ and PEt₂Ph, the rate is dominated by the k₁ term and the equilibrium lies far to the right.

Full-size image

The first-order rate constants k₁, for addition to the tropylium ring decrease markedly down the series PBu₃ⁿ>PEt₂Ph>P(4-MeOC₆H₄)₃>P(4-MeC₆H₄)₃>P(C₆H_{11 3}>PPh₂(4-MeC₆H₄)>PPh₃>P(2-CNC₂H₄)₃>P(OBuⁿ)₃ (overall variation 10⁴). This reactivity order parallels the decreasing electron availability at the phosphorus centres, as confirmed by the linear correlation between log k₁ and the Tolman Σ_χ values for the nucleophiles. Excellent Hammett and Brønsted correlations are also observed for ring addition by a range of P(4-XC₆H₄)₃ nucleophiles. The Brønsted slope, , of 0.7 conirms the major importance of basicity in determining nucleophilicity towards cation 1. Kinetic studies of the related additions of PBu₃ⁿ to the cations [M(CO)₃(η⁷-C₇H₇]⁺ (M = Mo, W) reveal the rate law, Rate = k₁[M][PBu₃ⁿ, and show only a small dependence of k₁ on the nature of metal (Cr>WMo; 2:1.1:1). These data, together with the associated activation parameters, support a mechanism involving direct addition (k₁) of the phosphorus nucleophiles to the tropylium ring, and are inconsistent with initial rate-determining attack at the metal centre.