Synthesis of nonracemic allylic hydroxy phosphonates via alkene cross metathesis

Allylic hydroxy phosphonates and their derivatives can be interconverted by using cross metathesis with second generation Grubbs catalyst. The absolute stereochemistry of the starting phosphonate is conserved in the product. Cross metathesis reaction of the acrolein-derived phosphonate 2a yields a series of functionalized allylic hydroxy phosphonates. However, the cross metathesis reaction is often accompanied by competing dimerization and alkene migration reactions leading to a reduction in yield. The cinnamaldehyde- and crotonaldehyde-derived phosphonates 2b and 2c were also examined. In general, the metathesis reactions of phosphonates 2b and 2c are considerably slower than those for phosphonate 2a leading to mixtures. Several hydroxyl-protected derivatives of the phosphonate 2a (methyl carbonate 3a, acetate 4a, N-tosyl carbamate 5a, TBDMS 6a, and acetoacetate 7a) undergo metathesis without competing side reactions to give substituted allylic phosphonates in good to excellent yield.     

Isobaric analogue resonances in proton elastic scattering from 84Sr

The cross section for the reaction ⁸⁴Sr(p, p₀)⁸⁴Sr has been measured for proton energies in the range E_p = 4.18?6.73 MeV. Resonance parameters were determined for 15 isobaric analogue resonances. Spectroscopic factors calculated for the analogues by means of the R-matrix theory and the Green function method are compared with Spectroscopic factors determined from the ⁸⁴Sr(d, p)⁸⁵Sr reaction. Angular distributions were measured at E_p = 7 and 12 MeV in order to obtain optical model parameters.     

Effect of ligand structure on the pathways for iron release from human serum transferrin

Rate constants for the removal of iron from N-terminal monoferric transferrin have been measured for a series of phosphate and phosphonocarboxylic acids in pH 7.4 0.1 M hepes buffer at 25 degrees C. The bidentate ligands pyrophosphate and phosphonoacetic acid (PAA) show a combination of saturation and first-order kinetics with respect to the ligand concentration. Similar results are observed following a single substitution at the 2-position of PAA to give 2-benzyl-PAA and phosphonosuccinic acid. In contrast, disubstitution at the 2-position to form 2,2-dibenzyl-PAA leads to a marked reduction in iron removal via the first-order pathway. Rate constants were also measured for tripolyphosphate and phosphonodiacetic acid, which are elongated versions of PP(i) and PAA. In both cases, this elongation completely eliminates the first-order component for iron release while having relatively little impact on the saturation pathway. The sensitivity of the first-order component to the structure of the ligand strongly indicates that this pathway involves the binding of the ligand to a specific site on the protein and cannot be attributed to changes in the overall ionic strength of the solution as the ligand concentration increases. It is proposed that this structural sensitivity reflects steric restrictions on the ability of the incoming ligand to substitute for the synergistic carbonate anion to form a relatively unstable Fe-ligand-Tf ternary intermediate, which then dissociates to FeL and apoTf.     

An expeditious total synthesis of both diastereoisomeric lipid dihydroxytetrahydrofurans from Notheia anomala

Short, high yielding syntheses of both diastereomers of the naturally occurring oxylipids 1 and 2 using a combination of organocatalytic hydroxylation of an aldehyde, alkene cross metathesis, and palladium(0) catalyzed cyclization chemistry (six-step process) are reported. Furthermore, the influence of the catalyst on the cross metathesis reaction of the homoallylic 1,2-diol has been studied in detail.