Total synthesis of pachastrissamine (jaspine B) enantiomers from d-glucose

Synthesis of both enantiomers of pachastrissamine is described from a common chiral template. The stereoselective construction of the central tetrahydrofuran units was based on the pseudodesymmetrization of a pentodialdo-1,4-furanose derivative taking advantage of the latent symmetry present.     

The isochroman- and 1,3-dihydroisobenzofuran-annulation on carbohydrate templates via [2+2+2]-cyclotrimerization and synthesis of some tricyclic nucleosides

The synthesis of enantiopure tricyclic systems comprising isochroman or dihydroisobenzofuran units integrated with sugar templates has been documented. The alkyne cylotrimerization reaction has been employed with easily accessible sugar diynes for the key bicyclic ring construction and thus a provision to alter the functional groups on the newly formed aromatic rings. By selecting two representative trimerization products, we have synthesized the tricyclic nucleosides by simple synthetic manipulations.     

Tutte polynomials for trees

We define two two-variable polynomials for rooted trees and one two-variable polynomial for unrooted trees, all of which are based on the coranknullity formulation of the Tutte polynomial of a graph or matroid. For the rooted polynomials, we show that the polynomial completely determines the rooted tree, i.e., rooted trees T₁ and T₂ are isomorphic if and only if f(T₁) = f(T₂). The corresponding question is open in the unrooted case, although we can reconstruct the degree sequence, number of subtrees of size k for all k, and the number of paths of length k for all k from the (unrooted) polynomial. The key difference between these three polynomials and the standard Tutte polynomial is the rank function used; we use pruning and branching ranks to define the polynomials. We also give a subtree expansion of the polynomials and a deletion-contraction recursion they satisfy.     

Regio- and diastereoselective reduction of nonenolizable alpha-diketones to acyloins mediated by indium metal

[reaction: see text] Alpha-diketones are efficiently reduced with indium metal in methanol-water in the presence of NH(4)Cl, LiCl, or NaCl to give regio- and diastereoselectively the corresponding acyloins in good to excellent yield. The cleavage of the acyloins under Pb(OAc)(4)/MeOH-PhH condition provides a convenient and regioselective access to highly functionalized cyclopentane carboxaldehydes, potential building blocks in organic syntheses.     

Influence of dispersing agents and solution conditions on the solubility of crude kaolin

Experiments measuring the solubility of kaolin particles in terms of the concentration of aluminum and silicon ions in supernatant were carried out as a function of the pH of the slurry over a wide range of dosages of different dispersing agents varying from 0.5 to 12 mg/(g solids). The concentrations of the metal ions in supernatant were found to be strongly affected by the type and the dosage of the dispersants and pH of the solution. In this study, the mechanism of the reaction between the dispersing agents and kaolin particles was studied and the dissolution capacities of metal ions (aluminum and silicon) were identified from kaolin particles in the absence and presence of dispersing agents. The three anionic dispersing agents used were sodium polyacrylate (Na-PAA), sodium hexametaphosphate (Na-HMP), and sodium silicate (Na-silicate), based on the industrial application of these agents and their ability to produce a stable dispersion for this purpose.     

Asymmetric synthesis of the carbapenam core from serine

The stereospecific synthesis of the functionalized carbapenam core 16 from the serine-derived trisubstituted pyrrolidine 9 is reported. The synthetic strategy relies on synthesizing an appropriately functionalized pyrrolidine, followed by an intramolecular azetidone formation utilizing a modified Mukiyama reagent. The efficient one-pot conversion of the benzenesulfonamide-protected pyrrolidine 9 to the Cbz-protected pyrrolidine 10 is also reported.     

Hydroxylated pyrrolidines. Enantiospecific synthesis of all-cis 2,3,4,5-substituted pyrrolidine derivatives from serine

We report the enantiospecific synthesis of the sterically congested all-cis 2,3,4,5-substituted pyrrolidines 4, 5, and 6, from either D- or L-serine. Hemiaminal intermediate 13 is converted to the fully substituted pyrrolidine 15 by way of a tandem Wittig-Michael reaction. The endo stereochemistry of the C-3 methyl group of compound 15 is set by stereoselective reduction of the double bond in 11, driven by a preference for hydrogenation from the rear side of the molecule. The all-cis configuration of these fully substituted pyrrolidines has been established by X-ray analysis of compound 6. Removal of the benzenesulfonyl group from the highly substituted and functionalized intermediate 15 is successfully accomplished by sodium naphthalenide reduction.     

A Proof of the Jungnickel-Tonchev Conjecture on Quasi-Multiple Quasi-Symmetric Designs

A proof of the following conjecture of Jungnickel and Tonchev on quasi-multiple quasi-symmetric designs is given: Let D be a design whose parameter set (v,b,r,k,) equals (v,sv,sk,k, s) for some positive integer s and for some integers v,k, that satisfy (v-1) = k(k-1) (that is, these integers satisfy the parametric feasibility conditions for a symmetric (v,k,)-design). Further assume that D is a quasi-symmetric design, that is D has at most two block intersection numbers. If (k, (s-1)) = 1, then the only way D can be constructed is by taking multiple copies of a symmetric (v,k, )-design.     

Influence of phosphorylation on the foamability and stability of bovine serum albumin and citrus peel pectin mixed foams

We study the influence of phosphorylation on the foamability and stability of bovine serum albumin (BSA), phosphorylated BSA (pBSA), and citrus peel pectin (CPP) mixed foams as a function of BSA–CPP, pBSA–CPP mixing ratios, at a fixed solution pH of 4.5. Our results show that pBSA solutions result in more stable foams as compared with their BSA counterparts. We further show that the addition of CPP leads to BSA–CPP and pBSA–CPP complexation which increases the foamability and stability of foams as compared with protein-only foams. Also, foam stability is highest for pBSA–CPP mixed foams with mixing ratio pBSA:CPP?=?1:1 due to the combined effect of pBSA–pBSA and pBSA–CPP interactions.