Periodic acids structural relations

The essential distinction between the approaches used to formulate and evaluate proteins, compared with conventional low molecular weight drugs, lies in the need to maintain several levels of protein structure and the unique chemical and physical properties that these higher-order structures convey. Proteins are condensation polymers of amino acids, joined by peptide bonds. The levels of protein architecture are typically described in terms of the four orders of structure [23,24] depicted in Fig. 2. The primary structure refers to the sequence of amino acids and the location of any disulfide bonds. Secondary structure is derived from the steric relations of amino acid residues that are close to one another. The alpha-helix and beta-pleated sheet are examples of periodic secondary structure. Tertiary... 

When nine moles of phenyllithium in ether acted upon tetraacetyl-glucosyl chloride, the reaction mixture being subsequently decomposed with water, four products resulted. From the ether layer a quantitative yield of methyldiphenylcarbinol was recovered. Acetylation of the residue from the water layer, followed by fractional crystallization led to two crystalline substances and a residual sirup. The first crystalline product was (tetraacetyl-j3-D-glucopyranosyl)benzene (IV). The second m. p. 142-143°, [a]o24 — 2.3° (chloroform), appeared to be isomeric with IV. It oxidized to benzoic acid and deacetylated to give a sirup which consumed two moles of periodate with liberation of one mole of formic acid. While these properties are to be expected for a structure related to IV, this substance differed from both of the anomeric (tetraacetyl-n-glucopyranosyl)benzenes, nor did it appear to be a mixture of them. Its exact constitution is not yet known. 

We will give further details about the periodic electronic structure calculations method as we will use results obtained with this method to support the discussion. First, we will describe how cluster approach can be used to investigate reactions catalyzed by acidic zeolites. Next, periodic electronic stmcture calculations will be used to enlighten the effects of the approximations of the cluster approach. These approximations relate mainly with the missing description of the zeolite framework contributions on the molecules involved in the reactions. Finally, by increasing the size of the aromatics involved in the isomerization reactions, we will show how steric constraints affect the course of a reaction. 

Jeanloz R, Forchielli E. Hyaluronic acid and related compounds III. Determination of the structure of chitin by periodate oxidation. Helv Chim Acta 1950 33 1690-1697. 

The Lewis acid-catalysed orientation reversal in the reaction between substituted cyclohexa-1,3-dienes and 2,6-dimethyl-l,4-benzoquinone ° has been employed in an interesting synthesis of quassin (218). ° Thus, reaction at room temperature of the diene (215) with the above quinone in the presence of an equivalent quantity of Bp3,OEt2 gave the adduct (216) which was converted by several subsequent steps into (218). In the absence of the catalyst the alternative adduct (217) was obtained. Periodic acid oxidation of substituted o-cresols ° and of 2-methoxyphenols in methanol solution affords intermediate o-quinol methyl ethers or o-quinone dimethyl ketals which dimerize to give dienediones with structures related to those of (216) and (217). Another report concerns the formation of a Diels-Alder dimer upon hypochlorite oxidation of 2,2 -methylenebis(4-methyl-6-t-butyl)phenol. ... 

Most of the structural and biochemical work related to KDO is based on the estimation of the compound or its derivatives by the periodate-thiobarbituric acid (TBA) assay in its various modifications. Indeed, KDO (see Fig. 3) was discovered9 through the formation of a characteristic, purple, TBA chromophore (Xmax 549 nm) from its 8-phosphate (2), which is the product of the condensation of D-arabinose 5-phosphate with enolpyruvate phosphate, catalyzed by 3-deoxy-8-0-phosphonooctulosonate synthetase (EC 4.1.2.16) (see Scheme 1 and Section V,2). 

---