Erythritol, conformation

More recently Frechet and Gitsov [130] used a similar approach as above and synthesized a novel series of dendritic copolymers derived from a central penta-erythritol core unit. These hybrid star molecules behaved as unimolecular micelles with different core-shell conformational-structures as a response to the polarity of the solvent used. 

A very interesting tautomeric system is presented by the civ-fused tetrahydro[l,3,2]dioxaborino [5,4-cf]-l,3,2-dioxaborin (122). This is prepared from a threitol type precursor and is obtained as a mixture with isomer (123) in a ratio of 3 1 (Equation (2)). The particular stereochemistry of (122) permits the molecule to adopt a conformation in which the two boron atoms and two of the oxygen atoms assume a four-centered transition state (124), thus allowing establishment of a dynamic equilibrium with the isomeric structure (123) (Scheme 3). The trans-fused analogue of (122), prepared from an erythritol type precursor, is unable to enter into this tautomeric equilibrium (80LAH76). 

Erythritol 1 is a tetraol with a central eryf/rro-conflgured diol group. In combination with the terminal hydroxyl functions there are several conformations to act as a chelate ligand. In most of its characterized solid-state stmctures, erythritol is coordinated to two central atoms by acting as a bis-l,2-diolato ligand, at which the deprotonation of the hydroxyl groups is a consequence of the synthesis from alkaline solutions and/or complexation of more or less Lewis acidic central atoms. A complex of this type is obtained upon the reaction of erythritol with two equivalents of [(NH3)2Pd(OH)2] in aqueous solution which leads to the centrosymmetric structure of 9 (O Fig. 1) [18],... 

While palladium(II) and copper(II) build solely 1,2-diolato complexes with erythritol which leads to five-membered chelate rings, boron(III) is involved in the six-membered rings as in the bis(phenylboronic acid ester) 13 (O Fig. 2). Erythritol adopts a zigzag conformation similar to that in 9 but the oxygen atoms are grouped alternatively on opposite sites of the C4-chain. The six-membered chelate rings in half-chair conformation provide a suitable bond pattern for a boron center involved in the delocalized jr-hond system of the phenyl suhstituent. 

Threitol 2 is a tetraol with a central f/zreo-contigured diol group. While erythritol has to adopt a sickle conformation in order to locate all its oxygen atoms on the same side of the C4 chain, threitol attains this in its zigzag conformation. 

Molybdenum and tungsten also use the central tetraol set of dulcitol, however, in a sickle conformation, to form dimolybdates respectively ditungstates with a coordination pattern similar to that found in the erythritol complex 14 (O Fig. 2) [25,26,27,43]. 

Dimethylenepenta- erythritol The two spiro-1,3-dioxan rings each adopt a chair conformation Le Fevre et al., 1958b... 

The diastereoselection of the intramolecular photocycloaddition of 1,4-erythritol dicinnamates (161b) has been explained by diastereoisomeric transition states involving different steric constraints and on the basis of a simulation of the diastereomeric ground-state conformations believed to lead to the observed adducts. Modification of the chiral auxiliary in 161c led to disappointing selectivities and the chemical yields in the desired 5-truxinate remained low. 

The most useful way to depict the various conformational states of an acyclic sugar chain is by means of a formalized drawing that shows the relative dihedral angles of the substituents at each end of a carbon-carbon bond. Two such types of representation are the sawhorse and Newman (Boeseken) formulas, as illustrated for erythritol. The zigzag type of representation shown has the advantage that it can be employed to display the relative orientations of groups along a chain of several atoms that lie approximately in a plane (for example, the plane of the paper). 

The regioselective complexation of D-mannitol, -galactitol, -xylitol, -ribitol and -erythritol with bis(phosphlne)platinum(II) carbonate complexes has been studied, and conformational analyses of the products by H n.m.r have been performed. Also a study on the preferred conformations of hex-l,S-dien-3,4-diols, which includes reference to hydroxylation reactions, suggesting an approach to hexitol and higher alditol syntheses has been reported. ... 

A review with 190 refs, on conformations and absolute configurations of acyclic diols and polyols and their benzoates in solution, as determined by chiroptical methods including the exciton chirality concept, has been published. The conformations of aqueous erythritol and L-threitol in relaticMi to their sweetness properties have been analysed by molecular dynamics simulation. H- And C-n.m.r. experiments have been performed to analyse the conformations and stereochemistry of the four diastereomeiic thiazolidine sulfoxides 1. ... 

Protein stability may be regarded as the opposite of denaturation. The stability of enzymes (and proteins) can be increased in many ways, e.g., by microenvironmental changes, immobilization, and protein engineering (78). Enzymes are more stable in the presence of polyols (ethylene glycol, glycerol, erythritol, and sorbitol), polymers (PEG, dextrans), and carbohydrates (sucrose, lactose, and trehalose). Hydrophilic enzymes are stabilized by the presence of salts (LiCl, NaCl, and KCl), whereas hydrophobic enzymes are hardly affected by salts. Proteins are also stabilized by compounds that bind specifically to the folded conformation. Most of the metalloenzymes and the enzymes that have an anion-binding site fall into this category. 

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