131326-32-4Relevant articles and documents
Synthesis of achiral, but unsymmetric, seven-membered rhodium(I)-chelates for hydrogenation in the chiral environment of alkyl polyglucoside micelles
Fehring,Kadyrov,Ludwig,Holz,Haage,Selke
, p. 120 - 129 (2007/10/03)
Chiral rhodium(I) chelates containing a seven-membered ring are well-known active catalysts for the asymmetric hydrogenation of amino acid precursors. A high conformational flexibility allows their enantioselectivity to be strongly influenced by modifiers. Now we show the nature of the counter-ions to have a large influence in apolar solvents. In addition, the presence of micelle forming alkyl polyglycosides as amphiphiles causes a remarkable increase in the enantiomeric excess (%ee). However, on achiral catalysts this enantioselectivity inducing effect scarcely exceeds the standard deviation for the gas chromatographic determination of the enantiomeric ratio. This is also true for the application of unsymmetric P,P′-ligands such as 3-phosphinopropyl-phosphinites or butane-1,4-diyl-bis(phosphines) carrying different P′-aryl groups, for which synthetic routes are given.
PEPTIDE BOND FORMATION USING AN ENZYME MIMICKING APPROACH
Gennari, Cesare,Molinari, Francesco,Piarulli, Umberto,Bartoletti, Marcella
, p. 7289 - 7300 (2007/10/02)
A man-made enzyme-model based on a concerted proton transfer step (bifunctional catalysis) which mimics the corresponding step in non-ribosomal peptide synthesis was developed.Important features of the model are the following: (a) a bifunctional acid-base catalyst for the thiolester aminolysis rate acceleration, (b) two thiol-containing arms mimicking the "swinging arms" of the enzyme, and (c) symmetry elements so that the process can be iterated with consequent formation of the polypeptide chain.Peptide bond formation was obtained by intramolecularly catalyzed thiolester aminolysis to give 5 in 80percent isolated yield (Scheme IV, V) and with at least a 103-fold rate acceleration in comparison with the corresponding non catalyzed process (4 -> 6)(Scheme IV, Table 1).The reaction is also 4-20 times faster than the analogous process 4 -> 6 run in the presence of 0.1M external catalyst (Et3N-ButCOOH or 2-Pyridone).Important structural and reaction parameters are discussed.A second intramolecular aminolysis reaction gave tripeptide 8 in lower yield (35percent) because of higher steric congestion in the transition state.
