Enantioselective Michael Addition to α,β-Unsaturated Aldehydes: Combinatorial Catalyst Preparation and Screening, Reaction Optimization, and Mechanistic Studies
作者:Ivana Fleischer、Andreas Pfaltz
DOI:10.1002/chem.200902449
日期:2010.1.4
Shortcut to chiral catalysts: An efficient combinatorial strategy based on back reaction screening by ESI‐MS allows rapid evaluation of organocatalysts for the asymmetric Michael addition to α,β‐unsaturated aldehydes (see scheme). An unexpected nonlinear effect has been observed in this reaction, resulting from a double nucleophilic–electrophilic activation mechanism involving two catalyst molecules
a cyanine chromophore analogous to Cysup III}. A single photointermediate (bRsub cy}/I), reminiscent of the K phototransient of bR, ismore » observed and is attributed to a cis isomer. The low activation and preexponential parameters which characterize the thermal relaxation of bRsub cy}/I are discussed in terms of cis yields} transisomerization in a rhodopsin binding site.« less
as reconstituted chromophore−protein complexes were investigated as model compounds for the protonated Schiff base chromophore in bacteriorhodopsin (bR) both experimentally and theoretically. Charge distribution, donor−acceptor strength, and the shift of the absorption energy are correlated. The effect of the external electrostatic field was tested with a compound carrying an additional nonconjugated
into DNA opposite Q by the Klenow fragment of Escherichia coli DNApolymerase I were improved, in comparison with those of the Q-Pa pair. These improvements result from the increased hydrophobicity and stacking stability of Pa' by the introduction of the propynyl group to Pa, providing valuable information for the further development of unnatural base pairs toward the expansion of the genetic alphabet