- L-proline-catalyzed asymmetric michael addition of 2-oxindoles to enones: A convenient access to oxindoles with a quaternary stereocenter
-
A new organocatalytic approach for 1,4-conjugate addition of 2-oxindoles to α,β-unsaturated ketones using the combination of readily available and nonexpensive l-proline and achiral trans-2,5-dimethylpiperazine as catalytic system is provided. The reaction results in oxindole derivatives with vicinal quaternary and tertiary carbon centers in up to 99% yield and 91% ee. Georg Thieme Verlag Stuttgart.
- Freund, Matthias H.,Tsogoeva, Svetlana B.
-
p. 503 - 507
(2011/04/18)
-
- Synthesis of proline-derived dipeptides and their catalytic enantioselective direct aldol reactions: Catalyst, solvent, additive and temperature effects
-
A series of dipeptides of l-proline-l-amino acid and l-proline-d-amino acid were synthesized to evaluate the catalytic effect for asymmetric direct aldol reactions. In the direct aldol reaction, a catalyst of l-proline-l-amino acid achieves better enantioselectivity than the corresponding l-proline-d-amino acid catalyst. Solubility of the dipeptide catalysts in the solvents is a key point for achieving a better yield of the direct aldol reaction, while hydrogen bonding of solvent does not play an important role in attaining better enantioselectivity and yield. Yield and enantioselectivity of the direct aldol reaction in water were improved by NMM and SDS additives, but the results that were done in plain DMSO were even better.
- Chen,Sung,Sung, Kuangsen
-
experimental part
p. 839 - 845
(2010/08/06)
-
- Chemical Characterization of Diketopiperazines in Beer
-
Diketopiperazines (DKPs) corresponding to cyclic dipeptides have been detected in a variety of natural products as well as in processed foods, beverages, and food and beverage ingredients. A series of seven proline-based diketopiperazines, namely, cyclo(Ala-Pro), cyclo(Val-Pro), cyclo(Ile-Pro), cyclo(Leu-Pro), cyclo(Met-Pro), cyclo(Phe-Pro), and cyclo(Pro-Pro), has now been identified in beer. A marketplace cross-section of five commercial beers was studied, involving products manufactured in different countries using distinctly different raw materials and brewing styles; maximum concentrations of individual diketopiperazines in various beers ranged from below detection limit to approximately 24 ppm. The flavor characteristics of these compounds were described variously as bitter, mouth coating, drying, astringent, salty, metallic, and grainy when evaluated in water at concentrations ranging from 10 to 50 ppm. However, it is questionable whether or not the diketopiperazines reported here make a significant contribution to either the aroma or taste of most beers.
- Gautschi, Markus,Schmid, Joachim P.,Peppard, Terry L.,Ryan, Thomas P.,Tuorto, Raymond M.,Yang, Xiaogen
-
p. 3183 - 3189
(2007/10/03)
-
- Anchoring of Amino Acids on Hydroxy Group-Containing Resins and Their Application to Peptide Synthesis Using N-Tritylamino Acid 1-Benzotriazolyl Esters
-
Trt- and Fmoc-amino acids has been attached to p-alkoxybenzylalcohol resin (ABAR, 1) and diphenylmethanol resin (DPMR, 2) using triphenylphosphan (TPP) and diethyl azodicarboxylate (DEAD) at 0 deg C in tetrahydrofuran.The derived resins have been applied in "solid-phase" peptide synthesis using N-tritylamino acid 1-benzotriazolyl esters 9.
- Barlos, Kleomenis,Gatos, Dimitrios,Kallitsis, John,Papaioannou, Dionysios,Sotiriou, Petros,Schaefer, Wolfram
-
p. 1031 - 1036
(2007/10/02)
-