99092-02-1Relevant articles and documents
Thermodynamically controlled chemoselectivity in lipase-catalyzed aza-Michael additions
Rivera-Ramírez, José Domingo,Escalante, Jaime,López-Munguía, Agustín,Marty, Alain,Castillo, Edmundo
, p. 76 - 82 (2015/01/30)
Chemoselective synthesis of N-protected β-amino esters involving lipase-catalyzed aza-Michael additions and α,β-unsaturated precursors is mainly hampered by the two electrophilic sites present on these compounds. In order to control the chemoselectivity a solvent engineering strategy based on the thermodynamic behaviour of products in media of different polarity was designed. This strategy allowed to obtain aza-Michael adducts from benzylamine and different acrylates with high selectivity. In almost all reactions carried out in n-hexane, a non-polar solvent, aminolysis was avoided while the corresponding Michael adducts were exclusively synthesized in 53-78% yields. On the contrary, in reactions carried out in a polar solvent such as 2-methyl-2-butanol the aminolysis products were favoured. Thermodynamic analyses of these processes using the COSMO-RS method helped to understand some of the key factors affecting chemoselectivity and confirmed that a reliable estimation of the thermodynamic interactions of solutes and solvents allows an adequate selection of a reaction media that may lead to chemoselectivity.
Isomer differentiation via collision-induced dissociation: The case of protonated a-, β2- and β3-phenylalanines and their derivatives
Lam, Adrian K. Y.,O'Hair, Richard A. J.
experimental part, p. 1779 - 1790 (2011/11/05)
A combination of electrospray ionisation (ESI), multistage and high-resolution mass spectrometry experiments is used to examine the gas-phase fragmentation reactions of the three isomeric phenylalanine derivatives, a-phenylalanine, b2-phenylalanine and b3-phenylalanine. Under collision-induced dissociation (CID) conditions, each of the protonated phenylalanine isomers fragmented differently, allowing for differentiation. For example, protonated b3-phenylalanine fragments almost exclusively via the loss of NH3, only b2-phenylalanine via the loss of H2O, while a- and b2- phenylalanine fragment mainly via the combined losses of H2ORCO. Density functional theory (DFT) calculations were performed to examine the competition between NH3 loss and the combined losses of H2O and CO for each of the protonated phenylalanine isomers. Three potential NH3 loss pathways were studied: (i) an aryl-assisted neighbouring group; (ii) 1,2 hydride migration; and (iii) neighbouring group participation by the carboxyl group. Finally, we have shown that isomer differentiation is also possible when CID is performed on the protonated methyl ester and methyl amide derivatives of a-, b2- and b3-phenylalanines.
A Facile Synthesis of α-Amino Esters via Reduction of α-Nitro Esters Using Ammonium Formate as a Catalytic Hydrogen Transfer Agent
Ram, Siya,Ehrenkaufer, Richard E.
, p. 133 - 135 (2007/10/02)
Various nitroesters 3 were selectively and rapidly reduced to their corresponding amino esters 4 in very good yield using anhydrous ammonium formate as a catalytic hydrogen transfer agent.
N,N-Bis(trimethylsilyl)methoxymethylamine as a Convenient Synthetic Equivalent for +CH2NH2: Primary Aminomethylation of Esters
Okano, Kohji,Morimoto, Toshiaki,Sekiya, Minoru
, p. 883 - 884 (2007/10/02)
The introduction of a primary aminomethyl unit at the α position of esters can be achieved in high yield by the silyl trifluoromethanesulphonate-catalysed reaction of ketene silyl acetals (2) with N,N-bis(trimethylsilyl)methoxymethylamine (1).
