- First Practical Protection of α-Amino Acids as N, N-Benzyloxycarbamoyl Derivatives
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The consecutive treatment of N-Cbz amino protected compounds with LiHMDS and CbzCl provides a practical method for the preparation of N,N-benzyloxycarbamoyl (N,N-di-Cbz) derivatives in good yield. When α-amino acids are used the protection occurs without racemization. The method is compatible with a wide range of other functional and protecting groups. The procedure is also valid for the synthesis of mixed N,N-carbamoyl derivatives.
- Hernandez, J. Nicolas,Martin, Victor S.
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p. 3590 - 3592
(2007/10/03)
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- Mapping the aspartic acid binding site of Escherichia coli asparagine synthetase B using substrate analogs
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Novel inhibitors of asparagine synthetase, that will lower circulating levels of blood asparagine, have considerable potential in developing new protocols for the treatment of acute lymphoblastic leukemia. We now report the indirect characterization of th
- Parr, Ian B.,Boehlein, Susan K.,Dribben, Anthony B.,Schuster, Sheldon M.,Richards, Nigel G. J.
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p. 2367 - 2378
(2007/10/03)
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- Carbon Dioxide as a Phosgene Replacement: Synthesis and Mechanistic Studies of Urethanes from Amines, CO2, and Alkyl Chlorides
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Several carbamate esters were synthesized from amines, carbon dioxide, and alkyl chlorides.The effect of added base on the yield and selectivity of carbamate ester formation was found to be highly important with the use of sterically hindered guanidine bases giving the best results.Relative rate studies were carried out giving the following order of reactivity between carbamate anions in acetonitrile with benzyl chloride giving carbamate esters: Et2NCO2(-) = Bu2NCO2(-) > t-BuNHCO2(-) = CyNHCO2(-) = s-BuNHCO2(-) > PhNHCO2(-) > CyCH2NHCO2(-) = n-octylNHCO2(-) = n-BuNHCO2(-).Rate studies were carried out with the diethyl, s-butyl, phenyl, and n-butyl carbamates and activation parameters were determined to be Et2NCO2(-), ΔH(excit.) = 11.8 kcal/mol, ΔS(excit.) = -33 eu; s-BuNHCO2(-), ΔH(excit.) = 12.8 kcal/mol, ΔS(excit.) = -33 eu; PhNHCO2(-), ΔH(excit.) = 14.3 kcal/mol, ΔS(excit.) = -28 eu; n-BuNHCO2(-), ΔH(excit.) = 23.4 kcal/mol, ΔS(excit.) = -3 eu.The unusual results obtained from the use of n-BuNHCO2(-) prompted further studies which showed that the rate of the reaction was inversely dependent on carbon dioxide pressure (20 psig CO2, k = 4.84E-4 M-1 s-1; 120 psig CO2, k = 1.83E-4 M-1 s-1).Nitrogen NMR spectroscopy indicated, via a labeling study with 15N amines and 13C enriched carbon dioxide, the formation of doubly inserted product from the addition of two carbon dioxides to ethylamine in acetonitrile.
- McGhee, William,Riley, Dennis,Christ, Kevin,Pan, Yi,Parnas, Barry
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p. 2820 - 2830
(2007/10/02)
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- PREPARATION OF ESTERS OF AMINO ACIDS AND OF PEPTIDES UNDER MILD CONDITION
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A new method of obtaining esters of N-protected amino acids and peptides from complexes of their sodium salts with 15-crown-5 that are soluble in organic solvents is proposed.
- Mazurov, A. A.,Antonenko, S. V.,Andronati, S. A.
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p. 208 - 210
(2007/10/02)
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