90899-85-7Relevant articles and documents
Rapid and efficient microwave-assisted synthesis of N-carbamoyl-L-amino acids
Verardo, Giancarlo,Geatti, Paola,Strazzolini, Paolo
, p. 1833 - 1844 (2008/02/02)
A rapid and efficient method for the synthesis of N-carbamoyl-L-amino acids is reported. The procedure, involving the reaction between urea and α-amino acids sodium salts, was performed under microwave conditions using an unmodified domestic microwave oven. A careful study of the operative conditions indicated proline (1d) as the less reactive substrate and phenylglycine (1e) as the more reactive one among all the α-amino acids tested. Substitution of urea with potassium cyanate produced a low conversion into the corresponding N-carbamoyl derivative, and a possible explanation of this result is reported. Copyright Taylor & Francis Group, LLC.
Investigation of N-carbamoylamino acid nitrosation by {NO + O2 in the solid-gas phase. Effects of NOx speciation and kinetic evidence for a multiple-stage process
Lagrille, Olivier,Taillades, Jacques,Boiteau, Laurent,Commeyras, Auguste
, p. 271 - 284 (2008/03/14)
Nitrosation of N-carbamoylamino acids (CAA) by gaseous NO + O2, an interesting synthetic pathway to amino acid N-carboxyanhydrides (NCA), alternative to the phosgene route, was investigated on N-carbamoyl-valine either in acetonitrile suspension or solventless conditions, and compared to the classical nitrosating system NaNO2 + CF3COOH (TFA), the latter being quite less efficient in terms of either rate, stoichiometric demand, or further tractability of the product. The rate and efficiency of the NO + O2 reaction mainly depends on the O2/NO ratio. Evaluation of the contribution of various nitrosating species (N 2O3, N2O4, HNO2) through stoichiometric balance showed the reaction to be effected mostly by N 2O3 for O2/NO ratios below 0.3, and by N 2O4 for O2/NO ratios above 0.4. The relative contribution of (subsequently formed) HNO2 always remains minor. Differential scanning calorimetry (DSC) monitoring of the reaction in the solid phase by either HNO2 (from NaNO2 + TFA), gaseous N 2O4 or gaseous N2O3, provides the associated rate constants (ca. 0.1, 2 and 108 s-1 at 25°C, respectively), showing that N2O3 is by far the most reactive of these nitrosating species. From the DSC measurement, the latent heat of fusion of N2O3, 2.74 kJ ·mol-1 at -105 °C is also obtained for the first time. The kinetics was investigated under solventless conditions at 0°C, by either quenching experiments or less tedious, rough calorimetric techniques. Auto-accelerated, parabolic-shaped kinetics was observed in the first half of the reaction course, together with substantial heat release (temperature increase of ca. 20°C within 1-2 min in a 20-mg sample), followed by pseudo-zero-order kinetics after a sudden, important decrease in apparent rate. This kinetic break is possibly due to the transition between the initial solid-gas system and a solid-liquid-gas system resulting from water formation. Overall rate constants increased with parameters such as the specific surface of the solid, the O 2/NO ratio, or the presence of moisture (or equivalently the hydrophilicity of the involved CAA), however without precise relationship, while the last two parameters may directly correlate to the increasing acidity of the medium. Copyright
Mechanism of Asymmetric Production of L-Aromatic Amino Acids from the Corresponding Hydantoins by Flavobacterium sp.
Yokozeki, Kenzo,Hirose, Yoshiteru,Kubota, Koji
, p. 737 - 746 (2007/10/02)
The mechanism of asymmetric production of L-aromatic amino acids from the corresponding hydantoins by Flavobacterium sp.AJ-3912 was examined by investigating the properties of the enzymes involved in the hydrolysis of 5-substituted hydantoins corresponding to aromatic amino acids (AAH).The enzymatic hydrolysis of AAH by Flavobacterium sp.AJ-3912 consisted of the following two successive reactions; a hydrolytic ring opening reaction of DL-AAH to L- and D-form N-carbamyl aromatic amino acids (NCA), involving an enzyme (hydantoin hydrolase) followed by a hydrolytic cleaving reaction of the L-form NCA to L-aromatic amino acids involving another enzyme (N-carbamyl-L-aromatic amino acid hydrolase, abbreviated as L-NCA hydrolase).The ring opening reaction involving hydantoin hydrolase was not stereospecific, but the NCA cleaving reaction involving L-NCA hydrolase was completely L-specific.The pathway for the conversion of the by-produced D-form NCA to L-aromatic amino acids was as follows; conversion of D-form NCA to D-AAH through the reverse reaction of hydantoin hydrolase, and then conversion of the D-AAH to L-AAH through spontaneous racemization, followed by the successive hydrolysis of the L-AAH to L-aromatic amino acids by hydantoin hydrolase and L-NCA hydrolase.
