- Synthesis of 2-monofunctionalized 2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7- diones
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New (1R*,5S*)-2-R-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7- diones containing the terminal carboxy or hydroxy group in the substituent R were synthesized by cyclocondensation of 4,5-dihydroxyimidazolidin-2-one with 1-R-ureas. Single-crystal X-ray diffraction analysis showed that 2-carboxyethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione crystallizes as a racemate.
- Kravchenko,Maksareva,Belyakov,Sigachev,Chegaev,Lyssenko,Lebedev,Makhova
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p. 192 - 197
(2007/10/03)
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- A pH-dependent cyanate reactivity model: Application to preparative N-carbamoylation of amino acids
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Recent developments in peptide synthesis have underlined the importance of optimising, on a preparative scale, the N-carbamoylation of amino acids by aqueous cyanate. To this purpose, a theoretical model of aqueous cyanate reactivity was designed. The parameters of the model were evaluated, for various pH and temperatures, from a critical survey of the literature, together with additional experimental data. Computer-simulated kinetics based on this model showed the reaction efficiency to be significantly dependent on pH, and suggested optimum conditions to be moderate temperatures and pH 8.5-9. Discussion of the practical convenience of these theoretical results led us to prefer 40-50 °C and a pH range of 7-8 as reaction conditions, thus maintaining reaction times within a few hours. Various N-carbamoyl amino acids (ureido derivatives of glycine, L-valine, L-alanine, L-leucine, DL-methionine, Nε-trifluoroacetyl-L-lysine, β-alanine) were thus successfully synthesised on the gram to kilogram scales.
- Taillades, Jacques,Boiteau, Laurent,Beuzelin, Isabelle,Lagrille, Olivier,Biron, Jean-Philippe,Vayaboury, Willy,Vandenabeele-Trambouze, Odile,Giani, Olivia,Commeyras, Auguste
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p. 1247 - 1254
(2007/10/03)
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- New functional glycoluril derivatives
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Functional glycoluril (2,4,6,8-tetraazabicyclo[3.3.0]octan-3,7-dione) derivatives containing 2-hydroxyethyl, carboxyl and amino groups were synthesised.
- Chegaev,Kravchenko,Lebedev,Strelenko
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- Mechanism of Asymmetric Production of D-Amino Acids from the Corresponding Hydantoins by Pseudomonas sp.
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The mechanism of asymmetric production of D-amino acids from the corresponding hydantoins by Pseudomonas sp.AJ-11220 was examined by investigating the properties of the enzymes involved in the hydrolysis of DL-5-substituted hydantoins.The enzymatic production of D-amino acids from the corresponding hydantoins by Pseudomonas sp.AJ-11220 involved the following two successive reactions; the D-isomer specific hydrolysis, i.e., the ring opening of D-5-substituted hydantoins to D-form N-carbamyl amino acids by an enzyme, D-hydantoin hydrolase (D-HYD hydrolase), followed by the D-isomer specific hydrolysis, i.e., the cleavage of N-carbamyl-D-amino acids to D-amino acids by an enzyme, N-carbamyl-D-amino acid hydrolase (D-NCA hydrolase).L-5-Substituted hydantoins not hydrolyzed by D-HYD hydrolase were converted to D-form 5-substituted hydantoins through spontaneous racemization under the enzymatic reaction conditions.It was proposed that almost all of the DL-5-substituted hydantoins were stoichiometrically and directly converted to the corresponding D-amino acids through the successive reactions of D-HYD hydrolase and D-NCA hydrolase in parallel with the spontaneous racemization of L-5-substituted hydantoins to those of DL-form.
- Yokozeki, Kenzo,Kubota, Koji
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p. 721 - 728
(2007/10/02)
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- β-UREIDO ACIDS AND DIHYDROURACILS. PART 15. EFFECT OF ALLYLIC STRAIN ON RING OPENING OF 1,6-DISUBSTITUTED DIHYDROURACILS
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The rate profiles for the alkaline hydrolysis of some dihydrouracil and dihydro-orotic acid derivetives have been measured in order to assess the effect of allylic strain on the ring opening of 1,6-disubstituted dihydrouracils.The introduction of a 1-nitrogen-substituent in the 6-substituted compounds brings about a substantial decrease (40-500 times) in the observed rate constant which is second order in hydroxide ion (k1k3/k-1).The rate decreases of the addition step, k1, are moderate and in the range expected from the observed shifts in conformational equilibra towards the axial conformation which gives rise to a hindered transition state.The major contribution to the rate decreases from the ring-opening step, k3/k-1, and have been attributed to strains of the type associated with gem-dimethyl effect upon ring closure.
- Koedjikov, Asen H.,Blagoeva, Iva B.,Pojarlieff, Ivan G.,Stankevic, Eva J.
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p. 1077 - 1082
(2007/10/02)
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