- Flame-induced addition of urea to unsaturated carboxylic acids
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When a hydrogen-oxygen flame was blown against an aqueous solution of urea and maleic acid, N-carbamoylaspartic acid was generated. This compound seemed to be formed by the addition of an amidinoxyl radical to a C-C double bond of the acid, followed by a thermal rearrangement of an amidinoxy to a ureido group.
- Terasaki, Masanori,Nomoto, Shinya,Mita, Hajime,Shimoyama, Akira
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p. 855 - 856
(2007/10/03)
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- Formation of N-Carbamoylaspartic Acid and Its Cyclisation to Orotic Acid
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The stereochemistries of the reactions between cyanate and aspartic acid and 3-methylaspartic acid have been examined.The product of the first reaction, N-carbamoylaspartic acid 3, can cyclise to give either dihydroorotic acid 5 or 5-carboxymethylmydantoin 4.Acid catalysed cyclisation gives the latter while catalysis by the enzyme dihydroorotase gives the former.Introduction of a double bond into 3 changes the course of non-enzymatic cyclisation and a six-membered ring compound orotic acid 1 is the product.It is proposed that the double bond prevents intramolecular hydrogen bonding.
- Bruce, Michael J.,Butler, Anthony R.,Russell, Kate V.
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p. 319 - 322
(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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