Ureide formation

Ureide formation is intimately associated with the reduction of N2 in legumes. This conclusion is based on several lines of evidence. Nodulated soybeans contain higher concentrations of ureides than nonnodulated plants (Ku-shizaki eta/., 1964 Matsumoto e/a/., 1975,1977a Fujihara eta/., 1977), and removal of nodules resulted in a decrease in ALN concentration in soybeans (Fujihara and Yamaguchi, 1978a). The growth of soybean (Matsumoto et ai, 1975 Israel and McClure, 1980 McNeil and LaRue, 1984) and cowpea (Pate et ai, 1980) plants in the presence of nitrate resulted in a decrease in the ureide content of the xylem sap which correlated with the decrease in nodule mass and Nj-fixing activity. 

AMP to 8.3 mAf for UMP and 20 mA/for XMP. Doremus and Blevins have reported some properties for this enzyme from soybean nodules. Purine nucleosidase (EC 3.2.2.1) was described as having a pH optimum of 7 - 8 and a of 0.3 mM for inosine (Christensen and Jochimsen, 1983). Nucleosidase has been purified from cowpea nodules (Atkins et ai, 1989). The native molecular weight was 160,000 with a subunit molecular weight of 30,600. This enzyme was apparently cytoplasmic and was markedly xanthosine specific. The values for xanthosine and inosine were similar (0.80 and 0.83 mM, respectively). Neither of these enzymes has exhibited any specific relationship to ureide formation. 

These studies do not define the source of purines (i.e., de novo synthesis or turnover) for ureide biogenesis in vivo. It is known that de novo purine nucleotide synthesis increases rapidly within the first hour of germination (Obendorf and Marcus, 1974 Anderson, 1979) with ATP synthesis predominating over GTP synthesis, presumably to provide the energy requirements for polyribosome formation and protein synthesis. The synthesis of these nucleotides has not been linked to ureide formation, although turnover apparently does occur. 

Hydantoin itself can be detected ia small concentrations ia the presence of other NH-containing compounds by paper chromatography followed by detection with a mercury acetate—diphenylcarba2one spray reagent. A variety of analytical reactions has been developed for 5,5-disubstituted hydantoias, due to their medicinal iaterest. These reactions are best exemplified by reference to the assays used for 5,5-diphenylhydantoiQ (73—78), most of which are based on their cycHc ureide stmcture. Identity tests iaclude the foUowiag (/) the Zwikker reaction, consisting of the formation of a colored complex on treatment with cobalt(II) salts ia the presence of an amine (2) formation of colored copper complexes and (3) precipitation on addition of silver(I) species, due to formation of iasoluble salts at N. ... 

This subsection examines the hydrolytic stability of cyclic structures containing a ureido link. Schematically, ring closure can be achieved by N-alkylation or by /V-acylation of the second N-atom of the ureido moiety. The former results in the formation of, e.g., hydantoins and dihydropyrimidines. The latter ring closure leads to, e.g., barbituric acids. Taken together, cyclic ureides can also be regarded as ring structures that contain an imido function with an adjacent N-atom. We begin our discussion with the five-membered hydantoins, to continue with six-membered structures, namely dihydropyrimidines, barbituric acids, and xanthines. 

In the currently accepted mechanistic pathway outlined in Scheme 7, the key step in the Biginelli sequence involves the acid-catalyzed formation of an Wacyliminium ion intermediate of type 719 from the aldehyde and urea precursors <1997JOC7201, 2000ACR879, 20040R1>. Interception of the iminium ion 719 by the CH-acidic carbonyl component 715, presumably through its enol tautomer, produces an open-chain ureide 720, which subsequently cyclizes to hexahydropyrimidine 721. Acid-catalyzed elimination of water from 721 ultimately leads to the... 

Bundgaard, H. 1985b. Formation of prodrugs ofamines, amides, ureides, andimMe traJsinEnzymology Vol. 112, PartA, edited by K. J. Widder and R. Gree, 347-359. New York Academic Press, Inc. 

The phenol/glucose/urea resin, to which formaldehyde was later to be added, showed the usual sequence of products formation, but by the end of the acidic reaction stage, there were no distinct glucose or glucosyl ureide species identifiable by 13C-NMR or HPLC. After neutralization and addition of formalin, signals for formalin immediately showed in the 49 to 55 ppm (methoxy) and 82 to 90 ppm (hemiformal and hemiacetal) regions of the spectrum. After the end of an hour of reaction with formaldehyde, the 13C-NMR spectrum of the reaction mixture showed that the signals due to phenolic species had reduced in size relative to the sulfolane internal reference, but their number had multiplied... 

Sonne, J. C., Buchanan, J. M., and Delluva, A. M., Biological precursors of uric acid I. The role of lactate, acetate, and formate in the synthesis of the ureide groups of uric acid. J. Biol. Chem. 173, 69-79 (1948). 

Treatment of the ureide 129 or its 4-methyl derivative with diazomethane results in the formation of the monomethylated, and then the dimethylated spirohydantoin 131. This also demonstrates the ease of cyclization of these ureido derivatives. Similar reactions occur with 1,2-dihydro-2-oxo-3-ureidopyrido[2,3-h]pyrazine. If the methylated hydantoin 131 is treated with nitrous acid, the 1-nitroso compound 132 is formed. On alkaline hydrolysis this yields the 2-methylamino compound 133. The corresponding reactions with the 2-oxo isomer of 131 failed as... 

Hexobarbital is prepared by reacting together methyl urea and methyl-a-methyl-a-cyclo-hexen-1-yl-a-cyano acetate when an open-chain ureide is formed as an intermediate with the elimination of a molecule of methanol. This upon hydrolysis affords spontaneous closure of the ring thereby resulting into the formation of hexobarbital. 

The formation of diastereomeric ureides from chloro-fomnate reagents has been used in quantitative assays and for the preparative separation of both secondary and tertiary amines. Quantitative assays for promethazine, a tertiary amine of the phenothiazine group of pharmaceuticals, have been developed. Maibaum [100] carried out a three-stage reaction in which the racemic promethazine was reacted with vinyl chloroformate and the carbamate was subsequently hydrolysed to the secondary amine. The enantiomeric ratio of the amine was then determined as the urea following reaction with a chiral isocyanate. In a later development, Witte et al. [lOI] directly derivatized the same compound with (— )-menthyl chloroformate (17) and separated the diastereomers by HPLC. (—)-Menthyl chloroformate has also been used to resolve the enantiomers of nomicotine as... 

Formation of diastereomeric ureides from chiral chloroformates... 

The so-called ureide plants use allantoin and allantoic acid as a nitrogen store from which ammonia may be liberated by further degradation (E 2.2), In the liver of lungfish a glycine-allantoin cycle (Fig. 182) causes the formation of urea (cf. the formation of urea via L-ornithine derivatives, D 19). 

However, the authors prepared the bis-ureide 28 under acidic conditions to carry out the additional experiments, and subsequently, this isolated bis-ureide was reacted with different substrates under basic conditions to form the Biginelli product. This ambiguous proof with no details concerning the formation of bis-ureide 28 under basic conditions promoted an additional MS spectrometry study reported by Santhosh and coworkers [40] in order to clarify if other plausible pathways were able for this base-catalyzed Biginelli reaction. However, the authors were not able to find, under the same reaction conditions, the peak for the corresponding bis-ureide intermediate 28 proposed by Ji and cowoikers [39c]. 

Heinrich and Wilson further found, using labeled bicarbonate, that CO2 was extensively incorporated into the ureide carbon of uracil (position 2). The extent of its incorporation was about the same in the uracil ureide carbon as in position 6 of purines, which was previously shown to be derived from CO2. Labeled formate, which is a precursor of the ureide carbons of purines, did not label any part of the pyrimidine skeleton. ... 

Another enzyme, barbiturase, which catalyzed the hydrolysis of barbituric acid to urea and malonic acid (Fig. 13), has been partially purified and freed of urease activity. The mechanism involved in this reaction has not yet been established. It seems most plausible that the initial cleavage would yield a half ureide of malonic acid, since it is not likely that a single enzyme could simultaneously cleave two linkages in the same molecule. So far there has been no evidence to support the formation of a half ureide of malonic acid. 

In the mechanism of the Biginelli synthesis [265], the rate-determining step is the acid-catalyzed formation of an acylimine 35 from aldehyde and urea. By N-protonation (or metal-N-coordination), the imine 35 is activated (as an iminium ion) and intercepted by the P-ketoester (as enol or metal enolate) to give rise to an open-chain ureide 36, which subsequently cyclizes (via the cyclic ureide 37 and its dehydration) to afford the dihydropyrimidinone 33. Biginelli compounds of type 33 have been synthesized independently in multistep sequences [266]. 

Many animal tissues synthesized nucleic acids de novo from elementary precursors as well as from preformed purines in the diet. Other tissues, such as bone marrow, had a limited capacity for purine synthesis by the de novo route and appeared to utilize preformed purine compounds that were manufactured in the liver (450). In this experiment, the amount of formate-C incorporated into the bases of DNA of marrow cells was measured in control and hepatectomized rabbits. In control animals, the ratio of the specific activity of thymine to adenine was approximately 1, indicating a similar degree of incorporation of formate-C into the purine ureide carbons and into the thymine methyl group of DNA in bone marrow cells in vivo. In hepatectomized rabbits, the total incorporation of formate-C was substantially depressed but the thymine adenine ratio was increased to 27. The conclusion that the liver supplied preformed purines to the marrow cells was supported by the earlier observation that marrow cells in vitro utilized preformed adenine quite efficiently for nucleic acid synthesis (451). 

In general, hydrazides may be prepared by many of the methods analogous to those used in the preparation of amides. For example, hydrazine salts of carboxylic acids and reactions of hydrazine with esters, acyl halides, acyl anhydrides, and amides may be used to produce hydrazides. A reaction analogous to the Hofmann degradation is the formation of hydrazides from ureides (acylureas) [54] (Eq. 4). 

Analytical methods A variety of procedures have been reported for the measurement of ureides, including those based on the detection of urea and, in the case of ALN and ALA, on the selective formation and subsequent determination of glyoxalate. Methods for measuring substituted ureas include enzymatic or chemical degradation to form urea followed by the urease-catalyzed conversion of urea into carbon dioxide and ammonium with subsequent analysis (e.g., Nessler reaction, dichloroindophenol method) of the ammonium or colorimetric procedures such as the diacetylmonoxime reaction (which detects the carbamyl group—CONH2). The use of specific enzymes confers a degree of specificity to the former procedures. The latter procedure, however, detects ureides as a class of reactive compounds and does not differentiate between various ureido compounds. 

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