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Title: Resolution and Configuration of Alloxanic Acid
Title: Covalent Adducts of Dehydrouric Acid
Title: Structural Revision of Uric Acid Glycol Monoethers
Title: Conformational Isomerism in Covalent Diadducts of
Dehydrouric Acid
Title: New Mechanism for Enzymic Oxidative Degradation of Purines
Faculty: PMF Sveučilite u Zagrebu
Author: SOKOLIĆ LEA
Date of defense: 04/07/93
Language: hrvatski
Number of pages: 81
Summary: A new approach to this old problem has been used to
elucidate the coherent mechanism of uricolysis. The regiochemistry of
oxidation of uric acid was studied by 5-14C-labelling. The degradation to
14CO2 and carboxy-14C-allantoate demonstrated that the 4-position of
allantoin and the carboxylate of uroxanate have their origin in C-5 of
urate. None of the mechanisms that have been proposed would have predicted
this result. Thus, the rearrangement must occur by ring-opening at the
1,6-position and by 1,2-carboxylate shift to give allantoin-5-carboxylate,
which either decarboxylates to allantoin or undergoes hydrolysis to
uroxanate. Use of 8-13C-urate in combination with NMR location of the label
disclosed a regiospecific pattern in conversions to 2-13C-allantoin
catalysed by various uricases and peroxidase. The rates of uricase-mediated
oxidation were essentially identical in H2O and D2O, but a sizeable isotope
effect was observed for the decay of incipient intermediate, indicating a
rate-determining proton transfer in the first nonenzymic stage of the
consecutive transformation to allantoin.
Keywords: purine, ring-transformation, rearrangement, allantoic acid, allantoin, 13C-labelling, 14C-labelling, NMR, uric acid, oxidation, peroxidase, regiochemistry, uricase, uricolysis, uroxanic acid
Title: Regiochemistry and Stereochemistry of Uricolytic Processes
Faculty: PMF Sveučilite u Zagrebu
Author: MODRIĆ NEVENKA
Date of defense: 12/27/91
Language: hrvatski
Number of pages: 79
Summary: New approach to configurational correlations takes
advantage of the fact that the branching uricolytic pathways to
(+)-allantoin and (+)-alloxanate both involve a common levorotatory
precursor. Optical antipodes of alloxanic acid and its derivatives, the key
compounds in this approach, were prepared by resolution via brucine salts.
Resolution of brucine salts gave (-)-caffolide, which undergoes a
decarboxylative breakdown into the racemic amide of alloxanic acid. The
regiochemical course of oxidation of 5-13C-urate mediated by uricase from
A. flavus (pD 7.2, D2O/phosphate) was followed directly by NMR. 13C-shifts
and timing of signals corresponded to consecutive transformations of the
primary 5-hydroxy-5-13C-isourate (87.5 ppm), 1,6-opened product (87.1),
allantoin-5-carboxylate (175.6), and 4-13C-allantoin (176.9). Spectra of
products from oxidation in borate buffer disclosed a different course and
regiochemistry in breakdown of 4-13C-urate. Incorporation of the label into
4-13C-alloxanate (171.8 ppm) and 4-13C-allantoin (173.4), revealed a
1,5-contraction of the pyrimidine ring. A general route to ethers of
alloxanic acid ureides is described, revising their originally assigned
bicyclic structures.
Keywords: purine, uric acid, oxidation, rearrangement, allantoin, alloxanic acid, caffolide, 5-hydroxy-isouric acid, intermediate, NMR/13C-labelling, ring-modifying reactions, resolution, regiochemistry, stereochemistry, uricase, uricolysis
Title: New Mechanism for Enzymic Oxidative Degradation of Purines
Faculty: PMF Sveučilite u Zagrebu
Mentor: POJE MIRKO
Date of defense: 04/07/93
Number of pages: 81
Author: Sokolić dr Lea
Degree level: Ph.D.
Title: Regiochemistry and Stereochemistry of Uricolytic Processes
Faculty: PMF Sveučilite u Zagrebu
Mentor: POJE MIRKO
Date of defense: 12/27/91
Number of pages: 79
Author: Modrić dr Nevenka
Degree level: Ph.D.
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