STUDIES OF BIOORGANIC CHEMISTRY. PART I: INTERACTIONS OF METAL IONS WITH NUCLEOTIDES: INVESTIGATIONS BY OXYGEN-17 NMR. PART II: SYNTHESES OF CHIRAL MALONIC ACIDS (MAGNESIUM, ATP, CHIRAL MALONATES)

SHUYEN LEE HUANG, Purdue University

Abstract

I. Determining the chelation pattern between Mg('2+) and adenine nucleotides is an important step towards the understanding of substrate specificity of the enzymes that catalyze phosphoryl transfer reactions. ('31)P NMR has been used to investigate this problem. However, it has been shown that changes in ('31)P chemical shifts may not be directly related to the site of binding. We proposed to study this problem by using ('17)O NMR based on the observation that binding of metal ion causes the ('17)O NMR signal of nucleotides to broaden. Our results indicate that Mg('2+) interacts with both the (alpha)- and (beta)- phosphate of ADP, and all of the (alpha)-, (beta)-, and (gamma)-phosphates of ATP. The extent of (alpha) coordination in MgATP is somewhat smaller. These results establish the "macroscopic" structure of MgADP and MgATP. The use of substitution-inert Co('3+) complexes of ADP and ATP of known structure demonstrates the site specificity of the line-broadening effect in ('17)O NMR. Nonspecific factors such as change in pH, viscosity, paramagnetic impurities and chemical exchange processes have been shown not to dominate our results. II. Malonic acid (HOOCH(,2)COOH), an important precursor in the biosynthesis of fatty acids and polyketides, is a pro-prochiral molecule of the type C(,aabb). It is possible to convert malonic acid into a chiral molecule by placing a ('13)C isotope in one of the carboxyl groups and deuterium in one of the methylene hydrogens, and to use these chiral malonic acids to study the stereochemical course of polyketide biosynthesis. In this part of the thesis the stereospecifically labeled chiral malonic acids, HOOCCHD('13)COOH (R & S isomers) and HOO('13)C('13)C DHCOOH (R & S isomers), are prepared starting from (1,4-('13)C) acetylenedicarboxylic acid and (2,3-('13)C) acetylenedicarboxylic acid, respectively. The synthesis proceeded by: hydrogenation of acetylenedicarboxylic acid to maleic acid; isomerization of maleic acid to fumaric acid; conversion of fumaric acid to L-malic acid; and oxidation of L-malic acid to malonic acid. The unique IR and NMR spectral features of the intermediates involved are also discussed.

Degree

Ph.D.

Subject Area

Organic chemistry

COinS