PART I: DEVELOPMENT AND CHARACTERIZATION OF A PALLADIUM HYDROGENATION SYSTEM. PART II: SYNTHESIS AND METABOLISM OF EPSILON-N-METHYLLYSINES.

摘要

Part I. Formic acid, a good solvent for most peptides is used as a convenient hydrogen donor for catalytic transfer hydrogenation. (alpha)-N-CBZ-lysine in the presence of an equal weight of palladium black in 88% formic acid is completely deprotected in 30s, in stirred reactor. Lower concentrations of formic acid (4.4%) in methanol also result in rapid removal (5-10 min) of both benzyl ester and CBZ protecting groups at room temperature. Under those conditions the t-Boc group is stable as indicated by a 98% yield of t-Boc-aspartic acid obtained from t-Boc-aspartate (beta)-O-benzyl ester. The reaction with N-CBZ-methionylglycine ethyl ester is complete in 10 minutes with a 92% yield. The refractory N-benzyl and nitro groups of (epsilon)-N-benzyl and nitroarginine are also removed under the same conditions but require approximately 10 and 5 hours of reaction respectively. Palladium black packed in a column was shown to be an even more convenient method for deprotecting peptides. Thus a peptide solution in 4.4% formic acid in methanol is quantitatively deprotected by passing through a 0.9 x 2 cm loosely packed column of freschly prepared palladium black ((TURN)600 mg). Its products are removed after such procedure by simple evaporation of the eluent. A column reactor eliminates the need to separate product from catalyst as a separate step and reduces the manipulation of the catalyst and limits its exposure to the atmosphere thus prolonging its life. We also report the unique uses of formic acid and sodium boro-hydride as hydrogen sources that chemically react with palladium loading it with hydrogen under mild conditions. A column of 600 mg palladium black after such chemical hydrogenation is physically increased in size to almost 175% of its original volume. The actual volume of hydrogen stored upon treatment with formic acid amounts to about 61 cc per gram palladium or a Stoichiometry of hydrogen to palladium of about (1:2). The palladium/hydrogen reactant can be efficiently utilized to deprotect peptides and reduce olefinic compounds in the absence of a hydrogen donor. This procedure might be useful for the deprotection of delicate peptides and reduction of olefinic compounds sensitive to low or high pH. The palladium/hydrogen complex functions well under both alkaline and acidic conditions. The hydrogens in the palladium/hydrogen complex exchange freely with protoic solvents hydrogens. This property is utilized in deuteration of such a column by incubation with D(,2)O and the subsequent use of the palladium/deuterium complex in labeling of olefinic compounds.;Part II. Methyllysines were synthesized from various procursors and their metabolism was studied. Radioactivity from ingested (epsilon)-N-{('3)H} methyl and dimethyllysine residues of reductively methylated casein are rapidly and efficiently absorbed and incorporated into tissues of the chicken. Introduction of label into choline, carnitine and methionine suggests that methyl groups of dietary (epsilon)-N-methyl and dimethyllysine residues are utilized for the synthesis of several one-carbon pool compounds. In a controlled synthetic diet, feeding of methylated casein supported a better growth in chicken in the absence of the essential supplement choline, and thus a possible use of reductive methylation of proteins in poultry nutrition is suggested.