The mechanism of the reaction of high temperature solid state catalytic isotope exchange (HSCIE) of hydrogen in peptides with spillover-tritium at 140-180 degrees C was analyzed. This reaction was used for preparing [(3)H]enkephalins such as [(3)H]DALG with specific activity of 138 Ci/mmol and [(3)H]LENK with specific activity of 120 Ci/mmol at 180 degrees C. The analogues of [(3)H]ACTG(4-10) with specific activity of 80 Ci/mmol, [(3)H]zervamicin IIB with specific activity of 70 Ci/mmol and [(3)H]conotoxin G1 with specific activity 35 Ci/mmol were produced. The obtained preparations completely retained their biological activity. [(3)H]Peptide analysis using (3)H NMR spectroscopy on a Varian UNITY-600 spectrometer at 640 MHz was carried out. The reaction ability of amino fragments in HSCIE was shown to depend both of their structures and on the availability and the mobility of the peptide chain. The reaction of HSCIE with the beta-galactosidase from Termoanaerobacter ethanolicus was studied. The selected HSCIE conditions allow to prepare [(3)H] beta-galactosidase with specific activity of 1440 Ci/mmol and completely retained its the enzymatic activity.

New catalytic reaction between a solid bioorganic compound and activated spillover tritium (ST), based on High-temperature Solid-state Catalytic Isotopic Exchange (HSCIE) was examined. The HSCIE mechanism and determination of the reactivity of hydrogen atoms in amino acids, peptides and proteins was investigated. Quantum mechanical calculations of the reactivity of hydrogen atoms in amino acids in the HSCIE reaction were done. The carbon atom with a greater proton affinity undergoes a greater exchange of hydrogen for tritium in HSCIE. The electrofilic nature of spillover hydrogen in the reaction of HSCIE was revealed. The isotope exchange between ST and the hydrogen of the solid organic compound proceeds with a high degree of configuration retention at the carbon atoms. The HSCIE reaction enables to synthesize tritium labeled proteins with a specific activity of 20-30 mCi/mg and kept biological activity.

No abstract

The solid-state reaction of isotope exchange of L-alanine (L-AIa) with spillover-hydrogen activated on a Rh(Pd)-supt~orted catalyst was studied. The reactivity of the carbon atoms and the activation energies of isotope exchange of the hydrogen at the C(2~ and C(3) atoms of the t.-Ala molecule were determined using tritium NMR. The ab initio calculations of the activation energy of a model reaction between the alanine molecule and a hydroxonium cation were carried out. The mechanism and plausible structures of the transition states of this reaction were proposed.Key words: isotope exchange, quantum-chemical calculations, activation energy, hydrogen spillover.The interaction of gaseous hydrogen with metals of the platinum group results in molecular sorption, atomic chemisorption, and dissolution of hydrogen in the metal. In the case of supported catalysts such as Pd/BaSO 4 and Pd/A1203, the H atoms bound to the surface metal atoms can migrate to the support (spillover hydrogen, SH). t This activated hydrogen, located on the support surface, can enter the reactions characteristic of hydrogen on the surface of metals of the platinum group. The hydrogenation of unsaturated compounds, reduction of WO 3 to tungsten bronze, and isotope exchange in the hydroxyl groups of the inorganic supports, proceeding with participation of SH are known. Stereoselective hydrogenation of the aromatic group with the formation of an optically active compound 2 proceeds in a solid "heterogeneous catalyst--asymmetric crystals of a substituted phenol" mixture under the action of SH at room temperature. The nature of SH has not been established unambiguously up to the present despite the fact that processes using hydrogen spillover have been known for many years. According to several existing hypotheses, it is a solvated proton, 3 a proton-electron pair, 4 or an atomized hydrogen, s No theoretical studies using a quantum-chemical simulation of the reactions with participation of SH have beet~ published yet.Reaction based on applying high-temperature solidstate catalytic isotope exchange (HSCIE) 6,7 appears to be particularly efficient for the synthesis of biologically active compounds labeled by hydrogen isotopes. Intense isotope exchange between the H atoms of a solid organic compound and the activated hydrogen occurs in the solid mixture formed by a metal of the platinum group, a solid organic compound, and an inorganic support. As a rule, HSCIE proceeds to a large extent with retention of configuration of the asymmetric carbon atoms. H SCI E was the first reaction that made it possible to obtain organic compounds uniformly labeled with tritium; such compounds were inaccessible previously. The present work is dedicated to a theoretical and experimental study of the mechanism of HSCIE with tritium in alanine. ExperimentalSolid-state isotope exchange between L-alanine and tritium. A solid mixture containing 0.5 mg of L-alanine (L-Ala) {"Sigma") was placed into an ampule (10 mL). For this purpose, 25 mg of activated carbon (Norit A, "Serva") c...