Nine isotopomers of tryptamine and its halogen derivatives, labeled with deuterium, tritium in side chain, i.e., [(1R)-2H]-, [(1R)-3H]-, 5-F-[(1R)-2H]-, 5-F-[(1R)-3H]-, 5-Br-[(1R)-2H]-, double labeled [(1R)-2H/3H]-, 5-F-[(1R)-2H/3H]-, and ring labeled [4-2H]-, and [5-2H]-tryptamine, were obtained by enzymatic decarboxylation of l-Trp and its appropriate derivatives in deuteriated or tritiated media, respectively. Intermediates: [5′-2H]-l-Trp used for further decarboxylation was synthesized by enzymatic coupling of [5-2H]-indole with S-methyl-l-cysteine, and [4′-2H]-l-Trp was obtained by isotope exchange 1H/2H of the authentic l-Trp dissolved in heavy water induced by UV-irradiation. Doubly labeled [(1R)-2H/3H]- and 5-F-[(1R)-2H/3H]-tryptamine were obtain by decarboxylation of l-Trp or [5′-F]-l-Trp carried out in 2H3HO incubation medium.
The reaction mechanisms of the enzymatic deamination of tryptamine catalysed by the enzyme monoamine oxidase (MAO, EC 1.4.3.4) were investigated using the kinetic isotope effect and solvent isotope effect methods. The numerical values of these deuterium effects in the (1S) and (1R) positions of tryptamine were determined using the non-competitive spectrophotometry. The deuterium-labelled isotopologue [(1S)-(2)H]tryptamine was obtained in two steps by enzymatic coupling of indole with S-methyl-l-cysteine in a deuterated medium followed by enzymatic decarboxylation of the resulting [2-(2)H]-l-tryptophan. [(1R)-(2)H]tryptamine was obtained by enzymatic decarboxylation of l-tryptophan in the fully deuterated medium.
Abstract. The enzymatic deamination of 5-fl uorotryptamine and 5-hydroxytryptamine, 5-HT, catalysed by enzyme monoamine oxidase A (MAO-A, EC 1.4.3.4) was investigated using the kinetic (KIE) and solvent (SIE) isotope effects methods. The numerical values of deuterium isotope effects in the (1R) positions of 5-F-tryptamine were determined using non-competitive spectrophotomeric method. Isotopologue 5-F-[(1R)--2 H]-tryptamine, needed for kinetic studies was obtained by enzymatic decarboxylation of 5-fl uoro-L-tryptophan, 5-F-L-Trp, in fully deuteriated medium.
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