Synthesis of oxygen‐18 isotope labeled amino acids and dipeptides and its effects on carbon‐13 NMR

Abstract

SUMHARYOxygen-18 isotope labeled at the carboxyl group of glycine, L-alanine and L-proline were synthesized by acid catalyzed exchange or acid hydroll1;s of respective methyl ester derivatives of amino acids in HCl/H . Quantitative enrichment of ycine was achieved by the acid hydrofysis of amino fietonitrile in Hlf'O.In order to conserve the isotopic epfjichment [ 0) dipepti s were synthesized by solid phase method.[

Efficient Total Chemical Synthesis of 13C=18O Isotopomers of Human Insulin for Isotope‐Edited FTIR

“…[17] We then carried out the Boc-protection/isotope exchange reaction in the reverse order. First, we conducted the exchange reaction of H-(1- 13 C)Phe-OH with a 1:1 mixture of H 2 18 O/dioxane at 100 °C; [18] After a few cycles of the exchange reaction, satisfactory enrichment was obtained. Lyophilization followed by Boc-protection in dioxane/water and rapid acid-base extraction workup gave essentially pure Boc-(1- 13 C= 18 O)Phe.…”

Multiple-Turnover Isotopic Labeling of Fmoc- and Boc-Protected Amino Acids with Oxygen Isotopes

“…Isotopically labeled amino acids have found wide application in structure elucidation of peptides and proteins. In addition to 17 O NMR studies, − 2D-IR techniques are emerging as important new tools for probing protein folding and ligand binding. − Due to its time resolution in the subpicosecond range, time-resolved 2D-IR spectroscopy can report the rapid evolution of nonequilibrium conformational states to reveal folding pathways. − These techniques rely upon site-specific incorporation of 18 O-labeled amino acids into peptides and proteins to serve as spectroscopic probes. − To date, only aliphatic, aromatic, and sulfur-containing amino acids have been utilized in such studies because currently used methods for preparing 18 O-labeled amino acids result in uniform 18 O-labeling of side chain and α-carboxylic acids. − …”

“…18 O-labeling is normally conducted by heating the carboxylic acid with 18 OH 2 in the presence of a strong acid to catalyze exchange (Scheme ). By using an excess of 18 O water, the reported yields for isotopic enrichments are typically 75−85%. ,− A labeling procedure for Fmoc-protected amino acids with multiple rounds of acid-catalyzed 18 OH 2 equilibration recently reported 18 O enrichments of 90−96% for Phe, Ala, Gly, and Phe . This method can be very efficient with respect to 18 OH 2 consumption, but the protecting groups typically used for functionalized side chains (Boc, Trt, t Bu, etc.)…”

Synthetic methodologies in organic chemistry involving incorporation of [17O] and [18O] isotopes

“…The [ 18 O] enrichment of the amino acids was obtained by the same way . Amino acids with two [ 18 O] atoms in the carboxyl moiety were synthesized by Murphy and Clay easily from the amino acids and H 2 18 O through exchange in acidic H 2 18 O, without racemization.…”