Enantioselective synthesis of isotopically labelled L‐α‐amino acids preparation of ¹³C‐, ¹⁸O‐and ²H‐labelled L‐serines and L‐threonines

Abstract

[3‐18O]‐L‐serine, [3‐13C]‐L‐serine, [3‐18O]‐L‐threonine, [3,4‐13C2]‐L‐threonine and [3‐2H]‐L‐threonine are prepared from simple commercially available, isotopically enriched starting materials like H218O, [13C]‐paraformaldehyde, [13C2]‐acetaldehyde and [1‐2H]‐acetaldehyde. The introduction of the side chain is based on the reaction of the anion of the bislactimether of cyclo‐(D‐Val‐Gly) with a suitable reagent. For serine this is isotopically labelled benzylchloromethylether, whereas for threonine labelled acetaldehyde is used in combination with chlorotitaniumtris[diethylamide], introducing both stereocentres in one single step. The isotopomers of serine and threonine are obtained on the gram scale in good yields and high enantiomeric and diasteriomeric excesses. New syntheses for [18O]‐benzylalcohol and isotopically enriched benzylchloromethylether are reported. Following the presented synthetic scheme these amino acids can be labelled at any position or at any combination of positions.

Local and distant protein structural changes on photoisomerization of the retinal in bacteriorhodopsin

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] O]threonine-labeled BR was prepared by growing Halobacterium salinarum (JW-3) in a defined medium similar to that described by Gochnauer and Kushner (26), except that the D-amino acids and NH 4 Cl were omitted and the L-threonine was replaced by 0.25 g͞liter L- [3-18 O]threonine. Under these conditions, lipid extraction and amino acid analysis with radiotracers show that typically about two-thirds of the threonine residues are labeled, with no scrambling of the label (27). The mutated genes for T17V, T24V, T46V, T47V, T55V, T89S, T90V, T121V, T142N, T178N, and T205V were constructed and introduced into Halobacterium salinarum as described (28).…”

Preparation and Characterization of [5‐13C]‐(2S,4R)‐Leucine and [4‐13C]‐(2S,3S)‐Valine − Establishing Synthetic Schemes to Prepare Any Site‐Directed Isotopomer of L‐Leucine, L‐Isoleucine and L‐Valine

“…Following the chain of reactions shown in Scheme 3, 13 could be converted into (2S)-isoleucine (2). The reactions in Schemes 2 and 3 lead to any 13 C, 15 ⁿ isotopomer of (2S)-isoleucine (2). Because any atom in isoleucine (2) has a well-defined source and no complications arise from prochiral groups, there is no need to further check this scheme.…”

“…The yield from 7 to 1 is 40 %. The reactions described in Schemes 1 and 2 lead to any site-directed 13 C and 15 N isotopomer of (2S)-valine (1) up to the unitary labeled form. To show that this scheme allows the chiral discrimination between the two diastereotopic methyl groups, [4-13 C]valine was prepared.…”

Chemo-Enzymatic Synthesis of Thymidine13C-Labelled in the 2′-Deoxyribose Moiety

“…The site-directed incorporation of stable isotopes into biomolecules such as amino acids [1] and cofactors [2] as well as biologically active macromolecular complexes, and their subsequent detection by means of non-invasive isotopesensitive techniques (e.g. solid-state NMR, [3] EPR, [4] FTIR, [5] and UV Laser Resonance Raman [6] spectroscopy) provides valuable information concerning the structure and function of the isotopically enriched site at an atomic level.…”