Enantioselective synthesis of isotopically labelled L-α-amino acids. Preparation of 13C-, 18O- and 2H-labelled L-serines and L-threonines

[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 bislactimeter 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 isopomers 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. (author)