Stereoselectivity in the Oligomerization of Racemic TryptophanN-Carboxyanhydride (NCA-Trp) as Determined by Isotope Labeling and Mass Spectrometry

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The polycondensation of tryptophan N-carboxyanhydride (NCA-Trp) is investigated in the presence and in the absence of POPC (1-O-palmitoyl-2-O-oleoyl-sn-glycerol-3-O-phosphocholine) liposomes with the aim to study and to quantify possible stereoselective effects of the process. A novel technique, based on isotope labeling of one enantiomer, and high performance liquid chromatography mass spectrometry (LC-MS) allow determination of the individual stereoisomer distribution of oligomers up to n=10. For the first time, the preferential homochiral growth and the relative stereoisomer distributions for each oligomer length are directly demonstrated.