Stereoselectivity in the oligomerization of racemic tryptophan N-carboxyanhydride (NCA-Trp) as determined by isotope labeling and mass spectrometry

The polycondensation of tryptophan N-carboxyanhydride (NCA-Trp) is investig ated in the presence and in the absence of POPC (1-O-palmitoyl-2-O-oleoyl-s n-glycerol-3-O-phosphocholine) liposomes with the aim to study and to quant ify possible stereoselective effects of the process. A novel technique, bas ed on isotope labeling of one enantiomer, and high performance liquid chrom atography mass spectrometry (LC-MS) allow determination of the individual s tereoisomer 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.