Boc-Phenylglycine: The Reagent of Choice for the Assignment of the Absolute Configuration of alpha-Chiral Primary Amines by (1)H NMR Spectroscopy.

The absolute configuration of an alpha-substituted primary amine can be easily determined by direct comparison of the (1)H NMR spectra of the (R)- and the (S)-Boc-phenylglycine derivatives. A simplified model, based on extensive conformational analysis and NMR data, is presented that associates the spatial location of the substituents around the asymmetric carbon of the amine with the signs of Deltadelta(R)()(,)(S)(). The substituent with a negative Deltadelta(R)()(,)(S)() occupies the position of L(1) in Figure 7 and that with a positive Deltadelta(R)()(,)(S)() the position of L(2). From this model the absolute configuration (R/S) of the chiral center can be determined.The BPG amides give rise to much higher Deltadelta(R)()(,)(S)() values than the classical reagents MTPA and MPA and offer a greater guarantee for the correct assignment of the absolute configuration.