‘N-Stereogenic Quaternary Ammonium Salts’ from L-Amino Acids: Synthesis, Separation, and Absolute Configuration

Diastereoisomeric linear and cyclic 'N-chiral quaternary ammonium salts' (QASs) were efficiently synthesized from corresponding L-amino acids in high yields. The diastereoisomers of each pair of 'N-chiral QASs' were successfully separated. The absolute configurations of these QASs were determined predominately by X-ray single-crystal analysis. The H-1-NMR data of 'N-chiral QASs' provided characteristic information on the configuration of the N-chiral center. 'N-Chiral QASs' exemplified by [N(R)]-2a and [N(S)]-2a are stable in protic and aprotic solvents within a broad pH and temperature range.