1-aminophosphonic acids or reacted with Boc2O to yield N-Boc-protected 1-aminophosphonates. The enantiomers of 2-benzylthio-1-(t-butoxycarbonylamino)propylphosphonate were obtained from the racemate by chiral HPLC and converted to phosphonic acidanalogs of (R)- and (S)-homocysteine, (R)- and (S)-2-aminobutyric acid and (S)-methionine, all of ee >97% as determined by chiral HPLC.