A new procedure has been developed for synthesizing enantiomerically pure β-amino acids, α-hydroxy-β-amino acids and certain alkaloids from aspartic acid. By protection, anhydride formation and regioselective reduction, L-aspartic 10 is converted to the N-tosylamino lactone 12. Hydroxylation of 12 by an oxaziridine gives the trans-2-hydroxy-3-N-tosylamino derivative 20. Opening of 12 and 20 by trimethylsilyl iodide and ethanol affords the iodo-homoserine esters 13 and 21 respectively. Submission of 13 and 21 to Gilman reagents followed by saponification and deprotection gives 4-substituted 3-amino and 3-amino-2-hydroxybutyric acids (15 and 23), exemplified by the syntheses of cyclohexylnorstatine (25), and the components of bestatin (23, R=Ph) and microginin (14). Certain β-amino acids are transformed into solenopsin A (33) and indolizidine 209D (41).