Synthesis of optically active 2-alkyl-3,4-iminobutanoic acids. beta-amino acids containing an aziridine heterocycle

All four stereoisomers of 2-alkyl-3,4-iminobutanoic acid, a novel class of beta -amino acids bearing a chemically versatile aziridine ring, were synth esized starting with aspartic acid. The synthetic strategy involves the int roduction of an alkyl group at the beta -position of fully protected optica lly active aspartic acid followed by the construction of an aziridine ring making use of the alpha -carboxylate and alpha -amino groups. The alpha -ca rboxylate was reduced to the corresponding alcohol, which was then subjecte d to cyclization to form an aziridine ring with the N-protected amino group . Removal of the protection groups yielded the target compounds.