Stereoisomers and analogues of amastatin, [(2S, 3R)-3-amino-2-hydroxy-5-methylhexanoyl]-L-Val-L-Val-L-Asp, were synthesized and their inhibitory activities towards aminopeptidase A (AP-A) and other arylamidases tested. Among the four stereoisomers of a new amino acid residue in amastatin, the 2S stereoisomers exhibited strong activity. In a series of compounds in which the C-terminal amino acid of amastatin was substituted by other amino acids, the one containing Asp or Glu showed the strongest activity towards AP-A. In a series of compounds in which the second or third residue from the amino terminal of amastatin was substituted by other amino acids, the one containing hydrophobic amino acids showed strong activity. In the study of the relationship of the length of the peptide chain and inhibitory activity, the activity towards AP-A was seen to increase until the length of the peptide reached that of a tetrapeptide.
Reaction of tributyltin cyanide with optically active 2-N-benzyloxyearbonylamino aldehydes 1 gives the corresponding O-tributylstannyl cyanohydrins 2 and 3 stereoselectively. Compounds 2 and 3 are transformed in situ into the methyl 3-N-benzoyloxycarbonyl-amino-2-hydroxy esters 4 and 5, respectively, via the imidate hydrochloride intermediates. Saponification of 4 and 5 provide 3-amino-2-hydroxy acids 6 and 7, respectively, key intermediates in the preparation of Bestatin, Amastatin, and analogues.