Sulfur-Containing Acylamino Acids. I. Syntheses and Angiotensin I Converting Enzyme-Inhibitory Activities of Sulfur-Containing N-Mercaptoalkanoyl Amino Acids

N-Mercaptoalkanoyl derivatives of sulfur-containing amino acids were synthesized and examined for inhibitory effects on angiotensin I converting enzyme (ACE) extracted from rabbit lung. Inhibition of ACE was determined by means of a spectrometric assay with hippuryl-L-histidyl-L-leucine as a substrate. Among the synthesized sulfur-containing compounds, N- (2-benzyl-3-mercaptopropanoyl) -S-methyl-L-cysteine (13a) and N- (2-benzyl-3-mercaptopropanoyl) -S-ethyl-L-cysteine (13c) showed the most potent inhibitory effects on ACE activity. The IC50 values of 13a and 13c on ACE activity were 0.028 and 0.020 μM, respectively.