Antifertility and Antiproteolytic Activity of Activated N‐Carbobenzoxy Amino Acid Esters

N‐Carbobenzoxy L‐phenylalanine, glycine, L‐leucine, and L‐proline derivatives, their vinyl esters, and their 1, 2‐dibromoethyl esters were tested for antifertility activity in mice. Intraperitoneal administration reduced the pregnancy percentage and the number of fetuses per litter, Intravaginal administration reduced the pregnancy percentage significantly, with N‐carbobenzoxyglycine vinyl ester, N‐carbobenzox‐yglycine‐1,2‐dibromoethyl ester, N‐carbobenzoxy‐L‐leucine‐ 1,2‐dibromoethyl ester, and N‐carbobenzoxy‐L‐proline‐1,2‐dibromoethyl ester producing 100% inhibition at 10 mg/kg/day. Sperm enzyme hydrolysis of the nonspecific substrate azocasein was inhibited significantly by certain N‐Carbobenzoxy amino acid esters in vitro. Specific substrate N‐benzoyl‐L‐arginine ethyl ester hydrolysis was also inhibited. Compounds that inhibited N‐benzoyl‐L‐arginine ethyl ester hydrolysis also demonstrated in vivo intravaginal antifertility activity.