1. Sixteen triterpenoid compounds, related to glycyrrhetic acid, have each been tested for anti-pepsin, anti-pepsinogen, anti-trypsin and anti-chymotrypsin activity. Their actions are compared with the known inhibitory actions of the triterpenoid, carbenoxolone, which is clinically effective in the healing of chronic gastric ulceration in man.

2. One of these compounds, 3-O-lauroyl-11-oxo-18α-olean-12-en-30-oic acid is known to be clinically ineffective in the healing of human gastric ulceration, and is found to have no inhibitory action upon any of the enzymes tested.

3. Anti-pepsin activity is affected by the nature of the side chain in the C-3 position, by substitution in the C-30 position, and by cleaving the A-ring. Anti-pepsinogen activity is affected by substitution into the C-28 position and/or by loss of the 11-oxo group.

4. The results enable suggestions to be made for the synthesis of new anti-pepsin and potential anti-ulcer triterpenoid derivatives.

5. The homologous enzymes, human pepsin 3 and swine pepsin A, are each affected similarly by the sixteen compounds. The correlation between effects of the compounds on pairs of enzymes may thus be used as a measure of the structural similarity of the enzymes. The correlation coefficients are high among the individual pepsins and among the individual pepsinogens.

6. It is also suggested that those triterpenoids which have anti-trypsin and anti-chymotrypsin activity may have a potential value in diseases in which pancreatic enzymes are released.

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