Succinyl-L-proline

Aspartame (L-aspartyl-L-phenylalanine methyl ester, is a widely used artificIal sweetener. In humans and other animals aspartame is initially hydrolyzed to L-aspartyl-L-phenylalanine by intestinal esterases. L-Aspartyl-L-phenylalanine inhibits angiotensin converting enzyme purified from rabbit lungs with a Ki of 11 +/- 2 microM, equipotent to the IC50 of 12 microM for 2-D-methyl-succinyl-L-proline which has been reported to be an orally active antihypertensive agent in rats. Thus the possibility exists that L-aspartyl-L-phenylalanine inhibits angiotensin converting enzyme in humans consuming large quantities of aspartame. Both aspartame itself and the diketopiperazine formed from it, 3-carboxymethyl-6-benzyl-2,5-diketopiperazine, are weak inhibitors with Ki's greater than 1 mM.

Captopril is a remarkably effective new antihypertensive drug designed and developed as a potent and specific inhibitor of angiotensin-converting enzyme, a zinc metallopeptidase that participates in the synthesis of a hypertensive peptide, angiotensin II, and in the degradation of a hypotensive peptide, bradykinin. Earlier studies with a snake venom peptide (teprotride or SQ 20881) that could be administered only by injection demonstrated that specific inhibitors of angiotensin-converting enzyme could be highly effective as antihypertensive drugs, and helped to clarify the specificity and mechanism of action of the enzyme. A hypothetical model of the active center of angiotensin-converting enzyme based on its presumed analogy to the well characterized zinc metallopeptidase carboxypeptidase A was used to guide logical sequential improvements of a weakly active prototype inhibitor that led eventually to the highly optimized structure of captopril. The hypothetical working model of the active site of angiotensin-converting enzyme used to develop captopril continues to provide a firm basis for development of new types of specific inhibitors of this biologically important enzyme.