Aspartic proteinase inhibitors

BINAP-Ru is effective for the diastereoselective hydrogenation of some chiral yS-keto esters (Fig. 32.13). Reaction of N-Boc-protected (S)-y-amino / -keto esters 13A catalyzed by the (R)-BINAP-Ru complex results in the syn alcohols 13B exclusively [52]. The stereocenter at the / -position is controlled by the chirality of the catalyst therefore, use of the S catalyst affords the anti isomer, as predicted. Derivatives of statine, a key component of the aspartic proteinase inhibitor pep-... 

Scheme 6-28. Statine 65, part of aspartic proteinase inhibitor.

Aspartic proteinase inhibitors in which the scissile bond is replaced by a phosphinic acid group (shown below) have been reported [28]. 

Serine Proteinase Inhibitor I Serine Proteinase Inhibitor II Cysteine Proteinase Inhibitor Aspartic Proteinase Inhibitor Polyphenol Oxidase... 

HIV proteinase inhibitors may display a specific anti-Sap activity leading to a reduced number of C. albicans yeasts on epithelial cells. Therefore, development of specific aspartic proteinase inhibitors might be useful in the treatment of mucosal candidiasis. The precise function of Candida Saps in the adherence process is not known, but two hypotheses can be advanced (1) the Candida Saps could act as ligands to surface proteins of the specific host cells, which do... 

For the preparation of aspartic proteinase inhibitors, Jones et al. [7] needed epimeric A -protected alcohols (see Table 1, entry 2). In this stereocontrolled synthesis of hydroxyethylene dipeptide isoteres, a chiral Grignard reagent was used in a reaction with a protected aminoaldehyde [7]. In this reaction, a 6 1 ratio of diastomers 4SAR) was obtained. The stereochemistry of the products was controlled by the complexation of the reagent with the protected amine the S-epimer predominates because of a chelation-controlled addition of the Grignard. 

The mutation of the hydroxyl group positioned in R-configuration at the C(3) atom of the central statine (rSta) residue of the inhibitor gives rise to AAGbind of -0.51 kcal/mol, which is very close to the experimental value of -0.8 kcal/mol. It may be noted here that the starting configuration of the inhibitor in the enzyme-inhibitor complex is the same as that of pepstatin. The crystal structure of rhizopus pepsin or any other aspartic proteinase... 

K. Suguna, E. A. Padlan, C. W. Smith, W. D. Carlson, and D. R. Davies, Binding of a reduced peptide inhibitor to the aspartic proteinase from Rhizopus Chinensis Implications for a mechanism of action, Proc. Natl. Acad. Sci. USA 84 7009 (1987). 

Based on their sequence homology, disulfide connectivity, and cysteine location within the sequence and chemistry of the reactive site. Pis can be assigned to distinct families, as classified by Laskowski and Kato. Kunitz-type, Bowman—Birk-type, Potato type I and type II, and squash inhibitors are members of these families shown in Table 3. For inhibitors not falling into these classifications more families have been proposed. Pis can also be classified by their target/mode of action. Plants have been found to express Pis that target serine proteinases, cysteine proteinases, aspartic proteinases, and metallo-proteinases. Serine and cysteine protease inhibitors are the best-studied PIs. ... 

The mechanism of the aspartic proteinases involves two essential catalytic aspartate residues. There is some controversy in the literature as to whether the mechanism involves an acyl en me intermediate or an amino enzyme intermediate (4). However, there is no direct evidence for either intermediate so additional studies with inhibitors and pseudosubstrates along with crystallographic analysis will ultimately be required to resolve these questions. 

The active-site cleft has a less open arrangement in renins than in the other aspartic proteinases. Many loops as well as the helix hc (residues 224-236) belonging to the C-domain (residues 190-302) are significantly closer to the active site in the renin structures compared to those of endothiapepsin-inhibitor complexes. This is partly due to a difference in relative position of the rigid body comprising the C-domain. For instance, there is a domain rotation of 4° and translation of 0.1 A in the human renin complex with respect to the endothiapepsin-difluorostatone complex. 

This rather rigid poly-proline loop, together with the loop comprised of residues 241-250, lies on either side of the active site flap formed by residues 72-81. Hence, in the renins, the cleft is covered by the flaps from both lobes rather than from the N-lobe alone as in other pepsin-like aspartic proteinases. This gives renin a superficial similarity to the dimeric, retroviral proteinases where each subunit provides an equivalent flap that closes down on top of the inhibitor [44,45]. 

There is also great similarity between aspartic proteinases in terms of interactions with the transition-state analog inhibitors at the catalytic center. The catalytic aspartyl side chains and the inhibitor hydroxyl group are essentially superimposable in both renin complexes. The isostere C-OH bonds lie at identical positions when the structures of inhibitor complexes of several aspartic proteinases are superposed, in spite of the differences in the sequence and secondary structure. Most of the complex array of hydrogen bonds found in endothiapepsin complexes are formed in renin with the exception of that to the threonine or serine at 218, which is replaced by alanine in human renin. The similarity can be extended to all other pepsin-like aspartic proteinases and even to the retroviral proteinases [44,45]. This implies that the recognition of the transition state is conserved in evolution, and the mechanisms of this divergent group of proteinases must be very similar. 

If the main-chain hydrogen bonding of substrates is conserved among aspartic proteinases, how are the differences in specificities achieved Table 1 defines the enzyme residues that line the specificity pockets for both mouse and human renin. In modeling exercises (e.g., Reference 4) it was assumed that specificities derive from differences in the sizes of the residues in the specificity pockets (Sn) and their ability to complement the corresponding side chains at positions Pn in the substrate/inhibitor. A detailed analysis now shows that this simple assumption only partly accounts for the steric basis of specificity. 

For example, in the specificity subsite S3 the phenyl rings of Phe P3 occupy almost identical positions in both renin inhibitor complexes. Modeling studies have predicted the specificity subsite S3 to be larger in renins than in other aspartic proteinases [4] due to substitution of smaller residues, Pro 111, Leul 14, and Alai 15, in place of larger ones in mammalian and fungal proteinases. However, a compensatory movement of a helix (hN2) makes the pocket quite compact and complementary to the aromatic ring as shown in Figure 5. Thus, the positions of an element of secondary structure differ between renin and other aspartic proteinases with a consequent important difference in the specificity pocket. 

Blundell TL, Cooper J, Foundling SI, Jones DM, Atrash B, Szelke M. On the rational design of renin inhibitors X-ray studies of aspartic proteinases complexed with transition state analogues. Biochemistry 1987 26 5585-5590. 

Szelke M. Chemistry of renin inhibitors. In Kostka V, ed. Aspartic Proteinases and Their Inhibitors. Berlin Walter de Gruyter, 1985 421-441. 

Cooper JB, Foundling SI, Blundell TL, Boger J, Jupp R, Kay J. X-ray studies of aspartic proteinase-statine inhibitor complexes. Biochemistry 1989 28 8596-8603. 

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