No abstract

A series of novel synthetic dipeptides, containing a C-terminal glyoxal grouping (-COCHO), have been tested as inhibitors against typical members of the serine- and cysteine-proteinase families. For example, the sequences benzyloxycarbonyl (Cbz)-Pro-Phe-CHO (I) and Cbz-Phe-Ala-CHO (II), which fulfil the known primary and secondary specificity requirements of chymotrypsin and cathepsin B respectively, have been found to be potent reversible inhibitors of their respective target proteinase. Thus I was found to inhibit chymotrypsin with a Ki of approximately 0.8 microM, whereas II exhibits a Ki of approximately 80 nm against cathepsin B. These Ki values are some 10-fold and 3-fold lower than those reported for the corresponding peptide-aldehyde inhibitors of chymotrypsin and cathepsin B upon which the peptidyl-glyoxals were fashioned. Unexpectedly, the sequence Cbz-Pro-Ala-CHO, which was designed to inhibit elastase-like proteinases, exhibited no inhibitory activity towards porcine pancreatic elastase, even when used at concentrations as high as 200 microM.

Homochiral N-protected a-amino glyoxals are readily accessible by oxidation of a-diazoketones derived from natural amino acids and dipeptides using dimethyldioxirane in acetone; the glyoxals can be trapped efficiently in reactions such as Wittig olefination and condensation with amines and vicinal diamines.Without functional group protection amino glyoxals of type 1 would be expected to undergo spontaneous polymerisation. With appropriate N-protection they should be reasonably stable, yet amenable to a range of useful synthetic transformations through the highly electrophilic aldehyde group. They are , for example, potential precursors of hydrolytically stable pseudopeptides or peptide isosteres.1We have developed a general route (Scheme 1) to amino glyoxals in the N-protected form 2 from a range of L-amino acids. The route is equally applicable to any N-protected peptide with a free carboxylic acid group and the reaction conditions appear to tolerate most forms of N-protection. So far we have successfully employed Boc, Z, phthaloyl and ethoxycarbonyl groups. The N-protected amino acids and dipeptides 3 shown in Table 1 were transformed into the corresponding diazoketones 4 using standard procedures.* The key step in the sequence was oxidation of the diazoketones to glyoxals 2 using distilled dimethyldioxirane (DMD) 5 in acetone,3.4 a process recently reported for simple achiral 0 1 Me Me x:5

No abstract

A series of synthetic peptides in which the C-terminal carboxyl grouping (-CO(2)H) of each has been chemically converted into a variety of ene dione derivatives (-CO-CH=CH-CO-X; X = -H, -Me, -OBut, -OEt, -OMe, -CO-OMe), have been prepared and tested as inactivators against typical members of the serine and cysteine protease families. For example, the sequences Cbz-Pro-Phe-CH=CH-CO-OEt (I) which fulfils the known primary and secondary specificity requirements of the serine protease chymotrypsin, and Cbz-Phe-Ala-CH=CH-CO-OEt (II) which represents a general recognition sequence for cysteine proteases such as cathepsins B, L and S, have been tested as putative irreversible inactivators of their respective target proteases. It was found that, whereas II, for example, functioned as a time-dependent, irreversible inactivator of each of the cysteine proteases, I behaved only as a modest competitive reversible inhibitor of chymotrypsin. Within the simple ester sequences Cbz-Phe-Ala-CH=CH-CO-R, the rank order of inhibitor effectiveness decreases in the order R = -OMe > -OEt >> -OBut. It was also found that the presence of both an unsaturated double bond and an ester (or alpha-keto ester) moiety were indispensable for obtaining irreversible inactivators. Of the irreversible inactivators synthesized, Cbz-Phe-Ala-CH=CH-CO-CO-OEt (which contains a highly electrophilic alpha-keto ester grouping) was found to be the most effective exhibiting, for example, second-order rate constants of approximately 1.7 x 10(6)M(-1)min(-1) and approximately 4.9 x 10(4)M(-1)min(-1) against recombinant human cathepsin S and human spleenic cathepsin B, respectively. This initial study thus holds out the promise that this class of inactivator may well be specific for the cysteine protease subclass.