Synthesis of peptidyl ene diones: selective inactivators of the cysteine proteinases.

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.

Tuning and enhancing enantioselective quenching of calixarene hosts by chiral guest amines.

The synthesis of a propranolol amide derivative of p-allylcalix[4]arene is described, which has been designed to behave as a molecular sensor capable of distinguishing chiral amines on the basis of their shape and chirality. This molecule can discriminate between the enantiomers of phenylalaninol through the quenching of the fluorescence emission in methanol in contrast to an (S)-dinaphthylprolinol calix[4]arene derivative, which can discriminate between the enantiomers of phenylglycinol, but not phenylalaninol. The separation between the naphthyl fluorophores and the hydrogen-bonding sites within the chiral cavity can be tuned to recognize guest amines with similar separation between aryl groups and hydrogen-bonding sites. The formation of metal ion complexes of the p-allylcalix[4]arene propranolol amide derivative is shown to induce a more regular and rigid cone conformation in the calix[4]arene macrocycle, which generates a significant enhancement in the observed enantiomeric discrimination.

Cation Complexation by Chemically Modified Calixarenes. 11. Complexation and Extraction of Alkali Cations by Calix[5]- and -[6]arene Ketones. Crystal and Molecular Structures of Calix[5]arene Ketones and Na(+) and Rb(+) Complexes.

A series of four calix[5]arenes and three calix[6]arenes (R-calixarene-OCH(2)COR(1)) (R = H or Bu(t)) with alkyl ketone residues (R(1) = Me or Bu(t)) on the lower rim have been synthesized, and their affinity for complexation of alkali cations has been assessed through phase-transfer experiments and stability constant measurements. The conformations of these ketones have been probed by (1)H NMR and X-ray diffraction analysis, and by molecular mechanics calculations. Pentamer 3 (R = R(1) = Bu(t)) possesses a symmetrical cone conformation in solution and a very distorted cone conformation in the solid state. Pentamer 5 (R = H, R(1) = Bu(t)) exists in a distorted 1,2-alternate conformation in the solid state, but in solution two slowly interconverting conformations, one a cone and the other presumed to be 1,2-alternate, can be detected. X-ray structure analysis of the sodium and rubidium perchlorate complexes of 3 reveal the cations deeply encapsulated by the ethereal and carbonyl oxygen atoms in distorted cone conformations which can be accurately reproduced by molecular mechanics calculations. The phase-transfer and stability constant data reveal that the extent of complexation depends on calixarene size and the nature of the alkyl residues adjacent to the ketonic carbonyls with tert-butyl much more efficacious than methyl.