In vitro activities of synthetic host defense propeptides processed by neutrophil elastase against cystic fibrosis pathogens.

The antimicrobial and hemolytic activities of a host defense peptide can be controlled by its modification as a propeptide of reduced net charge, which can then be processed by neutrophil elastase, a serine protease involved in chronic airway inflammation and infections associated with cystic fibrosis.

Exploring the chemistry of penicillin as a beta-lactamase-dependent prodrug.

The penam nucleus can be modified to behave as a beta-lactamase-dependent 'prodrug' by incorporation of a vinyl ester side chain at the 6-position. Enzyme-catalysed hydrolysis of the beta-lactam ring uncovers the thiazolidine-ring nitrogen as a nucleophile that drives a rapid intramolecular displacement on the side chain. Attachment of 7-hydroxy-4-methylcoumarin as the releasable group of this side chain generated a penicillin structure that can function as a fluorescence-based reporter substance/diagnostic for the presence of low levels of beta-lactamase enzyme in solution. Mechanistic details of the reaction pattern are documented and the scope and limitations of exploiting the structural modification are discussed.

Toward the development of a cephalosporin-based dual-release prodrug for use in ADEPT.

In previous work we have shown that a cephalosporin structure bearing an S-aminosulfenimine at the 7-position behaved as a beta-lactamase-dependent dual-release prodrug. Scission of the beta-lactam ring of such a structure led to the rapid loss of the sulfur-attached side chain moiety via an intramolecular displacement, while the 3'-group was lost via the well-established elimination process at that position. In the present work we report on an evaluation of the scope and limitations of exploiting the S-aminosulfenimine functionality to generate a cephalosporin-based prodrug incorporating two biologically active components. Starting from 7-ACA, a viable synthetic cycle was put in place that avoided formation of the Delta(2) isomer throughout and that allowed incorporation of aminoglutethimide at the 3'-position and of a tosyl S-aminosulfenimine at the 7-position. The direct incorporation of a biologically active sulfonamide (ethoxzolamide) or a sulfamate (coumate) at this latter position was not achieved as a result of the difficulty of generating the corresponding sulfur diimides. An indirect route for the formation of an S-aminosulfenimine was put in place, as was a general method of alkylation (Mitsunobu reaction) of the tosyl S-aminosulfenimine following its incorporation.

Penicillins as beta-lactamase-dependent prodrugs: enabling role of a vinyl ester exocyclic to the lactam ring.

Incorporation of a vinyl ester exocyclic to the beta-lactam ring of a penicillin nucleus enables this to act as a beta-lactamase-dependent prodrug - rapid release of the (unactivated) alkoxy component of the vinyl ester is triggered by enzyme-catalysed hydrolysis of the beta-lactam ring, whilst buffer-catalysed hydrolysis of the structure at neutral pH is particularly slow.

Substrate variants versus transition state analogues as noncovalent reversible enzyme inhibitors.

Reversible inhibitors are associated with fewer side effects than covalently binding ones and are, therefore, advantageous for treatment of conditions involving endogenous enzymes. Transition state analogue structures provide one design paradigm for such inhibitors; this paradigm seeks to exploit the capability of an enzyme active site to stabilise a transition state or associated intermediate. In contrast, structures that retain the functionality, and scissile bond of the substrate, can also act as reversible inhibitors; these are referred to here as substrate variants to distinguish them from substrate analogues. Their mode of inhibition depends on destabilisation of a reaction-path transition state or states. As the mode of destabilisation can be quite varied the scope to exploit substrate variants as reversible inhibitors is substantial. The two design paradigms are contrasted here and the case of substrate variants is delineated with a well-defined set of structures. These include the naturally occurring polypeptides BPTI (an inhibitor of a serine-based protease) and cathepsin propeptides (inhibitors of cysteine-based proteases) as well as the synthetic small-molecules cilastatin (an amide inhibitor of a zinc-based protease) and substituted mono- and tripeptides as inhibitors of cathepsins K and L.

A substrate variant as a high-affinity, reversible inhibitor: insight from the X-ray structure of cilastatin bound to membrane dipeptidase.

An analysis of the X-ray structure of cilastatin bound to membrane dipeptidase, together with docking studies, is presented here to reveal how a simple amide may act as a high-affinity, reversible, amidase inhibitor. Cilastatin binds as a normal substrate and is orientated in a perfect near-attack conformer for formation of a tetrahedral intermediate with the zinc-bound water/hydroxide. This intermediate is fated, however, only to revert to its starting components as scission of the amide bond is prevented by the precise fit of cilastatin within the active site. The cilastatin alkyl end groups that are tightly buttressed against amino acid residues on opposite sides of the active site, are aligned along the C-N reaction coordinate axis thereby preventing collapse of the intermediate via rupture of the C-N bond. Such a feature could have more general applicability in the explicit design of substrate variants as selective, tight-binding, and reversible inhibitors.

Extending the beta-Lactamase-Dependent Prodrug Armory: S-Aminosulfeniminocephalosporins as Dual-Release Prodrugs.

Cephalosporins bearing an S-aminosulfenimine (R'(R' ')NSN=) side chain at the 7-position are prototypic examples of a novel class of beta-lactamase-dependent prodrug. Enzyme-catalyzed hydrolysis of the beta-lactam ring in these structures triggers release of both the 3'-acetoxy group and the side chain sulfur-attached S-amino moiety as R'(R' ')NH. This reactivity pattern should allow site-specific corelease of two distinct drug components from a cephalosporin, thereby providing a singular enhancement to the capacity of a cephalosporin as a prodrug nucleus; a key advantage of a dual-release prodrug is the potential to establish synergy between the coreleased structures. Areas for exploitation of this new structure type are antibody-directed enzyme prodrug therapy (ADEPT), which is a key emerging anticancer therapy, and the further development of site-specific-release prodrugs to combat the problem of beta-lactamase-based resistance to antibiotics.