Important research at the interface of organic chemistry and biochemistry requires the collaboration of synthetic organic chemists and biochemists to identify, then design and synthesize, organic "ligands" needed to probe specific interactions with, and the functions of, macromolecular biological systems. These organic ligands are usually challenging synthetic organic targets because of the functionality and stereochemical control necessary to achieve the required specific interactions. We have therefore established a group of synthetic organic chemistry postdoctoral researchers that is working primarily on collaborative projects with biochemists and molecular biologists at Florida State University. It is anticipated that these efforts will lead to significant contributions in the area of drug design and development, as well as in the elucidation of enzyme structure and function and the understanding of the biochemical bases of some diseases. One of our major current collaborations is described below.

Synthesis of Matrix Metalloproteinase Inhibitors. This collaboration with Professor Amy Sang requires the design and synthesis of potent, selective inhibitors of the matrix metalloproteinase (MMP) family of enzymes. The MMPs are a group of about ten closely-related proteases that utilize an active-site zinc ion for catalysis, and that play various roles in degrading connective tissue proteins such as collagens and proteoglycans. They are involved in normal processes such as angiogenesis and wound healing, and in pathological processes such as arthritis, and cancer cell invasion and metastasis. Potent but selective inhibitors of individual MMPs are required for studies of the mechanisms of cancer cell invasion and of angiogenesis in in vitro model systems using cultured breast cancer cell lines and endothelial cell lines, respectively. Specific potent inhibitors of one or more of the MMPs are added to the extracellular medium, and the extent of cell invasion or of tubule formation in a collagen gel matrix is assayed as a function of inhibitor concentration, in order to elucidate the roles of specific MMPs in the biochemical steps of these processes.

Figure 1. Schematic of Proposed MMP Active Site Binding Interactions

Previous studies in our laboratory led to the discovery of two new classes of potent MMP inhibitors. The design strategy has entailed synthesizing tri- to hexapeptide substrate analogs in which either the C=O group, the NH group, or both groups of the scissile peptide bond are replaced by other moieties. The C=O group of the scissile bond of the substrate presumably interacts with the active site zinc atom in the MMP (Figure 1), while the amino acid sidechains of the residues adjacent to the scissile bond interact with subsites on the surface of the enzyme's active site. With respect to the scissile bond replacement moiety, it must be a peptide bond isostere that the enzyme cannot hydrolyze; it also should have tetrahedral geometry so that it may act as a transition-state analog inhibitor, which is generally able to take advantage of stronger binding interactions (Figure 1) with the enzyme than is a ground state (substrate) analog.

Figure 2. Potent MMP Inhibitors

The two peptide mimetics containing novel zinc-binding functionalities that resulted from this strategy are sulfodiimines and mercaptosulfides (Figure 2). A number of potent and somewhat selective inhibitors of the major members of the MMP family have been developed, but their application to the proposed studies on cell-mediated matrix breakdown is obviated by their lack of sufficient aqueous solubility and by the need for greater selectivity in their inhibition of individual MMPs. We have been attempting to solve both of these problems by modifying these lead inhibitors to include more hydrophilic sidechains and to add features that will take advantage of differences in binding regions in the active sites of members of this enzyme family. Since the stereochemistry at each chiral center in the inhibitor has to be controlled in each case, methods for carrying out asymmetric syntheses of dipeptide analogs containing each of the desired functionalitities have to be developed.

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