The main aims of our research program involve the synthesis of target bioactive hormones and opioids selected from conformational analysis and bioassays. The syntheses will be carried out in solution by solid phase peptide methodologies. Our synthetic projects include somatostatin analogs and lanthionine containing hormones and opioids. We will incorporate peptidomimetics such as cyclic structures, chiral methylated amino acids and retro-inverso structures. Specifically, the somatostatin related cyclohexapeptide [Pro-Phe-D-Trp-Lys-Thr-Phe] will be modified in the bridging region using dioxopiperazine residues, lanthionine derivatives, and multiple chiral methylations in the side chains. We also seek to prepare novel lanthionine opioids, calcitonins, oxytocins and vasopressins among others. To accomplish these tasks, we are developing new synthetic routes of lanthionine structural units. Recently, a new method of peptide synthesis was developed in our laboratories, using the urethane protected alpha-amino acid N- carboxyanhydrides (UNCAs). We are applying this approach to prepare analogs of the LHRH decapeptide. We gain crucial information on the structure/bioactivity relationships using 2-D 1H-NMR experiments, including 2-D total correlation spectroscopy (TOCSY) and rotating frame Overhauser enhancement spectroscopy (ROESY), in conjunction with molecular modeling techniques such as distance geometry, energy minimization, cluster analysis and molecular dynamics. We are also exploring 2-D 13C-1H heteronuclear techniques, such as the omega1 hetero half filtered TOCSY (HETLOC) and the multiple quantum coherence spectroscopy (HMQC) in order to define the backbone conformation of our analogs and measure the rotamer populations of the side chains of the target molecules. In addition, proton and carbon relaxation rates are being implemented to determine the dynamics of the main chains and side chains of these novel constrained analogs. The structural results together with bioassays carried out in the laboratories of our collaborators enable us to refine our selections of target molecules for synthesis. Currently, three different somatostatin receptors are available. Since these are genetically expressed in different organs, each receptor can be an important target for our program. Our somatostatin related ligands will be tested to determine potency and selectivity for each specific receptor subtype. The results will provide crucial information to define structural requirements for recognition of each receptor. From this integrated approach, we hope to design and synthesize new candidate drug molecules.
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