Nine analogues of dolastatin 11, a potent antineoplastic agent from an Indian Ocean sea hare which interferes with microfilaments, were synthesized, including two natural ones. Although none of these analogues showed stronger activity than dolastatin 11, their syntheses gave better understanding of the structure-activity relationships for dolastatin 11 as described below. The complete lack of activity of the hydroxy acid obtained by hydrolysis of dolastatin 11 showed that the 30-membered ring may be necessary for activity. The high activity of the 3- and 7-nor derivatives showed that the 3- and 7-methyl groups are not needed for strong activity; the former is a drug candidate since it can be prepared pure more economically than dolastatin 11. The synthesis of Ala-epi-dolastatin 11 showed that this stereoisomer has greatly decreased activity, and that it is the persistent by-product in the dolastatin 11 synthesis. Molecular modeling studies showed most of these analogues to have conformations very sin-filar to those of dolastatin 11. However, the very weak activities of the two conformationally-restricted analogues synthesized suggests that none of the three lowest-energy conformations of dolastatin 11 is the binding conformation to F-actin. Two natural analogues isolated from Pacific Ocean blue-green algae were synthesized. The synthesis of the very active majusculamide C confirmed its structure, but the synthesis of the much less active lyngbyastatin 1 showed its configuration in the Ibu unit to have been assigned incorrectly, and that Ibu-epi-dolastatin 12 is a natural product which accompanies it. The broadness of the peaks in the NMR spectra of these two natural products was shown to be due to rotation about their Ibu-Ala amide bonds.

In pursuit of the working model of how glucagon interacts with the glucagon receptor and how glucagon antagonists exert their different activities, 42 glucagon analogues were designed and synthesized. An attempt to determine the minimum sequence for binding affinity of glucagon analogues was carried out and resulted in several potent truncated glucagon antagonists with substantial binding affinity, such as phenylbutyryl-glucagon(10-29) amide. Furthermore, a new method for determining the bioactive conformations of peptide hormones has been designed. In a positional cyclization scanning study, several conformationally constrained glucagon analogues containing disulfide or lactam bridges were synthesized, and the biological assay results showed that the alpha-helical conformation is required for the maximal receptor recognition. This study resulted in two superpotent glucagon analogues, c[Lys⁵, Glu⁹]glucagon amide and c[Lys¹⁷, Glu²¹]glucagon amide, which have picomolar binding affinities. A structure-activity relationship study of glycine at position 4 was performed to determine the importance of flexibility in the N-terminal region of glucagon. Four glucagon analogues were designed and synthesized, and all showed extremely potent antagonistic activity with improved binding affinity. Also, the potent glucagon antagonist [desHis¹, desPhe⁶, Glu⁹] glucagon amide was synthesized on a large scale (ca. 1.5 g), and the effect of the glucagon antagonist on diabetic ketoacidosis was studied in vivo in alloxan-induced diabetic dogs. The glucagon antagonist clearly showed its effectiveness in controlling serum bicarbonate concentration, while the control experiment with saline demonstrated increased diabetic ketoacidosis. This study clearly showed the possibility of using glucagon antagonists as therapeutic agents for the treatment of diabetic ketoacidosis. The conformation of the potent glucagon antagonist [desHis¹, desPhe⁶, Glu⁹] glucagon amide was studied using 2D NMR spectroscopy, and deuterated dodecylphosphocholine micelles were utilized to imitate the membrane environment. In this investigation, TOCSY, DQF-COSY, and NOESY spectra of the glucagon antagonist in a deuterated DPC micelle solution were acquired at pH 6.0 and 37°C. Restrained molecular dynamics (simulated annealing) using 332 distance restraints and 16 torsion angle restraints resulted in a conformation which displayed a similar C-terminal conformation, but a distinctly different N-terminal region, as compared to the conformation of glucagon. The newly discovered salt bridge between Ser² and Glu⁹ presumably resulted from the increased flexibility of the N-terminal region by the deletion of Phe⁶ and substitution of Glu⁹, which may shed light on how small changes in the sequence of peptides can significantly modify the conformation.

Given the success of organic ligands in transition metal catalysis, we incorporated the chirality of amino acids into new ligands for asymmetric catalysis. Moreover, it was hoped that through the incorporation of the bulky benzophenone imine moieties (-N=CPh₂), that the "pendant chirality" of the amino acids could be reflected in the "central chirality" about the transition metal. An achiral diamine serves to bring two optically active amino acid residues in close proximity to form an "active site." The two amido and two imine-nitrogens have been shown to bind Ni(II) in a square planar fashion to give C₂-symmetric complexes. Several metal complexes of Ni(II), Cu(II), and Zn(II) have been synthesized and screened for catalytic activity. While initial studies involving the epoxidation and cyclopropanation of simple olefins proved futile, the alkylation of aldehydes with a chiral Zn complex was successful. Dimethylzinc and diethylzinc have been added to several aldehydes in the presence of tetracoordinate Zn-complex. Using 3 mol% of catalyst derived from L-phenylalanine, aromatic aldehydes were alkylated quantitatively in 86-91% e.e. Aliphatic aldehydes underwent the same reaction in slightly higher e.e.'s (94-96% e.e.). The enantioselectivities were best when THF was used as a solvent, and e.e.s were drastically reduced when toluene was used. A solid phase variant was also shown to be effective as a catalyst, with somewhat reduced e.e.'s (e.g. 86% e.e. → 79% e.e.) for (S)-1-phenyl-propanol, when compared with the solution variant. Robust diphenylketimine derivatives have been synthesized from Merrifield and Wang resins, respectively. Condensation of HCl salts of primary amines, or free bases of primary amines in the presence of HOSO₂C₆H₄CH₃ proceeds in CH₂Cl₂, CH₃CN, or toluene at temperatures between RT and 80°C to form the corresponding Schiff bases. Analytical methods for following reactions of the Schiff bases included FT-IR and ¹³C-NMR. Examples of stereoselective reductive-alkylation of imino esters, cyclization of the resultant β-amino alcohols to aziridines, regioselective ring opening and detachment of the products are presented. Attachment of tetradentate ligands and binding of transition metals [Ni(II), Cu(II), Co(II) and Zn(II)] has also been demonstrated.

[2+2+1] iron and cobalt mediated cycloadditions have been applied towards the synthesis of 3-amino and 3-oxycyclopentadienones. These methods have provided an efficient means of generating [3.3.0], [4.3.0], and [5.3.0] bicyclic-cyclopentadienone ring systems. In an effort to probe the reactivity of our metal complexed dienones, we proceeded to subject them to cycloaddition reactions. With this goal in mind, we applied oxidative demetallation conditions to provide the metal free bicyclic-cyclopentadienones. Cycloaddition of the bicyclic-dienones with a number of pi donors and acceptors provided chemo and regioselective cycloadducts in an efficient fashion. Final studies included investigations of the iron cyclopentadienones in diastereoselective reactions.

A central goal of modern biology is to develop a detailed, predictive understanding of the relationships of three-dimensional structure and biological function. However, to establish the biologically active conformation is challenging because most small linear peptides are inherently flexible, and at present, our knowledge of 3D structural information of ligand-receptor complexes is very limited. Hence, some strategies have been developed to prepare peptidomimetics with constrained conformations. Both local conformational constraints and global conformational constraints can provide important insights into the structural and topographical basis of biological activity. A series of novel cis-4-substituted proline analogues were designed and synthesized. Highly stereoselective alkylations at the gamma-position of glutamic ester were achieved, followed by reduction, mesylation, and cyclization to afford the proline derivatives in good yields and high diastereoselectivity. These cis-4-substituted proline analogues could be used as conformation ally restricted templates in local constrained peptidomimetics. We also have developed a general and efficient approach for the synthesis of indolizidinone amino acids with stereospecific appendages of side chain functionality at both the C-4 and C-8 positions, which can serve as restricted reverse turn mimetics in global constrained peptidomimetics. Our synthetic reverse turn mimetic targets were designed to serve as surrogates of the dipeptides Phe-Gly and Phe-Arg which contain two important pharmacophore elements in Leu-Enkephalin and melanotropin peptides, respectively. Introduction of side chain functionality at C-8 was achieved by using beta-substituted pyroglutamate as a synthetic precursor which was prepared via Michael addition reaction between a Ni(II) complex of the chiral Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone and 3-(trans-enoyl)-oxazolidin-2-one. The side chains at C-4 were introduced by bromination of dehydroamino acid intermediates followed by Suzuki cross-coupling.

The multistep synthesis of the redox active adenine analog [e]-ferrocenyl-4-aminopyrimidine is reported. The redox active system will be incorporated into oligonucleotides to study the electron transfer through the molecular pi-system of DNA in future studies. Attempts were made to synthesize a cyclopenta-4-aminopyrimidine derivative which possesses an endocyclic double bond in the cyclopentane ring. This intermediate can be subsequently coupled with cyclopentadienyl iron dicarbonyl (Fp) group and, after thermal decarbonylation, form the desired ferrocene ring. Many double bond precursors are prepared, including dibromide, acetate, alcohol, ketone and phenylseleno derivatives of cyclopentapyrimidine. However efforts to form an endocyclic double bond turned out to be unsuccessful. Exocyclic double bond derivatives of cyclopentapyrimidine have also been prepared. An improved chiral synthesis of [e]-ferrocenyl-4-aminopyrimidine is achieved, in which a Curtius rearrangement to form an O-benzylcarbamate was done using a formyl ferrocene carboxylic acid. The yield of the final cyclization step was also greatly improved. The synthesis of methyl-(2,5-dimethoxy-4-fluorophenyl)-acetate, a thymine isostere precursor, is reported. It will be used as a substitute for a thymine base in a peptide nucleic acid (PNA) synthesis in the future. Regioselective bromination of 2-fluoro-hydroquinone introduced a bromo group at the desired position. After protection of hydroxyl groups in this product, a carboxylic acid ethyl ester group was introduced. Finally, an Arndt-Eistert reaction was used to extend the carboxylic acid by one carbon to the corresponding phenyl acetic acid ethyl ester. A chemical model mimicking the biosynthesis of the cyanide ligand in the enzyme hydrogenase is developed. In this model a thiocarbamate is first formed and subsequently dehydrated by polyphosphate ethyl ester(PPE) to make a thiocyanate. Finally, the cyanide moiety is transferred to the metal center. The direct dehydration of a carboxamidoiron species to form a cyano ligand is also reported.

Peptide ligands and protein receptors play critical roles in the regulation of nearly every biological system. However, peptides are characteristically highly flexible and thus identifying the basic conformational elements necessary for recognition between a peptide ligand and it's receptor at the molecular level remains a formidable task. Great emphasis in peptide research has thus focused on the determination of the receptor-bound conformation adopted by bioactive peptides by synthesizing constrained analogues of the peptides. Knowledge of the three dimensional interaction between a peptide ligand and a receptor could be invaluable in understanding bioactivity and in the design of therapeutics. To determine the bioactive conformation of our novel chimeric peptides for the opioid and cholecystokinin receptors, constrained analogues were designed to limit the conformations that the peptides would adopt. In this regard, [5,5]- and [6,5]-bicyclic dipeptide mimetics were designed and synthesized to constrain a dipeptide unit and by extension limit the flexibility of the peptide. The bicyclic dipeptide mimetics were synthesized from precursors obtained by the beta-alkylation of aspartic acid and from the Kazmaier-Claisen rearrangement reaction. A protocol for the alkylkation of aspartic acid with allyl bromide, benzyl bromide, and benzyl disulfide was developed. The bicyclic dipeptide mimetics were then introduced into the peptides whose biological activity was evaluated at both the opioid and cholecystokinin receptors. The peptides showed good binding and functional activities at the CCK receptors, but low activities at the opioid receptors.

A highly efficient approach to 2,3-disubstituted indoles has been presented. The indole precursors, isonitriles, were used as powerful geminal radical donors/acceptors. The novel isonitrile-alkyne free radical cascade has been efficiently mediated by tin and sulfur. In the case of sulfur, interesting 2,3-dithioindoles were formed. This new class of compounds has exhibited great promise as versatile indole intermediates. In particular, nucleophilic additions at C-10 of the 2,10-dithioindoles were achieved using carbon, sulfur and amine nucleophiles. The versatility of 2,10-dithioindoles was further demonstrated using rhodium-mediated sulfur ylide chemistry. We achieved an intramolecular sulfur ylide reaction which led to a gramine-type addition product 270. Furthermore, sulfur ylides were formed intermolecularly and rearranged to give highly substituted indoles. In studies aimed at the synthesis of the spirotryprostatins, our 2,10-dithioindoles were used in the synthesis of both a simple C-3 spiro-oxindole compound 249 and a diketopiperazine-containing indole derivative 256. This demonstrated the exciting potential of our indole-forming reaction and elaboration methodologies in natural product synthesis.

Pain is perhaps the most unpleasant sensation humans experience. While pain is important in preventing further injury and as a detection mechanism for ill-health; effective relief of pain, especially chronic or neuropathic, is a critical quality of life issue. As discoveries are made regarding opioid receptor-acceptor-ligand interactions, ligands that bind specifically to a receptor subtype can modify behavior without triggering side effects. Topographical space control is an important consideration in ligand design. According to Ramachandran¹, α-amino acids are confined to the following low-energy conformations, α-helix, β-sheets, extended structures, and β-turns. Endogenous peptides such as the enkephalins and endomorphins activate the opioid receptor subtypes, δ- and μ-, respectively, and are involved in the pain cascade. Research herein concerns the synthesis of δ-opioid peptidomimetics that replace the Gly-Gly unit of Leu-enkephalins with a β-turn mimetic moiety. Additionally, using the bioactive nostocyclopeptolides as templates, smaller cyclized imino-bridged peptides were designed. These peptides were developed with the mu-opioid subtype requirements in mind.

The solution phase synthesis of amide-linked derivatives of sialic acid has been achieved. The N-acetyl group on sialic acid was removed via N-BOC protection of the lactam and ensuing displacement with NaOMe. Subsequent removal of the BOC protecting group group with TFA resulted in the free amine which was then coupled with the free acid using BOP, Hunig's base, and NMP. These compounds may afford greater solubility than previously synthesized amide-linked carbohydrate amino acids and may give rise to novel helical structures. The efficacy of using monomer units of sialic acid in solid-phase oligomer synthesis has also been studied. The peracetylated FMOC-protected derivative of sialic acid which has been shown to be amenable to solid-phase synthesis has also been synthesized. However, difficulties were encountered during the solid-phase synthesis of these sialooligomers due to transacetylation of the acetate groups to re-form the N-acetyl bond.