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This work presents research toward the total synthesis of the promising antibiotic lactonamycin and related polyketides specifically, a scalable, inexpensive, and universal process to access this family of natural products. Lactonamycin exhibits a wide range of promising biological activity. Most notable among these is the potent activity displayed against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. Lactonamycin and each of the aforementioned structurally related polyketide natural products serve as good targets for synthetic efforts, particularly lactonamycin. Further impetus for total synthesis is provided by the interesting structural features of these related polyketides and the synthetic challenges associated with these features. The structure of lactonamycin contains several unique connectivities including a novel hexacyclic ring structure distinguished by a densely oxygenated DEF-ring system with three contiguous quaternary stereogenic centers. An approach to lactonamycin and its related polyketides has been developed, in particular two methodologies: (1) the tandem conjugate addition-Dieckmann condensation and (2) a quinone nitrile-oxide cycloaddition. These methods have allowed a unified approach to this class of biologically active natural products. The synthesis of the ABCD-ring system of lactonamycin has been accomplished in eleven steps by utilizing a novel tandem cyanide conjugate addition/Dieckmann condensation as a key step. This powerful annulation reaction was developed in a model system prior to application to the synthesis of the ABCD-rings of lactonamycin. Flexibility was observed in the nucleophile used to initiate the cyclization, holding promise for an application to the related polyketides tetracenomycin C, elloramycin, saintopin, saintopin E. This methodology has also allowed for a formal synthesis of tetracenomycin A2. Model studies on the highly oxygenated DEF-ring system were conducted. A high yielding, regioselective dipolar cycloaddition of a hydroxymethyl-substituted naphthoquinone with an appropriately substituted nitrile oxide was developed and implemented in the full ABCD-ring system of lactonamycin, providing rapid entry to an isoxazole intermediate possessing virtually all of the atoms necessary to construct the skeleton of lactonmycin. Diastereoselective installation of a final tertiary hydroxyl remained after [3+2] cycloaddition. Several methods geared toward solving this challenging synthetic problem are presented to better understand how it may be overcome. This dissertation describes a plan and progress toward lactonamycin that has allowed for the synthesis of a unique substrate where these methodologies may be utilized to complete the first total synthesis of lactonamycin.

This dissertation describes chemical investigations involving 11 Argentinean plant species and a sample of Chilean propolis. In total, 18 known and four novel compounds were isolated and identified. The compounds were tested in various antimicrobial assays. Three novel triterpenes, 3,4- seco-olean-12-en-3,28-dioic acid (4), 3alpha,-hydroxyolean-11-en-28,13 beta-olide (5), and 3alpha-hydroxyolean-11:13(18)-dien-28-oic acid ( 6) were isolated from the aerial parts of the Argentinean shrub, Junellia tridens (Lag.) Mold. (Verbenaceae). Another five compounds, oleanolic acid (1), oleanonic acid (2) and epioleanolic acid (3), all biosynthetically related to the three new oleananes, as well as epibetulinic acid (7) and sitosterol (8), were also isolated. LC-MS data are provided on the occurrence of these triterpenes in six other species of Junellia. We report the minimum inhibitory concentrations (MICs) of compounds 1--8 against Mycobacterium tuberculosis, and conclude that they are responsible for the antitubercular activity originally observed in the crude plant extract. Four other plants showing preliminary antitubercular activity were also investigated. The EtOAc extracts of Acantholippia seriphioides and Adesmia ameghinoi contained oleanolic acid (1) as their main constituent. The organic soluble portions of Chiliotrichium diffusum and Lathyrus magellanicus contained large amounts of ursolic acid (12) and sitosterol (8), respectively. Bioassay of the predominant compounds in these plants indicated that triterpenes were responsible for the antitubercular activity observed in the crude extracts. Fractionation of propolis (a product of honey beehives) from Colliguay in Central Chile led to the isolation, identification and bioassay of a novel gamma-lactone (14), five flavonoids (15--19), two diarylheptanoids (20--21), and a prenylated coumarin (22). All structures were elucidated primarily by 1D and 2D NMR and mass spectrometry. Based on the traditional use of propolis as an antimicrobial agent, the bioactivity of the purified compounds was determined against Staphylococcus aureus, Escherichia coli, Enterococcus faecium, and Candida albicans . Microscopic analysis of pollen present in the propolis provided clues to its botanical origins.

The use of liposomes for the delivery of therapeutic agents to tumor sites took a major step forward with the introduction of sterically stabilized liposomes (PEG-liposomes). Several research groups reported the increased localization of PEG-liposomes at tumor sites. Once PEG-liposomes reach these sites, it can be desirable to increase the rate of release of encapsulated compound(s). The use of radiation for this purpose is attractive, because it can be delivered in a spatially and temporally selective manner. An effective strategy for the photopertubation of PEG-liposomes relies on the photoinitiated polymerization of reactive lipids in the liposomal bilayer. Previous studies indicated that the inclusion of the photoreactive 1,2-bis[10-(2' ,4'-hexadienoyloxy)decanonyl]-sn-glycero-3-phosphocholine (bis-SorbPC17,17) among the lipids of PEG-liposomes had little effect on their permeability until the PEG-liposomes were exposed to UV light. Photoexposure increased the permeability of the PEG-liposomes 200-fold. Research in this dissertation was focused upon increasing the reactivity of PEG-liposomes to UV and ionizing radiations. Additionally, the most favorable formulations were then used for the encapsulation of chemotherapeutic compounds that are currently on the market. Results in this dissertation indicate the ability to encapsulate water soluble compounds with high efficiency and subsequently release those compounds with minimal UV light exposure and with ionizing radiation doses that approach therapeutic levels.

Novel methods for synthesis of monoprotected homobifunctional polyethylene glycols and subsequent synthesis and application of heterobifunctional derivatives in protein immobilization and separation is described. In addition, modification of proteins with PEG and properties of the conjugates are presented. Heterobifunctional PEG derivatives having a chelate at one end and at the other one specific ligands for proteins have been synthesized. Metal binding constants and kinetic parameters of these bifunctional chelate polymers were found in excellent correlation with the binding affinities shown by corresponding unconjugated groups. These heterobifunctional PEG derivatives were used to characterize the partitioning behavior of several proteins in Affinity Two-Phase Partitioning, ATPP, at different conditions. Both sides of these bioaffinity chelating polymers were found to be effective in the partitioning of these model proteins. These modified heterobifunctional affinity chelating polymers were also adsorbed in aqueous media to different chelating adsorbents used in IMAC separation. In this scheme an IMA-adsorbent could be transformed to a more selective affinity separation mode, by adding an affinity-chelating ligand. The attached ligand could be removed by weakening the metal interactions between the two chelates in the system which allow the column to operate again in the original IMAC mode, if desired. The amount of these bioligands bound to the columns were a function of the type of the IMA-adsorbents, pH, salts and the metal immobilized on the gels. Trypsin and avidin were bound on columns loaded with a PAB-PEG-chelate and a biotin-PEG-chelate respectively. As a typical example, bound trypsin was eluted from the columns with the trypsin inhibitor, benzamidine, acting as a competitive ligand. The bioligands were eluted reversibly from the IMA-adsorbents, using free IDA as a competitive ligand, using low pH buffers or EDTA. PEG derivatives of 5000 daltons, were chemically fixed to non essential groups on trypsin through amidation with amino groups using two different methods. Kinetic studies were performed upon modification to determine the activity and stability of the modified biomolecule under these conditions. In both cases the modified enzyme adduct, retained their original biological activities and showed substantial changes in properties.

Topographical constraint is the most powerful approach for the design of bioactive peptides to explore the bioactive conformation of crucial side-chain pharmacophores of amino acid residues in peptide-receptor recognition and signal transduction. Novel topographically constrained amino acids β-isopropylphenylalanine and 2',6'-dimethyl-2,3-methanophenylalanine have been designed and synthesized. Incorporation of the four optically pure β-isopropylphenylalanine stereoisomers into deltorphin I produced four peptide analogues of [β-iPrPhe]Deltorphin I with differentiated bioactivities. The most potent and selective analogue, [(2S,3R)-β-iPrPhe]Deltorphin I showed an IC₅₀ nM binding affinity, and a 29000 fold selectivity for the δ-opioid receptor over the μ opioid receptor. Combined molecular modeling and NMR studies indicated that the (2S,3R)-β-iPrPhe³ residue in the analogue favors the trans rotamer, and can induce the linear peptide to form a low-energy folded conformation which was proposed as the bioactive conformation for the δ-opioid receptor. Coupling four optically pure, conformationally constrained β-methyl-2',6'-dimethyltyrosine (TMT) with L-Tic formed four dipeptide analogues of TMT-L-Tic. The most potent and selective analogue, (2S,3R)-TMT-L-Tic showed 9 nM binding affinity and 4000 fold selectivity to the δ vs μ opioid receptor. The lowest-energy conformation of (2S,3R)-TMT-L-Tic was suggested to be the bioactive one in which TMT side chain is trans and Tic side chain is in a gauche (+) conformation. Bicyclic oxytocin antagonist [dPen¹, cyclo(Glu⁴ Lys⁸)]OT (BC-OT) (pA₂ = 8.10) is an excellent template to examine further topographical ideas. Substitution of Tyr² with the topographically constrained para-methoxy-β-methyl-2',6'-dimethyltyrosine (p-MeOTMT) amino acids produced two very potent antagonists [(2S,3S)-p-MeOTMT²]BC-OT (pA₂ = 8.26) and [(2R,3R)-p-MeOTMT²]BC-OT(pA₂ = 7.80), and two inactive analogues [(2S,3R)-p-MeOTMT²]BC-OT and [(2R,3S)-p-MeOTMT²]BC-OT. These interesting results can be attributed to the biased side-chain conformation, gauche(+) and gauche(-) in (2S,3S)-p-MeOTMT and (2R,3R)-p-MeOTMT respectively, and trans in both (2S,3R)-p-MeOTMT and (2R,3S)-p-MeOTMT residues. Rational design of non-peptide mimetics from peptide leads is still elusive. Based on the δ-opioid selective lead [(2S,3R)-TMT¹]DPDPE and SAR of δ-opioid selective ligands, the first generation of non-peptide mimetics have been designed and synthesized. The new lead SL-3111 showed binding affinity IC₅₀ = 8 nM, and over 2000 fold selectivity for the δ-opioid receptor over the μ receptor.

The synthesis of a series of N-9-fluorenylmethoxycarbonyl (N-FMOC) protected amino acid glycosides is reported. These (1-2)-trans glycosides came directly from Koenigs-Knorr type glycosylations under Hanessian's silver triflate conditions, except for the synthesis of N-acetylgalactosamine FMOC amino acid in which silver perchlorate conditions were used to promote α-glycoside formation. The effect of D-amino acid aglycones was investigated under glucosylation conditions, and a yield dependence on amino protection was seen in the enantiomers of threonine. Due to this match vs. mismatch dichotomy, both O'Donnell Schiff bases and FMOC-amino aglycones were used in the subsequent glycosylation reactions. Glycosides were made using the monosaccharides xylose, mannose, glucose, galactose, N-acetylglucosamine, N-acetylgalactosamine, and disaccharides lactose [galactose-β-(1-4)-glucose], cellobiose [glucose-β-(1-4)-glucose] and melibiose [galactose-α-(1-6)-glucose]. All glycosides were converted to their respective FMOC-amino acid forms for direct use in solid-phase glycopeptide synthesis (SPGPS) using established methodology. A strategy into the synthesis of an FMOC-amino acid trisaccharide of Lewis ˣ (Leˣ) was also investigated in an effort to expand on the established glycoside methodology. Preliminary work with D-glucosamine and L-fucose is reported. Our synthetic rationale was based on retaining the peptide pharmacophore or message sequence constant as DCDCE (D-cys²ʼ⁵-enkephalin) with a serine-glycine tether, and making changes only in the environment of the amino-acid glycoside. Changes in amino acid, amino acid chirality, and in the sugar moiety itself would provide a stereochemical investigation into the requisite orientation and electronics for optimum blood-brain barrier (BBB) penetration, opiate receptor binding, and analgesia. Several glycopeptides were synthesized, and all were purified in both reduced and oxidized forms (if containing cysteine). A highly optimized glycopeptide synthetic strategy has been developed and will be presented and critiqued. Pharmacological analysis involving serum stability studies, BBB-penetration studies, GPI/MVD physicochemical studies and mu/delta-opiate receptor studies were completed on all glycopeptides. SAM-1095, the most potent of the glycopeptides synthesized, was resynthesized on a large scale, and this compound was assessed for in vivo pharmacology, along with the non-glycosylated version SAM-995. Preliminary results demonstrate an analgesic effect similar to that of the narcotic morphine. Assessment of all pharmacology will afford a platform for future SAR-based glycopeptide investigations.

Values for the melting points, total enthalpies of melting, and total entropies of melting of organic compounds are required in order to accurately estimate properties such as aqueous solubility and vapor pressure. These measurements, therefore, are critical to predicting how a chemical will behave both in the body and in the environment. Despite their importance, relatively few methods are available for predicting these properties from chemical structure. One reason for the lack of available methods is that these properties are easily obtained experimentally. The major reason, however, is that the development of general models for their prediction is extraordinarily challenging. This study first develops a model for estimating the melting points of organic compounds. The model incorporates additive functional group descriptors as well as non-additive descriptors of molecular geometry. The model is trained on the melting points of nearly 3000 compounds, has an R² value of 0.873 and an average error of 29.8 Kelvin degrees. The melting point model is then used to estimate the total enthalpy of melting through the incorporation of an additional geometric descriptor of molecular eccentricity, ε. Eccentricity is a measure of the extent to which the structure of a molecule deviates from a sphere. The total enthalpy model is trained on data for 191 compounds. The model has an R² value of 0.910 and an average error of 3812 J/mol. The total entropy of melting is then estimated from the predicted enthalpy value by incorporating an additional parameter in the model, τ, as a measure of molecular flexibility. The total entropy model is trained on data for the same 191 compounds as the enthalpy model. It has an R² value of 0.928 and an average error of 9.8 J/Kmol. The total enthalpy and entropy models have average absolute errors that are similar to those obtained using existing techniques that are more complex. The melting point method, however, is significantly more accurate and widely applicable than the additive models that are currently available.

A number of alpha-melanotropin (α-MSH) analogues have been designed de novo, synthesized and bioassayed at different melanocortin receptors from frog skins, mice and humans. These ligands were designed from two scaffolds, Somatostatin and Deltorphin-II, by two new hybrid approaches, one of which utilizes the modified cyclic structure (H-DPhe-Cys---Cys-Thr-NH₂) of a Somatostatin analogue--Sandostatin®, while the other incorporates the hydrophobic tail of Deltorphin-II (Glu-Val-Val-Gly-NH₂). Some of the ligands designed, H-DPhe-c [XXX-YYY-ZZZ-Arg-Trp-AAA]-Thr-NH₂ [XXX and AAA = Cys, DCys, Pen, DPen; YYY = His, His(1-Me), His(3-Me); ZZZ = Phe and side chain halogen substituted Phe, DPhe, DNal(1') and DNal(2 ')] and c[XXX-YYY-ZZZ-Arg-Trp-Glu]-Val-Val-Gly-NH₂ [XXX = nothing, Gly, β-Ala, γ-Abu, 6-Ahx; YYY = His, His(3-Bom), (S)-cyclopentylglycine (CPG); ZZZ = Phe, DPhe; DNal(2')], show unique selectivity and potency among the receptors tested. In particular, one of the ligands, Delt-38B--c[Gly-CPG-DNal(2')Arg-Trp-Glu]-Val-Val-Gly-NH₂, is a human melanocortin receptor (hMC1R) antagonist (IC₅₀ = 12 nM) the first potent hMC1R antagonist discovered. These results provide strong evidence supporting our hypothesis that ligand scaffolds for different G-protein coupled receptors (GPCRs) can be used to design ligands for other GPCRs. In addition, the structures of some of the ligands have been analyzed by high field solution NMR and their conformation evaluated by modeling with MacroModel. The conformations obtained from these methods help us better understand the structural basis the selectivities and ligand-receptor interactions.