MSc (Chemistry) / Department of Chemistry / See the attached abstract below

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21425号 / 工博第4535号 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 浜地 格, 教授 杉野目 道紀, 教授 秋吉 一成 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Lyconadin A is a pentacyclic Lycopodium alkaloid isolated from the club moss Lycopodium companatum with anticancer activity. Our approach sought to incorporate a 7-exo–6-exo acyl radical cyclization cascade to access the bicyclo[5.4.0]undecane framework of lyconadin A. Our studies created methodology for the synthesis of 5-alkyl and 3,5-dialkyl-6-carbomethoxy-2-pyridones and sterically demanding epoxide substrates. These epoxide substrates underwent an unanticipated Payne rearrangement.Cranomycin is a potent antibiotic with antiprotozoal activity. Structurally it is a cyclopentane ring system with substitution at each carbon in the ring. Another interesting structural aspect is the existence of three contiguous quaternary stereocenters including two tertiary alcohols and a tert-alkylamine. Our strategy led to the development of a highly diastereoselective synthesis of vicinal tertiary diol systems. We have successfully synthesized the cyclopentenone system shown above, from which we hope to assemble cranomycin.

Screening small molecule libraries is a powerful method for identifying biologically active substances. Current compound libraries are typically comprised of a large number of structurally similar compounds designed around bioactive core structures of known molecules. While the number of tested compounds are increasing, there has been a decline in drug-discovery success due to only a small region of chemical space being represented in these compound libraries. In addition, newly discovered biological targets tend not to be modulated by currently known natural products and molecular scaffolds. Diversity-oriented synthesis (DOS) aims to construct structurally novel and diverse products in a highly efficient manner to generate small-molecule libraries with a high degree of structural diversity and function. There is a need for new organic methodologies to access these atypical molecular scaffolds. The work presented here utilizes photochemical and titanium-mediated methodologies to access novel molecular scaffolds in two distinct directions: 1) by utilizing [2+2] photocycloaddition of pyridone-enynes to access functionalized cyclobutanoids capable of further modification and 2) by developing a novel Bredt’s rule-arrest Kulinkovich-de Meijere reaction to produce alkaloid building blocks with useful functionality. 2-Pyridones are known to undergo photo-initiated [2+2] and [4+4] cycloadditions with themselves and other conjugated -systems. These transformations provide rapid access to highly functionalized cyclobutanoid and cyclooctanoid derivatives capable of further manipulation to access both known and novel chemical space. Utilizing [2+2] photocycloaddition of pyridones conjugated with enyne partners we prepared polycyclic cyclobutanoids with excellent regio- and stereoselectivity. Further, these products were functionalized to give complex tetracyclic molecular scaffolds. The described approach to the 5-8-5 framework of the fusicoccane family features a key intramolecular [4+4] photocycloaddition of tethered pyridones. Intelligent design of the tether and proper choice of solvent affords rapid assembly of the polycyclic framework and sets the relative stereochemistry of five stereogenic centers. The strategy for construction of cyclooctanoid natural products is part of a long standing program to utilize the powerful photochemical properties of 2 pyridone. A novel approach for rapid access to a structurally diverse array of amino-ketone scaffolds employing a Kulinkovich-de Meijere reaction of inexpensive lactam-olefin building blocks has been developed. The formation of cyclopropylamines from alkenes and amides, the Kulinkovich-de Meijere reaction, involves two carbon-carbon bond-forming steps. Strategic use of a tricyclic intermediate can arrest the process if the second step requires formation of a bridgehead double bond. This intramolecular transformation results in formation of carbocyclic amino ketone building blocks. Further manipulation provides access to novel three-dimensional chemical space from these building blocks to produce a spectrum of fused bicyclic scaffolds in a divergent yet predictable manner. These products allow access to complex molecular space that can serve as a platform for medicinal and biochemical investigations. / Chemistry

2-Pyridones are known to undergo a facile [4+4] photocycloaddition with themselves and other conjugated molecules. These transformations provide an access to complex molecular structures such as highly substituted cyclooctanoid derivatives, which normally represent a significant synthetic challenge. Moreover, the 2-pyridone photoadducts can be further elaborated into various biologically relevant products. The work presented here broadens the horizons of the [4+4] photocycloaddition in two distinct directions: 1) by utilizing [4+4] photocycloaddition in a total synthesis of crinipellin natural products possessing antibiotic and antitumor activity and 2) by developing a novel type of [4+4] photocycloaddition that employs a conjugated enyne as a partner of 2- pyridone. Our approach to the tetraquinane core of the crinipellins features intramolecular [4+4] photocycloaddition of a tethered furan-pyridone molecule followed by a four-step transannular ring closure. The sequence allows for a rapid assembly of a molecular framework by installing 19 of the 20 required carbon atoms and all but two stereogenic centers. The described synthesis represents an interesting new approach to these polycyclic molecules and a way to access crinipellin analogues. The enyne-pyridone [4+4] photocycloaddition led to formation of intriguing 1,2,5-cyclooctatriene-based products. Presence of the allene functionality was used as a lever in exploring the possibilities for derivatization of these photoadducts. Our investigations of enyne-pyridone photocycloaddition have come a long way: from the first proof-of-concept intermolecular trials producing complex mixtures, through the initial investigations of the intramolecular variant that taught us how to direct the reaction to the necessary mode ([2+2] vs. [4+4] photocycloaddition), and eventually to the controlled formation of stable allenic photoadducts and their further transformation into a diverse set of functionalized molecular scaffolds. We found that the inherent kinetic instability of 1,2,5-cyclooctatrienes facilitates several pathways of strain relief: allene-allene [2+2] dimerization, photooxidative decarbonylation when the irradiation is conducted in presence of air, isomerization of the 1,2-diene fragment into a 1,3-diene and the acid-promoted Cope rearrangement. Additionally, enyne-pyridone photoadducts can undergo transannular ring closure when treated with bromine and also be transformed into valuable bicyclo [5.1.0] octane structures that incorporate a rare example of a stable cyclopropanone by a fast and selective epoxidation-rearrangement process. Several important goals were achieved in the described research study. First, strategic incorporation of [4+4] photocycloaddition as one of the key steps in targeted synthesis of natural products has demonstrated the potential of this powerful reaction. Second, an efficient new approach to a tetraquinane skeleton was developed and successfully executed. Third, the fundamental basis for the novel photochemical transformation (enyne-pyridone cycloaddition) was set and major trends for this reaction were established resulting in obtaining stable allenic photoadducts. Finally, chemical properties and reactivity of stabilized amide-bridged 1,2,5-cyclooctatriene photoproducts were investigated breaking the ground for future involvement of these intermediates in synthetic strategies towards biologically active natural products and their analogues. / Chemistry

There is a profound need for new antibiotics which overcome bacterial resistance. The predominant source for these is natural products; however, they are often quickly rendered ineffective due to antibiotic resistance. A proven method in drug discovery is improving the properties of natural products through diverted total synthesis (DTS). Of particular interest is promysalin, which is produced by Pseudomonas putida, and selectively inhibits the growth of Gram-negative pathogenic bacteria Pseudomonas aeruginosa at nanomolar concentrations. The work herein describes modifications to the side chain which were shown to modulate antibacterial potency and specificity. A similarly inspired approach to countering antibiotic resistance is the targeted modification of a single carbon to silicon, motivated by the proven success of this substitution shown in pharmaceuticals and amino acids. The target for this modification is albocycline, a known macrolactone antibiotic that exhibits potent antibiotic activity against S. aureus. Replacing the C4 carbon of albocycline with silicon will provide sila-albocycline with enhanced hydrogen bonding properties and altered lipophilicity due to the slight changes from the carbon to silicon atom. In addition, there is anticipated intrinsic stability of the silanol toward rearrangement reactions than carbon-based. The proposed synthesis diverts from the known total synthesis of albocycline, as reported by the Andrade Group. This work details the efforts made towards the total synthesis of sila-albocycline. Lastly, there is untapped potential for UV-promoted photochemistry to create molecular scaffolds, which may lead to novel synthetic routes to complex molecules in addition to providing new polycycles that may expand current medicinal products. The work herein describes the synthesis of tethered chloro- and methoxy-substituted benzyl alcohols to 2-pyridones and the resulting products when exposing the solution to ultraviolet light. This generated new polycycles with complex structures which have unexplored biological or medicinal properties. / Chemistry

<p>Bicyclic dihydrothiazolo fused 2-pyridones have been studied as a new class of antibacterial agents, termed pilicides, that target the formation of adhesive bacterial surface organelles (pili) in pathogenic bacteria. Synthetic methods to further functionalize the bicyclic 2-pyridone scaffold have been developed in order to increase water-solubility and thereby facilitate biological evalua-tions. This was accomplished by introducing aminomethylenes at the open position C-6. Tertiary amines were introduced via a microwave–assisted Mannich reaction and a synthetic route based on a formyl intermediate gave access to primary, secondary and tertiary amines, but also to other interesting functionalities. Biological evaluation confirmed that several of the function-alized compounds inhibited pili formation in uropathogenic <i>E. coli</i>., as dem-onstrated by assays of hemagglutination, biofilm formation and adherence to bladder cells. Co-crystallizing one of the pilicides with the target protein gave information about the binding site and based on this a mechanism of action was proposed, which was supported experimentally by surface plas-mon resonance and single point mutations in the protein.</p><p>Furthermore, the previously developed acylketene imine reaction used to prepare bicyclic thiazolo fused 2-pyridone pilicides has been developed to allow preparation of other ring-fused 2-pyridone systems. Benzo[a]quinolizine-4-ones and indolo[2,3-a]quinolizine-4-ones could be prepared in a fast and simple manner starting from dihydroisoquinolines and a β-carboline. Finally, this method could also be applied for the preparation of heteroatom analogs of the previously studied sulfur containing pilicides. Biological evaluations established that the sulfur atom can be replaced by oxygen and still maintain the ability to prevent pili assembly.</p>

There are many applications of small organic compounds, e.g. as drugs or as tools to study biological systems. Once a compound with interesting biological activity has been found, medicinal chemists typically synthesize small libraries of compounds with systematic differences to the initial “hit” compound. By screening the new ensemble of compounds for their ability to perturb the biological system, insights about the system can be gained. In the work presented here, various ways to synthesize small libraries of ring-fused 2‑pyridones have been developed. Members of this class of peptidomimetic compounds have previously been found to have a variety of biological activities, e.g. as antibacterial agents targeting virulence, and as inhibitors of the aggregation of Alzheimer b‑peptides. The focus in this work has been to alter the core skeleton, the central fragment, of the previously discovered biologically active 2‑pyridones and evaluate the biological effects of these changes. Several new classes of compounds have been constructed and their preparations have included the development of multi-component reactions and a method inspired by diversity-oriented synthesis. Some of the new compounds have been evaluated for their effect on the fibrillation of different amyloid proteins. Both the Parkinson-associated amyloid protein a-synuclein and the bacterial protein CsgA that is involved in bacterial biofilm formation are affected by subtle changes of the compounds’ central fragments. This is an example of the usefulness of central-fragment alterations as a strategy to probe structure-activity relationships, and the derived compounds may be used as tools in further study of the aggregation of amyloid proteins.

Bicyclic dihydrothiazolo fused 2-pyridones have been studied as a new class of antibacterial agents, termed pilicides, that target the formation of adhesive bacterial surface organelles (pili) in pathogenic bacteria. Synthetic methods to further functionalize the bicyclic 2-pyridone scaffold have been developed in order to increase water-solubility and thereby facilitate biological evalua-tions. This was accomplished by introducing aminomethylenes at the open position C-6. Tertiary amines were introduced via a microwave–assisted Mannich reaction and a synthetic route based on a formyl intermediate gave access to primary, secondary and tertiary amines, but also to other interesting functionalities. Biological evaluation confirmed that several of the function-alized compounds inhibited pili formation in uropathogenic E. coli., as dem-onstrated by assays of hemagglutination, biofilm formation and adherence to bladder cells. Co-crystallizing one of the pilicides with the target protein gave information about the binding site and based on this a mechanism of action was proposed, which was supported experimentally by surface plas-mon resonance and single point mutations in the protein. Furthermore, the previously developed acylketene imine reaction used to prepare bicyclic thiazolo fused 2-pyridone pilicides has been developed to allow preparation of other ring-fused 2-pyridone systems. Benzo[a]quinolizine-4-ones and indolo[2,3-a]quinolizine-4-ones could be prepared in a fast and simple manner starting from dihydroisoquinolines and a β-carboline. Finally, this method could also be applied for the preparation of heteroatom analogs of the previously studied sulfur containing pilicides. Biological evaluations established that the sulfur atom can be replaced by oxygen and still maintain the ability to prevent pili assembly.

New methodology for the synthesis of several 4H-pyrido[1,2-a]pyrimidin-4-ones has been developed from commercially available 2-aminopyridines and β-oxo esters catalysed by Montmorillonite under solvent-free conditions in good yields. This methodology was expanded for the synthesis of 4H-pyrimido[1,2-a]pyrimidin-4-one derivatives from 2-aminopyrimidine and different β-keto esters. The new methodology for the synthesis of N-alkylated 6-methyl 2-pyridones and N-alkylated 2-methyl 4-pyridones, from commercially available starting materials was developed. For the synthesis of N-alkylated 6-methyl 2-pyridones, 2-methoxy-6-methyl pyridine and a number of different alkylating reagents have been employed as starting materials. For the synthesis of N-alkylated 2-methyl 4-pyridones, 4-chloro 2-methyl pyridine was used successfully to make the desired pyridone in 3 steps. Selective mono-metallation at the 6-methyl substituent of N-alkylated 6-methyl 2-pyridones and N-alkylated 2-methyl 4-pyridones with n-BuLi/KHMDS at -78 °C proceeded smoothly, and the reactivity of the lithiated intermediates towards a wide range of electrophile (diketones, aldehydes, alkylating reagents) was studied. A straightforward synthesis of desirable 4H-quinolizin-4-one scaffolds by condensation of N-benzyl 6-methyl 2-pyridones with dicarbonyl compounds, and the formation of the desired quinolizinone after the condensation step was achieved. An unexpected quinolizinone bearing a fused β-lactam ring was isolated and its structure confirmed by single crystal X-ray diffraction analysis.