The formation of aberrant disulfide bonds is a structural consideration for the manufacturing of the extracellular domain of human CD83 (hCD83ext), a potential therapeutic protein. In certain instances, hCD83ext protein products, even when stored frozen, tend to dimerize or even multimerize through the formation of aberrant intermolecular disulfide bonds. Herein, we discovered an analytical inconsistency and applied a modified sample preparation protocol for proper structural analysis of hCD83ext products which are heterologously expressed in Escherichia coli and subsequently purified. In addition, a mutant derivative with the Cys100Ser mutation was identified as an improved version which did not form dimers or multimers. The identification of this mutant variant as a more potent therapeutic protein than other hCD83ext species demonstrated that the structural variation associated with disulfide bond formation can be a critical issue for rigorous control of the quality and bioactivity of therapeutic proteins. The application of this mutant variant for protein therapeutic is currently under exploration. As a comparative study, the hCD83ext was expressed as a glutathione-S-transferase (GST) fusion in two E. coli B strains, i.e. BL21 and Origami B having a reductive and oxidative cytoplasm. The final therapeutic products of hCD83ext produced by the two expression hosts exhibited significant differences in protein conformation and molecular properties, which presumably resulted from different disulfide patterns. The study highlights the importance of developing proper host/vector systems and biomanufacturing conditions for the production of recombinant therapeutic proteins with a consistent product quality. Cys27 in the hCD83ext was identified as a target for molecular manipulation. Two E. coli strains of BL21(DE3) and Origami B(DE3) were used as the expression host to produce the Cys27 mutants. It was observed that Cys27 was involved in the in vivo formation of intramolecular disulfide bonds when hCD83ext was expressed in Origami B(DE3). The Origami-derived protein products had a higher tendency than the BL21-derived counterparts for multimerization via the in vitro formation of intermolecular disulfide bonds. Various analyses were conducted to identify the structural differences among these mutant variants. Most importantly, molecular stability was enhanced by the Cys27 mutations since the Cys27 mutants derived from either BL21 or Origami were much less susceptible to degradation compared to wild-type hCD83ext. This study highlights the implications of aberrant disulfide bond formation on the production of therapeutic proteins. To address an inconsistent bioactivity issue that is primarily due to the aberrant formation of disulfide bonds associated with the presence of five cysteine residues, i.e. AA 27, 35, 100, 107, and 129, the molecular role that each cysteine plays upon the formation of intramolecular or intermolecular disulfide bonds was characterized, using various hCD83ext mutant variants derived by two E. coli expression hosts, i.e. BL21(DE3) and Origami B(DE3). Among the five cysteines, Cys100 and Cys129 can act as a bridging cysteine for in vitro multimerization via the formation of intermolecular disulfide bonds. The multimerization can be alleviated to some extent with less free Cys129 residues, associated with the possible formation of Cys27-Cys129 intramolecular disulfide bond. As a result, introducing the Cys27 mutation can increase the multimerization presumably via freeing more Cys129 residues. In addition, protein stability can be improved in the presence of the Cys27 mutation. The formation of the Cys27-Cys129 intramolecular disulfide bond appears to be more effective in the presence of the Cys100 mutation, resulting in the suppression of multimerization. The two conserved cysteine residues, i.e. Cys35 and Cys107, can be potentially linked to form an intramolecular disulfide bond, particularly when the protein is produced in Origami B(DE3).

The first section of this dissertation (Chapter I-III) describes the development of new methodologies for the rhodium catalyzed C-N bond formation between sp3 hybridized carbon atom of phenyl substituted alpha-lactams and the nitrogen atom of indole derivatives. Phenyl substituted alpha-lactams generated in situ from the corresponding alpha-bromoamides reacted with indoles in the presence of rhodium catalyst to afford the ring opening products of alpha-lactams. The scope of this methodology was extended to various types of indole derivatives including electron donating and withdrawing substituents. Furthermore, a series of functionalized phenyl substituted alpha-lactams generated in situ reacted with indole to assess the viability of this methodology. The developed method provides an atom-economical approach for the formation of substituted alpha-amino amides in good to excellent yields. The main goal of the research described in the second section (Chapter IV-VII) is the synthesis of the corannulene-based molecular receptors with polar tethers and their immobilization on silica gel. First, we have considered a preparation of bis-corannulenoanthracene, formally possessing the pentacene core as a potential precursor for a series of barrelene based bis-corannulene receptors with polar groups. Bis-corannulenoanthracene was synthesized by the double Diels-Alder cycloaddition of isocorannulenofuran with bis-benzyne precursor, followed by deoxygenation of the endoxide adducts. While bis-corannulenoanthracene is stable enough to be isolated and stored, its pentacene core undergoes facile cycloaddition with maleic anhydride to afford bis-corannulene molecular receptor with the barrelene tether adorned with the anhydride moiety. The 1H NMR titration experiments carried out in chlorobenzene-d5 proved the high binding affinity of the receptor toward C60. In addition, the presence of polar anchors on its tether allowed for its deposition on silica gel through the (3-aminopropyl)triethoxysilane linker.

Within the last few years, a significant contribution to the discovery of sp2C−H activation processes and useful applications for cross-coupling C−C bond formation has been achieved by the use of ruthenium(II) arene catalysts. The aim of this thesis is to describe a modular approach for the synthesis of several ruthenium(II) arene complexes with the potential for C−H activation. Another cutting-edge field, catalytic enantioselective functionalization of C−H bonds by transitional metal catalysts, has also been realized within the last few years. It represents a highly atom- and step-economic approach toward the generation of structural complexity. However, the majority of current methodologies rely on the usage of late third- row transition metals such as pallidum, iridium and rhodium. There is a need that motivates the search for cheaper, relative earth abundant metals that could have similar catalytic ability. Herein is also represented a preliminary study of a ruthenium(II)-catalyzed enantioselective access to chromane moiety enabled by chiral transient directing group.

Development of C–N bond formation chemistry is a continuing field of study. Recently copper based Chan-Evans-Lam cross-coupling was discovered, and although our understanding of the mechanism has grown, there are still many unanswered questions to be explored. Herein, we set out to develop a series of copper complexes that can stabilize different oxidation states in an attempt to probe how this impacts the mechanism. Initially complexes of copper(II) with 1,10 phenanthroline (phen) and related ligands were generated for use with CEL coupling. The complexes were probed electrochemically and photophysically and found that the 4,5-diazafluorenone complex 4 had a Cu2+/Cu+ potential +1.1 V relative to phen. We observed that the copper complex 4, which stabilize the Cu+, gave the greatest yield of the desired product. Following this study, we aimed to synthesize novel N-heterocyclic carbene copper complexes, which could better stabilize the copper(II) and copper(III) states. Several ligands and derivatives were synthesized, and copper(II) complexes were made using Cu(OAc)2 as a direct metalation agent. This complex was characterized via several spectroscopic methods and it was found to be a copper(II) complex. Initially this complex was thought to be relatively air stable but it was found to slowly decomposed to a novel di-copper bis-imidazolium complex over the course of 96 hours. While the identity of some of the intermediates are unknown, crystals of a potential end point were grown. A series of preliminary C–N coupling reactions show that the NHC copper(II) complexes are possible catalysts in alcoholic solvents.

No description available.

No / Mechanochemical chemoenzymatic peptide and amide bond formation catalysed by papain was studied by ball milling. Despite the high-energy mixing experienced inside the ball mill, the biocatalyst proved stable and highly efficient to catalyse the formation of α,α- and α,β-dipeptides. This strategy was further extended to the enzymatic acylation of amines by milling, and to the mechanosynthesis of a derivative of the valuable dipeptide L-alanyl-L-glutamine. / We thank RWTH Aachen University for support from the Distinguished Professorship Program funded by the Excellence Initiative of the German federal and state governments. EPSRC, grant no. EP/L019655/1.

In Michael J. Krische research group we are developing new transition metal catalyzed Carbon-Carbon (C-C) forming reactions focusing on atom economy and byproduct free, environmental friendly approaches. We have developed a broad family of C-C bond forming hydrogenations with relative and absolute stereocontrol which provide an alternative to stoichiometric organometallic reagents in certain carbonyl and imine additions. Inspiring from the group work my goal was to develop new reactions, extend the scope of our group chemistry and their application towards synthesis of biologically active natural products. I have been part of enantioselective Rh catalyzed Aldol reaction of vinyl ketones to different aldehydes. Also, we have found that iridium catalyzed transfer hydrogenation of allylic acetates in the presence of aldehydes or alcohols results in highly enantioselective carbonyl allylation under the conditions of transfer hydrogenative. Based on this reactivity a concise enantio- and diastereoselective synthesis of 1,3-polyols was achieved via iterative chain elongation and bidirectional iterative asymmetric allylation was performed, which enables the rapid assembly of 1,3-polyol substructures with exceptional levels of stereocontrol. The utility of this approach stems from the ability to avoid the use of chirally modified allylmetal reagents, which require multistep preparation, and the ability to perform chain elongation directly from the alcohol oxidation level. This approach was utilized for the total synthesis of (+)-Roxaticin from 1,3-propanediol in 20 longest linear steps and a total number of 29 manipulations. Further, advancements were made in iridium catalyzed C-C bond formation under transfer hydrogenation. While methallyl acetate does not serve as an efficient allyl donor, the use of more reactive leaving group in methallyl chloride compensate for the shorter lifetime of the more highly substituted olefin π-complex. Based on this insight into the requirements of the catalytic process, highly enantioselective Grignard-Nozaki-Hiyama methallylation is achieved from the alcohol or aldehyde oxidation levels. Also, a catalytic method for enantioselective vinylogous Reformatsky- type aldol addition was developed in which asymmetric carbonyl addition occurs with equal facility from the alcohol or aldehyde oxidation level. Good to excellent levels of regioselectivity and uniformly high levels of enantioselectivity were observed across a range of alcohols and aldehydes. / text

Cross-coupling reactions, where a transition metal catalyst facilitates the formation of a new carbon-carbon or carbon-heteroatom bond between two coupling partners, has become one of the most widely used, reliable, and robust family of transformations for the construction of molecules. The Nobel Prize was awarded to pioneers in this field who primarily used aryl iodides, bromides, and triflates as electrophilic coupling partners. The expansion of the reaction scope to non-traditional electrophiles is an ongoing challenge to enable an even greater number of useful products to be made from simple starting materials. The major goal of this thesis research is to improve and expand upon this field by using esters as electrophiles via the activation of the strong C(acyl)−O bond. Esters are particularly robust in comparison to other carboxylic acid derivatives used in cross-coupling reactions. Success on the activation of such inert functional group using catalysis has both fundamental and practical value. By discovering new reaction modes of this abundant functional group, synthetic routes to access novel or industrially important molecules can be improved. Chapter 1 of this thesis describes a literature overview of what has been accomplished in the field of cross coupling reactions using carboxylic acid derivatives as electrophilic coupling partners. Chapter 2 discloses the first palladium Suzuki-Miyaura couplings of phenyl esters to produce ketones. The method is efficient and robust, giving good yields of useful products. The reaction is proposed to proceed via an oxidative addition to the strong C(acyl)−O bond of the ester. In contrast to previous efforts in this field that use traditional catalysts such as Pd(PPh3)4, the developed reaction requires use of an electron-rich, bulky N-heterocyclic carbene ligand, which facilitates the strong bond activation. Furthermore, a palladium-catalyzed cross-coupling between aryl esters and anilines is reported, enabling access to diverse amides. The reaction takes place via a similar activation of the C−O bond by oxidative addition with a Pd−NHC complex, which enables the use of relatively non-nucleophilic anilines that otherwise require stoichiometric activation with strong bases to react. Chapter 3 discloses a nickel-catalyzed amide bond formation using unactivated and abundant esters. In this transformation, an accessible nickel catalyst can facilitate the activation of diverse aliphatic and aromatic esters to enable direct amide bond formation with amines as nucleophiles. No stoichiometric base, acid, or other activating agent is needed, providing exceptional functional group tolerance and producing only methanol as a by-product. This reaction is of both fundamental and practical importance because it is the first to demonstrate that simple conditions can enable Ni to cleave the C–O bond of an ester to make an oxidative addition product, which can be subsequently coupled with amines. This discovery contrasts industrially-common and wasteful methods that still require stoichiometric activating agents or multistep synthesis. Chapter 4 describes the evaluation of different types of cross-coupling reactions using methyl esters as electrophilic coupling partner. A high-throughput screening technique has been applied to this project. A combination between specific ligands, known by their efficiency to activate strong C−O bonds, and literature-based conditions has been designed for the chosen transformations. Using this strategy, two promising hits have been obtained using the same NHC ligand: a decarbonylative Suzuki-Miyaura and a decarbonylative borylation reaction.

Small molecule walkers developed to date take advantage of the reversibility of dynamic covalent bond formation to transport molecular fragments along molecular tracks using both diffusion processes and ratchet mechanisms. However, external intervention (the addition of chemical reagents and/or irradiation with light) is required to mediate each step taken by the walker unit in systems reported so far. In this Thesis, the first synthetic small molecule able to walk back-and-forth upon an oligoethylenimine track without external intervention via intramolecular Michael and retro- Michael reactions is described. The 1D random walk is highly processive and exchange takes place between adjacent amine groups in a stepwise fashion. The walker is used to perform a simple task: quenching of the fluorescence of an anthracene group situated at one end of the track as a result of the walking progress. In the presence of excess of base, the molecule preferentially ‘walks’ towards the favoured final foothold of tracks of increasing length and it is possible to monitor the population of all or a few positional isomers over time. In each case the molar fraction of walkers reaching the final foothold is determined quantitatively by 1H NMR. Control over the rate of exchange is achieved by varying the amount of base added. The dynamic migration of a small molecule upon the track is a diffusion process limited to one dimension and as such can in principle be described using the one dimensional random walk. Chapter I identifies a set of fundamental walker characteristics and includes an overview of the DNA-based and small molecule transporting systems published to date. Chapter II describes the inspiration for this work and model studies which lay the groundwork for the research presented in this thesis. The initial track architecture and optimisation of reaction conditions are demonstrated using a simple model compound which then led to the development and a detailed investigation of a first synthetic small molecule able to walk upon an oligoethylenimine track without external intervention. Chapter III presents a modified synthetic route towards the desired walker-track architectures and a comprehensive investigation of the dynamic properties of a series of tracks of increasing length upon which the walker migrates in a unidirectional fashion. The Outlook contains closing remarks about the scope and significance of the presented work as well as ideas for the design of novel small-molecule walkers, some of which are well under way in the laboratory. Chapter II (with the exception of model studies included at the beginning of the chapter) is presented in the form of article that has recently been published. No attempt has been made to re-write this work out of context other than merging content of the article with the supplementary information published together with the article. Chapter II is reproduced in the Appendix in its published format.

This thesis describes the development and mechanistic studies of carbocyclization reactions of allene-substituted olefins and 1,3-dienes, catalyzed by palladium(0) and palladium(II). These reactions results in the formation of [n,3,0] bicyclic systems (n = 3-5) with high stereoselectivity and in good to excellent yields. The first carbocyclization presented is a novel palladium(0)-catalyzed cyclo- isomerization of allene-substituted olefins. Secondly an efficient aerobic biomimetic system has been developed for a Pd(II)-catalyzed allylic oxidative carbocyclization of allene-substituted olefins. Additionally, during the studies of palladium-catalyzed carbocyclizations of allene-substituted olefins, it was found that in the absence of palladium a mild thermal ene-reaction occurs. In this manner stereodefined, functionalized bicyclic compounds are obtained with good regioselectivity and in high yields. The third and fourth carbocyclization developed are a palladium(II)-catalyzed oxidation and a palladium(0)-catalyzed intramolecular telomerization of allene-substituted 1,3-dienes. A mechanistic study of the palladium(II)-catalyzed oxidation of allene-substituted 1,3-dienes was made, and reaction intermediates could be isolated. The stereochemistry of the reaction intermediates was assigned, and this made it possible to suggest a mechanism for the reaction. The presented mechanism is a trans carbopalladation of the 1,3-diene, where the allene act as the carbon nucleophile. Due to different stereochemical outcomes of the stoichiometric and catalytic reactions, this mechanism could only explain the stoichiometric reaction. Another mechanism for the catalytic reaction was suggested, which rationalizes both the regio- and stereochemistry of the products.