The research investigations presented herein are concerned with the syntheses and applications of arylboronic acids and their derivatives; with a particular focus on their accessibility or utility in certain of the most significant modern transition metal-catalysed reactions to involve organoborons. Chapter 1 provides an introduction to the field of organoboron chemistry, from its roots employing borane and related highly reactive derivatives for uncatalysed hydroboration of olefins and acetylenes, to the modern classes of organoboron reagents of the greatest significance to the related contemporary transition metal-catalysed methodologies. Furthermore particular emphasis is placed on the discussion of arylboronic acids, their synthesis, and application to transition metal catalysis as a result of their propensity to undergo useful transmetallation events. Chapter 2 details the use of a commercially available sulfonated monophosphine ligand in the rhodium-catalysed 1,2-addition reaction employing aryl aldehydes and arylboronic acids in aqueous media. The high and continued activity of the catalytic complex is demonstrated by it being successfully recycled five consecutive times in the arylation reaction of an aryl aldehyde; as well as being active for the arylations of more sterically demanding aryl methyl ketone substrates. Chapter 3 details the design and synthesis of a novel bench-stable azidomethylene substituted arylboronate ester. The reactivity of this compound and a related analogue in both the coppercatalysed azide alkyne cycloaddition reaction and the Suzuki coupling reaction are detailed, culminating in the proof-of-concept use of such versatile synthetic building blocks in the synthesis of a drug-substance derivative. Chapter 4 details alternative synthetic approaches to that used in Chapter 3 in order to access bifunctional azidomethylene substituted arylboronate esters. In particular the application of Miyaura borylation of arylhalides bearing benzylic azides is addressed as a means to rapidly access substrates which are otherwise shown to be incompatible with classical s-block synthetic intermediates.

The boronic acid functional group is known to bind compounds with the diol group tightly and reversibly in aqueous environment and has been used as a recognition moiety for the design of carbohydrate sensors. The first chapter of the dissertation studies the synthesis and substitution effect on the affinity and selectivity of a known boronic acid-based glucose sensor. In such a sensor design effort, the availability of a signaling event, whether it is fluorescence or UV, is crucial. The second chapter studies the detailed mechanism on how a well-known fluorescent boronic acid compound changes fluorescent properties upon binding. A new mechanism has been established which corrected a decade old mistake. In the third chapter, a series of boronic acid-based sensors were designed and synthesized for sialic acid, which is part of tetrasaccharide found on many cell surface carbohydrates. Such sialic acid sensors could be very useful for the development of new type of anti-influenza therapy. The fourth is on the design and synthesis novel and selective inhibitors for phosphodiesterase 4 (PDE4), which are potential anti-asthma agents.

Carbohydrates are known to play important roles in a large number of physiological and pathological processes. Conceivably, “binders” of carbohydrates of biological importance could be used as diagnostic and therapeutic agents. Currently, lectins are the major available tools in research for carbohydrate recognition. However, the available lectins often have cross-reactivity issues, along with the high costs and stability issues. Therefore, there is a critical need to develop alternatives (lectin mimics). In this regard, there have been very active efforts in developing different “binders”, such as small molecule lectinmimics and aptamers. Among all the small molecule lectinbmimics developments, boronic acid stands out as the most important building blocks of the sensors design for carbohydrates biomarkers due to its intrinsic binding affinities with diols. To address a fundamental question that whether boronic acid also binds to six-membered ring sugars, with very limited precedents, we provided a concrete experimental evidence of the binding. Specifically, a series of isoquinolinylboronic acids were found to have remarkably high binding affinities with fluorescence change upon binding to representative sugars. Most importantly, these isoquinolinylboronic aicds showed weak but very encouraging bindings with six-membered sugar model. All these promising results paves the way of using boronic acids, especially isoquinolinylboronic acid as building blocks for chemosensors design for biological carbohydrates biomarkers, which universally contain six-membered ring and liner diols. Aptamer provides another alternative way for sensors development for carbohydrates biomarkers as lectin mimics. Compared to lectins, they are normally cheaper and more stable. However, there is much less options. Another challenging area for aptamer-based lectin mimics development is the difficulty to differentiate changes in glycosylation patterns of a glycoprotein, which affect the function of a glycoprotein and thus recognized as biomarkers. To address this major challenge, our group first demonstrated that the incorporation of a boronic acid into DNA would allow for the aptamer selection process to gravitate towards the glycosylation site. To examine the generality of boronic acid incorporation, increase the structural diversity, and broaden the application of boronic acid-modified DNA, a series of B-TTP analogues with simplified structures were designed, synthesized, and successfully incorporated into DNA. A simple route was also developed using 1,7-octadiyne as a linker for both Sonogashira coupling with thymidine and CuAAC tethering of a boronic acid moiety. This paves the way for the preparation of a large number of B-TTPs with different structural features for aptamer selection or array analysis. Finally, bacterial quorum sensing has received much attention in recent years because of its relevance to pathological events such as biofilm formation. As one of the very first groups that developed a series of antagonists for AI-2 mediated quorum sensing, we herein designed and synthesized a series of analogues based on the structures of two lead inhibitors identified through virtual screening. Besides, we also examined their inhibitory activities, twelve of which showed equal or better inhibitory activities compared with the lead inhibitors. The best compound showed an IC50 of about 6 mM in a whole cell assay using Vibrio harveyi as the model organism. This encouraging results and SAR discuss also paves the way for the finding of more potent compound through further structure optimization.

The development of reversible and irreversible inhibitors of steroid sulfatase (STS) and protein tyrosine phosphatase 1B (PTP1B) is reported herein. STS belongs to to the aryl sulfatase family of enzymes that have roles in diverse processes such as hormone regulation, cellular degradation, bone and cartilage development, intracellular communication, and signalling pathways. STS catalyzes the desulfation of sulfated steroids which are the storage forms of many steroids such as the female hormone estrone. Its crucial role in the regulation of estrogen levels has made it a therapeutic target for the treatment of estrogen-dependent cancers. Estrone sulfate derivatives bearing 2- and 4-mono- and difluoromethyl substitutions were examined as quinone methide-generating suicide inhibitors of STS with the goal of developing these small molecules as activity-based probes for proteomic profiling of sulfatases. Kinetic studies suggest that inhibition by the monofluoro derivatives is a result of a quinone methide intermediate that reacts with active-site nucleophiles. However, the main inhibition pathway of the 4-difluoromethyl derivative involved an unexpected process in which initially formed quinone methide diffuses from the active site and decomposes to an aldehyde in solution which then acts as a potent, almost irreversible STS inhibitor. This is the first example where this class of inactivator functions by in situ generation of an aldehyde. 6- and 8-mono- and difluoromethyl coumarin derivatives were also examined as quinone methide-generating suicide inhibitors of STS. The 6-monofluoromethyl derivative acted as a classic suicide inhibitor. The partition ratio of this compound was found to be very large indicating that this class of compounds is not likely suitable as an activity-based probe for proteomic profiling of sulfatases. Boronic acids derived from steroid and coumarin platforms were also examined as STS inhibitors with the goal of improving our understanding of substrate binding specificity of STS. Inhibition constants in the high nanomolar to low micromolar range were observed for the steroidal derivatives. The coumarin derivatives were poor inhibitors. These results suggest that the boronic acid moiety must be attached to a platform very closely resembling a natural substrate in order for it to impart a beneficial effect on binding affinity compared to its phenolic analog. The mode of inhibition observed was reversible and kinetic properties corresponding to the mechanism for slow-binding inhibitors were not observed. PTP1B catalyzes the dephosphorylation of phosphotyrosine residues in the insulin receptor kinase and is a key enzyme in the down regulation of insulin signaling. Inhibitors of PTP1B are considered to have potential as therapeutics for treating type II diabetes mellitus. The difluoromethylenesulfonic (DFMS) acid group, one of the best monoanionic phosphotyrosine mimics reported in the literature, was examined as a phosphotyrosine (pTyr) mimic in a non-peptidyl platform for PTP1B inhibition. The DFMS-bearing inhibitor was found to be an approximately 1000-fold poorer inhibitor than its phosphorus analogue. It was also found that the fluorines in the DFMS inhibitor contributed little to inhibitory potency. In addition, [sulfonamido(difluoromethyl)]-phenylalanine (F2Smp) was examined as a neutral pTyr mimic in commonly used hexapeptide and tripeptide platforms. F2Smp was found to be a poor pTyr mimic. These inhibition studies also revealed that the tripeptide platform is not suitable for assessing pTyr mimics for PTP1B inhibition. Taken together, the kinetic data on the inhibition of STS and PTP1B provide valuable information relevant for future design of inhibitors of these two therapeutic targets.

The development of reversible and irreversible inhibitors of steroid sulfatase (STS) and protein tyrosine phosphatase 1B (PTP1B) is reported herein. STS belongs to to the aryl sulfatase family of enzymes that have roles in diverse processes such as hormone regulation, cellular degradation, bone and cartilage development, intracellular communication, and signalling pathways. STS catalyzes the desulfation of sulfated steroids which are the storage forms of many steroids such as the female hormone estrone. Its crucial role in the regulation of estrogen levels has made it a therapeutic target for the treatment of estrogen-dependent cancers. Estrone sulfate derivatives bearing 2- and 4-mono- and difluoromethyl substitutions were examined as quinone methide-generating suicide inhibitors of STS with the goal of developing these small molecules as activity-based probes for proteomic profiling of sulfatases. Kinetic studies suggest that inhibition by the monofluoro derivatives is a result of a quinone methide intermediate that reacts with active-site nucleophiles. However, the main inhibition pathway of the 4-difluoromethyl derivative involved an unexpected process in which initially formed quinone methide diffuses from the active site and decomposes to an aldehyde in solution which then acts as a potent, almost irreversible STS inhibitor. This is the first example where this class of inactivator functions by in situ generation of an aldehyde. 6- and 8-mono- and difluoromethyl coumarin derivatives were also examined as quinone methide-generating suicide inhibitors of STS. The 6-monofluoromethyl derivative acted as a classic suicide inhibitor. The partition ratio of this compound was found to be very large indicating that this class of compounds is not likely suitable as an activity-based probe for proteomic profiling of sulfatases. Boronic acids derived from steroid and coumarin platforms were also examined as STS inhibitors with the goal of improving our understanding of substrate binding specificity of STS. Inhibition constants in the high nanomolar to low micromolar range were observed for the steroidal derivatives. The coumarin derivatives were poor inhibitors. These results suggest that the boronic acid moiety must be attached to a platform very closely resembling a natural substrate in order for it to impart a beneficial effect on binding affinity compared to its phenolic analog. The mode of inhibition observed was reversible and kinetic properties corresponding to the mechanism for slow-binding inhibitors were not observed. PTP1B catalyzes the dephosphorylation of phosphotyrosine residues in the insulin receptor kinase and is a key enzyme in the down regulation of insulin signaling. Inhibitors of PTP1B are considered to have potential as therapeutics for treating type II diabetes mellitus. The difluoromethylenesulfonic (DFMS) acid group, one of the best monoanionic phosphotyrosine mimics reported in the literature, was examined as a phosphotyrosine (pTyr) mimic in a non-peptidyl platform for PTP1B inhibition. The DFMS-bearing inhibitor was found to be an approximately 1000-fold poorer inhibitor than its phosphorus analogue. It was also found that the fluorines in the DFMS inhibitor contributed little to inhibitory potency. In addition, [sulfonamido(difluoromethyl)]-phenylalanine (F2Smp) was examined as a neutral pTyr mimic in commonly used hexapeptide and tripeptide platforms. F2Smp was found to be a poor pTyr mimic. These inhibition studies also revealed that the tripeptide platform is not suitable for assessing pTyr mimics for PTP1B inhibition. Taken together, the kinetic data on the inhibition of STS and PTP1B provide valuable information relevant for future design of inhibitors of these two therapeutic targets.

In this research, a method for site-selective attachment of synthetic molecules into glycoproteins using Boronic acid (BA)-directed tosyl chemistry is proposed. The synthetic BA-tosyl chemical probes are composed of boronic asid as a affinity ligand, a tosyl group as a reactive group and a terminal alkyne group for reporting. In neutral and alkaline environment, boronic acid can act as a targeting head to react with the cis-diol of carbohydrates and therefore forms a covalently reversible boronic diester ring. The newly formed boronate ring can withdraw the probe moeular close to the molecular surface of glycoproteins of interest. Followed by a SN2 reaction with the nucleophilic residues of labeled glycoproteins, the report alkyne group can covalently shift to the protein surface apart from the BA-tosyl skeleton. With the competition of polyols, the BA modified carbohydrates can be recovered to the native glycan structures. The traceless labeling strategy developed in the work has been demonstrated in the specific interaction with a known glycoprotein feutin with negatives controls. We believe that the successful development of this methodology can certainly accelerate the study of glycoproteomics and glycobiology.

This thesis is focused on two main areas of organic synthesis, palladium-catalyzed functionalization of alkenes and allylic alcohols, as well as development of new allylboration reactions. We have developed a palladium-catalyzed selective allylic trifluoroacetoxylation reaction based on C−H functionalization. Allylic trifluoroacetates were synthesized from functionalized olefins under oxidative conditions. The reactions proceed under mild conditions with a high level of diastereoselectivity. Mechanistic studies of the allylic C−H trifluoroacetoxylation indicate that the reaction proceeds via (η3-allyl)palladium(IV) intermediate. Palladium-catalyzed regio- and stereoselective synthesis of allylboronic acids from allylic alcohols has been demonstrated. Diboronic acid B2(OH)4 was used as the boron source in this process. The reactivity of the allylboronic acids were studied in three types of allylboration reactions: allylboration of ketones, imines and acyl hydrazones. All three processes are conducted under mild conditions without any additives. The reactions proceeded with remarkably high regio- and stereoselectivity. An asymmetric version of the allylboration of ketones was also developed. In this process chiral BINOL derivatives were used as catalysts. The reaction using γ-disubstituted allylboronic acids and various aromatic and aliphatic ketones afforded homoallylic alcohols bearing two adjacent quaternary stereocenters with excellent regio-, diastereo- and enantioselectivity (up to 97:3 er) in high yield. The stereoselectivity in the allylboration reactions could be rationalized on the basis of the Zimmerman-Traxler TS model.

No description available.

This thesis describes the combination of non-stabilized nucleophiles and prochiral/racemic electrophiles in transition metal catalyzed asymmetric transformations. These enantioselective reactions have tremendous potential for the formation of chiral building blocks and new structural motifs that can be found in a variety of natural products and their derivatives. The first part of the thesis focuses on the synthetic approach towards anti-cancer active diterpenoid structures. The two key steps involve a Cu-catalyzed asymmetric conjugate addition of alkylzirconocenes to enones and an intramolecular oxidative cyclisation. Particular investigations into the cyclisation are made with organocatalysis, transition metal catalysis and electrochemistry for the formation of these tricyclic scaffolds. In the second part this work builds on the Rh-catalyzed asymmetric Suzuki-Miyaura coupling of benzeneboronic acids and cyclic allyl chlorides, which has been developed in our group. Here, the main point is to use more challenging coupling partners, such as heteroaromatic boronic acids, which are coupled to racemic cyclic allyl halides. The utility of this method is demonstrated by performing further transformations and an asymmetric synthesis of the natural product (+)- isoanabasine. The last chapter describes the development of a new asymmetric Hiyama coupling of arylsiloxanes with racemic cyclic allyl chloride. Attempts are made to generate substrates that are not accessible via the asymmetric Suzuki - Miyaura reaction. After extensive optimisation a variety of arylsiloxanes is generated and tested with the best conditions to prove its utility in comparison to the asymmetric Suzuki-Miyaura coupling.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18232号 / 工博第3824号 / 新制||工||1586(附属図書館) / 31090 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 杉野目 道紀, 教授 吉田 潤一, 教授 村上 正浩 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM