No / 2-phenylethylamine is an endogenous constituent of the human brain and is implicated in cerebral transmission. This bioactive amine is also present in certain foodstuffs such as chocolate, cheese and wine and may cause undesirable side effects in susceptible individuals. Metabolism of 2-phenylethylamine to phenylacetaldehyde is catalysed by monoamine oxidase B but the oxidation to its acid is usually ascribed to aldehyde dehydrogenase and the contribution of aldehyde oxidase and xanthine oxidase, if any, is ignored. The objective of this study was to elucidate the role of the molybdenum hydroxylases, aldehyde oxidase and xanthine oxidase, in the metabolism of phenylacetaldehyde derived from its parent biogenic amine. Treatments of 2-phenylethylamine with monoamine oxidase were carried out for the production of phenylacetaldehyde, as well as treatments of synthetic or enzymatic-generated phenylacetaldehyde with aldehyde oxidase, xanthine oxidase and aldehyde dehydrogenase. The results indicated that phenylacetaldehyde is metabolised mainly to phenylacetic acid with lower concentrations of 2-phenylethanol by all three oxidising enzymes. Aldehyde dehydrogenase was the predominant enzyme involved in phenylacetaldehyde oxidation and thus it has a major role in 2-phenylethylamine metabolism with aldehyde oxidase playing a less prominent role. Xanthine oxidase does not contribute to the oxidation of phenylacetaldehyde due to low amounts being present in guinea pig. Thus aldehyde dehydrogenase is not the only enzyme oxidising xenobiotic and endobiotic aldehydes and the role of aldehyde oxidase in such reactions should not be ignored.

Wong Wei-yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 221-242). / Abstracts in English and Chinese. / Thesis committee --- p.i / Declaration --- p.ii / Acknowledgements --- p.iii / Abstract in Chinese --- p.iv / Abstract in English --- p.vi / List of abbreviations --- p.viii / List of figures --- p.xi / List of tables --- p.xv / Content: --- p.xvi / General introduction --- p.1 / Aldehyde dehydrogenase superfamily --- p.3 / Background of antiquitin --- p.5 / Plant antiqutins (ALDH7B) --- p.5 / Animal antiquitins (ALDH7A) --- p.8 / Human antiquitin information on NCBI --- p.14 / Rationale of studying the inducibility of annquitin and overexpression of it in HEK293 and HepG2 cells --- p.16 / Flowchart 1 Procedure of antiquitin expression studies in the HEK293 and HepG2 cells under stress --- p.19 / Flowchart 2 Procedure to study antiquitin expression in the HEK293 and HepG2 cells after in silico promoter search --- p.20 / Flowchart 3 Procedure to study antiquitin overexpressed HEK293 and HepG2 cells --- p.21 / Chapter Chapter 1 --- Inducibility of antiquitin in the HEK293 and HepG2 cells under hyperosmotic stress / Chapter 1.1 --- Introduction --- p.22 / Chapter 1.1.1 --- Cellular response to hyperosmotic stress --- p.22 / Chapter 1.1.2 --- Methods to study the responses of cells under hyperosmotic stress --- p.24 / Chapter 1.2 --- Materials --- p.26 / Chapter 1.2.1 --- Cell culture media --- p.26 / Chapter 1.2.2 --- Buffers for RNA use --- p.26 / Chapter 1.2.3 --- Buffers for DNA use --- p.27 / Chapter 1.2.4 --- Other chemicals --- p.27 / Chapter 1.3 --- Methods --- p.28 / Chapter 1.3.1 --- Culture of HEK293 and HepG2 cells --- p.28 / Chapter 1.3.2 --- Hyperosmotic stress on HEK293 and HepG2 cells --- p.29 / Chapter 1.3.3 --- MTT assay --- p.29 / Chapter 1.3.4 --- Total RNA extraction --- p.30 / Chapter 1.3.5 --- Reverse transcription polymerase chain reaction (RT-PCR) --- p.30 / Chapter 1.3.6 --- Polymerase chain reaction (PCR) --- p.31 / Chapter 1.3.7 --- Quantification of PCR products --- p.31 / Chapter 1.3.8 --- Statistical analysis --- p.33 / Chapter 1.4 --- Results --- p.34 / Chapter 1.4.1 --- Viability of HEK293 and HepG2 cells under hyperosmotic stress --- p.34 / Chapter 1.4.2 --- Validation of RNA quality --- p.34 / Chapter 1.4.3 --- Validation and determination of PCR conditions --- p.40 / Chapter 1.4.4 --- Inducibility of antiquitin in HEK293 cells under hyperosmotic stress / Chapter 1.4.5 --- Inducibility of antiquitin in HepG2 cells under hyperosmotic stress --- p.43 / Chapter 1.4.6 --- Inducibility of aldose reductase under hyperosmotic stress --- p.43 / Chapter Chapter 2 --- "In silico studies of human antiquitin promoter, genomics sequences and open reading frame" --- p.54 / Chapter 2.1 --- Introduction --- p.54 / Chapter 2.1.1 --- Eukaryotic promoters --- p.55 / Chapter 2.1.2 --- Key events in transcriptional initiation --- p.55 / Chapter 2.1.3 --- Alternative splicing of mRNA --- p.57 / Chapter 2.1.4 --- Bipartite nuclear localization signal (NLS) --- p.57 / Chapter 2.2 --- Methods --- p.60 / Chapter 2.2.1 --- Putative promoter studies of human antiquitin --- p.60 / Chapter 2.2.2 --- Putative promoter studies of Arabidopsis thaliana antiquitin --- p.60 / Chapter 2.2.3 --- Analysis for the alternative splicing of human antiquitin mRNA --- p.60 / Chapter 2.2.4 --- Analysis for the nuclear localization signal (NLS) of human antiquitin amino acid sequence --- p.61 / Chapter 2.2.5 --- Nucleotide / amino acid sequence analyses --- p.61 / Chapter 2.3 --- Results --- p.62 / Chapter 2.3.1 --- Computer search for the putative cis-acting elements on human antiquitin promoter --- p.62 / Chapter 2.3.2 --- Comparison of cis-acting elements found on human antiquitin promoter with those on Arabidopsis thaliana antiquitin promoter --- p.62 / Chapter 2.3.3 --- Possibilities of alternative splicing isoforms of human antiquitin / Chapter 2.3.4 --- Possibilities of bipartite nuclear localization signals on human antiquitin protein --- p.83 / Chapter Chapter 3 --- Overexpression of antiquitin in HEK293 and HepG2 cells and their characterization / Chapter 3.1 --- Introduction --- p.86 / Chapter 3.1.1 --- Cell cycle of a human somatic cell --- p.88 / Chapter 3.1.2 --- Detection of changes in the transcriptome --- p.90 / Chapter 3.1.3 --- Human genome U133 Plus 2.0 array --- p.95 / Chapter 3.1.4 --- Detection of changes in the proteome --- p.96 / Chapter 3.1.5 --- MALDI-TOF MS --- p.97 / Chapter 3.2 --- Materials --- p.99 / Chapter 3.2.1 --- Solutions for cell culture use --- p.99 / Chapter 3.2.2 --- Solutions for cloning --- p.99 / Chapter 3.2.3 --- Buffers for cell cycle analysis --- p.99 / Chapter 3.2.4 --- Buffers for two-dimensional (2D) electrophoresis --- p.100 / Chapter 3.2.5 --- Solutions for silver staining --- p.101 / Chapter 3.2.6 --- Solutions for Coomassie blue protein staining --- p.102 / Chapter 3.2.7 --- Solutions for Western blotting --- p.102 / Chapter 3.2.8 --- Solutions for mass spectrometry --- p.103 / Chapter 3.3 --- Methods --- p.104 / Chapter 3.3.1 --- Hypoosmotic stress --- p.104 / Chapter 3.3.2 --- Heat shock --- p.104 / Chapter 3.3.3 --- Oxidative stress treatment / Chapter 3.3.4 --- Chemical hypoxia --- p.104 / Chapter 3.3.5 --- Treatment of forskolin --- p.106 / Chapter 3.3.6 --- Culture of SHSY5Y cells and its differentiation --- p.106 / Chapter 3.3.7 --- Cloning of pBUDCE4.1/ATQ --- p.106 / Chapter 3.3.8 --- PCR product purification --- p.107 / Chapter 3.3.9 --- Preparation of pEGFP.N1 vector for co-transfection --- p.109 / Chapter 3.3.10 --- Transfection of HEK293 and HepG2 cells --- p.109 / Chapter 3.3.11 --- Assays to characterize transient transfected HEK293 and HepG2 cells --- p.110 / Chapter 3.3.11.1 --- Transfection efficiency monitoring --- p.110 / Chapter 3.3.11.2 --- Cell cycle analysis --- p.112 / Chapter 3.3.11.3 --- Cell doubling time measurement --- p.112 / Chapter 3.3.11.4 --- Stress responsiveness --- p.113 / Chapter 3.3.11.5 --- Oligonucleotide array analysis --- p.113 / Chapter 3.3.11.5.1 --- Total RNA extraction --- p.113 / Chapter 3.3.11.5.2 --- Oligonucleotide array preparations --- p.113 / Chapter 3.3.11.5.3 --- Data analysis --- p.114 / Chapter 3.3.11.6 --- Two-dimensional (2D) electrophoresis --- p.115 / Chapter 3.3.11.6.1 --- Total protein extraction --- p.115 / Chapter 3.3.11.6.2 --- Protein quantification --- p.115 / Chapter 3.3.11.6.3 --- First dimension electrophoresis: isoelectric focusing (IEF) --- p.115 / Chapter 3.3.11.6.4 --- Second dimension electrophoresis: SDS- --- p.116 / Chapter 3.3.11.6.5 --- Silver staining --- p.116 / Chapter 3.3.11.6.6 --- Spots detection --- p.117 / Chapter 3.3.11.7 --- Preparations of samples for MALDI-TOF MS --- p.117 / Chapter 3.3.11.7.1 --- Silver de-staining --- p.117 / Chapter 3.3.11.7.2 --- In-gel tryptic digestion --- p.118 / Chapter 3.3.11.7.3 --- Peptide extraction --- p.118 / Chapter 3.3.11.7.4 --- ZipTip® samples desalting and concentrating --- p.119 / Chapter 3.3.11.7.5 --- MALDI-TOF MS --- p.119 / Chapter 3.3.11.8 --- Western blotting --- p.119 / Chapter 3.3.11.8.1 --- Antibodies probing --- p.120 / Chapter 3.3.11.8.2 --- Enhanced chemiluminescence's (ECL) assay --- p.121 / Chapter 3.4 --- Results --- p.122 / Chapter 3.4.1 --- Inducibility of antiquitin in HEK293 cells under xenobiotic stimulus --- p.122 / Chapter 3.4.2 --- Inducibility of antiquitin in HEK293 and HepG2 cells under chemical hypoxia --- p.122 / Chapter 3.4.3 --- Inducibility of antiquitin in HEK293 and HepG2 cells under hypoosmotic stress --- p.122 / Chapter 3.4.4 --- Inducibility of antiquitin in HEK293 and HepG2 cells under heat shock --- p.122 / Chapter 3.4.5 --- Inducibility of antiquitin in HEK293 and HepG2 cells under forskolin challenge --- p.128 / Chapter 3.4.6 --- Expression of antiquitin in differentiating SHSY5Y cells by retinoic acid and N2 supplement --- p.128 / Chapter 3.4.7 --- Overexpression of antiquitin in HEK293 and HepG2 cells --- p.128 / Chapter 3.4.8 --- Viability of transfected HEK293 and HepG2 cells under hyperosmotic stress --- p.136 / Chapter 3.4.9 --- Cell doubling times of transfected HEK293 and HepG2 cells --- p.143 / Chapter 3.4.10 --- Cell cycle analysis of transfected HEK293 and HepG2 cells --- p.143 / Chapter 3.4.11 --- "Western blot analysis of cyclin D, cyclin A and cyclin B of transfected HEK293 and HepG2 cells" --- p.148 / Chapter 3.4.12 --- RNA quality control tests for oligonucleotide array analysis --- p.148 / Chapter 3.4.13 --- Oligonucleotide array analysis on transfected HEK293 and HepG2 cells --- p.155 / Chapter 3.4.14 --- Two-dimensional electrophoresis of transfected HEK293 and HepG2 cells --- p.169 / Chapter 3.4.15 --- MALDI-TOF MS of transfected HEK293 and HepG2 cells --- p.169 / Chapter 3.4.16 --- Genes and proteins upregulnted in the antiquitin transfected HEK293 and HepG2 cells --- p.190 / Discussion --- p.197 / Reference --- p.221 / Appendix Materials used in the project --- p.243

by Tang Wai Kwan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 91-110). / Abstracts in English and Chinese. / Acknowledgements / 論文摘要 / Abstract / Abbreviations / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Aldehyde Dehydrogenase Extended Family --- p.1 / Chapter 1.1.1 --- Phylogenetic Tree --- p.2 / Chapter 1.1.2 --- Physiological Functions --- p.4 / Chapter 1.1.3 --- Structural Conservations --- p.7 / Chapter 1.2 --- ALDH-1 and ALDH-2 --- p.9 / Chapter 1.3 --- Antiquitin --- p.11 / Chapter 1.4 --- Osmoregulation --- p.14 / Chapter 1.4.1 --- Osmoprotectant --- p.14 / Chapter 1.4.2 --- Betaine Aldehyde Dehydrogenase --- p.15 / Chapter 1.5 --- Objectives of the Present Study --- p.18 / Chapter Chapter 2 --- Purification and Characterization of Seabream ALDH-2 and Antiquitin --- p.20 / Chapter 2.1 --- Introduction --- p.20 / Chapter 2.2 --- Materials --- p.21 / Chapter 2.3 --- Methodology / Chapter 2.3.1 --- Preparation of Crude Tissue Extract --- p.22 / Chapter 2.3.2 --- Synthesis of α-Cyanocinnamate Sepharose --- p.22 / Chapter 2.3.3 --- Synthesis of p-Hydroxyacetophenone Sepharose --- p.23 / Chapter 2.3.4 --- Purification of ALDH-2 --- p.23 / Chapter 2.3.5 --- Purification of Antiquitin --- p.24 / Chapter 2.3.6 --- Enzyme and Protein Assays --- p.24 / Chapter 2.3.7 --- Electrophoretic Procedures / Chapter 2.3.7.1 --- Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) --- p.26 / Chapter 2.3.7.2 --- Native PAGE --- p.27 / Chapter 2.3.7.3 --- Isoelectric focusing (IEF) --- p.27 / Chapter 2.3.8 --- N-terminal Amino Acid Sequencing --- p.28 / Chapter 2.4 --- Results / Chapter 2.4.1 --- Tissue Distribution of ALDH --- p.29 / Chapter 2.4.2 --- Purification and Molecular Properties of ALDH-2 --- p.31 / Chapter 2.4.3 --- Kinetic Properties of ALDH-2 --- p.42 / Chapter 2.4.4 --- Purification and Molecular Properties of Antiquitin --- p.49 / Chapter 2.4.5 --- Kinetic Properties of Antiquitin --- p.54 / Chapter Chapter 3 --- Discussion / Chapter 3.1 --- Tissue Distribution --- p.66 / Chapter 3.2 --- N-terminal Amino Acid Sequencing --- p.67 / Chapter 3.3 --- Purification of Seabream ALDH --- p.68 / Chapter 3.3.1 --- Separation of Two ALDH isoforms --- p.69 / Chapter 3.3.2 --- Binding Affinity of α-Cyanocinnamate Sepharose --- p.70 / Chapter 3.3.3 --- Purification --- p.72 / Chapter 3.4 --- Electrophoretic Properties --- p.73 / Chapter 3.5 --- pH and Temperature Stability --- p.74 / Chapter 3.6 --- Substrate Specificity --- p.77 / Chapter 3.7 --- Possible Functions of Antiquitin --- p.80 / Chapter 3.8 --- Future Prospects --- p.84 / Chapter Chapter 4 --- Conclusion --- p.90 / Chapter Chapter 5 --- References --- p.91

Antiquitin (ATQ) belongs to the superfamily of aldehyde dehydrogenase (ALDH). It is an evolutionarily conserved protein as shown from its high amino acid sequence identity between human and its plant counterparts. Therefore, ATQ is believed to play an important physiological role. Until now, however, studies on ATQ are limited and its cellular function is uncertain. Recently, we have first demonstrated the aldehyde oxidizing ability of ATQ purified from the liver of black seabream (Acanthopagrus schlegeli). To further investigate this protein, different attempts have been made. / Recombinant ATQ has been successfully expressed in E. coli. Kinetics studies showed that it possessed similar characteristics with its native enzyme. The recombinant protein was produced in large amount for protein crystallization. Crystal of ATQ was obtained and its X-ray structure was solved to 2.8 A in complex with NAD+. Tetrameric ATQ was a dimer of dimer. Three domains can be found in the subunit structure of ATQ, the NAD+-binding domain, catalytic domain and oligomerization domain. In each of the NAD+-binding domain, one molecule of NAD + could be found. The overall structure of ATQ was similar to other tetrameric ALDHs, but the coenzyme binding was in a single "hydride transfer" conformation and the density was well-defined which was contrast to most ALDH structures. Structural study of the substrate-binding pocket explained the failure of ATQ in oxidizing several aldehydes which is specific to certain members of ALDH. / The ATQ full-length cDNA of black seabream was obtained. It consisted of 2309 by with a 153 nucleotide long 5' UTR, and a 209 nucleotide long 3' UTR. An ORF of 1533 by which encoded a protein with 511 amino acids was found. This putative protein showed the highest of 87% sequence identity with zebrafish ATQ, and ∼60% with plant ATQs. Tissue distribution was studied by RT-PCR. A high level of mRNA expression was observed in liver and kidney. Subcellular localization study using green fluorescent protein (GFP) fusion protein showed that ATQ was expressed in cytoplasm. However, another in-frame initiation methionine (M1) was found 31 residues before this generally accepted methionine (M2). Both iPSORT analysis and experimental studies using GFP fusion protein indicated that the 31 amino acid peptide contained a mitochondrial-targeting signal. / Tang Wai Kwan. / "July 2005." / Adviser: Fong Wing Ping. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3603. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 130-145). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

No / Aliphatic aldehydes have a high affinity toward aldehyde dehydrogenase activity but are relatively poor substrates of aldehyde oxidase and xanthine oxidase. In addition, the oxidation of xenobiotic-derived aromatic aldehydes by the latter enzymes has not been studied to any great extent. The present investigation compares the relative contribution of aldehyde dehydrogenase, aldehyde oxidase, and xanthine oxidase activities in the oxidation of substituted benzaldehydes in separate preparations. The incubation of vanillin, isovanillin, and protocatechuic aldehyde with either guinea pig liver aldehyde oxidase, bovine milk xanthine oxidase, or guinea pig liver aldehyde dehydrogenase demonstrated that the three aldehyde oxidizing enzymes had a complementary substrate specificity. Incubations were also performed with specific inhibitors of each enzyme (isovanillin for aldehyde oxidase, allopurinol for xanthine oxidase, and disulfiram for aldehyde dehydrogenase) to determine the relative contribution of each enzyme in the oxidation of these aldehydes. Under these conditions, vanillin was rapidly oxidized by aldehyde oxidase, isovanillin was predominantly metabolized by aldehyde dehydrogenase activity, and protocatechuic aldehyde was slowly oxidized, possibly by all three enzymes. Thus, aldehyde oxidase activity may be a significant factor in the oxidation of aromatic aldehydes generated from amines and alkyl benzenes during drug metabolism. In addition, this enzyme may also have a role in the catabolism of biogenic amines such as dopamine and noradrenaline where 3-methoxyphenylacetic acids are major metabolites.

Pneumothorax, or a collapsed lung, is a serious medical condition resulting when air or fluid escapes the lung into the chest cavity and prevents the lung from inflating. Few viable means of sealing the damaged and leaking tissues are currently available, leading to longer hospital stays, multiple interventions, and increasing costs of care. The motivation of this dissertation is to engineer a novel polysaccharide-based therapeutic surgical sealant, which can be utilized to seal trauma-induced damage to the outer lining of the lung, i.e. pleura, preventing or reversing lung collapse to restore normal breathing function. The use of polysaccharides, such as alginate and hyaluronan, has become increasingly prevalent in biomedical and tissue engineering applications due to the ability to add functionality through chemical modification, allowing for tunable mechanical and physical properties. These hydrophilic polymer chains can be crosslinked to form hydrogels, which can retain large volumes of water and can mimic the properties of tissues found within the body. In this work, polysaccharide hydrogel sealants were engineered with well-regulated gelation and mechanical properties, and further modified to achieve adhesion to biological tissues. This was accomplished by mimicking the mechanical and physical properties of the complex tissues, and crosslinking the hydrogels in situ using a visible light-initiated system. Methacrylated alginate and oxidized alginate were successfully synthesized and utilized to fabricate adhesive sealant patches, which can adhere and seal damaged tissues in vivo. Methacrylation was implemented to allow covalent photo-crosslinking between adjacent polymer chains in solution. Here, a novel anhydrous chemistry was developed to allow for precise control over the degree of methacrylation and thus tune the mechanical properties of the resulting hydrogels by modulating the number of crosslinkable side-groups attached to the polysaccharide chain. To increase the adhesive properties of the resulting hydrogels, oxidation of the polysaccharide chain was subsequently implemented to form functional aldehyde groups capable of protein interactions through the formation of imine bonds on biological tissue surfaces. To test the performance of this multifunctional material, burst pressure testing was executed, revealing the relationship between the two distinct chemical modifications performed and the mechanical and adhesive properties of the resulting sealant. In addition, methacrylated alginate was utilized to synthesize therapeutic, drug-encapsulating hydrogel nanoparticles, which when incorporated within the polysaccharide-based surgical sealant allow for local drug release. The ability to control drug release at the site of application further broadens the potential uses of this surgical sealant patch and will be discussed further within this dissertation.

The mechanisms of idiosyncratic drug reactions (IDRs) are unknown; however, most appear to be immune-mediated. Their idiosyncratic nature and the paucity of animal models make mechanistic studies very difficult. One of the few animal models is penicillamine-induced autoimmunity in Brown Norway rats. The major focus of this thesis was the use of this model to study the interaction between penicillamine and macrophages, the involvement of Th17 cells, and extension of this model to idiosyncratic drug-induced liver injury. One of the costimulatory signals leading to T cell activation appears to be reversible Schiff-base formation between an amine on T cells and an aldehyde on macrophages. We hypothesized that penicillamine binds to these aldehydes leading to macrophage activation and autoimmunity. By using biotinylated aldehyde-reactive agents such as ARP, we demonstrated the existence of aldehydes on the surface of macrophages. We synthesized biotinylated-penicillamine and it also binds to macrophages. Several proteins to which ARP binds were identified providing clues to the signal transduction pathways leading to macrophage activation. Biological consequences of this binding were investigated with a microarray study. ARP binding was also observed in the macrophage cell line, RAW264.7, and incubation with penicillamine stimulated the production of TNF-α, IL-6, and IL-23. Hydralazine and isoniazid, which are known to cause a lupus-like syndrome in humans and irreversibly bind to aldehyde groups, were also found to activate RAW264.7 cells. Th17 cells are prominent in autoimmune syndromes and Th17-associated cytokines such as IL-17 were elevated in the penicillamine-treated animals that developed autoimmunity. We have hypothesized that some drug-induced liver injury has an autoimmune component. A pilot study quantified serum concentrations of 26 cytokines/chemokines in patients with various forms of acute liver failure (ALF): idiosyncratic drug-induced ALF, acetaminophen-induced ALF, and viral hepatitis. IL-17 was elevated in 60% of patients with idiosyncratic drug-induced ALF, which supports an autoimmune component in these patients; however, it was also elevated in many cases of acetaminophen-induced ALF, presumably released by the innate immune system. These studies provide important insights into the mechanism of penicillamine-, hydralazine-, and isoniazid-induced autoimmunity and also provide clues to other IDRs that may have an autoimmune component.

While unprotected amino aldehydes are typically not isolable due to imine formation and consequent polymerization, stable unprotected aziridine aldehydes are useful and available reagents. Moreover, reversible hemiacetal and hemiaminal formation enable these compounds to reveal both their electrophilic and nucleophilic functional groups. This exceptional arrangement allows for aziridine aldehyde dimers to participate in and disrupt the mechanisms of an array of well-known organic reactions, including isocyanide-based multicomponent reactions. The scope and selectivity patterns of aziridine aldehyde induced amino acid or peptide macrocyclization have been investigated. A small library of constrained tri-, tetra-, and penta-peptide macrocycles – representing the most difficult cyclic peptides to synthesize – has been prepared. The scope of aziridine aldehyde participation in multicomponent reactions was also expanded to Ugi and Passerini reactions that do not employ tethered amine and acid functional groups. In order to facilitate cellular imaging of peptide macrocycles a fluorescent isocyanide reagent was prepared and applied to prepare mitochondrial targeting macrocycles. Thioester isocyanide reagents were synthesized to enable rapid assembly of cycle-tail peptides through ligation technology.

Due to inherent rigidity of oligoproline peptides, forcing the C- and N-terminus in proximity for cyclization can be of significant challenge. To address this issue, a cyclization condition involing the help of amphoteric aziridine aldehydes has been developed. This one step cyclization protocol generally proceeds in high yields and goes to completion in relatively short period of time. Despite their cyclic nature, the resulting molecules display spectroscopic characteristics of polyproline II helices. These macrocycles should facilitate systematic studies of various conformational states of polyproline-containing protein regions.

Due to inherent rigidity of oligoproline peptides, forcing the C- and N-terminus in proximity for cyclization can be of significant challenge. To address this issue, a cyclization condition involing the help of amphoteric aziridine aldehydes has been developed. This one step cyclization protocol generally proceeds in high yields and goes to completion in relatively short period of time. Despite their cyclic nature, the resulting molecules display spectroscopic characteristics of polyproline II helices. These macrocycles should facilitate systematic studies of various conformational states of polyproline-containing protein regions.