The amide unit constitutes the backbone of proteins, and it is present in a large number of pharmaceutically active molecules, polymeric materials such as nylon and Kevlar, as well as in food additives like aspartame. Amides are produced in enormous amounts every year, thus, environmentally friendly and selective methods for their formation are of great importance. This thesis deals with the direct formation of amides from non-activated carboxylic acids and amines with the aid of group (IV) metal complexes. Water is the only by-product of this environmentally benign process. This fact stands in contrast to the most common methods for amide formation to date, which involve the use of waste-intensive, expensive and often toxic coupling reagents. The catalytic protocols presented herein use titanium, zirconium and hafnium complexes under mild reaction conditions to produce amides in good to excellent yields. Furthermore, carbamates are demonstrated to be suitable sources of gaseous amines for the formation of primary and tertiary amides under catalytic conditions. In addition, preliminary results from on-going mechanistic investigations of the zirconium- and hafnium-catalyzed processes are presented. / Amidbindningen är en kemisk enhet som utgör ryggraden i proteiner, och som även återfinns i en stor mängd läkemedelsmolekyler, polymera material som nylon och Kevlar, samt i tillsatser i livsmedelsindustrin, exempelvis aspartam. Amider produceras i enorma mängder varje år, och det är av stor vikt att utveckla miljövänliga och selektiva metoder för deras framställning. Denna avhandling behandlar direkt amidering av icke-aktiverade karboxylsyror och aminer med hjälp av katalytiska mängder metallkomplex, baserade på titan, zirkonium och hafnium. Den enda biprodukten från denna amideringsreaktion är vatten. Jämfört med de metoder som generellt används idag för amidsyntes, så är de presenterade metoderna avsevärt mer miljövänliga med avseende på toxicitet hos reagensen såväl som på mängden avfall som genereras. Dessutom redovisas här en katalytisk metod för syntes av primära och tertiära amider genom att använda olika karbamat som källa till gasformiga aminer, vilka annars kan vara praktiskt svåra att arbeta med. Preliminära resultat från en pågående mekanistisk studie av de zirkonium- och hafnium-katalyserade processerna är också inkluderade. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Accepted.</p>

No description available.

In the last decade, there has been a surge of interest from the chemistry community in developing synthetic catalysts that emulate the remarkable rate accelerations observed for enzymatic reactions. One approach utilized by enzymes involves preorganization of substrate(s) using a favourable binding event to orient the substrate(s) in a reactive arrangement. Although the “induced intramolecularity” is entropically unfavourable, it is facilitated by the enzymes and utilized to accelerate the subsequent chemical transformation. Chemists have often used a conceptually related stepwise approach in which temporary tethers are assembled to induce a temporary intramolecularity. This preorganization often enables difficult intermolecular reactions, and typically leads to increased regio-, chemo-, and stereoselectivity in chemical reactions. Seeking to develop a catalytic approach, we focused our efforts in developing a mild, carbonyl-catalyzed hydration protocol for - and -amino nitriles to give the corresponding - and -amino amide and acid. This work highlights the value of employing induced intramolecularity in accessing structurally important chemical motifs that otherwise require harsh reaction conditions. Additionally, this thesis presents the background material, design process, optimization and scope of this reactivity.

The iron-molybdenum cofactor (FeMo cofactor) is the catalytic center of nitrogen fixation in molybdenum-dependent nitrognease enzymes. The resting state cofactor is a complex [MoFe7S9X] cluster, in which the central ligand X is a central hexacoordinated monoatomic light atom (2p), and the exact identity of X is uncertain. The heteroligated, nitrogen-containing core environment of the cofactor cluster may also be relevant to active states, as several mechanistic proposals for cofactor catalysis incorporate substrate-derived nitrogenous moeities into the cluster core during turnover. To this end, we have explored synthetic pathways to the dinuclear and tetranuclear nitrogen-containing iron-sufur clusters, which may mimic the heteroligated core environment of the cofactor. Dinuclear iron-amide clusters Fe2(μ-NHtBu)2[N(SiMe3)2]2 (46) and Fe2(μ-NHtBu)2(μ-S)[N(SiMe3)2]2 (47) are useful precursors for the preparation of [Fe4(NtBu)n(S)4-nCl4]z cubane complexes that span all mixed imide/sulfide core compositions between the classic [Fe4S4] and the more recently reported [Fe4(NtBu)4] homoleptic motifs. The [Fe4NS3] core of the n = 1 cluster is particularly noteworthy in being essentially isometric with the analogous [Fe4S3X] subunit of the FeMo cofactor structure. Synthetic compounds are characterized by single crystal X-ray crystallography, cyclic voltammetry, and UV-Vis, 1H NMR spectroscopies.

Zugl.: Bayreuth, Univ., Diss., 2009

Nesse trabalho foi desenvolvido um método de síntese quimioenzimática de organo-seleno aminas (1-((2, 3 ou 4 selenocianato)fenil)etanonas) e amidas (N-(1-(2, 3 ou 4-(etilseleno)fenil)etil)acetamida) enantiomericamente enriquecidas. Inicialmente, as organo-seleno aminas, na forma racêmica, foram sintetizadas a partir das orto-, meta- e para- aminoacetofenonas. A incorporação do átomo de selênio nas cetonas aromáticas foi realizada através da reação de selenocianato de potássio com sais de diazônio, preparados a partir das aminoacetofenonas, para levar as o, m ou p-selenocianato acetofenonas (28-65 %). Reações desses compostos com NaBH4, formaram os intermediários organo-selenoboro, que foram posteriormente alquilados com haletos de alquila de modo a formar as organo-seleno acetofenonas (1-(2, 3 ou 4-(etilseleno)fenil)etanona) (63-78 %). As Organo-seleno aminas racêmicas foram preparadas por aminação redutiva das cetonas correspondentes (39-73 %). Após desenvolvido o protocolo de síntese das organo-seleno aminas, nós estudamos a resolução cinética desses compostos através de reação de acetilação mediada por lipases. Um estudo inicial foi conduzido com a amina para substituído, como substrato modelo, de modo a buscar a lipase, solvente, temperatura, razão lipase/substrato e acilante apropriados para a resolução cinética. De acordo com os resultados obtidos, as condições ideais para se conduzir a resolução cinética foi CAL-B como biocatalisador, hexano como solvente e acetato de etila ou metóxi-acetato de etila como acilante a 30°C. Utilizando esse protocolo, as organo-seleno amidas foram preparadas com excelentes excessos enantioméricos (99 %). / In this work, we have developed a chemoenzymatic method to enantiomerically synthesize enriched organoselenium amines (1-(2, 3 or 4 -(ethylselanyl)phenyl)ethanamine) and amides (N-(1-(2, 3 or 4-(ethylselanyl)phenyl)ethyl)acetamide). Initially, the organoselenium amines, in the racemic form, were synthesized from ortho-, meta- and para- aminoacetophenones. The incorporation of the selenium atom into the aromatic ketones was achieved by the use of reaction of potassium selenocyanate and diazonium salts, prepared from aminoacetophenones, to afford selenocyanate acetophenones (28-65 %). These compounds were alkylated with alkyl halide to yield the organoselenium acetophenones (1-(2, 3 or 4-(ethylselanyl)phenyl)ethanone) (63-78 %) which were converted into their corresponding racemic organoselenium amines by reductive amination (39-73 %). After developing the protocol for the synthesis of racemic organoselenium amines, we studied the kinetic resolution of these compounds by their acetylation mediated by lipases. An initial study was carried out with the organoselenium amine para substituted, as a model substrate, in order to screen for appropriate lipase, solvent, temperature, lipase/substrate ratio and acylant. This study showed that the ideal condition to conduct the kinetic resolution was CAL-B as biocatalyst, hexane as solvent and ethyl acetate or ethyl methoxyacetate as acylant at 30°C. By using this protocol, the organoselenium amides were prepared in excellent enantiomeric excess (99 %).

In the last decade, there has been a surge of interest from the chemistry community in developing synthetic catalysts that emulate the remarkable rate accelerations observed for enzymatic reactions. One approach utilized by enzymes involves preorganization of substrate(s) using a favourable binding event to orient the substrate(s) in a reactive arrangement. Although the “induced intramolecularity” is entropically unfavourable, it is facilitated by the enzymes and utilized to accelerate the subsequent chemical transformation. Chemists have often used a conceptually related stepwise approach in which temporary tethers are assembled to induce a temporary intramolecularity. This preorganization often enables difficult intermolecular reactions, and typically leads to increased regio-, chemo-, and stereoselectivity in chemical reactions. Seeking to develop a catalytic approach, we focused our efforts in developing a mild, carbonyl-catalyzed hydration protocol for - and -amino nitriles to give the corresponding - and -amino amide and acid. This work highlights the value of employing induced intramolecularity in accessing structurally important chemical motifs that otherwise require harsh reaction conditions. Additionally, this thesis presents the background material, design process, optimization and scope of this reactivity.

N-acylethanolamines (NAEs) are a family of signaling lipids derived from a minor membrane lipid constituent N-acylphosphatidylethanolamine (NAPE). In Arabidopsis, NAE mediates physiological functions such as seedling growth, flowering, and response to stress via abscisic acid (ABA) –dependent and –independent signaling pathways. The function of NAEs is terminated by a highly conserved fatty acid amide hydrolase (FAAH). Studies in model plant Arabidopsis showed the significant role of NAEs that makes it relevant to elucidate the conserved metabolic pathway of NAEs in crop species such as tomato. It is hypothesized that there is a functional FAAH in tomato that hydrolyzes NAEs. To test this hypothesis, AtFAAH was used as a template to identify putative FAAH sequences in tomato, using BLASTX. Six SlFAAH sequences with the conserved amidase signature sequence and the catalytic triad, formed by Lys205, Ser281, and Ser305 in AtFAAH, were identified. Phylogenetic analysis of putative SlFAAH homologs and other FAAH family proteins (Arabidopsis, rice and moss), using CLUSTALW, revealed the two sequences that are closely related to the functionally characterized AtFAAH1. Using molecular visualization system (PyMOL), protein structures of putative SlFAAH1and 2 were predicted and compared with AtFAAH; both sequences showed similar domain structure to AtFAAH, with minor differences in spatial arrangement. For further biochemical characterization, full-length coding sequence of SlFAAH1 and SlFAAH2 were isolated and cloned into a heterologous expression system. The expressed protein will be characterized for its hydrolytic activity against radiolabelled NAE substrates. Furthermore, transcript levels for SlFAAH1 and SlFAAH2 will be quantified and correlated with the NAE levels in various tissues to predict their role in tissue-specific NAE hydrolysis. Together, these molecular and biochemical characterization studies in tomato are expected to further validate the conserved nature of NAE metabolic pathway in plants.

No description available.

In plants, saturated and unsaturated N-acylethanolamines (NAEs) with acyl chains 12C to 18C are reported for their differential levels in various tissues and species. While NAEs were shown to play a vital role in mammalian neurological and physiological functions, its metabolism and functional implications in plants however, remains incomplete. Fatty acid amide hydrolase (FAAH) is one of the metabolic enzymes that breaks the amide bond in NAEs to release free fatty acid and ethanolamine. We identified FAAH in Physcomitrella patens and expressed heterologously in E. coli using Gateway cloning system. Radiolabeled NAE 16:0 and 20:4 were used as substrates to test amide hydrolase activity in vitro. In order to understand the role of PpFAAH in vivo, knock out (KO) and overexpressors (OE) were generated by homologous recombination. PpFAAH KO construct was generated by inserting 5‟- and 3‟-flanking regions into pMP1159 plasmid. Full length PpFAAH with stop codon was cloned into pTHUBlGATE vector in order to make OE construct. KO and OE constructs were then transformed into protoplasts of P. patens by using PEG-mediated transformation to generate mutant lines. To identify potential interacting proteins of PpFAAH, it was cloned into pDEST15 plasmid with N-terminus GST tag. Interaction between GST-tagged PpFAAH and proteins from 14-day old protonema will be visualized by SDS-PAGE and then subjected to LC-MS/MS analysis for identification. Our long-term goal is to conduct comprehensive analyses of NAE metabolite mutants to determine their role in growth and development, and mediating stress responses in P. patens.