Design, synthesis and development of novel indolocarbazole derivatives as potential anti-cancer agents

This thesis describes work carried out on the design of new routes to a range of bisindolylmaleimide and indolo[2,3-a]carbazole analogs, and investigation of their potential as successful anti-cancer agents. Following initial investigation of classical routes to indolo[2,3-a]pyrrolo[3,4-c]carbazole aglycons, a new strategy employing base-mediated condensation of thiourea and guanidine with a bisindolyl β-ketoester intermediate afforded novel 5,6-bisindolylpyrimidin-4(3H)-ones in moderate yields. Chemical diversity within this H-bonding scaffold was then studied by substitution with a panel of biologically relevant electrophiles, and by reductive desulfurisation. Optimisation of difficult heterogeneous literature conditions for oxidative desulfurisation of thiouracils was also accomplished, enabling a mild route to a novel 5,6-bisindolyluracil pharmacophore to be developed within this work. The oxidative cyclisation of selected acyclic bisindolyl systems to form a new planar class of indolo[2,3-a]pyrimido[5,4-c]carbazoles was also investigated. Successful conditions for this transformation, as well as the limitations currently prevailing for this approach are discussed. Synthesis of 3,4-bisindolyl-5-aminopyrazole as a potential isostere of bisindolylmaleimide agents was encountered, along with a comprehensive derivatisation study, in order to probe the chemical space for potential protein backbone H-bonding interactions. Synthesis of a related 3,4-arylindolyl-5-aminopyrazole series was also undertaken, based on identification of potent kinase inhibition within a closely related heterocyclic template. Following synthesis of approximately 50 novel compounds with a diversity of H-bonding enzyme-interacting potential within these classes, biological studies confirmed that significant topo II inhibition was present for 9 lead compounds, in previously unseen pyrazolo[1,5-a]pyrimidine, indolo[2,3-c]carbazole and branched S,N-disubstituted thiouracil derivative series. NCI-60 cancer cell line growth inhibition data for 6 representative compounds also revealed interesting selectivity differences between each compound class, while a new pyrimido[5,4-c]carbazole agent strongly inhibited cancer cell division at 10 µM, with appreciable cytotoxic activity observed across several tumour types.

Optimised crystal morphologies for active pharmaceutical ingredients and related studies

The majority of active pharmaceutical ingredients (APIs) are crystalline solids in their pure forms. Crystalline solids have definable morphologies, i.e. shape and size. Crystal morphology is determined by both the internal structure of the crystals and external factors during growth from solution. The morphology of a crystal batch can affect key processes during manufacturing. Companies generally accept whatever morphology the manufacturing process provides and deal with any subsequent problems by costly trouble‒shooting. Rational design of optimised morphologies for crystalline pharmaceutical solids would be a very significant technical and commercial advance. Chapter one introduces the concept of crystal nucleation and growth. The phenomenon of polymorphism alongside the causes and impact is discussed. A summary of the scope of instrumentation used in the investigation of crystal polymorphism and morphology, including crystal size distribution (CSD), is also included. Chapter two examines the research carried out during an exploration of the optimum crystallisation parameters of phenacetin. Following a morphological study, the impact this induces on particle density and flow properties is examined. The impact of impurities on the crystallisation properties of phenacetin is investigated. Significantly, the location of impurities within individual crystals is also studied. The third chapter describes an industrial collaboration looking at the resolution and polymorphic study of trometamol and lysine salts of ketoprofen and 2‒phenylpropionic acid (2‒PPA). Chapter four incorporates a solid state study on three separate compounds: 2‒chloro‒4‒nitroaniline, 4‒hydroxy‒N‒phenylbenzenesulfonamide and N‒acetyl‒D‒glucosamine‒6‒O‒sulfate. 2‒Chloro‒4‒nitroaniline and 4‒hydroxy‒N‒phenylbenzenesulfonamide both produced interesting, extreme morphologies which warranted further investigation as part of a collaborative study. Following a summarisation of results in chapter five, chapter six contains the full experimental details, incorporating spectral and other analytical data for all compounds synthesised during the course of the research.

Telescoped approach to aryl hydroxymethylation in the synthesis of a key pharmaceutical intermediate

An efficient synthetic approach leading to introduction of the hydroxymethyl group to an aryl moiety via combination of the Bouveault formylation and hydride reduction has been optimized using a rational, mechanistic-based approach. This approach enabled telescoping of the two steps into a single efficient process, readily amenable to scaleup.

An investigation into the tropospheric chemistry of acidic aerosols and ammonia in the laboratory

This thesis describes a broad range of experiments based on an aerosol flow-tube system to probe the interactions between atmospherically relevant aerosols with trace gases. This apparatus was used to obtain simultaneous optical and size distribution measurements using FTIR and SMPS measurements respectively as a function of relative humidity and aerosol chemical composition. Heterogeneous reactions between various ratios of ammonia gas and acidic aerosols were studied in aerosol form as opposed to bulk solutions. The apparatus is unique, in that it employed two aerosol generation methods to follow the size evolution of the aerosol while allowing detailed spectroscopic investigation of its chemical content. A novel chemiluminescence apparatus was also used to measure [NH4+]. SO2.H2O is an important species as it represents the first intermediate in the overall atmospheric oxidation process of sulfur dioxide to sulfuric acid. This complex was produced within gaseous, aqueous and aerosol SO2 systems. The addition of ammonia, gave mainly hydrogen sulfite tautomers and disulfite ions. These species were prevalent at high humidities enhancing the aqueous nature of sulfur (IV) species. Their weak acidity is evident due to the low [NH4+] produced. An increasing recognition that dicarboxylic acids may contribute significantly to the total acid burden in polluted urban environments is evident in the literature. It was observed that speciation within the oxalic, malonic and succinic systems shifted towards the most ionised form as the relative humidity was increased due to complete protonisation. The addition of ammonia produced ammonium dicarboxylate ions. Less reaction for ammonia with the malonic and succinic species were observed in comparison to the oxalic acid system. This observation coincides with the decrease in acidity of these organic species. The interaction between dicarboxylic acids and ‘sulfurous’/sulfuric acid has not been previously investigated. Therefore the results presented here are original to the field of tropospheric chemistry. SHO3-; S2O52-; HSO4-; SO42- and H1,3,5C2,3,4O4-;C2,3,4O4 2- were the main components found in the complex inorganic-organic systems investigated here. The introduction of ammonia produced ammonium dicarboxylate as well as ammonium disulfite/sulfate ions and increasing the acid concentrations increased the total amount of [NH4+].

Comparison of deterministic, stochastic and fuzzy logic uncertainty modelling for capacity extension projects of DI/WFI pharmaceutical plant utilities with variable/dynamic demand

The last 30 years have seen Fuzzy Logic (FL) emerging as a method either complementing or challenging stochastic methods as the traditional method of modelling uncertainty. But the circumstances under which FL or stochastic methods should be used are shrouded in disagreement, because the areas of application of statistical and FL methods are overlapping with differences in opinion as to when which method should be used. Lacking are practically relevant case studies comparing these two methods. This work compares stochastic and FL methods for the assessment of spare capacity on the example of pharmaceutical high purity water (HPW) utility systems. The goal of this study was to find the most appropriate method modelling uncertainty in industrial scale HPW systems. The results provide evidence which suggests that stochastic methods are superior to the methods of FL in simulating uncertainty in chemical plant utilities including HPW systems in typical cases whereby extreme events, for example peaks in demand, or day-to-day variation rather than average values are of interest. The average production output or other statistical measures may, for instance, be of interest in the assessment of workshops. Furthermore the results indicate that the stochastic model should be used only if found necessary by a deterministic simulation. Consequently, this thesis concludes that either deterministic or stochastic methods should be used to simulate uncertainty in chemical plant utility systems and by extension some process system because extreme events or the modelling of day-to-day variation are important in capacity extension projects. Other reasons supporting the suggestion that stochastic HPW models are preferred to FL HPW models include: 1. The computer code for stochastic models is typically less complex than a FL models, thus reducing code maintenance and validation issues. 2. In many respects FL models are similar to deterministic models. Thus the need for a FL model over a deterministic model is questionable in the case of industrial scale HPW systems as presented here (as well as other similar systems) since the latter requires simpler models. 3. A FL model may be difficult to "sell" to an end-user as its results represent "approximate reasoning" a definition of which is, however, lacking. 4. Stochastic models may be applied with some relatively minor modifications on other systems, whereas FL models may not. For instance, the stochastic HPW system could be used to model municipal drinking water systems, whereas the FL HPW model should or could not be used on such systems. This is because the FL and stochastic model philosophies of a HPW system are fundamentally different. The stochastic model sees schedule and volume uncertainties as random phenomena described by statistical distributions based on either estimated or historical data. The FL model, on the other hand, simulates schedule uncertainties based on estimated operator behaviour e.g. tiredness of the operators and their working schedule. But in a municipal drinking water distribution system the notion of "operator" breaks down. 5. Stochastic methods can account for uncertainties that are difficult to model with FL. The FL HPW system model does not account for dispensed volume uncertainty, as there appears to be no reasonable method to account for it with FL whereas the stochastic model includes volume uncertainty.

Broadband optical cavity absorption spectroscopy in the near-ultraviolet: applications in atmospheric chemistry

A novel spectroscopic method, incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS), has been modified and extended to measure absorption spectra in the near-ultraviolet with high sensitivity. The near-ultraviolet region extends from 300 to 400 nm and is particularly important in tropospheric photochemistry; absorption of near-UV light can also be exploited for sensitive trace gas measurements of several key atmospheric constituents. In this work, several IBBCEAS instruments were developed to record reference spectra and to measure trace gas concentrations in the laboratory and field. An IBBCEAS instrument was coupled to a flow cell for measuring very weak absorption spectra between 335 and 375 nm. The instrument was validated against the literature absorption spectrum of SO2. Using the instrument, we report new absorption cross-sections of O3, acetone, 2-butanone, and 2-pentanone in this spectral region, where literature data diverge considerably owing to the extremely weak absorption. The instrument was also applied to quantifying low concentrations of the short-lived radical, BrO, in the presence of strong absorption by Br2 and O3. A different IBBCEAS system was adapted to a 4 m3 atmosphere simulation chamber to record the absorption cross-sections of several low vapour pressure compounds, which are otherwise difficult to measure. Absorption cross-sections of benzaldehyde and the more volatile alkyl nitrites agree well with previous spectra; on this basis, the cross-sections of several nitrophenols are reported for the first time. In addition, the instrument was also used to study the optical properties of secondary organic aerosol formed following the photooxidation of isoprene. An extractive IBBCEAS instrument was developed for detecting HONO and NO2 and had a sensitivity of about 10-9 cm-1. This instrument participated in a major international intercomparison of HONO and NO2 measurements held in the EUPHORE simulation chamber in Valencia, Spain, and results from that campaign are also reported here.

Chemistry of B1- and B10- boranes containing halogen or pseudohalogen groups

The research described in this thesis involved the chemistry of borane-species which contain one or more halide or pseudohalide groups. Both monoboron species e.g. [BH3X]- and "cluster" borane species e.g. [B10H9X]2- and I-Se B11H10 were studied. The first chapter is a review of the syntheses, properties and reactions of halide and pseudohalide species containing from one to ten boron atoms. Chapter Two is a theoretical investigation of' the electronic and molecular structures of two series of boranes i. e. [BH3X]- and [B10H9X]2- where X = H, CI, CN, NCS, SCN and N3. The calculational method used was the Modified Neglect of Differential Overlap (MNDO) method of Dewar et al. The results were compared where possible with experimental results such as the X-ray crystallographically determined structures of [BH3CI]- and [B10H10]2-. Chapter Three concerns halogenated selenaborane clusters and reports an improved synthesis of 12-Br-SeB11H10 and the first structural data for a simple non-metal containing selenaborane cage with the X-ray crystallographically determined structure of 12-1-SeB11H10. Finally, an indepth n.m.r. study of Se2B9H9 is also reported together with attempts to halogenate this compound. The last two chapters are based on single boron systems. Chapter Four concerns the synthetic routes to amine-boranes and -cyanoboranes from [BH4]- and [BH3CN]- substrates. This chapter discusses some difficulties encountered when polyamines were used in these reactions. The characterisation of an unusual ketone isolated from some of these reactions, the X-ray crystallographically determined structure of 4-dimethylamino-pyridine-cyanoborane and a new route to pyrazabole dimeric species are also discussed. The final chapter reports on work carried out at producing BH2X (X = H, CN) adducts of aminophosphines. Three routes were attempted to generate P-B and N-B bonded species with varying degrees of success. Some unusual products of these reactions are discussed including [Ph2(O) PPPh2 ] [Ph2NH]2, the structure of which was determined by X-ray crystallography.

The synthesis and biological evaluation of lanostane and cholestane-type natural products

The main objective of this thesis is to outline the synthetic chemistry involved in the preparation of a range of novel lanostane and cholestane derivatives, and subsequent investigation into their biological activity in cancer cells. The biological results obtained throughout the project have driven the strategic synthesis of new compounds, in an effort to optimise the anti cancer potential of lanostane and cholestane derivatives. The first chapter begins with an overview of steroidal compounds and details a literature review of the natural sources of these moieties, as well as their biosynthesis and reported synthetic derivatives. The biological activity of interesting natural and synthetic analogues is also discussed. In addition, an insight into some currently prescribed pharmaceutical compounds, with functional groups relevant to this project, is presented. The second chapter discusses the methods employed for the synthesis of these novel lanostane and cholestane derivatives, and comprises three main sections. Firstly, various oxidation products of lanosterol are synthesised, mainly via epoxidations of the C-8,9 and C- 24,25 alkenes, and also allylic oxidations at these positions. Secondly, amine derivatives of lanosterol are formed by cleaving the lanostane side chain, thereby yielding a new cholestane nucleus, and performing several reductive aminations on the resulting key aldehyde intermediates. Various amines such as piperidine, morpholine, diethylamine and aniline are employed in the reductive amination reactions to yield novel cholestane steroids with amine side chains. Finally, starting from stigmasterol and proceeding with the same methodology of cleaving the steroidal side chain and subsequently performing reductive aminations, novel cholestane derivatives of the biologically active amines are synthesised. The cytotoxicity of these compounds against CaCo-2 and U937 cell lines is presented in terms of percentage viability of cells, IC50 value and apoptosis. The MTT assay is used to determine the percentage viability of cells, and the IC50 data is generated from the MTT results. Apoptosis is measured in terms of fold increase relative to a carrier control. In summary, the compounds formed are discussed in terms of chemical synthesis, spectroscopic interpretation and biological activity. The main reaction pathways involved in the chemistry within this project are various oxidations and reductive amination. The final chapter is a detailed account of the full experimental procedures for the compounds synthesised during this work, including characterisation using spectroscopic and analytical data.

Crystallisation and crystal forms of carbohydrate derivatives

This thesis is focused on the synthesis and solid state analysis of carbohydrate derivatives, including many novel compounds. Although the synthetic chemistry surrounding carbohydrates is well established in the literature, the crystal chemistry of carbohydrates is less well studied. Therefore this research aims to improve understanding of the solid state properties of carbohydrate derivatives through gaining more information on their supramolecular bonding. Chapter One focuses on an introduction to the solid state of organic compounds, with a background to crystallisation, including issues that can arise during crystal growth. Chapter Two is based on glucopyranuronate derivatives which are understudied in terms of their solid state forms. This chapter reports on the formation of novel glucuronamides and utilising the functionality of the amide bond for crystallisation. TEMPO oxidation was completed to form glucopyranuronates by oxidation of the primary alcohol groups of glucosides to the carboxylic acid derivatives, to increase functionality for enhanced crystal growth. Chapter Three reports on the synthesis of glucopyranoside derivatives by O-glycosylation reactions and displays crystal structures, including a number of previously unsolved acetate protected and deprotected crystal structures. More complex glycoside derivatives were also researched in an aim to study the resultant supramolecular motifs. Chapter Four contains the synthesis of aryl cellobioside derivatives including the novel crystal structures that were solved for the acetate protected and deprotected compounds. Research was carried out to determine if 1-deoxycellodextrins could act as putative isostructures for cellulose. Our research displays the presence of isostructural references with 1-deoxycellotriose shown to be similar to cellulose III11, 1-deoxycellotetraose correlates with cellulose IV11 and 1-deoxycellopentose shows isostructurality similar to that of cellulose II. Chapter Five contains the full experimental details and spectral characterisation of all novel compounds synthesised in this project and relevant crystallographic information.

Precursor chemistry for oxide related materials

This thesis describes modelling, synthesis, spectroscopic and physical characterisation, as well as application of Magnesium, Calcium and Copper β-diketonate, β-ketoiminate, β-diiminate, Schiff base, amide and fluorenyl compounds. The selected compounds could potentially find application in materials deposition using Atomic Layer Deposition (ALD), MOCVD, CVD and Sol-Gel techniques. Quantum chemical modelling was used as a tool to perform the comprehensive and rapid study of magnesium and calcium precursor molecules in order to predict which of them would be more successful in ALD of metal oxides. Precursor chemistry plays a key role in ALD, since precursors must be volatile, thermally stable, chemisorb on the surface and react rapidly with existing surface groups. This Thesis describes one aspect of this, surface reactivity between ligands and hydroxyl groups, via a gas-phase model with energetics computed at the level of Density Functional Theory (DFT). A number of different synthetic strategies, both aerobic and anaerobic, were investigated for the synthesis of the described metal complexes. These included the use of different metal starting reagents such as, anhydrous and hydrated inorganic metal salts, metal alkyls and Grignard reagents. Some of previously unreported metal complexes of homoleptic and heteroleptic magnesium, calcium and copper β-diketonates, β-ketoiminates, β-diiminates, amides and Schiff base type were synthesised and characterised: [Mg(hfpd)2(DipPa)], [Mg(hfpd)2(MapH)2], [Mg(hf-ebp)(THF)2], [Mg(tf-Pap)Cl(THF)2], [Ca(PhNacnac)2], [Cu(tf-Pap)2], [Cu(PhNacnac)2], [Cu(hf-ebp)], [Cu(DipPa)] and [Cu(DipPa)2(4,4’-bypy)]. A comprehensive study on the thermal properties of magnesium, calcium and copper β-diketonates, β-ketoiminates, β-diiminates, Schiff base, amide and fluorenyl complexes was performed using TGA and sublimation of selected compounds. Atomic Layer Deposition of MgO using magnesium β-ketoiminate – [bis{(4-N-phenyl)-2-pentonato} magnesium] and β-diketonate - [bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)(THF)magnesium hydrate] was performed on Si(100) substrates at 180°C and 0.2 Torr using O2 plasma.

Taming hazardous chemistry in flow: The continuous processing of diazo and diazonium compounds

The synthetic utilities of the diazo and diazonium groups are matched only by their reputation for explosive decomposition. Continuous processing technology offers new opportunities to make and use these versatile intermediates at a range of scales with improved safety over traditional batch processes. In this minireview, the state of the art in the continuous flow processing of reactive diazo and diazonium species is discussed.

Chamber investigations of atmospheric mercury oxidation chemistry

Mercury is a potent neurotoxin even at low concentrations. The unoxidised metal has a high vapour pressure and can circulate through the atmosphere, but when oxidised can deposit and be accumulated through the food chain. This work aims to investigate the oxidation processes of atmospheric Hg0(g). The first part describes efforts to make a portable Hg sensor based on Cavity Enhanced Absorption Spectroscopy (CEAS). The detection limit achieved was 66 ngm−3 for a 10 second averaging time. The second part of this work describes experiments carried out in a temperature controlled atmospheric simulation chamber in the Desert Research Institute, Reno, Nevada, USA. The chamber was built around an existing Hg CRDS system that could measure Hg concentrations in the chamber of<100 ngm−3 at 1 Hz enabling reactions to be followed. The main oxidant studied was bromine, which was quantified with a LED based CEAS system across the chamber. Hg oxidation in the chamber was found to be mostly too slow for current models to explain. A seven reaction model was developed and tested to find which parameters were capable of explaining the deviation. The model was overdetermined and no unique solution could be found. The most likely possibility was that the first oxidation step Hg + Br →HgBr was slower than the preferred literature value by a factor of two. However, if the more uncertain data at low [Br2] was included then the only parameter that could explain the experiments was a fast, temperature independent dissociation of HgBr some hundreds of times faster than predicted thermolysis or photolysis rates. Overall this work concluded that to quantitatively understand the reaction of Hg with Br2, the intermediates HgBr and Br must be measured. This conclusion will help to guide the planning of future studies of atmospheric Hg chemistry.

Chemistry and synthesis of 3(2H)-furanones and 4,5-dihydro analogues: mechanistic investigations and stereochemical control

The subject matter of this thesis relates to the chemistry of the five-membered oxygen heterocycles – 3(2H)-furanones and their 4, 5-dihydro analogues. Chapter one of the thesis is a review of the relevant chemistry of the compounds: their synthesis and key transformations. In chapter two, new research on 3(2H)-furanones is outlined in two parts. The first describes an investigation into the cyclisation of α'-trialkylsilyloxyenone adducts with arenesulfenyl and selenenyl chlorides into the corresponding sulfur and selenium substituted 3(2H)-furanones without the involvement of a Lewis acid catalyst. The study, largely involving in situ NMR techniques, identified key features associated with the formation and reaction of the chlorosulfide and chloroselenide intermediates, including operation of the Thorpe-Ingold effect. The knowledge gained in this study was applied (the second part) to the synthesis of vinyl substituted furanone systems from α'-trialkylsilyloxydienones where choice of the reaction conditions and electrophilic reagent was a key feature. An important difference in the behaviour of arenesulfenyl and selenenyl halides towards conjugated dienes emerged from this work. This phase of the research concluded with a new synthesis of geiparvarin, a natural product possessing anti-tumour properties.

Preserving patent policy space and securing access to medicines in developing countries: the role of states and pharmaceutical corporations

This thesis examines the tension between patent rights and the right to health and it recognizes patent rights on pharmaceutical products as one of the factors responsible for the problem of lack of access to affordable medicines in developing countries. The thesis contends that, in order to preserve their patent policy space and secure access to affordable medicines for their citizens, developing countries should incorporate a model of human rights into the design, implementation, interpretation, and enforcement of their national patent laws. The thesis provides a systematic analysis of court decisions from four key developing countries (Brazil, India, Kenya, and South Africa) and it assesses how the national courts in these countries resolve the tension between patent rights and the right to health. Essentially, this thesis demonstrates how a model of human rights can be incorporated into the adjudication of disputes involving patent rights in national courts. Focusing specifically on Brazil, the thesis equally demonstrates how policy makers and law makers at the national level can incorporate a model of human rights into the design or amendment of their national patent law. This thesis also contributes to the ongoing debate in the field of business and human rights with regard to the mechanisms that can be used to hold corporate actors accountable for their human rights responsibilities. This thesis recognizes that, while states bear the primary responsibility to respect, protect, and fulfil the right to health, corporate actors such as pharmaceutical companies also have a baseline responsibility to respect the right to health. This thesis therefore contends that pharmaceutical companies that own patent rights on pharmaceutical products can be held accountable for their right to health responsibilities at the national level through the incorporation of a model of civic participation into a country’s patent law system.

Novel co-crystals of the nutraceutical sinapic acid

Sinapic acid (SA) is a nutraceutical with known anti-oxidant, anti-microbial, anti-inflammatory, anti-cancer, and anti-anxiety properties. Novel co-crystals of SA were prepared with co-formers belonging to the category of GRAS [isonicotinic acid (INC), nicotinamide (NIA)], non-GRAS [4-pyridinecarbonitrile (PYC)], and active pharmaceutical ingredients (APIs) [6-propyl-2-thiouracil (PTU)] list of compounds. Structural study based on the X-ray crystal structures revealed the intermolecular hydrogen-bonded interactions and molecular packing. The crystal structure of sinapic acid shows the anticipated acid-acid homodimer along with discrete hydrogen bonds between the acid carbonyl and the phenolic moiety. The robust acid-acid homodimer appears to be very stable and is retained in the structures of two co-crystals (SA[middle dot]NIA and SA[middle dot]PYC). In these cases, co-crystallization occurs via intermolecular phenol O-H[three dots, centered]Naromatic hydrogen bonds between the co-formers. In the SA[middle dot]PTU[middle dot]2MeCN co-crystal the acid-acid homodimer gives way to the anticipated acid-amide heterodimer, with the phenolic moiety of SA hydrogen-bonded to acetonitrile. Attempts at obtaining the desolvated co-crystal led to lattice breakdown, thus highlighting the importance of acetonitrile in the formation of the co-crystal. Among the co-crystals examined, SA[middle dot]INC (5 weeks), SA[middle dot]NIA (8 weeks) and SA[middle dot]PYC (5 weeks) were found to be stable under accelerated humidity conditions (40 [degree]C, 75% RH), whereas SA[middle dot]PTU[middle dot]2MeCN decomposed after one week into individual components due to solvent loss.