Synthesis of polyphenylene cylinders with different sizes and connectivity patterns as well as study of their linear congeners

In dieser Arbeit wird die Synthese von Polyphenylenzylindern (PPZ) und strukturell verwandten Molekülen beschrieben, die in unterschiedlichen Größen und verschiedenartigen Bindungsmustern dargestellt wurden. Aufgrund ihres Aufbaus sind sie direkte Vorläufermoleküle von Kohlenstoffnanoröhren (CNT)s. Ziel war es, zunächst zu untersuchen, ob sich PPZs darstellen lassen. In einem anschließenden Schritt wurde die nasschemische Synthese von CNTs untersucht, die auf diesem Weg bisher noch nicht erreicht werden konnte. Die hier studierten Strukturen führten zu vielversprechenden Ergebnisse auf diesem Weg, da die oxidative Cyclodehydrierung – eine intramolekulare Anellierung – zur Bildung von ca. 50% der notwendigen Bindungen führte.

Expanding the scope of poly(ethylene glycol)s for bioconjugation to squaric acid-mediated PEGylation and pH-sensitivity

Poly(ethylene glycol) (PEG) is used in a broad range of applications due to its unique combination of properties and is approved use in formulations for body-care products, edibles and medicine. This thesis aims at the synthesis and characterization of novel heterofunctional PEG structures and the establishment of diethyl squarate as a suitable linker for the covalent attachment to proteins. Chapter 1 is an introduction on the properties and applications of PEG as well as the fascinating chemistry of squaric acid derivatives. In Chapter 1.1, the synthesis and properties of PEG are described, and the versatile applications of PEG derivatives in everyday products are emphasized with a focus on PEG-based pharmaceuticals and nonionic surfactants. This chapter is written in German, as it was published in the German Journal Chemie in unserer Zeit. Chapter 1.2 deals with PEGs major drawbacks, its non-biodegradability, which impedes parenteral administration of PEG conjugates with polyethers exceeding the renal excretion limit, although these would improve blood circulation times and passive tumor targeting. This section gives a comprehensive overview of the cleavable groups that have been implemented in the polyether backbone to tackle this issue as well as the synthetic strategies employed to accomplish this task. Chapter 1.3 briefly summarizes the chemical properties of alkyl squarates and the advantages in protein conjugation chemistry that can be taken from its use as a coupling agent. In Chapter 2, the application of diethyl squarate as a coupling agent in the PEGylation of proteins is illustrated. Chapter 2.1 describes the straightforward synthesis and characterization of squaric acid ethyl ester amido PEGs with terminal hydroxyl functions or methoxy groups. The reactivity and selectivity of theses activated PEGs are explored in kinetic studies on the reactions with different lysine and other amino acid derivatives, followed by 1H NMR spectroscopy. Further, the efficient attachment of the novel PEGs to a model protein, i.e., bovine serum albumin (BSA), demonstrates the usefulness of the new linker for the PEGylation with heterofunctional PEGs. In Chapter 2.3 initial studies on the biocompatibility of polyether/BSA conjugates synthesized by the squaric acid mediated PEGylation are presented. No cytotoxic effects on human umbilical vein endothelial cells exposed to various concentrations of the conjugates were observed in a WST-1 assay. A cell adhesion molecule - enzyme immunosorbent assay did not reveal the expression of E-selectin or ICAM-1, cell adhesion molecules involved in inflammation processes. The focus of Chapter 3 lies on the syntheses of novel heterofunctional PEG structures which are suitable candidates for the squaric acid mediated PEGylation and exhibit superior features compared to established PEGs applied in bioconjugation. Chapter 3.1 describes the synthetic route to well-defined, linear heterobifunctional PEGs carrying a single acid-sensitive moiety either at the initiation site or at a tunable position in the polyether backbone. A universal concept for the implementation of acetal moieties into initiators for the anionic ring-opening polymerization (AROP) of epoxides is presented and proven to grant access to the degradable PEG structures aimed at. The hydrolysis of the heterofunctional PEG with the acetal moiety at the initiating site is followed by 1H NMR spectroscopy in deuterium oxide at different pH. In an exploratory study, the same polymer is attached to BSA via the squarate acid coupling and subsequently cleaved from the conjugate under acidic conditions. Furthermore, the concept for the generation of acetal-modified AROP initiators is demonstrated to be suitable for cholesterol, and the respective amphiphilic cholesteryl-PEG is cleaved at lowered pH. In Chapter 3.2, the straightforward synthesis of α-amino ω2-dihydroxyl star-shaped three-arm PEGs is described. To assure a symmetric length of the hydroxyl-terminated PEG arms, a novel AROP initiator is presented, who’s primary and secondary hydroxyl groups are separated by an acetal moiety. Upon polymerization of ethylene oxide for these functionalities and subsequent cleavage of the acid-labile unit no difference in the degree of polymerization is seen for both polyether fragments.

Glykopolymere für biomedizinsche Anwendungen : Synthese von mannosylierten N-(2-Hydroxyprpyl)methacrylamid Polymersystemen für die Adressierung von Zellen des Immunsystems

Das Ziel dieser Arbeit lag darin mannosylierte Polymersysteme hauptsächlich auf der Basis von N-(Hydroxy)propylmethacrylat zu synthetisieren, um gezielt Zellen des Immunsystems zu adressieren. Dazu wurden zunächst verschiedene Reaktivesterpolymere auf der Basis von Pentafluorophenylmethacrylat (PFPMA) unter Verwendung der RAFT-Polymerisation mit enger Molekulargewichtsverteilung und unterschiedlichen Anteilen an LMA (Laurylmethacrylat) hergestellt.rnUm eine genaue Aussage über den Aufbau eines statistischen PFPMA-LMA Copolymers treffen zu können, wurde die Copolymerisation von PFPMA und LMA mittels Echtzeit 1H-NMR Kinetikmessungen untersucht. Dies ermöglichte es, die Copolymerisationsparameter zu berechnen und genaue Aussagen über den Aufbau eines statistischen PFPMA-LMA Copolymers zu treffen. Die so erhaltenen Reaktivesterpolymere wurden dann in einer polymeranalogen Reaktion unter Erhalt des Polymerisationsgrades in die gewünschten HPMA-Polymere umgewandelt. Um die quantitative Umsetzung ohne auftretende Nebenreaktionen zu untersuchen, wurden verschiedene Reaktionsbedingungen gewählt und unterschiedliche Analysemethoden verwendet. Damit konnte gezeigt werden, dass es möglich ist, über den Reaktivesteransatz qualitativ hochwertige amphiphile Polymersysteme herzustellen, die auf anderen Wegen schwer zu synthetisieren und charakterisieren sind. Ein weiterer Vorteil dieser Syntheseroute ist, dass gleichzeitig sowohl Marker für die Visualisierung der Polymere in vitro und in vivo, als auch Targetliganden für die Adressierung bestimmter Zellen eingeführt werden können. Dafür wurde hauptsächlich Mannose als einfache Zuckerstruktur angebunden, da bekannt ist, dass mannosylierte Polymersysteme von Zellen des Imunsystems aufgenommen werden. Zusätzlich konnten die mannosylierten Polymere mit hydrophobem Wirkstoff beladen werden, wobei die Stabilität von beladenen Mizellen anhand der Einlagerung eines hydrophoben radioaktiven Komplexes genauer untersucht werden konnte.rnAnschließende in vitro Experimente der mannosylierten Polymermizellen an dendritischen Zellen zeigten wie erwartet eine mannosespezifische und verstärkte Aufnahme. Für eine mögliche Untersuchung dieser Systeme in vivo mittels PET konnte gezeigt werden, dass es möglich ist HPMA Polymere radioaktiv zu markieren, wobei auch erste Markierungsversuche mit einem langlebigen Radionuklid für Langzeitbiodistributionsstudien durchgeführt werden konnte.rn

Synthesis and dynamic study of atropisomeric compounds containing boron-carbon bond

In this thesis we studied the stereodynamic behavior of 1,2-azaborines variously substituted on boron (7a, 7b, 13). Depending on the hindrance of the asymmetric aryl substituent the resulting conformations could be stereolabile or configurationally stable. Through dynamic NMR and lineshape simulation, the energy rotational barriers of the different conformers are obtained. When the barrier is higher than 22-23 kcal/mol stable atropisomers that are fisically separable could be obtained (case of compound 13) and the free activation energy barrier is determinable by kinetic analysis. Absolute configuration of two atropisomers were assigned by comparison between computational calculations and experimental ECD. Isosteric compound 21 is then synthesized in order to compare the rotational barrier around B-Caryl with the one around Cnaphth-Caryl bond.

The binding mode of side chain- and C3-modified epothilones to tubulin

The tubulin-binding mode of C3- and C15-modified analogues of epothilone A (Epo A) was determined by NMR spectroscopy and computational methods and compared with the existing structural models of tubulin-bound natural Epo A. Only minor differences were observed in the conformation of the macrocycle between Epo A and the C3-modified analogues investigated. In particular, 3-deoxy- (compound 2) and 3-deoxy-2,3-didehydro-Epo A (3) were found to adopt similar conformations in the tubulin-binding cleft as Epo A, thus indicating that the 3-OH group is not essential for epothilones to assume their bioactive conformation. None of the available models of the tubulin-epothilone complex is able to fully recapitulate the differences in tubulin-polymerizing activity and microtubule-binding affinity between C20-modified epothilones 6 (C20-propyl), 7 (C20-butyl), and 8 (C20-hydroxypropyl). Based on the results of transferred NOE experiments in the presence of tubulin, the isomeric C15 quinoline-based Epo B analogues 4 and 5 show very similar orientations of the side chain, irrespective of the position of the nitrogen atom in the quinoline ring. The quinoline side chain stacks on the imidazole moiety of beta-His227 with equal efficiency in both cases, thus suggesting that the aromatic side chain moiety in epothilones contributes to tubulin binding through strong van der Waals interactions with the protein rather than hydrogen bonding involving the heteroaromatic nitrogen atom. These conclusions are in line with existing tubulin polymerization and microtubule-binding data for 4, 5, and Epo B.

Enhancing BOLD response in the auditory system by neurophysiologically tuned fMRI sequence

Auditory neuroscience has not tapped fMRI's full potential because of acoustic scanner noise emitted by the gradient switches of conventional echoplanar fMRI sequences. The scanner noise is pulsed, and auditory cortex is particularly sensitive to pulsed sounds. Current fMRI approaches to avoid stimulus-noise interactions are temporally inefficient. Since the sustained BOLD response to pulsed sounds decreases with repetition rate and becomes minimal with unpulsed sounds, we developed an fMRI sequence emitting continuous rather than pulsed gradient sound by implementing a novel quasi-continuous gradient switch pattern. Compared to conventional fMRI, continuous-sound fMRI reduced auditory cortex BOLD baseline and increased BOLD amplitude with graded sound stimuli, short sound events, and sounds as complex as orchestra music with preserved temporal resolution. Response in subcortical auditory nuclei was enhanced, but not the response to light in visual cortex. Finally, tonotopic mapping using continuous-sound fMRI demonstrates that enhanced functional signal-to-noise in BOLD response translates into improved spatial separability of specific sound representations.

Solution structure and interaction of cupiennin 1a, a spider venom peptide, with phospholipid bilayers

The solution structure of cupiennin 1a, a 35 residue, basic antibacterial peptide isolated from the venom of the spider Cupiennius salei, has been determined by nuclear magnetic resonance (NMR) spectroscopy. The peptide was found to adopt a helix−hinge−helix structure in a membrane mimicking solvent. The hinge may play a role in allowing the amphipathic N-terminal helix and polar C-terminal helix to orient independently upon membrane binding, in order to achieve maximal antibacterial efficacy. Solid-state 31P and 2H NMR was used to further study the effects of cupiennin 1a on the dynamic properties of lipid membranes, using zwitterionic chain deuterated dimyristoylphosphatidylcholine (d54-DMPC) and anionic dimyristoylphosphatidylglycerol (DMPG) multilamellar vesicles. In d54-DMPC alone, cupiennin 1a caused a decrease in the 31P chemical shift anisotropy, indicating some interaction with the lipid head groups, and a decrease in order over the entire acyl chain. In contrast, for the mixed (d54-DMPC/DMPG) lipid system cupiennin 1a appeared to induce lateral separation of the two lipids as evidenced by the 31P spectra, in which the peptide preferentially interacted with DMPG. Little effect was observed on the deuterated acyl chain order parameters in the d54-DMPC/DMPG model membranes. Furthermore, 31P NMR relaxation measurements confirmed a differential effect on the lipid motions depending upon the membrane composition. Therefore, subtle differences are likely in the mechanism by which cupiennin 1a causes membrane lysis in either prokaryotic or eukaryotic cells, and may explain the specific spectrum of activity.

Novel sst5-selective somatostatin dicarba-analogues: synthesis and conformation-affinity relationships

We describe synthesis, conformational studies, and binding to the five somatostatin receptors (sst 1-5) of a few analogues of the cyclic octapeptide octreotide (1), where the disulfide bridge was replaced by a dicarba group. These analogues were prepared by on-resin RCM of linear hepta-peptides containing two allylglycine residues; first- and second-generation Grubbs catalyst efficiencies were compared. The C=C bridge was hydrogenated via two different methods. Binding experiments showed that two analogues had good affinity and high selectivity for the sst5 receptor. Three-dimensional structures of the active analogues were determined by (1)H NMR spectroscopy. Conformation-affinity relationships confirmed the importance of D-Phe(2) orientation for sst2 affinity. Moreover, helical propensities well correlates with the peptide sst5 affinity. The presence of the bulky aromatic side chain of Tyr(Bzl)(10) favored the formation of a 3(10)-helix and enhanced the sst5 selectivity suppressing the sst2 affinity. Finally, a new pharmacophore model for the sst5 was developed.

Syntheses and characterization of monomeric Mo(VI) complexes with bidentate phosphine oxide ligands and dimeric and tetrameric Mo(V) clusters with benzoic acid and phosphinic acid derivatives, containing MoO2, Mo2O2(μ-O)2 and Mo4O4(μ3-O)4

Mo(VI) oxo complexes have been persistently sought after as epoxidation catalysts. Further, Mo(V) oxo clusters of the form M4(µ3-X)4 (M = transition metal, X = O, S) have been rigorously studied due to their remarkable structures and also their usefulness as models for electronic studies. The syntheses and characterizations of new Mo(VI) and Mo(V) oxo complexes have been described in this dissertation. Two new complexes MoO2Cl2Ph2P(O)CH2COOH and MoO2Cl2Ph2P(O)C6H4tBuS(O) were synthesized from reactions of “MoO2Cl2” with ligands Ph2P(O)CH2COOH and Ph2P(O)C6H4tBuS(O). Tetrameric packing arrangements comprised of hydrogen bonds were obtained for the complex MoO2Cl2Ph2P(O)CH2COOH and the ligand Ph2P(O)CH2COOH. Further the stability of an Mo-O bond was preferred over the Mo-S bond even though this resulted in the formation of a more strained seven membered ring. Tetranuclear Mo(V) complexes of the form [Mo4(µ3-O)4(µ-O2PR2)4O4], (PR2 = PPh2, PMe2) were synthesized using reactions of MoO2(acac)2 with diphenyl and dimethyl phosphinic acids, in ethanol. In the crystal structure of these complexes four Mo=O units are interconnected by four triply bridging oxygen atoms and bridging phosphinate ligands. The complex exhibited fourfold symmetry as evidenced by a single 31P NMR peak for the P atoms in the coordinated ligands. Reaction of WO2(acac)2 with Ph2POOH in methanol resulted in a dimeric W(VI) complex [(CH3O)2(O)W(µ-O)( µ-O2PPh2)2W(O)(CH3O)2] which contained a packing disorder in its crystal structure. Similar reactions of MoO2(acac)2 with benzoic acid derivatives resulted in dimeric complexes of the form [Mo2O2(acac)2(µ-O)(µ-OC2H5)(µ-O2CR)] (R = C6H5, (o-OH)C6H4, (p-Cl)C6H4, (2,4-(OH)2)C6H3, (o-I)C6H4) and one tetrameric complex [Mo2O2(acac)2(µ-O)(µ-OC2H5)(µ-O2C)C6H4(p-µ-O2C)Mo2O2(acac)2(µ-O)(µ-OC2H5)] with terephthalic acid. 1H NMR proved very useful in the prediction of the formation of dimers with the substituted benzoic acids, which were also confirmed by elemental analyses. The reductive capability of ethanol proved instrumental in the syntheses of Mo(V) tetrameric and dimeric clusters. Synthetic details, IR, 1H and 31P NMR spectroscopy and elemental analyses are reported for all new complexes. Further, single crystal X-ray structures of MoO2Cl2Ph2P(O)CH2COOH, MoO2Cl2Ph2P(O)C6H4tBuS(O), [Mo4(µ3-O)4(µ-O2PR2)4O4], (PR2 = PPh2, PMe2), [(CH3O)2(O)W(µ-O)( µ-O2PPh2)2W(O)(CH3O)2] and [Mo2O2(acac)2(µ-O)(µ-OC2H5)(µ-O2CR)] (R = C6H5, (o-OH)C6H4) are also presented.

Cytotoxic diacetylenic spiroketal enol ethers from Plagius flosculosus

Three new diacetylenic spiroketal enol ethers named flosculins A (1), B (2), and C (3), along with five known compounds (4-8) of the same structural class, were isolated from the leaves of Plagius flosculosus. The structures were deduced by extensive 1D and 2D NMR spectroscopy and mass spectrometry. All isolated compounds exhibited significant cytotoxic activity against leukemia cells (Jurkat T and HL-60). Compounds 5-8 induced apoptosis in HL-60 cells with corresponding IC(50) values ranging from 4 to 6 microM.

New cytotoxic saturated and unsaturated cyclohexanones from Anthemis maritima

Two new cyclohexenones (antheminones A and B) and a new cyclohexanone, (antheminone C) along with five known compounds were isolated from the leaves of Anthemis maritima L. The structures were mainly deduced from extensive 1D and 2D NMR spectroscopy and mass spectrometry. The new compounds were tested in vitro for their cytotoxic activity against adherent and non-adherent cancer cell lines. Antheminones A and C exhibited significant antiproliferative activity against leukemia cells with IC(50) values ranging from 3.2 to 14 microM.

Bipyridyl- and biphenyl-DNA: A recognition motif based on interstrand aromatic stacking

The synthesis and incorporation into oligonucleotides of C-nucleosides containing the two aromatic, non-hydrogen-bonding nucleobase substitutes biphenyl (I) and bipyridyl (Y) are described. Their homo- and hetero-recognition properties in different sequential arrangements were then investigated via UV-melting curve analysis, gel mobility assays, CD- and NMR spectroscopy. An NMR analysis of a dodecamer duplex containing one biphenyl pair in the center, as well as CD data on duplexes with multiple insertions provide further evidence for the zipper-like interstrand stacking motif that we proposed earlier based on molecular modeling. UV-thermal melting experiments with duplexes containing one to up to seven I- or Y base pairs revealed a constant increase in T(m) in the case of I and a constant decrease for Y. Mixed I/Y base pairs lead to stabilities in between the homoseries. Insertion of alternating I/abasic site- or Y/abasic site pairs strongly decreases the thermal stability of duplexes. Asymmetric distribution of I- or Y residues on either strand of the duplex were also investigated in this context. Duplexes with three natural base pairs at both ends and 50 % of I pairs in the center are still readily formed, while duplexes with blunt ended I pairs tend to aggregate unspecifically. Duplexes with one natural overhang at the end of a I-I base pair tract can both aggregate or form ordered duplexes, depending on the nature of the natural bases in the overhang

Reactivity of hexanuclear ruthenium metallaprisms towards nucleotides and a DNA decamer

The reactivity of three hexacationic arene ruthenium metallaprisms towards isolated nucleotides and a short DNA strand was investigated using NMR spectroscopy, ESI mass spectrometry, UV/Vis and circular dichroism spectroscopy. The metallaprism built from oxalato-bridging ligands reacts rapidly in the presence of deoxyguanosine monophosphate (dGMP) and deoxyadenosine monophosphate, while the benzoquinonato derivative only reacts with dGMP. On the other hand, the larger metallaprism incorporating naphtoquinonato bridges remains stable in the presence of nucleotides. The reactivity of the three hexacationic metallaprisms with the decameric oligonucleotide d(CGCGATCGCG)2 was also investigated. Analysis of the NMR, MS, UV/Vis and CD data suggests that no adducts are formed between the oligonucleotide and the metallaprisms, but electrostatic interactions, leading to partial unwinding of the double-stranded oligonucleotide, were evidenced

Nickel(II)-, cobalt(II)-, copper(II)-, and zinc(II)-phthalate and 1-methylimidazole coordination compounds: synthesis, crystal structures and magnetic properties

Three new coordination polymers [M(Pht)(1-MeIm)2]n (where M=Cu (1), Zn (2), Co (3); Pht2−=dianion of o-phthalic acid; 1-MeIm=1-methylimidazole) and two compounds [M(1-MeIm)6](HPht)2 · 2H2O (M=Co (4), Ni (5)) have been synthesized and characterized by X-ray crystallography. The structures of 1–3 (2 is isostructural to 3) consist of [M(1-MeIm)2] building units connected by 1,6-bridging phthalate ions to form infinite chains. In complex 1, each copper(II) center adopts a square coordination mode of N2O2 type by two O atoms from different phthalate ions and two N atoms of 1-MeIm, whereas in 3 two independent metal atoms are tetrahedrally (N2O2) coordinated to a pair of Pht ligands and a pair of 1-MeIm molecules. There are only van der Waals interactions between the chains in 1, while the three-dimensional network in 3 is assembled by C–H⋯O contacts. In contrast to polymers 1–3 the structures of 4 and 5 (complexes are also isostructural) are made up of the [M(1-MeIm)6]2+ cation, two hydrogen phthalate anions (HPht−) and two H2O solvate molecules. The coordination around each metal(II) atom is octahedral with six nitrogen atoms of 1-MeIm. Extended hydrogen bonding networks embracing the solvate water molecules and a phthalate residue as well as the weak C–H⋯O interactions stabilize the three-dimensional structures. Magnetic studies clearly show that the magnetic ions do not interact with each other. Furthermore, in compound 4 we have another example of a highly anisotropic Co2+ ion with a rhombic g-tensor and large zero-field-splitting. The complexes were also characterized by IR and 1H NMR spectroscopy, thermogravimetric analysis, and all data are discussed in the terms of known structures.