This thesis is concerned with the preparation and reactions of some highly sterically hindered organosilicon compounds, mainly of the type TeiSiMe2X where Tsi denotes the (Me3Si)3C group. The first detailed study of the reactions of TsiS1Me20CN has shown that reactions with NaN3 in MeOH or KSCN or KOCN in MeCN give exclusively the corresponding TsiSiMe2X compounds (X = N3, NCS, or NCO), whereas those with other salts, viz. LiCl, CsF, KSCN, and KOCN, give the TsiSiMe2X species along· with other products, including in many cases TsiSiMe2NCO and TsiSiMe20H (from traces of water), and (in MeOH) TsiSiMe20Me. The reaction with MeOH alone was never found to give less than 10% ot TslSiMe20H, along with the expected TsiSiMe20Me, however carefully the MeOH was dried. The extreme sensitivity of the cyanate towards water was illustrated by the fact that the rate ot solvolysis in 'dry' MeOH was increased by~. 90% by addition of 0.05 vol-% of H2o, and the hydroxide was the sole product, whereas the rate for the triflate TsiSiMe2- OS02CF3 was increased by only 13% and the product was a 60:40 mixture of TsiSiMe20Me and TsiSiMe20H. The rate constant for the triflate increased linearly with the water concentration but that of the cyanate did not. The presence of NaOMe in MeOH led to rapid isomerization of the cyanate to the isocyanate, TsiSiMe2NCO, with the rate of isomerization being proportional to the base concentration: a possible explanation of this effect of base is suggested. Isomerization catalysed by ICI in CC14 was found to be of ca. second order with respect to both the cyanate and the IcI: A detailed kinetic study has been carried out of the the reactions of TsiSiMe2X compounds, with X c I, Br, Cl, or ON02' with various alkali metal salts, MY, viz. NaN3' CsF, KSCN, and KOCN in MeOH and with KSCN in MeCN. For X • I, Br, or Cl, the reactions have been shown to be much more complex than was previously thought, the compounds TsiSiMe20Me, TsiSiMe20H, and (Me3Si}2CHSiMe2oMe commonly being formed along with TsiSiMe2Y. The order of effectiveness of the salts in the formation of TsiSiMe2Y is CsF > NaN3 > KSCN > KOCN, except that for X - I the order for CsF and NaN3 is reversed. Approximate values of the activation parameters have been obtained: the activation entropies have very high negative values, consistent with formation of a very crowded transition state. The nitrate is markedly more reactive even than the iodide, and gives cleaner conversions into TsSiMe2Y compounds: the activation energies are much lower and the activation entropies much more negative than those tor the halides. Reactions of the compounds (Me3Si)2C(SiMe2H)(SiMe2Cl) with alkali metal salts have been shown to be much faster than those of TsiSiMe2Cl, casting doubt on an earlier suggestion that the ease of solvolysis of the former chloride might be due to anchimeric assistance by y-H.

<p>The positron emitting 68Ga radionuclide (T1/2 = 68 min) has the potential of practical interest for clinical PET. The metallic cation, 68Ga3+, is suitable for complexation reactions with chelators either naked or conjugated with macromolecules such as peptides and oligonucleotides. Such labeling procedures require pure and concentrated radiometal preparations, which cannot be sufficiently fulfilled by the presently available 68Ge/68Ga generator eluate. This thesis presents a method to increase the concentration and purity of 68Ga obtained from a commercial 68Ge/68Ga generator. DOTATOC (DOTA = 1,4,7,10-tetraazacyclo-dodecane-1,4,7,10-tetraacetic acid, TOC = D-Phe1-Tyr3–Octreotide) was used as a test molecule for comparing the labeling properties of different 68Ga preparations. In addition, DOTA-RDG (RGD = Cys2-6; c[CH2CO-Lys(DOTA)-Cys-Arg-Gly-Asp-Cys-Phe-Cys]-CCX6-NH2) and NODAGATATE (NODAGA = 1,4,7-triazacyclononane-1,4,7-triacetic, TATE = Tyr3 - Octreotate) were used to prove the concept. The use of the concentrated and purified 68Ga eluate along with microwave activation allowed quantitative 68Ga-labelling of peptide conjugates of ≤1 nanomolar quantities within 10 min. The specific radioactivity of the radiolabelled peptides was improved by a factor of >100 compared to previously applied techniques using non-treated generator eluate and conventional heating. A commercial 68Ge/68Ga generator in combination with this method for purification, concentration and microwave activated labeling resulted in a kit technology for 68Ga-tracer production.Four 17-mer oligonucleotides modified and functionalised with an hexylamine group in the 3'- or 5'- position were conjugated with DOTA and labelled with 68Ga using microwave activation. Chemical modification of the oligonucleotide backbone or sugar moiety did not influence the labelling nor the hybridisation ability of the oligonucleotides. However, the radioactivity organ biodistribution in rats differed dependent on the oligonucleotide structure. This indicated that metabolism and non-specific binding were affected by the backbone and sugar moiety structure.</p>

<p>Carbohydrates are a complex group of biomolecules with a high structural diversity. Their almost omnipresent occurrence has generated a broad field of research in both biology and chemistry. This thesis focuses on three different aspects of carbohydrate chemistry, synthesis, structure elucidation and the conformational analysis of carbohydrates.</p><p>The first paper describes the synthesis of a penta- and a tetrasaccharide related to the highly branched capsular polysaccharide from <i>Streptococcus pneumoniae </i>type 37. In the second paper, the structure of the O-antigenic repeating unit from the lipopolysaccharide of <i>E. coli </i>396/C1 was determined along with indications of the structure of the biological repeating unit. In addition, its structural and immunological relationship with <i>E. coli</i> O126 is discussed. In the third paper, partially protected galactopyranosides were examined to clarify the origin of an intriguing ⁴<i>J</i>_HO,H coupling, where a <i>W</i>-mediated coupling pathway was found to operate. In the fourth paper, the conformation of methyl a-cellobioside is studied with a combination of molecular dynamics simulations and NMR spectroscopy. In addition to the expected syn-conformation, detection and quantification of anti-<i>ø </i>and anti-<i>ψ</i> conformers was also possible.</p>

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.