Berlin, Techn. Univ., Diss., 2004. / Computerdatei im Fernzugriff.

No description available.

The influence of solvent and steric hindrance on the conversion of thiolsulfinates to trisulfides with hexamethyldisilathiane was investigated and a new polar mechanism, based on acceleration of the reaction by polar solvents and by fluoride ions, was proposed. The mono and dialkylation of 2,2-disubstituted 1,3-dithiane-1-oxides was investigated. Whereas those derived from menthone form only one diastereomer which cannot be alkylated further, those derived from acetone form two diastereomers. Only one of them can be alkylated further. Dehydration of the diastereomeric tertiary alcohols derived from directed aldol-reaction of γ-butyrolactones and methyl ketones yields diastereomeric conjugated enes in high yield and d.e. Michael-addition of benzyl thiols to these gives good yields and d.e. of the Michael-adducts. Deprotection of PMB-protected thiols with concomitant formation of disulfides was achieved by bromine in methanol or CH2Cl2. A seven-membered cyclic disulfide which contains the carbon backbone of the Perophora viridis trisulfide, albeit with two stereocentres in the incorrect configuration, was prepared.

Techn. Universiẗat, Diss., 2004--Berlin.

A variety of optically active macrocyclic crown ethers that serve as "host" systems that are capable of differentiating between enantiomeric "guest" molecules during host-guest complexation have been prepared via incorporation of chiral elements into the crown ring skeleton. The ability of these crown ethers to recognize the enantiomers of guest salts, i.e., (+) a-methyl benzylamine and to transport them enantioselectively in W-tube transport experiments were studied. The ability of these crown ethers to perform as chiral catalysts in an enantioselective Michael addition was studied. The extent of asymmetric induction, expressed in terms of the enantiomeric excess (%ee), was monitored by measuring the optical rotation of the product and comparing to the literature value.

Techn. Universiẗat, Diss., 2000--Berlin.

Universiẗat, Diss., 2004--Stuttgart.

Targeted covalent inhibitors (TCIs) are irreversible enzyme inhibitors that are designed to first bind to a targeted enzyme’s active site reversibly using non-covalent interactions between the molecular scaffold of the inhibitor and the surrounding amino acid residues of the enzyme’s binding site. They then form a covalent bond between the inhibitor’s electrophilic warhead and a nucleophilic amino acid residue located inside of the binding pocket. Cysteine (Cys), a redox-sensitive thiol, is found in many enzyme active sites and is used as the target for many current TCIs in clinical application. Electrophilic warheads such as acrylamides and chloroacetamides are known to readily undergo thiol-addition, and although they are commonly used in the development of enzyme inhibitors, few previous studies have explored the mechanism of thiol-addition and the intrinsic reactivities of these moieties. In this work, a robust kinetic assay was developed to perform mechanistic studies of thiol-addition to the electrophilic warhead derivatives N-phenylacrylamide (NPA), N-acryloylpiperidine (AcrPip), and N-phenylchloroacetamide (NPC). By reacting these warhead derivatives with thiol nucleophiles having various pKa values, we were able to construct Brønsted-type plots, resulting in shallow positive βNucRS- values for NPA, AcrPip and NPC (βNucRS- = 0.07 ± 0.04, 0.11 ± 0.03, and 0.21 ± 0.07, respectively), meaning that these electrophiles are relatively insensitive to thiolate nucleophilicity. However, while the trend in their reactivity across thiolate nucleophilicity is similar, their intrinsic reactivity was found to be vastly different. In conjunction with the Brønsted-type plot, temperature, ionic strength, and kinetic isotope effects were studied to afford information about the rate-limiting transition state and elucidate the mechanism of thiol-addition. NPA and AcrPip were found to undergo very similar thiol-additions, consistent with the microscopic reverse of the E1cbrev elimination, whereas NPC follows an SN2 type addition, consistent with the intuitive mechanism of addition to a haloacetamide.

No description available.

Research efforts have focused on synthesis of linear, long-chain branched, and novel crosslinked polyesters for applications spanning from pressure sensitive adhesives to biomedical applications. Altering polymer topology and functionality using different synthetic strategies was enabled tailoring the thermomechanical, rheological, and adhesive properties of polyesters. The synthesis and characterization of linear, long-chain branched, and crosslinked networks are described focusing on the structure-property relationships. Aliphatic low-Tg polyesters with linear and long-chain branched topology were synthesized using melt polycondensation for pressure sensitive adhesive applications. Relationships between molecular weight, polymer composition, and adhesive performance were investigated. Melt rheological studies and the characterization of adhesive properties indicated that adhesive performance was enhanced with increasing molecular weight. Moreover, a series of long-chain branched low-Tg polyester were investigated to determine the influence of branching and molecular weight. Tailoring the degree of branching enabled the control of rheological and adhesive properties. Characterization of adhesive properties revealed that long-chain branched polymers displayed an enhanced cohesive strength. In addition, utilization of different comonomer compositions allowed tailoring thermal and adhesive properties of low-Tg polyesters over a wide range. Biodegradable networks were synthesized for the first time using base-catalyzed Michael addition of acetoacetate functionalized polyesters with acrylates. Linear and star-shaped poly(caprolactone) (PCL) oligomers with different molecular weights were functionalized and crosslinked. Thermomechanical properties were evaluated as a function of precursor molecular weight and crosslink density. The glass transition temperature and the extent of crystallinity of the networks were dependent on the molecular weight of the PCL segment. Moreover, dynamic mechanical analysis (DMA) indicated that molecular weight of the oligomeric precursors influenced the plateau modulus of the networks as a result of the differences in crosslink density of the networks. In addition, covalently crosslinked networks were synthesized from Michael addition reaction of acetoacetate-functional oligomeric poly(trimethylene succinate)s and poly(trimethylene adipate)s with neopentylglycol diacrylate. The oligomeric polyesters with telechelic hydroxyl functionality were synthesized from renewable monomers, adipic acid, succinic acid, and 1,3-propanediol using melt polycondensation. The molecular weights of the precursors were varied systematically to probe the influence of molecular weight on thermomechanical properties of the networks. The extent of crystallinity and mechanical properties were dependent on the molecular weight of the oligomeric polyester precursors which also controlled crosslink density. Moreover, Michael addition chemistry was utilized to crosslink low-Tg polyesters to improve cohesive strength for PSA applications. In order to determine the influence of temperature and catalyst levels, crosslinking reactions were monitoring using measurement of loss and storage moduli during the reaction. Networks having different levels of gel fractions were investigated to elucidate the influence of degree of crosslinking on thermomechanical and adhesive properties of low-Tg polyesters. / Ph. D.