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.

Yes / Improved synthetic conditions allow preparation of TMSCCl3 in good yield (70 %) and excellent purity. Compounds of the type NBu4X [X=Ph3SiF2 (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4‐additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (1H, 19F, 13C and 29Si) under anaerobic conditions indicate that addition of TMSCCl3 to TBAT (both 0.13 M ) at −20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me3SiF, Ph3SiF and NBu4CCl3. The latter is stable to at least 0 °C and does not add nitroalkene from −20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl3 (both 0.13 M at −20 °C), when treated with TBAT, leads to immediate formation of the 1,4‐addition product, suggesting the reaction proceeds via a transient [Me3Si(alkene)CCl3] species, in which (alkene) indicates an Si⋅⋅⋅O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl3− addition to the nitroalkene. This is demonstrated by the fact that isolated NBu4[CH2=NO2] is an efficient promoter. Use of H2C=CH(CH2)2CH=CHNO2 in air affords radical‐derived bicyclic products arising from aerobic oxidation. / Engineering and Physical Sciences Research Council (EPSRC) Grant EP/K000578/1.

No description available.