Biomedical subjects

Tobias Schulte

Publications and source records attributed to Tobias Schulte.

6 recordsLinked to original sources

PubMed2006

Combined anterior and posterior instrumentation in severe and rigid idiopathic scoliosis.

A prospective clinical and radiographic evaluation of 33 consecutive patients with severe and rigid idiopathic scoliosis (average Cobb angle 93 degrees, flexibility on bending films 23%) were treated with combined anterior and posterior instrumentation with a minimum follow-up of 2 years. All patients underwent anterior release and VDS-Zielke Instrumentation of the primary curve. In highly rigid scoliosis, this was preceded by a posterior release. Finally, posterior correction and fusion with a multiple hook and pedicle screw construct was performed. Thirty patients were operated in one stage, three patients in two stages. Preoperative curves ranged from 80 to 122 degrees Cobb angle. Frontal plane correction of the primary curve averaged 67% with an average loss of correction of 2 degrees . The apical vertebral rotation of the primary curve was corrected by 49%. In all but three patients, sagittal alignment was restored. There were no neurological complications, deep wound infections or pseudarthrosis. Combined anterior and posterior instrumentation is safe and enables an effective three-dimensional curve correction in severe and rigid idiopathic scoliosis.

Adolescent↗

PubMed2005

Asymmetric multicomponent domino reactions and highly enantioselective conjugated addition of thiols to alpha,beta-unsaturated aldehydes.

An organocatalytic asymmetric multicomponent domino and a conjugated addition reaction to alpha,beta-unsaturated aldehydes are presented. The development is based, first, on an organocatalyzed highly enantioselective nucleophilic thiol addition to the beta-carbon atom in the iminium ion intermediate, followed by an electrophilic amination of the alpha-carbon atom to the enamine intermediate. The multicomponent reactions proceed to give enantiopure amino-thiols in moderate to good yields. Furthermore, the organocatalyzed thiol addition to alpha,beta-unsaturated aldehydes takes place in good yields and excellent enantioselectivities.

Journal Article↗

PubMed2005

Tin-free radical alkoxyamine addition and isomerization reactions by using the persistent radical effect: variation of the alkoxyamine structure.

Various C-centered radicals can efficiently be generated through thermal C-O-bond homolysis of alkoxyamines. This method is used to perform environmentally benign radical cyclization and intermolecular addition reactions. These alkoxyamine isomerizations and intermolecular carboaminoxylations are mediated by the persistent radical effect (PRE). In the paper, the effect of the variation of the alkoxyamine structure--in particular steric effects in the nitroxide moiety--on the outcome of the PRE mediated radical reactions will be discussed. Fourteen different nitroxides were used in the studies. It will be shown that reaction times can be shortened about 100 times upon careful tuning of the alkoxyamine structure. Activation energies for the C-O-bond homolysis of the various alkoxyamines are provided. The kinetic data are used to explain the reaction outcome of the PRE-mediated processes.

Journal Article↗

PubMed2005

Nitroxide-mediated radical processes.

In the present short review article recent achievements in nitroxide-mediated radical polymerizations are presented. The basic concept behind these reactions, which is the Persistent Radical Effect (PRE), will be briefly explained. The effect of the nitroxide structure on the polymerization process will be discussed. Moreover, results of nitroxide-mediated radical polymerizations in aqueous dispersions will be summarized. Finally, applications of the PRE to environmentally benign radical chemistry such as nitroxide-mediated alkoxyamine isomerization and carboaminoxylation reactions are presented. Moreover, the potential use of microwave-induced heating to conduct these thermal radical reactions will be discussed.

Cyclic N-Oxides↗

PubMed2004

Steric and electronic effects in cyclic alkoxyamines--synthesis and applications as regulators for controlled/living radical polymerization.

The synthesis of new six- and seven-membered cyclic alkoxyamines bearing ethyl groups at the alpha-N position of the alkoxyamines is described. The key step in the synthesis of the sterically hindered six-membered cyclic alkoxyamines is a Wadsworth-Horner-Emmons olefination with bisphosphonate 1. The seven-membered cyclic alkoxyamines were prepared from the corresponding six-membered keto alkoxyamines by ring-enlargement with trimethylsilyl(TMS)-diazomethane. The use of the new alkoxyamines as regulators/initiators for radical polymerization is discussed. Efficient controlled and living polymerization of styrene and n-butyl acrylate was obtained with the six-membered tetraethyl alkoxyamine 13. Controlled polymerizations can be conducted even at 90 degrees C. In addition, alkoxyamine 13 can be used for the preparation of AB diblock and ABA triblock copolymers with narrow polydispersities. The influence of the replacement of methyl groups in the alpha-position of the N atom in cyclic alkoxyamines by larger ethyl groups on the styrene polymerization (reaction time, PDI, kinetics of the C-O bond homolysis) is discussed. In addition, thermal decomposition of the new alkoxyamines was studied. Furthermore, the synthesis of N,N-bissilylated alkoxyamines is described. The silylated alkoxyamines are not suitable as regulators/initiators for the controlled/living radical polymerization. The C-O bonds in silylated alkoxyamines are stronger than the C-O bonds in analogous N,N-dialkylated alkoxyamines. The experimental results are verified by calculations with Gaussian 98 (A. 9).

Journal Article↗

PubMed2003

Silylated cyclohexadienes as new radical chain reducing reagents: preparative and mechanistic aspects.

Various silylated 1,4-cyclohexadienes are presented as superior tin hydride substitutes for the conduction of various radical chain reductions. Debrominations, deiodinations, and deselenations can be performed using these environmentally benign reagents. Furthermore, Barton-McCombie-type deoxygenations using silylated cyclohexadienes are described. Radical cyclizations, ring expansions, and Giese-type addition reactions with the new tin hydride substitutes are presented. The polymerization of styrene can be regulated using silylated cyclohexadienes. Rate constants for hydrogen atom abstraction from two 1-silyl-cyclohexadienes by primary C-radicals were determined. The effects of the cyclohexadiene substituents on the reaction outcomes are discussed. Finally, qualitative EPR experiments on silyl radical expulsion from silylated cyclohexadienyl radicals are presented.

Journal Article↗