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Publikationen - Natur- und Wirkstoffchemie

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Publikation

Wessjohann, L. A.; Schneider, A.; Kaluđerović, G. N.; Brandt, W.; Solid-phase synthesis of reduced selenocysteine tetrapeptides and their oxidized analogs containing selenenylsulfide eight-membered rings Mol. Divers. 17, 537-545, (2013) DOI: 10.1007/s11030-013-9454-x

A series of protected and reduced forms of model tetrapeptides that mimic the C-terminus of human thioredoxin reductases were obtained in good yields, using solid-phase peptide synthesis (SPPS). SPPS was performed on the Knorr Amide MBHA resin for Fmoc chemistry using especially protected cystein and selenocystein derivatives. All amino acids have been coupled according to the HBTU/HOBt/DIPEA method. Furthermore, the corresponding oxidized peptides containing eight-membered rings with intramolecular S–S and S–Se bridges were prepared via I2/MeOH or DMSO/TFA oxidation, respectively.
Publikation

Schneider, A.; Wessjohann, L. A.; Severi, J. A.; Wagner, V.; Comparison of Impurity Profiles of Lipiblock® vs. Orlistat using HPLC and LC-MS/MS Lat. Am. J. Pharm. 31, 91-96, (2012)

Comparative HPLC-UV and LC-MS/MS studies of impurity profiles of a reference sample (Xenical®, F. Hoffmann–La Roche Ltd., Switzerland) vs. generic (Lipiblock®, EMS–Sigma Pharma, a generic drug) were carried out with ethanol extracts of commercial samples. The generic formulation contained higher levels of common impurities as well as a considerable number of impurities not found in the reference product. The detected impurity profile of Lipiblock® revealed that it most likely is based on fermentation. Since the effect of the impurities is unknown, at this point fully synthetic Xenical® appears to offer a better safety margin than Lipiblock® which, however, compares quite well to other generic formulations.
Publikation

Schneider, A.; Wessjohann, L. A.; Comparison of impurity profiles of Orlistat pharmaceutical products using HPLC tandem mass spectrometry J. Pharm. Biomed. Anal. 53, 767-772, (2010) DOI: 10.1016/j.jpba.2010.05.010

HPLC-UV and MS/MS studies of impurity profiles of original (Xenical®, F. Hoffmann-La Roche Ltd., Switzerland) and generic (Cobese™, Ranbaxy Laboratories Limited, India, and Orsoten, KRKA, Russia) products were carried out. The drug and related impurities were extracted by dissolving commercial samples in ethanol. The generic formulations contained higher levels of impurities than the original product. Impurity profiles (HPLC-MS/MS) of the generic samples are similar among themselves, whilst different in comparison to the impurity profile of the original product. The number of detected impurities for generics (14 impurities in Cobese™ and 13 impurities in Orsoten) is higher than for the original product (3 impurities in Xenical®). Based on these analyses the overall analytical quality follows the order Xenical® (best) > Orsoten > Cobese™.
Publikation

Wessjohann, L.; Schneider, A.; Synthesis of Selenocysteine and Its Derivatives with an Emphasis on Selenenylsulfide (-Se-S-) Formation Chem. Biodivers. 5, 375-388, (2008) DOI: 10.1002/cbdv.200890038

A short survey of historic and current methods for the synthesis of selenocysteine, selenocystine, and derivatives and related compounds is presented, with an additional emphasis on the formation of selenocysteine‐derived SeS bridges. The majority of methods to the amino acid starts with protected and O ‐activated serine, but also other concepts are included such as radical or multicomponent strategies, the latter allowing also direct access to peptoids in one pot. Of special importance is the monomeric oxidative cyclization of selenocysteine–cysteine peptides to eight‐membered and larger rings with a selenenylsulfide bridge, a crucial element in several selenoproteins.
Publikation

Wessjohann, L. A.; Schneider, A.; Abbas, M.; Brandt, W.; Selenium in chemistry and biochemistry in comparison to sulfur Biol. Chem. 388, 997-1006, (2007) DOI: 10.1515/BC.2007.138

What makes selenoenzymes – seen from a chemist's view – so special that they cannot be substituted by just more analogous or adapted sulfur proteins? This review compiles and compares physicochemical properties of selenium and sulfur, synthetic routes to selenocysteine (Sec) and its peptides, and comparative studies of relevant thiols and selenols and their (mixed) dichalcogens, required to understand the special role of selenium in selenoproteins on the atomic molecular level. The biochemically most relevant differences are the higher polarizability of Se- and the lower pKa of SeH. The latter has a strikingly different pH-dependence than thiols, with selenols being active at much lower pH. Finally, selected typical enzymatic mechanisms which involve selenocysteine are critically discussed, also in view of the authors' own results.
Publikation

Schneider, A.; Brandt, W.; Wessjohann, L. A.; Influence of pH and flanking serine on the redox potential of S-S and S-Se bridges of Cys-Cys and Cys-Sec peptides Biol. Chem. 388, 1099-1101, (2007) DOI: 10.1515/BC.2007.114

In selenocysteine (Sec, U)-containing proteins the selenenylsulfide bridge and its reduced thiol-selenol counterpart are usually the significant species. An important role for serine as flanking amino acid in the redox potential of S-S and S-Se bridges was proposed for some thioredoxin reductases. To check the generality of this proposal, model tetrapeptides (GCCG, SCCG, GCCS, SCCS, GCUG, SCUG, GCUS, SCUS) were synthesized, including the GCUG sequence of human thioredoxin reductase. The influence on the redox potential of S-Se and S-S bridges as a function of pH and of serine at different positions reveals (i) a strong general pH dependence, and (ii) a significant influence of flanking serine on disulfide only at basic pH.
Publikation

Schneider, A.; Rodrigues, O. E.; Paixão, M. W.; Appelt, H. R.; Braga, A. L.; Wessjohann, L. A.; Stereoselective synthesis of Boc-protected L-seleno- and tellurolanthionine, L-seleno- and tellurocystine and derivatives Tetrahedron Lett. 47, 1019-1021, (2006) DOI: 10.1016/j.tetlet.2005.11.101

Optically active seleno- and telluro amino acids can be synthesized from serine via its β-lactone with selenides and tellurides under overall retention of the serine stereochemistry. Boc-protected l-selenolanthionine, l-tellurolanthionine, l-selenocystine, l-tellurocystine and l-tellurocysteine derivatives can be obtained in good yields.
Publikation

Braga, A. L.; Lüdtke, D. S.; Schneider, P. H.; Vargas, F.; Schneider, A.; Wessjohann, L. A.; Paixão, M. W.; Catalytic enantioselective aryl transfer: asymmetric addition of boronic acids to aldehydes using pyrrolidinylmethanols as ligands Tetrahedron Lett. 46, 7827-7830, (2005) DOI: 10.1016/j.tetlet.2005.09.026

Pyrrolidinylmethanols, easily accessible from readily available (S)-proline, were applied in zinc-catalyzed addition of arylboronic acids to aromatic aldehydes; the reaction was found to proceed in excellent yields and high enantioselectivities (up to 98% ee).
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  • Martin-Luther Universität Halle
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