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Deprotection Step (deprotection + step)
Selected AbstractsOn choosing the right ether for peptide precipitation after acid cleavageJOURNAL OF PEPTIDE SCIENCE, Issue 3 2008Beatriz G. de La Torre Abstract Methyl tert -butyl ether (MTBE) and diethyl ether (DEE) tend to be regarded as interchangeable for the ,cold ether' workup concluding the final acidolytic cleavage and deprotection step of solid-phase peptide syntheses. However, the use of MTBE to precipitate peptides from strong acid solutions is shown to give rise to t -butyl alkylation byproducts, readily detectable by MALDI-TOF MS. The problem can attain undesirable dimensions in the cleavage of peptide resins containing high proportions of aromatic residues, particularly in peptide nucleic acid (PNA) syntheses. In those cases, DEE workup is advisable, as it consistently leads to cleaner products. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] A Stereodivergent Synthesis of All Stereoisomers of Centrolobine: Control of Selectivity by a Protecting-Group ManipulationCHEMISTRY - A EUROPEAN JOURNAL, Issue 44 2009Bernd Schmidt Prof. Abstract All stereoisomers of the natural product centrolobine are selectively synthesized, by starting from a common precursor. Key steps are an enantioselective allylation with enantiomerically pure allylsilanes, a tandem ring-closing metathesis,isomerization reaction, and a Heck reaction by using an arene diazonium salt. By choosing appropriate conditions for the final deprotection step, either the cis -configured centrolobines or their epimers are selectively obtained. [source] An Expedient Synthesis of the Repeating Unit of the Acidic Polysaccharide of the Bacteriolytic Complex of Lysoamidase,CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2005Remy E. J. N. Litjens Abstract The first synthesis of the trisaccharide repeating unit of the acidic polysaccharide of the bacteriolytic complex of lysoamidase is presented. The construction is based on a linear glycosylation strategy that starts from the reducing end and employs thio- and selenoglycosides in a highly stereoselective manner by a single set of activation conditions. The thus-formed trisaccharide is selectively deprotected and oxidised, after which a final deprotection step furnishes the desired repeating unit. [source] Total Synthesis without Protection: Three-Step Synthesis of Optically Active Clavicipitic Acids by a Biomimetic RouteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2004Yuusaku Yokoyama Abstract A three-step synthesis of a mixture of optically active cis - and trans -clavicipitic acids 6, which are ergot alkaloids, was achieved, starting from 4-bromoindole (7) and dl -serine (dl - 2). This short synthesis was made possible by omitting the protection and deprotection steps from the synthetic route. The key step was the spontaneous cyclization of 4-vinyltryptophan (10) formed from the Heck reaction of 4-bromotryptophan (8) with 2-methyl-3-buten-2-ol (9) in aqueous media. During this investigation, we also found that the palladium-catalyzed reaction of 8 with 9 showed an interesting pH dependence; under strongly basic conditions, the Heck reaction occurred to give a C4 -vinylated product 10, whereas an N -allylated product 19b was formed under neutral or weakly basic conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Molecularly defined (L)-lactic acid oligomers and polymers: Synthesis and characterizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Kenichi Takizawa Abstract The synthesis of (L)-lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t -butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3-dicyclohexylcarbodiimide or 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride were high (70,100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X-ray scattering demonstrated a close correlation between the molecular structure of the well-defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977,5990, 2008 [source] The Cobalt Way to Angucyclinones: Asymmetric Total Synthesis of the Antibiotics (+)-Rubiginone,B2, (,)-Tetrangomycin, and (,)-8- O -MethyltetrangomycinCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010Christian Kesenheimer Dr. Abstract A cobalt(I)-mediated convergent and asymmetric total synthesis of angucyclinones with an aromatic B ring has been developed. In the course of our research, we synthesized three naturally occurring anguclinone derivatives, namely, (+)-rubiginone,B2 (1), (,)-8- O -methyltetrangomycin (2), and (,)-tetrangomycin (3). By combining 3-hydroxybenzoic acid, 3-methoxybenzoic acid, citronellal, and geraniol as starting materials in a convergent way, we were able to synthesize chiral triyne chains, which were cyclized with [CpCo(C2H4)2] (Cp=cyclopentadienyl) by means of an intramolecular [2+2+2] cycloaddition to their corresponding tetrahydrobenzo[a]anthracenes. Successive oxidation and deprotection steps led to the above-mentioned natural products 1,3. [source] | ||||||||||