Iodination of carbohydrate-derived 1,2-oxazines to enantiopure 5-iodo-3,6-dihydro-2H-1,2-oxazines and subsequent palladium-catalyzed cross-coupling reactions

• Michal Medvecký,
• Igor Linder,
• Luise Schefzig,
• Hans-Ulrich Reissig and
• Reinhold Zimmer

Beilstein J. Org. Chem. 2016, 12, 2898–2905, doi:10.3762/bjoc.12.289

• tendency of this olefin to polymerize under the conditions applied. Consequently, the change of the olefin component from the methyl to the tert-butyl ester allowed the preparation of the corresponding coupling product syn-14 in significantly better yield. The use of dehydroamino acids such as olefin 16

Studies on the synthesis of peptides containing dehydrovaline and dehydroisoleucine based on copper-mediated enamide formation

• Franziska Gille and
• Andreas Kirschning

Beilstein J. Org. Chem. 2016, 12, 564–570, doi:10.3762/bjoc.12.55

• ornithine as well as for the tripeptide 44 containing dehydroisoleucine with the correct stereochemistry. Keywords: catalysis; dehydroamino acids; Hartwig–Buchwald reaction; myxovalargin; peptides; Introduction Dehydroamino acids [1] are rare amino acids that are constituents of many oligopeptides from

• microbial sources. Typical examples are myxovalargin (1), argyrin (2) and nisin (3, Scheme 1). Dehydroamino acids and peptides are characterized by the presence of an olefinic double bond conjugated with the carboxyl or peptidic carbonyl group. Besides being α,β-unsaturated acids or amides, respectively

• , they can also be regarded as enamines. Due to the lack of reactivity of the amino group as well as the carboxylate, dehydroamino acids have hardly employed as building blocks in peptide synthesis. Therefore, the olefinic double bond is commonly introduced after the peptide backbone is assembled and

Conformation of dehydropentapeptides containing four achiral amino acid residues – controlling the role of L-valine

• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Maciej Makowski,
• Rafał Latajka and
• Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 660–666, doi:10.3762/bjoc.10.58

• important issue of the determination of the secondary structure and properties of peptides is the Z/E-isomerism of dehydroamino acids. This phenomenon can be critical for their biological activity [16][17][18] and for the secondary structure of the peptide chain. Generally, the (Z)-isomers are

• thermodynamically more stable and easier to obtain. As a consequence, the (Z)-isomers are much more common than the (E)-counterpart [19]. Dehydroamino acids contribute to a catalytic role in the active sites of some enzymes [20][21][22]. Additionally, the presence of these dehydrogenated analogues of amino acids is

• dehydroamino acids and NOE signals between the alpha protons of Gly(1) and Val(5) (see Table S9 in Supporting Information File 1). This result is inconsistent with previously published conformational preferences of dehydropeptides containing only one L-amino acid ester at the C-terminal position [37]. Toniolo