Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

• Zara M. Seibel,
• Jeffrey S. Bandar and
• Tristan H. Lambert

Beilstein J. Org. Chem. 2021, 17, 2077–2084, doi:10.3762/bjoc.17.134

• substitution is discussed. Compared to other methods, this protocol allows for a broader and more enantioselective access to pyroglutamate derivatives. Keywords: Brønsted base; cyclopropenimine; enantioselective catalysis; Michael addition; pyroglutamate; Introduction α-Substituted glutamates have value as

• chemistry remains quite sensitive to structural modifications, and thus there remains significant room for further development. Nevertheless, this work provides a convenient means to access a variety of these important structural motifs. Strategy for the synthesis of glutamate and pyroglutamate derivatives

• and several natural products with pyroglutamate substructures. Effect of the aryl substituent on reaction efficiency and selectivity. Proposed transition state model. Optimization of the cyclopropenimine-catalyzed addition of alanine imine 1 to methyl acrylate. Substrate scope of amino ester imine

GlypNirO: An automated workflow for quantitative N- and O-linked glycoproteomic data analysis

• Toan K. Phung,
• Cassandra L. Pegg and
• Benjamin L. Schulz

Beilstein J. Org. Chem. 2020, 16, 2127–2135, doi:10.3762/bjoc.16.180

• cysteines was set as a fixed modification, and dynamic modifications included deamidation of asparagine, monooxidised methionine, and the formation of pyroglutamate at N-terminal glutamic acid and glutamine. All variable modifications were set as “Common 1” allowing each modification to be present once on a

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• intermediary 4-hydroxypyroglutamic acids would have become available. This can be readily accomplished with ruthenium(IV) oxide. Application of this reagent to the acetate of methyl N-Boc-4-hydroxyprolinate [(2S,4R)-79] gave the protected pyroglutamate 80 which was transformed into dimethyl N-Boc-4

• intramolecular lactonization to form 83 by implementation of the Mitsunobu reaction. After opening of the lactone ring with trichloroethanol and silylation of the hydroxy group oxidation at C5 was performed in the usual way to give a pyroglutamate 84. Benzyl or p-methoxybenzyl esters 85a or 85b were next

• [86][87][88] or a Diels–Alder reaction using acylnitroso compounds [89]. However, when compared with these multistep approaches hydroxylation of pyroglutamic acid derivatives seems to be the simplest option. Treatment of the lithium enolate of benzyl N-Boc-pyroglutamate (S)-86 with Davis oxaziridine

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• to access several natural products and unnatural amino acids [58][75][76][77]. For example, Oba and co-workers performed conjugate additions to an α,β-unsaturated pyroglutamate derivative where the carboxylic acid was protected as a 5-methyl-2,7,8-trioxabicyclo[3.2.1]octane (ABO ester) [66] (Scheme 9

Synthesis and antibacterial activity of monocyclic 3-carboxamide tetramic acids

• Yong-Chul Jeong and
• Mark G. Moloney

Beilstein J. Org. Chem. 2013, 9, 1899–1906, doi:10.3762/bjoc.9.224

• -hydroxysuccinimide esters of N-acetylamino acids has been reported [19], we wished to exploit an alternative approach based upon C-acyloxylation of enolates followed by amine exchange, which had been shown to be very effective in a pyroglutamate series, since it offered synthetic simplicity and the potential for