Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• -rich (hetero)aryl halides was equally effective (Scheme 36). In addition, the preparation of unnatural amino acids in multigram scale [115], along with the syntheses of complex terpenes [116] and (+)-calcipotriol [117] have showcased the vast synthetic potential and broad applicability of NHPI esters

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• route for the synthesis of unnatural amino acids and amines. Remarkably, the procedure exhibited excellent compatibility with a wide range of alkyl radicals, including primary, secondary, tertiary, and α-heterosubstituted radicals generated from corresponding redox-active esters 3. Concurrently, Shang

Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• –Crafts reaction. Reaction between indoles and racemic 2,3-dihydroisoxazol-3-ol derivatives. Exploiting 5-aminoisoxazoles as nucleophiles. Reaction between unsubstituted indoles and 3-alkynylated 3-hydroxy-1-oxoisoindolines. Synthesis of unnatural amino acids bearing an aza-quaternary stereocenter

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

• Alessio Regni,
• Francesca Bartoccini and
• Giovanni Piersanti

Beilstein J. Org. Chem. 2023, 19, 918–927, doi:10.3762/bjoc.19.70

• ][64][65][66][67], we became fascinated in exploring whether photoredox catalysis could be applied for the activation of such unnatural amino acids to expedite the development of completely new synthetic pathways. In particular, 4-dimethylallyltryptophan (DMAT) is of interest for the following reasons

Palladium-catalyzed enantioselective three-component synthesis of α-arylglycine derivatives from glyoxylic acid, sulfonamides and aryltrifluoroborates

• Bastian Jakob,
• Nico Schneider,
• Luca Gengenbach and
• Georg Manolikakes

Beilstein J. Org. Chem. 2023, 19, 719–726, doi:10.3762/bjoc.19.52

• amino acids received increasing attention due to advances in protein-engineering and the development of protein-based therapeutics [3][4]. Among the different types of non-proteinogenic and unnatural amino acids, α-arylglycines play a particular important role. The arylglycine scaffold can be found in

• production of drugs, fertilizers, (biodegradable) polymers or nutritional supplements [2]. More importantly, α-amino acids form the backbone of all proteins and enzymes are therefore essential for almost all biological processes. In the last twenty years non-proteinogenic and chemically synthesized unnatural

NaI/PPh₃-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

• Dan Liu,
• Yue Zhao and
• Frederic W. Patureau

Beilstein J. Org. Chem. 2023, 19, 57–65, doi:10.3762/bjoc.19.5

• -active ester derived from methionine could be converted effectively to α-aminoalkylation product 3al in overall 70% yield, which thus provides a mild method for the functionalization and derivation of abundant natural or unnatural amino acids. Some functional groups such as a terminal alkene in 3am, a

Synthesis and late stage modifications of Cyl derivatives

• Phil Servatius and
• Uli Kazmaier

Beilstein J. Org. Chem. 2022, 18, 174–181, doi:10.3762/bjoc.18.19

• and Discussion Since a couple of years the focus of our research group is on the synthesis of unnatural amino acids and their incorporation into complex natural products. Many of these show interesting anticancer activities [26][27][28]. Some linear peptides, such as pretubulysin bind to tubulin [29

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• muscimol (I) and ibotenic acid (II) (Figure 1) have been isolated from several fungal species and are active on the γ-aminobutyric acid (GABA) and glutamate receptors of the central nervous system (CNS), respectively [8][9]. Various unnatural amino acids bearing a 1,2-oxazole moiety, such as

¹⁹F NMR as a tool in chemical biology

• Diana Gimenez,
• Aoife Phelan,
• Cormac D. Murphy and
• Steven L. Cobb

Beilstein J. Org. Chem. 2021, 17, 293–318, doi:10.3762/bjoc.17.28

• introduction of unnatural amino acids into proteins have been reviewed extensively elsewhere [5][6][7] and here we will only discuss the most recent advances. The chemical structures of a selection of 19F-labelled amino acid analogues that have been utilized in 19F NMR studies in chemical biology are shown in

• -butyloxyproline, with the 4R analogue exhibiting a higher propensity for the polyproline helix structure than the 4S [17]. This differentiated conformational bias observed highlights the potential application of these amino acids as unique probes for molecular recognition studies. The synthesis of unnatural amino

• acids carrying novel fluorine-based functionalities such as -SF5 has also recently achieved considerable interest. For instance, the work carried out within the Welch group, who reported the synthesis and NMR conformational characterization of the first heptapeptide containing a pentafluorosulfanylated

Naphthalene diimide–amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA

• Annike Weißenstein,
• Myroslav O. Vysotsky,
• Ivo Piantanida and
• Frank Würthner

Beilstein J. Org. Chem. 2020, 16, 2032–2045, doi:10.3762/bjoc.16.170

• Chemistry (CNC), Universität Würzburg, Theodor-Boveri-Weg, 97074 Würzburg, Germany 10.3762/bjoc.16.170 Abstract Two novel unnatural amino acids, prepared by linking a dicationic purple-coloured and fluorescent naphthalene diimide (NDI) at core position to amino acid side chains of variable length, strongly

Synthesis of new asparagine-based glycopeptides for future scanning tunneling microscopy investigations

• Laura Sršan and
• Thomas Ziegler

Beilstein J. Org. Chem. 2020, 16, 888–894, doi:10.3762/bjoc.16.80

• functional group that would require an additional protection orthogonal to the Fmoc/t-Bu protocol and the acetyl groups of the sugar moieties. However, numerous other natural or unnatural amino acids, functionalized or not, could be used for this reaction protocol. Results and Discussion For the synthesis of

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

• Sergii Afonin,
• Oleg Babii,
• Aline Reuter,
• Volker Middel,
• Masanari Takamiya,
• Uwe Strähle,
• Igor V. Komarov and
• Anne S. Ulrich

Beilstein J. Org. Chem. 2020, 16, 39–49, doi:10.3762/bjoc.16.6

• plasma stability in vivo, limited understanding of their mechanisms of action, and high in vivo toxicity. The former two drawbacks are being adequately resolved [9] (e.g., by modifying the peptide backbone [10], macrocyclization [11], or by use of unnatural amino acids [12]), and mechanistic

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• combinatorial library [88]. The work carried out by Davis and co-workers led to the metabolic incorporation of unnatural amino acids (uAAs) bearing a terminal alkene as CM substrates for protein modification [89]. The authors investigated the possibility to incorporate methionine (Met) analogues in a Met

Novel solid-phase strategy for the synthesis of ligand-targeted fluorescent-labelled chelating peptide conjugates as a theranostic tool for cancer

• Sagnik Sengupta,
• Mena Asha Krishnan,
• Premansh Dudhe,
• Ramesh B. Reddy,
• Bishnubasu Giri,
• Sudeshna Chattopadhyay and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2018, 14, 2665–2679, doi:10.3762/bjoc.14.244

• (Tfa) in the side chain of the growing polypeptide chain. The methodology could be extended to incorporate any basic natural or unnatural amino acids in a peptide chain in which the α-amino group is protected as Fmoc and the side chain amino group, in any position (β, γ, δ) along the carbon side chain

Homologated amino acids with three vicinal fluorines positioned along the backbone: development of a stereoselective synthesis

• Raju Cheerlavancha,
• Ahmed Ahmed,
• Yun Cheuk Leung,
• Aggie Lawer,
• Qing-Quan Liu,
• Marina Cagnes,
• Hee-Chan Jang,
• Xiang-Guo Hu and
• Luke Hunter

Beilstein J. Org. Chem. 2017, 13, 2316–2325, doi:10.3762/bjoc.13.228

• ; Introduction The incorporation of unnatural amino acids into a peptide structure can potentially reduce conformational disorder and hence improve the binding affinity of the peptide for its biological target. For example, conformationally rigid amino acids such as 1 (Figure 1) have been shown to dramatically

Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• library of compounds bearing the free amino acid function at C-3 and pertaining to the class of constrained tryptophan analogues. Keywords: constrained tryptophans; Diels–Alder; indoles; tetrahydrocarbazoles; unnatural amino acids; Introduction With the term of “unnatural” amino acids, a plethora of

• six-membered ring [8]. Moreover, fused bicyclic unnatural amino acids are present in the structures of two antiviral drugs, boceprevir (Merck) [9] and telaprevir (Vertex, Johnson & Johnson) [10] used against hepatitis C genotype 1 viral infections (Figure 1). In this research field, tryptophan

• of these compounds. In particular, the dependence upon the substitution pattern at nitrogen and at the outer-ring double bond, highlighted the need to select the appropriate promoter for each desired transformation. Examples of drugs embodying unnatural amino acids. Examples of biologically active

Orthogonal dual-modification of proteins for the engineering of multivalent protein scaffolds

• Michaela Mühlberg,
• Michael G. Hoesl,
• Christian Kuehne,
• Jens Dernedde,
• Nediljko Budisa and
• Christian P. R. Hackenberger

Beilstein J. Org. Chem. 2015, 11, 784–791, doi:10.3762/bjoc.11.88

• combines residue-specific incorporation of unnatural amino acids with chemical oxidative aldehyde formation at the N-terminus of a protein. Our approach relies on the selective introduction of two different functional moieties in a protein by mutually orthogonal copper-catalyzed azide–alkyne cycloaddition

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

Versatile synthesis of amino acid functionalized nucleosides via a domino carboxamidation reaction

• Vicky Gheerardijn,
• Jos Van den Begin and
• Annemieke Madder

Beilstein J. Org. Chem. 2014, 10, 2566–2572, doi:10.3762/bjoc.10.268

• relies on commercially available amino acid derivatives and should be applicable to a large series of natural and unnatural amino acids. Amino acid functionalized nucleosides. Reagents and conditions: a) i. Et3N, Pd(PPh3)4, THF, CO (4 bar), 70 °C, 48 h, ii. Et3N, di-tert-butyl dicarbonate, DMF, rt, 15

Automated solid-phase peptide synthesis to obtain therapeutic peptides

• Veronika Mäde,
• Sylvia Els-Heindl and
• Annette G. Beck-Sickinger

Beilstein J. Org. Chem. 2014, 10, 1197–1212, doi:10.3762/bjoc.10.118

• substitutions by alanine [124] or hydrophobic/ionic monomers [125] can help to identify key binding sites of peptides and their individual receptors. In addition, it is possible to perform cyclization [126] or modification of NPY with unnatural amino acids [127]. Cabrele et al. reported on a tyrosine methyl

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• [48]. Addition of an allylic nucleophile provides access to homoallylic alcohols I. These can be derivatized to unnatural amino acids, such as K [49] and L [50] or to aminosugar derivatives like M [29][51]. Additions of various nucleophiles to 1 have been summarized by Bols and co-workers in 2001 [52

Investigation of the network of preferred interactions in an artificial coiled-coil association using the peptide array technique

• Raheleh Rezaei Araghi,
• Carsten C. Mahrenholz,
• Rudolf Volkmer and
• Beate Koksch

Beilstein J. Org. Chem. 2012, 8, 640–649, doi:10.3762/bjoc.8.71

• the concept of rational drug design based on coiled-coil proteins [6]. In this context, the use of unnatural amino acids in peptidomimetics is advisable, to enhance enzymatic stability, limit conformational flexibility, and improve pharmacodynamics and bioavailability [7]. In order to manipulate helix

• ,g21Mut) resulted in a loss of binding, which strongly suggests that the quaternary structure does not only tolerate but is in fact dependent on the interaction of the central heptad of natural peptides with side chains of the unnatural amino acids on the chimera. As a negative control, the binding

Enantioselective synthesis of tricyclic amino acid derivatives based on a rigid 4-azatricyclo[5.2.1.0^2,6]decane skeleton

• Matthias Breuning,
• Tobias Häuser,
• Christian Mehler,
• Christian Däschlein,
• Carsten Strohmann,
• Andreas Oechsner and
• Holger Braunschweig

Beilstein J. Org. Chem. 2009, 5, No. 81, doi:10.3762/bjoc.5.81

• β-turn-inducing building blocks in peptidomimetics and for chiral auxiliaries in asymmetric organocatalysis. Keywords: amino acid; enantioselective synthesis; norbornane; polycyclic compounds; pyrrolidine; Introduction Unnatural amino acids with a rigid bowl-shaped backbone have received

Synthesis of new C^α-tetrasubstituted α-amino acids

• Andreas A. Grauer and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 5, doi:10.3762/bjoc.5.5

• aldehydes are prone to give aldol products under the reaction conditions used, we were able to obtain the target cyclic amino acids in low to moderate yields and in some cases with good diastereoselectivity. Keywords: amino acid synthesis; Cα-tetrasubstituted α-amino acids; unnatural amino acids

• ][14]. Therefore a variety of Cα-tetrasubstituted α-amino acids have been developed in recent years and reported in the literature [15][16][17][18][19]. Recently our group reported as a new class of such unnatural amino acids Cα-tetrasubstituted tetrahydrofuran amino acids (TAAs), which were prepared