N-Glycosides of indigo, indirubin, and isoindigo: blue, red, and yellow sugars and their cancerostatic activity

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 2840–2869, doi:10.3762/bjoc.20.240

• product can be explained by rearrangement of the rhamnosyl group from the oxygen to the nitrogen atom. Oxidative debenzylation of 5a afforded 5b in high yield. Unfortunately, all attempts to remove the pivaloyl protective groups failed. On the other hand, employment of tri-O-acetyl-α-ʟ-rhamnosyl

• , respectively. Because of our difficulties to remove the pivaloyl protective groups of rhamnoside 5b (Scheme 3), our group developed an alternative synthesis of indigo-N-glycosides based on the employment of dehydroindigo (13) instead of N-benzylindigo (1b) (Scheme 8) [21]. Known compound 13 was prepared in two

• pivaloyl-protected N-glycosyl anilines also proved to be unsuccessful, which pointed to steric reasons. Therefore, we studied in our group the use of the less sterically hindered formyl instead of acetyl or pivaloyl protective groups. The reaction of glucose (22a) with aniline afforded anomerically pure N

Chemoenzymatic synthesis of macrocyclic peptides and polyketides via thioesterase-catalyzed macrocyclization

• Senze Qiao,
• Zhongyu Cheng and
• Fuzhuo Li

Beilstein J. Org. Chem. 2024, 20, 721–733, doi:10.3762/bjoc.20.66

• . Developing more efficient and diverse macrocyclization strategies is urgently needed to overcome issues such as insufficient regioselectivity, intermolecular oligomerization, the overuse of protective groups, and other drawbacks [8]. In the biosynthetic logic, these natural products are produced by the large

• the current issues, such as insufficient regioselectivity, intermolecular oligomerization, and the overuse of protective groups. The biosynthetic studies demonstrated that thioesterase (TE) domains exhibit a high level of chemoselectivity and regioselectivity in late-stage macrocyclizations. This

Comparison of glycosyl donors: a supramer approach

• Anna V. Orlova,
• Nelly N. Malysheva,
• Maria V. Panova,
• Nikita M. Podvalnyy,
• Michael G. Medvedev and
• Leonid O. Kononov

Beilstein J. Org. Chem. 2024, 20, 181–192, doi:10.3762/bjoc.20.18

• (trifluoroacetyl vs chloroacetyl), at different concentrations (0.05 and 0.15 mol·L−1) led to mutually excluding conclusions concerning their relative reactivity and selectivity, which prevented us from revealing a possible influence of remote protective groups at O-9 on glycosylation outcome. According to the

• ]. As in other glycosylation reactions [22][23][24][25][26][27][28][29], the result of sialylation is affected by a variety of variables [30][31][32][33][34][35][36][37][38][39] including the nature of protective groups on either partner [26][38][40][41][42][43][44][45] and concentration of reagents [31

• ][33][34][37][39][43][44][46]. During a study of a possible influence of remote acyl protective groups [23] on the sialylation outcome (which could become possible through participation in stabilization of glycosyl cation [24][47][48] in a conformation with all-axial substituents in the pyranose ring

Preparation of β-cyclodextrin-based dimers with selectively methylated rims and their use for solubilization of tetracene

• Konstantin Lebedinskiy,
• Volodymyr Lobaz and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2022, 18, 1596–1606, doi:10.3762/bjoc.18.170

• selectively permethylated on the primary side is shown in Scheme 3. The method described by Varga [25] was not suitable for the preparation of 11 because of the strong reductive conditions required for the cleavage of benzyl protective groups. Other described procedures [23][24] also have disadvantages, such

• selectively methylated rims The important part of this work was proving the structure of the synthesized compounds because we worked with non-symmetrical CDs; moreover, we used protection–deprotection methods for partial methylation, so we could expect a cleavage or even migration of protective groups

A study of the DIBAL-promoted selective debenzylation of α-cyclodextrin protected with two different benzyl groups

• Naser-Abdul Yousefi,
• Morten L. Zimmermann and
• Mikael Bols

Beilstein J. Org. Chem. 2022, 18, 1553–1559, doi:10.3762/bjoc.18.165

• identity of protective groups on the secondary rim influence the reaction at the primary rim significantly, most probably by a collective inductive effect. When the reaction of 7 with DIBAL was carried out at higher temperature further debenzylation was observed with, according to MS, a triol 9 being

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• good yields via metal- and additive-free TBHP-promoted cross-dehydrogenative coupling (CDC) of readily accessible N-methyl-2-(aminomethyl)biphenyls and 2-(aminomethyl)biphenyls. This methodology is compatible with numerous functional groups (methoxy, cyano, nitro, chloro, and SEM and TBS-protective

• groups for phenols) and was further utilized in the first total synthesis of the natural product nobilone. Keywords: cross-dehydrogenative coupling; cyclization; fluorenones; nobilone; total synthesis; Introduction Fluorenones are an important class of aromatic natural products, and since the

Preparation of mono-substituted malonic acid half oxyesters (SMAHOs)

• Tania Xavier,
• Sylvie Condon,
• Christophe Pichon,
• Erwan Le Gall and
• Marc Presset

Beilstein J. Org. Chem. 2021, 17, 2085–2094, doi:10.3762/bjoc.17.135

• undesired transesterification reactions, which somewhat limits the usefulness of this strategy. Upon application of these precautions, yields ranging from 62% to 91% were obtained in most cases. Nevertheless, the use of some protective groups is obviously a limitation of the method as this second step was

DNA with zwitterionic and negatively charged phosphate modifications: Formation of DNA triplexes, duplexes and cell uptake studies

• Yongdong Su,
• Maitsetseg Bayarjargal,
• Tracy K. Hale and
• Vyacheslav V. Filichev

Beilstein J. Org. Chem. 2021, 17, 749–761, doi:10.3762/bjoc.17.65

• one or more N-modified phosphoramidate groups (Scheme 1, III) were obtained after the removal of the protective groups and β-cyanoethyl groups using ≈28% ammonia. We found out that a higher conversion was observed when performing the Staudinger reaction at 37 °C rather than at room temperature. The

Nanopatterns of arylene–alkynylene squares on graphite: self-sorting and intercalation

• Tristan J. Keller,
• Joshua Bahr,
• Kristin Gratzfeld,
• Nina Schönfelder,
• Marcin A. Majewski,
• Marcin Stępień,
• Sigurd Höger and
• Stefan-S. Jester

Beilstein J. Org. Chem. 2019, 15, 1848–1855, doi:10.3762/bjoc.15.180

• protective groups [28]. Subsequently, 1a/b were prepared by Pd-catalyzed oxidative cyclodimerization of the respective acetylene-terminated precursors under high-dilution conditions [29][30]. The separation of the crude products by recycling gel permeation chromatography (recGPC) yielded the monodisperse

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• (1-phenylethyl)aziridine-2-carboxylic acid and its derivatives till the beginning of 2019. The usefulness of any chiron depends on its availability and to some extent on versatility of the protective groups. In case of the 1-phenylethyl group its removal at any stage of synthesis is not limited to a

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts

• Rodrigo Abonia,
• Luisa F. Gutiérrez,
• Braulio Insuasty,
• Jairo Quiroga,
• Kenneth K. Laali,
• Chunqing Zhao,
• Gabriela L. Borosky,
• Samantha M. Horwitz and
• Scott D. Bunge

Beilstein J. Org. Chem. 2019, 15, 642–654, doi:10.3762/bjoc.15.60

• compounds [13][14][15][16]. Due to their valuable properties, they are also well exploited by the chemical industry as dyes and photochromic agents [17][18], protective groups in organic synthesis [19] and as building blocks for dendrimers [20] and nonlinear optical (NLO) properties [21] (Scheme 1

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

• hydrolysis, formation of methyl ester and silylation to give 7 after separation from the minor diastereoisomer. After selective hydrolysis of the acetal the hydroxymethyl fragment was oxidized and all protective groups were removed to give (2S,3R)-2 as the hydrochloride (Scheme 1). The observed

• positioned opposite to the incoming nucleophile. After removal of protective groups with iodotrimethylsilane 3-hydroxyglutamic acid (2) was obtained as the monoammonium salt [(2S,3R):(2S,3S), 94:6] or the hydrochloride [(2S,3R):(2S,3S), >98:2] (Scheme 3) [51]. Treatment of a trilithium salt of the N

Synthesis of α-D-GalpN₃-(1-3)-D-GalpN₃: α- and 3-O-selectivity using 3,4-diol acceptors

• Emil Glibstrup and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2018, 14, 2805–2811, doi:10.3762/bjoc.14.258

• azido precursor has been studied and optimized in terms of steps, yields and selectivity. It has been found that glycosylation of the 3,4-diol acceptor is an advantage over the use of a 4-O-protected acceptor and that both regio- and anomeric selectivity is enhanced by bulky 6-O-protective groups. The

• -protective groups, a 4-O-protective group should be avoided, i.e., use the diol acceptor. Bulky 6-O-protective groups on the donor enhance the α-selectivity. Bulky 6-O-protective groups on either the donor or the acceptor enhance the 3-O-regioselectivity. This simplification in synthesis allows for easier

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• molecular systems using simple organic chemistry procedures was still challenging at that time. One of the major synthetic breakthroughs was thus the use of cyanoethyl protective groups for TTF thiolates (Figure 4) [46][47]. Treatment of cyanoethyl-protected 1,3-dithiol-thiolates A with one or two

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

• Michael R. Imrich,
• Jochen Kraft,
• Cäcilia Maichle-Mössmer and
• Thomas Ziegler

Beilstein J. Org. Chem. 2018, 14, 2082–2089, doi:10.3762/bjoc.14.182

• starting from D-fructose. Two of these ligands were applied in enantioselective catalysis. Results and Discussion Starting from D-fructose, 1,2-isopropylidene-protected pyranosides with different protective groups (PG) at C-3, C-4 and C-5 can be prepared in two to four steps (Scheme 1). First, D-fructose

• -fructose derivatives with different protective groups at position 3, 4 and 5 the hydroxy group of 6a was first protected to afford 6b. After removing the isopropylidene group, positions 4 and 5 of the resulting diol 7c were protected to afford 7d. A convenient method for constructing anomeric 2-oxazolines

• the yield decreases heavily otherwise. Up to 14 equiv of 8 can be re-isolated after the reaction though. We applied the modified Ritter reaction to nine different 1,2-isopropylidene-proctected fructose derivatives as depicted in Table 1. With ether protective groups (Table 1, entries 1–5), the

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• , affording the desired product 2z in moderate yield with formation of inseparable byproducts (Table 4, entry 12). Thus, the use of silyl- and acetal-type protective groups is suitable for the present reaction. As reported previously [13], the fact that the present rearrangement reaction proceeds in a [1,3

Phosphoramidite building blocks with protected nitroxides for the synthesis of spin-labeled DNA and RNA

• Timo Weinrich,
• Eva A. Jaumann,
• Ute M. Scheffer,
• Thomas F. Prisner and
• Michael W. Göbel

Beilstein J. Org. Chem. 2018, 14, 1563–1569, doi:10.3762/bjoc.14.133

• therefore developed a third strategy based on photolabile protective groups [41][42][43] finally leading to phosphoramidite 6. This building block behaves in solid-phase RNA synthesis as any normal TOM protected amidite. It is completely stable against the conditions used for strand assembly, RNA

• . Therefore, the use of photolabile protective groups for nitroxides currently provides the most general approach for synthesizing spin labeled DNA and RNA. This strategy looks promising not only for TEMPO but also for other types of nitroxides such as TPA [20][21][27][29] or Ç [31][32][33]. Structures of

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• seemingly simple transformations needed for the assembly of lipid A, such as glycosylation towards fully orthogonally protected β(1→6)-linked diglucosamine backbone, sequential protective groups manipulation combined with successive instalment of multiple functional groups, N- and O-acylation with the long

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• with (cyclo)alkyl substituents can be prepared in a direct manner, residues with polar functional groups require suitable protective groups. The presence of particular functional groups in the side chain in some cases leads to remarkable side reactions of the alkyne moiety. Thus, electron-withdrawing

• sterically shielding protective groups have proven convenient, the trityl group turned out to be inefficient to generate a serine-analogous propargylamine. Trityl-protected imine 5m immediately decomposed, when treated with (trimethylsilyl)ethynyllithium. The preparation of glutamic acid-analogous

• propargylamines without an acidifying Cα-substituent. Synthesis of propargylamines containing polar or acidic functional groups The synthesis of propargylamines with polar substituents to mimic polar amino acids such as serine (alcohol), cysteine (thiol) or glutamine (carboxamide) requires special protective

Preactivation-based chemoselective glycosylations: A powerful strategy for oligosaccharide assembly

• Weizhun Yang,
• Bo Yang,
• Sherif Ramadan and
• Xuefei Huang

Beilstein J. Org. Chem. 2017, 13, 2094–2114, doi:10.3762/bjoc.13.207

• transformations commonly encountered in building block preparation [41]. At the same time, mild promoters are available for thioglycoside activation. The anomeric reactivities of thioglycosides towards glycosylation can be significantly influenced by the protective groups on the glycan ring as well as the size

• ]. Interestingly, when 87 was preactivated, two major intermediates were produced (α-triflate 88 and dioxalenium ion 89). The different outcome upon preactivation can be explained in terms of different electron-withdrawing properties of the protective groups present in these three donors. For 83, the Bz group

• amounts of aglycon transfer products can be reduced by decreasing the nucleophilicity of the acceptor aglycon through steric effects [87] or tuning protective groups of acceptors [84][86], in some cases by lowering the reaction temperature [85]. Conclusion While conceptually simple, the temporal

A novel application of 2-silylated 1,3-dithiolanes for the synthesis of aryl/hetaryl-substituted ethenes and dibenzofulvenes

• Grzegorz Mlostoń,
• Paulina Pipiak,
• Róża Hamera-Fałdyga and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 1900–1906, doi:10.3762/bjoc.13.185

• -dithiolanes, as well as the generation of the corresponding carbanions are widely applied in the umpolung chemistry [27][28] and in the chemistry of protective groups [29][30], but tetrasubstituted ethenes have never been prepared by using this approach. Conclusion The presented study showed that 2

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• low selectivity [46][47]. The selective monofunctionalization of 2-ABA was achieved by using protective groups such as 9-BBN [48] or Boc [39], which require subsequent removal. Other alternative synthetic strategies use substrates like 2-nitrobenzoyl chloride, 2-nitrobenzaldehyde, 2-aminobenzamides, 2

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

• Mikael Bols and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12

• Mikael Bols Christian Marcus Pedersen Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark 10.3762/bjoc.13.12 Abstract Silyl groups such as TBDPS, TBDMS, TIPS or TMS are well-known and widely used alcohol protective groups in organic chemistry. Cyclic

• silylene protective groups are also becoming increasingly popular. In carbohydrate chemistry silyl protective groups have frequently been used primarily as an orthogonal protective group to the more commonly used acyl and benzyl protective groups. However, silyl protective groups have significantly

• different electronic and steric requirements than acyl and alkyl protective groups, which particularly becomes important when two or more neighboring alcohols are silyl protected. Within the last decade polysilylated glycosyl donors have been found to have unusual properties such as high (or low) reactivity

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route

• Felicia D’Andrea,
• Giorgio Catelani,
• Lorenzo Guazzelli and
• Venerando Pistarà

Beilstein J. Org. Chem. 2016, 12, 2343–2350, doi:10.3762/bjoc.12.227

• the stereoselective synthesis of enantiopure inositol derivatives, also the possibility to pick and tag specific positions of the inositol ring, installing the protective groups earlier on the carbohydrate frame through the well-known sugar chemistry, is of extreme interest. Although some attractive

A robust synthesis of 7,8-didemethyl-8-hydroxy-5-deazariboflavin

• Matthias Bender,
• Henrik Mouritsen and
• Jens Christoffers

Beilstein J. Org. Chem. 2016, 12, 912–917, doi:10.3762/bjoc.12.89

• compound with high purity. Keywords: carbohydrates; heterocyclic compounds; protective groups; riboflavin derivatives; ribose derivatives; Introduction The deazariboflavin cofactor F420 plays an important role in bacterial methanogenesis [1][2] and was – in contrast to other, ubiquitous biological redox

• biosynthetic precursor compound to cofactor F420. In comparison with older routes to this target compound, the key innovation of our procedures is the introduction of two isopropylidene protective groups into the ribose side chain, which allowed the chromatographic purification of key intermediate product 11