Mechanochemical synthesis of poly(trimethylene carbonate)s: an example of rate acceleration

• Sora Park and
• Jeung Gon Kim

Beilstein J. Org. Chem. 2019, 15, 963–970, doi:10.3762/bjoc.15.93

• for the rate enhancement under ball-milling conditions. As another highly reactive organic catalyst, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was investigated next. The bicyclic guanidine base TBD has shown better efficiencies than DBU in many chemical transformations including the polymerization of

Selective formation of a zwitterion adduct and bicarbonate salt in the efficient CO₂ fixation by N-benzyl cyclic guanidine under dry and wet conditions

• Yoshiaki Yoshida,
• Naoto Aoyagi and
• Takeshi Endo

Beilstein J. Org. Chem. 2018, 14, 2204–2211, doi:10.3762/bjoc.14.194

• Yoshiaki Yoshida Naoto Aoyagi Takeshi Endo Molecular Engineering Institute, Kindai University, 11-6 Kayanomori, Iizuka, Fukuoka 820-8555, Japan 10.3762/bjoc.14.194 Abstract The efficient CO2 fixation by N-benzyl cyclic guanidine 1 was achieved by bubbling dry CO2 through CH3CN at 25 °C for 2 h

• characterized in detail by elemental analysis, FTIR-ATR, solid-state NMR, TGA, and DFT calculation. These analytical results obviously revealed the formation of a zwitterion adduct and bicarbonate salt from N-benzyl cyclic guanidine and CO2. Especially, the zwitterion adduct of the monocyclic guanidine

• derivative and CO2 was isolated and characterized for the first time. Keywords: bicarbonate salt; carbon dioxide adsorption; cyclic guanidine; repeatable capture and release; zwitterion adduct; Introduction Recently, various reactions with CO2 as a cheap and green carbon reagent have been developed not

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• both catalysts gave the Michael adduct in excellent yields, high ees were obtained only when 54b was used as organocatalyst (up to 94% ee, Scheme 16). During the last decade, squaramide catalysts have become a powerful alternative to the urea/thiourea and guanidine catalysts as multiple hydrogen bond

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

• either chiral organocatalysts or chiral metal complexes. Among the organocatalysts, chiral bifunctional guanidine 50 was applied by Feng et al. in 2015 to promote the reaction of nitromethane 51 with N-Boc-isatin imines 3 (Scheme 18) [71]. The reaction performed at −30 °C using 10 mol % of this catalyst

• cinchona alkaloid-derived thiourea. Aza-Henry reaction of N-Boc-isatin imines with nitromethane catalyzed by a bifunctional guanidine. Domino addition/cyclization reaction of N-Boc-isatin imines with 1,4-dithiane-2,5-diol (53) catalyzed by a tertiary amine-squaramide. Nickel-catalyzed additions of methanol

Oligonucleotide analogues with cationic backbone linkages

• Melissa Meng and
• Christian Ducho

Beilstein J. Org. Chem. 2018, 14, 1293–1308, doi:10.3762/bjoc.14.111

• monomer 30 to the corresponding carbodiimide 31 (Scheme 3). Using long-chain alkylamine controlled pore glass (CPG) loaded with 5′-amino-5′-deoxythymidine (32) as solid phase, the reaction cycle started with the guanidine-forming coupling of 31 and 32 to give 33, followed by acidic cleavage of the MMTr

• protecting group to yield the free 5'-amine 34. Subsequent iterative coupling–deprotection cycles resulted in the formation of the guanidinium-linked oligomer 35. After basic guanidine and purine deprotection and concomitant cleavage from the solid support, final acidic deprotection furnished A5T

• -workers succeeded in the preparation of corresponding guanidine-linked RNA analogues [58][59], though this is not within the main scope of this review. Bruice et al. reported that oligonucleotide analogues containing the cationic DNG-modification bind to DNA with retention of base-pairing fidelity

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• suggested to be a general base-catalyzed formation of dianionic phosphorane (Scheme 5). The second-order term, which was important especially in guanidine and amidine buffer, was assumed to refer to binding of BH+ to the anionic phosphodiester linkage more or less concerted with the general base-catalyzed

• on buffer concentration was observed. It should be, however, noted that kinetic measurements in the most interesting guanidine and amidine buffers failed, evidently owing to partial decomposition of the buffer constituents during the prolonged incubation at 90 °C. Both cleavage and isomerization were

• observed, but only the cleavage was subject to buffer catalysis, viz. general base catalysis. In aqueous solution, second-order dependence of rate on buffer concentration has never been reported. Besides imidazole, guanidine and primary amines have received special interest as cleaving agents of RNA [69

Enzymatic synthesis of glycosides: from natural O- and N-glycosides to rare C- and S-glycosides

• Jihen Ati,
• Pierre Lafite and
• Richard Daniellou

Beilstein J. Org. Chem. 2017, 13, 1857–1865, doi:10.3762/bjoc.13.180

• retaining mechanism). In the case of O-GTs, the nucleophile is an alcohol or a phenol (carbohydrates, serine, threonine, …), whereas in N-GTs, the nature of the nitrogen-containing group is more diverse (amines, amides, guanidine or even indoles) [12]. S- and C-GTs follow a similar mechanism with the

Mechanochemical synthesis of thioureas, ureas and guanidines

• Vjekoslav Štrukil

Beilstein J. Org. Chem. 2017, 13, 1828–1849, doi:10.3762/bjoc.13.178

• ) and glibenclamide (2), which belong to the class of sulfonylureas, and guanidine-derived metformin (3) are among the top selling oral hypoglycemics globally. Proguanil (4), a biguanide derivative, is widely prescribed to treat malaria, a disease that took over 430 000 lives in 2015 [6]. In the past 20

• years, molecules with incorporated (thio)urea and guanidine subunits, due to their ability to coordinate other molecules and ions via N–H hydrogen bonding, have also been considered as organocatalysts and anion sensors [7][8][9][10][11][12]. In Scheme 2, several examples of (thio)urea- and guanidine

• (Scheme 21), which was previously characterized as a simple guanidine adduct between saccharin and DCC, arose from the DCC insertion into the 5-membered saccharin ring. Under mechanochemical conditions, solvent-free or LAG milling of saccharin with N,N'-diisopropylcarbodiimide (DIC) failed to afford the

New electroactive asymmetrical chalcones and therefrom derived 2-amino- / 2-(1H-pyrrol-1-yl)pyrimidines, containing an N-[ω-(4-methoxyphenoxy)alkyl]carbazole fragment: synthesis, optical and electrochemical properties

• Daria G. Selivanova,
• Alexei A. Gorbunov,
• Olga A. Mayorova,
• Alexander N. Vasyanin,
• Igor V. Lunegov,
• Elena V. Shklyaeva and
• Georgii G. Abashev

Beilstein J. Org. Chem. 2017, 13, 1583–1595, doi:10.3762/bjoc.13.158

• ethanolic media resulted in the formation of 1,3-diarylsubstituted prop-2-en-1-ones 6a,b [23]. Cyclization of chalcones 6a,b with guanidine sulfate followed by oxidation with hydrogen peroxide gave rise to 2-amino-4,6-disubstituted pyrimidines 7a,b [24]. 2-(1H-Pyrrol-1-yl)pyrimidines 8a,b were synthesized

Base-promoted isomerization of CF₃-containing allylic alcohols to the corresponding saturated ketones under metal-free conditions

• Yoko Hamada,
• Tomoko Kawasaki-Takasuka and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 1507–1512, doi:10.3762/bjoc.13.149

• proton shift was published by using the bicyclic guanidine-type base, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), as a catalyst. In spite of these two preceding studies, we have also succeeded in attaining a similar level of chemical yields as well as stereoselectivity to the latter process by using far

A new member of the fusaricidin family – structure elucidation and synthesis of fusaricidin E

• Marcel Reimann,
• Louis P. Sandjo,
• Luis Antelo,
• Eckhard Thines,
• Isabella Siepe and
• Till Opatz

Beilstein J. Org. Chem. 2017, 13, 1430–1438, doi:10.3762/bjoc.13.140

• bound to a guanidine β-hydroxy fatty acid as a key correlation was observed between the signal of its α-methine proton at δ 4.46 and the resonance of a carbonyl at δ 171.9. This carbonyl showed HMBC correlation with α-methylene protons at δ 2.35 and the β-methine proton at δ 3.77. Additionally

• correlations between methylene protons at δ 3.03 and the guanidine carbon at δ 157.2 were found. The length of the side chain between the β-hydroxy and the guanidine group was affirmed by the fragment ion observed in the APCI–MS–MS spectrum of the parent [M + H]+ ion at m/z 256.2. Likewise, this spectrum

• should be generated by nucleophilic addition of an allyl anion equivalent to the resulting aldehyde 5. Guanidine formation and ozonolysis with subsequent oxidation to the carboxylic acid would then furnish the protected GHPD side chain building block 3 which can then be coupled to the cyclodepsipeptide

Derivatives of the triaminoguanidinium ion, 5. Acylation of triaminoguanidines leading to symmetrical tris(acylamino)guanidines and mesoionic 1,2,4-triazolium-3-aminides

• Jan Szabo,
• Julian Greiner and
• Gerhard Maas

Beilstein J. Org. Chem. 2017, 13, 579–588, doi:10.3762/bjoc.13.57

• -thiadiazolium-2-phenylaminides. We present now the results of our studies on the acylation of triaminoguanidines with carboxylic acid chlorides. Further, we show that N,N’,N’’-tris(benzylamino)guanidine reacts with acid chlorides to afford either the threefold N-acylation product or a mesoionic 1,2,4-triazolium

• the neutral guanidine derivatives 6 as intermediates. In fact, the latter compounds are converted into betaines 7 under the same reaction conditions (method B). In terms of yields, however, the direct, one-step route (method A) turned out to be the better choice, as was found for betaines 7b–d (Table

• °C) was performed in the presence of air. Similar to structurally related guanidines (N-ureido instead of N-acyl substitution [3]) and to N,N’,N’’-tris(isopropylideneamino)guanidine [10], the 1H NMR signals of tris(acylamino)guanidines 6 are in coalescence over a wide temperature range, without

Enduracididine, a rare amino acid component of peptide antibiotics: Natural products and synthesis

• Darcy J. Atkinson,
• Briar J. Naysmith,
• Daniel P. Furkert and
• Margaret A. Brimble

Beilstein J. Org. Chem. 2016, 12, 2325–2342, doi:10.3762/bjoc.12.226

• promising antibiotic activity. This review highlights the presence of enduracididine in natural products, its biosynthesis together with a review of analogues of enduracididine. Reported synthetic approaches to the cyclic guanidine structure of enduracididine are discussed, illustrating the challenges

• (1–6) are a rare structural class of amino acids that contain a unique five-membered cyclic guanidine moiety (blue, Figure 1). L-Enduracididine (1) and D-allo-enduracididine (4) were the first identified as amino acid components of potent depsipeptide antibiotics [1][2]. Free enduracididine (1) was

• enzyme mppR is a pyruvate aldose that catalyses the dehydration/cyclisation of 20 to give cyclic guanidine 21 [52], where transamination by mppQ gives enduracididine (1). Further transformation to L-β-hydroxyenduracididine (5) is then catalysed by mppO [52][53]. Synthetic investigations Synthesis of

A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis

• Mariano Goldberg,
• Denis Sartakov,
• Jan W. Bats,
• Michael Bolte and
• Michael W. Göbel

Beilstein J. Org. Chem. 2016, 12, 1870–1876, doi:10.3762/bjoc.12.176

• of the guanidinium benzoate salt the six membered rings of 10 adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine 10 catalyzes Diels–Alder reactions of anthrones and maleimides (25–30% ee). It also promotes as a strong Brønsted

• amino acid arginine, they play an important role in biochemistry, mainly by forming ion pairs. In addition, numerous guanidine derivatives with complex cyclic structures can be found in natural products [1]. Simple guanidines such as tetramethylguanidine have been used as strong Brønsted bases in

• countless applications [2][3]. The bicylic guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD, 1, Figure 1) [4], another important Brønsted base in preparative chemistry, may also act as a powerful nucleophilic catalyst [3]. Substituted analogs of TBD [5], such as the chiral compound 2, have become popular

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• :36.5 to 67.5:32.5 er). To demonstrate the utility of the transformation, the sulfur–carbon bond of 26a was reduced using Raney nickel to access (S)-naproxen (27), an anti-inflammatory drug (Scheme 6b). Inspired by the work of Pracejus, Tan and colleagues applied their C2-symmetric guanidine catalyst 30

• thiourea catalyst 92 in high yield and modest enantioselectivity (Scheme 22) [45]. Tan and co-workers have investigated the conjugate addition–enantioselective protonation of N-arylitaconimides 95 using a C2-symmetric guanidine catalyst (Scheme 23) [24][46]. Because E- and Z-enolates can exhibit different

• furnished 96 in high yield and enantioselectivity (Scheme 23a) [24]. Thiols also added efficiently to itaconimide 95 using the same guanidine catalyst system. In general, sterically hindered tertiary thiols added with higher enantioselectivity (85.5:14.5 to 88:22 er) than aromatic thiols (72:28 to 79.5:20.5

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

• Bin Yu,
• Hui Xing,
• De-Quan Yu and
• Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

• state for the observed stereoselectivity. Pyrrole attacked the ketone from the Si face to generate (R)-3-pyrrolyl-3-hydroxyoxindoles. Very recently, Feng et al. revealed that the bifunctional guanidine (L3)/CuI catalyst can catalyze asymmetric alkynylation of isatins with terminal alkynes, affording

Muraymycin nucleoside-peptide antibiotics: uridine-derived natural products as lead structures for the development of novel antibacterial agents

• Daniel Wiegmann,
• Stefan Koppermann,
• Marius Wirth,
• Giuliana Niro,
• Kristin Leyerer and
• Christian Ducho

Beilstein J. Org. Chem. 2016, 12, 769–795, doi:10.3762/bjoc.12.77

• diastereoselectively converted with a Grignard reagent into the amine 53 as a key step of the synthesis [78]. Cbz protection followed by ozonolysis with subsequent reductive amination and hydrogenolysis led to the 1,3-diamine 54. The cyclisation to the guanidine functionality was achieved with the novel

• , 92c) in order to investigate the role of the cyclic guanidine functionality (Figure 10) [77]. These compounds were all active against MRSA and VRE with varying MIC values (Table 2). The most active analogues of this series were 92a and 92b (Figure 10, highlighted in orange) with MIC values between 1

• activity (MIC = 4–8 μg/mL) (Table 2). These results indicated that the guanidine motif of analogues 91a, 92a and 92b (MICs between 0.25 μg/mL and 4 μg/mL) is preferred, but that amino analogues 92c and 92f still show good activity (MICs between 2 μg/mL to 8 μg/mL). The different stereochemistry at the

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

• total synthesis when the guanidine group has either to be liberated by the removal of the protecting groups or used for the introduction to the corresponding ornithine residue. These results demonstrate that the copper-mediated cross-coupling reaction depends on the functional groups present in the

Asymmetric α-amination of β-keto esters using a guanidine–bisurea bifunctional organocatalyst

• Minami Odagi,
• Yoshiharu Yamamoto and
• Kazuo Nagasawa

Beilstein J. Org. Chem. 2016, 12, 198–203, doi:10.3762/bjoc.12.22

• presence of a guanidine–bisurea bifunctional organocatalyst was investigated. The α-amination products were obtained in up to 99% yield with up to 94% ee. Keywords: α-amination; bifunctional catalyst; guanidine; hydrogen-bonding catalyst; urea; Introduction Asymmetric α-amination of β-keto esters is an

• particular, catalytic asymmetric α-amination of β-keto esters has been widely explored, using both metal catalysts and organocatalysts [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. We have developed a series of guanidine–bis(thio)urea bifunctional organocatalysts, and have used them in a variety of

• asymmetric reactions [19][20]. Recently, we disclosed an α-hydroxylation of tetralone-derived β-keto esters 2 using guanidine–bisurea bifunctional organocatalyst 1a in the presence of cumene hydroperoxide (CHP) as an oxidant (Figure 1a) [21]. This reaction provides the corresponding α-hydroxylation products

Synthesis of bi- and bis-1,2,3-triazoles by copper-catalyzed Huisgen cycloaddition: A family of valuable products by click chemistry

• Zhan-Jiang Zheng,
• Ding Wang,
• Zheng Xu and
• Li-Wen Xu

Beilstein J. Org. Chem. 2015, 11, 2557–2576, doi:10.3762/bjoc.11.276

• corresponding primary guanidine or diisopropylguanidine analogs (60 and 61, Scheme 20) [40], which could be used as potential G4 DNA ligands with high selectivity over duplexed DNA. Similar to the above strategies or methods, a number of researchers have developed various dialkyne substrates with varied spacers

The marine sponge Agelas citrina as a source of the new pyrrole–imidazole alkaloids citrinamines A–D and N-methylagelongine

• Christine Cychon,
• Ellen Lichte and
• Matthias Köck

Beilstein J. Org. Chem. 2015, 11, 2029–2037, doi:10.3762/bjoc.11.220

• guanidine moiety). The relative configuration of the stereogenic centers C-9 and C-10 was identical as described for nagelamide B (8). In contrast to citrinamine C (3), a different connection of the monomeric units was found for citrinamine D (4). Furthermore, 3 and 4 have an additional methoxy group at C-9

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

• Redouane Beniazza,
• Natalia Bayo,
• Florian Molton,
• Carole Duboc,
• Stéphane Massip,
• Nathan McClenaghan,
• Dominique Lastécouères and
• Jean-Marc Vincent

Beilstein J. Org. Chem. 2015, 11, 1950–1959, doi:10.3762/bjoc.11.211

• oxygenated species [7]. They also show that aminoguanidine could be added to the reaction mixture to effectively trap the reactive byproducts derived from ascorbate oxidation. Using these protective additives (excess of ligand and guanidine) bioconjugation reactions could be conducted from a Cu(II

Thiazole formation through a modified Gewald reaction

• Carl J. Mallia,
• Lukas Englert,
• Gary C. Walter and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 875–883, doi:10.3762/bjoc.11.98

• conversion and isolated yield (58%) with tetramethylethylenediamine (TMEDA) also giving a respectable yield of 50% (Table 1, entries 1 and 10). The stronger guanidine bases 1,1,3,3-tetramethylguanidine (TMG) and 1,8-diazabicycloundec-7-ene (DBU) both gave full consumption of the nitrile starting material

DNA display of glycoconjugates to emulate oligomeric interactions of glycans

• Alexandre Novoa and
• Nicolas Winssinger

Beilstein J. Org. Chem. 2015, 11, 707–719, doi:10.3762/bjoc.11.81

• -diazobenzoyl conjugates 1 and 2 with a guanidine nucleotide (G, derivatization at the 8-position) within DNA (Scheme 1) [18]. The conjugation was performed in solution on dsDNA and was used to introduce either lactose or cellobiose moieties (with and without linker). The substitution degree was proportional to

Sequence-specific RNA cleavage by PNA conjugates of the metal-free artificial ribonuclease tris(2-aminobenzimidazole)

• Friederike Danneberg,
• Alice Ghidini,
• Plamena Dogandzhiyski,
• Elisabeth Kalden,
• Roger Strömberg and
• Michael W. Göbel

Beilstein J. Org. Chem. 2015, 11, 493–498, doi:10.3762/bjoc.11.55

• required an HgO induced cyclization step, a mercury free variant is described herein. Keywords: antisense; fluorescence correlation spectroscopy; guanidine; miRNA 20a; peptide nucleic acids; Introduction Sequence specific artificial ribonucleases are an attractive research target for several reasons. On