Chain stopper engineering for hydrogen bonded supramolecular polymers

• Thomas Pinault,
• Bruno Andrioletti and
• Laurent Bouteiller

Beilstein J. Org. Chem. 2010, 6, 869–875, doi:10.3762/bjoc.6.102

• viscosity of these solutions can be controlled by adding monofunctional compounds, which interact with the chain extremities: chain stoppers. We have synthesized new substituted ureas and thioureas and tested them as chain stoppers for a bis-urea based supramolecular polymer. In particular, the bis-thiourea

• assemblies as a hydrogen bond donor. For this purpose, we synthesized the bis-thiourea S4, from the corresponding bis-thioisocyanate, because thioureas are known to be strong hydrogen bond donors and weak hydrogen bond acceptors [34][35]. Before evaluating the chain stopper efficiency of these compounds, i.e

• ., their interaction with EHUT, their self-association was probed. Self-association of bis-thiourea Chain stoppers S2 and S3 cannot self-associate because they contain only hydrogen bond acceptors, however this is not the case for S4, and it is of interest to determine the conditions under which S4 can be

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• thiourea, urea and guanidine. In this review we summarise the advances over the last decade in the synthesis of oligosaccharide mimetics that possess amide and pseudoamide linkages, as well as studies focussing on their supramolecular and recognition properties. Keywords: carbopeptoids; glycoclusters

• , carbamate and thiourea-linked sugars The replacement of amide groups by pseudoamide (NH–C = X)–Y; X, Y = O, N, S) has been widely used in peptide chemistry to induce well-defined secondary structures. In carbohydrate chemistry, the incorporation of pseudoamide-type intersaccharide linkages has an additional

• pseudooligosaccharides having cyanamide, urea and thiourea-linkages via the Staudinger reaction have been reported [69][70]. In our group, the carbodiimide approach was used to prepare calystegine B2 analogues with the urea-linked disaccharide structure (Figure 15). These compounds, however, did not show inhibitory

Convergent syntheses of Le^X analogues

• An Wang,
• Jenifer Hendel and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2010, 6, No. 17, doi:10.3762/bjoc.6.17

• glucosamine acceptors. The disaccharide 24 was further used in the preparation of the Lex analogues 1–3. Preparation of protected Lex analogues. The chloroacetate in disaccharide 24 was removed with thiourea (C5H5N/EtOH, 70 °C) to give the acceptor disaccharide 28 (61%), which was then fucosylated with the

• (OCH2CH2); 26.44, 25.14 (OCH2CH2CH2CH2); 23.25, 20.64, 20.58, 20.48, 20.48 (CH3CO). HRESIMS Calcd for C37H52Cl2NO16 [M+H]+ 836.2663, found 836.2634. 6-Chlorohexyl 2-acetamido-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-6-O-benzyl-2-deoxy-β-D-glucopyranoside (28). Thiourea (162 mg, 2.13 mmol, 6.0

Synthesis of a new class of aminocyclitol analogues with the conduramine D-2 configuration

• Latif Kelebekli,
• Yunus Kara and
• Murat Celik

Beilstein J. Org. Chem. 2010, 6, No. 15, doi:10.3762/bjoc.6.15

• . Photooxygenation of trans-7,8-diacetoxy- and cis-7,8-dichlorobicyclo[4.2.0]octa-2,4-diene afforded the bicyclic endoperoxides. Reduction of the latter with thiourea followed by a Pd(0) catalyzed ionization/cyclization reaction gave the corresponding oxazolidinone derivatives. Oxidation of the double bond with

• cyclooctatetraene (8) by the addition of mercury(II) acetate [31]. Tetraphenylporphyrin sensitized photooxygenation of diacetoxydiene 9 with singlet oxygen gave the expected endoperoxide 10. Reduction of the peroxide bond in 10 was performed with thiourea under very mild conditions to give the cis-diol 11 in 99

• the peroxide bond in 20 with thiourea under very mild conditions gave the cis-diol 21 in 95% yield. Diol 21 in THF was treated with 2 equiv of p-toluenesulfonyl isocyanate to give the intermediate bis-carbamate 22 which was then treated as described above for 12 with the same Pd(0) catalyst to afford

Synthesis of indolo[3,2-b]carbazole-based new colorimetric receptor for anions: A unique color change for fluoride ions

• Ajit Kumar Mahapatra,
• Giridhari Hazra and
• Prithidipa Sahoo

Beilstein J. Org. Chem. 2010, 6, No. 12, doi:10.3762/bjoc.6.12

• supramolecular chemistry [1][2]. Most of the synthetic chemosensors generally involve covalent linking of an optical-signaling chromophoric fragment to a neutral anion receptor containing urea [3], thiourea [4], amide [5], phenol [6][7], or pyrrole [8] subunits, which can provide one or more H-bond donor sites

Self-association of an indole based guanidinium-carboxylate-zwitterion: formation of stable dimers in solution and the solid state

• Carolin Rether,
• Wilhelm Sicking,
• Roland Boese and
• Carsten Schmuck

Beilstein J. Org. Chem. 2010, 6, No. 3, doi:10.3762/bjoc.6.3

• -indole-2-carboxylate 3 was reduced by reaction with hydrogen in the presence of Pd/C to provide the amine 4 in a yield of 98%. For the next stept, first, thiourea was N-Boc-protected at both amino-functions following a literature procedure [20]. Thiourea was deprotonated with sodium hydride and

• afterwards reacted with di-tert-butyl dicarbonate to give the di-Boc-protected thiourea 5 in 79% yield. The di-Boc-protected thiourea 5 was then reacted with the amine 4 in the presence of Mukaiyama’s reagent [21] and triethylamine as a base, which provided 6 in a yield of 71% [22]. Deprotection of the two

• (w), 2939 (w), 1668 (s), 1250 (s), 1215(s) cm−1; HR-MS (ESI) calcd for [M+H]+: 205.0972; found 205.0979. N,N’-Di-(tert-butoxycarbonyl)thiourea (5): To a stirred solution of thiourea (570 mg, 7.50 mmol) in dry tetrahydrofuran (150 mL) sodium hydride (1.35 g, 33.80 mmol, 60% in mineral oil) was added

Synthesis and enzymatic evaluation of 2- and 4-aminothiazole- based inhibitors of neuronal nitric oxide synthase

• Graham R. Lawton,
• Haitao Ji,
• Pavel Martásek,
• Linda J. Roman and
• Richard B. Silverman

Beilstein J. Org. Chem. 2009, 5, No. 28, doi:10.3762/bjoc.5.28

• diastereomers was formed, but both were oxidized to α-bromoketone 12. Condensation with thiourea gave the 2-aminothiazole (13). Diprotection of the amine with Boc groups and deprotection of the TBS ether gave trans-alcohol 15. A Mitsunobu reaction was used to install a nitrogen atom in the form of a phthalimide

• in the 5-position could have contributed to binding to restore some of the lost potency. Conclusion 2-Aminothiazole-based nNOS inhibitor 3 was synthesized via a condensation reaction between thiourea and the appropriate α-bromoketone. However, the inhibitor was less potent than the aminopyridine lead

• equiv, THF, −78 °C; ii) 5, THF, −78 °C to rt. Assembly of 2-aminothiazole fragment. i) AllylMgBr, ether, 0 °C, 15 min.; ii) TBSCl, imidazole, DMF, 35 °C, 16 h; iii) m-CPBA, rt, 48 h; iv) LiBr, AcOH, THF, rt, 16h; v) (COCl)2, DMSO, TEA, CH2Cl2, −78 °C, 1 h; vi) thiourea, EtOH, reflux, 5 h; vii) Boc2O

Zeolite catalyzed solvent- free one-pot synthesis of dihydropyrimidin- 2(1H)-ones – A practical synthesis of monastrol

• Mukund G. Kulkarni,
• Sanjay W. Chavhan,
• Mahadev P. Shinde,
• Dnyaneshwar D. Gaikwad,
• Ajit S. Borhade,
• Attrimuni P. Dhondge,
• Yunnus B. Shaikh,
• Vijay B. Ningdale,
• Mayur P. Desai and
• Deekshaputra R. Birhade

Beilstein J. Org. Chem. 2009, 5, No. 4, doi:10.3762/bjoc.5.4

• monastrol, a potent inhibitor of kinesin Eg5. Keywords: Biginelli reaction; DHPMs; neat; MCR; zeolite; Introduction The Biginelli reaction is a well-known multicomponent reaction involving a one-pot cyclocondensation of an aldehyde, β-ketoester and urea/thiourea [1][2][3]. Multicomponent reactions (MCRs

• ethyl acetoacetate, an aromatic aldehyde and urea under strongly acidic conditions furnished the corresponding DHPMs [1]. Unfortunately this method led to low to moderate yields of the desired DHPMs, particularly when substituted aromatic or aliphatic aldehydes and thiourea were employed [14][15][16][17

• aliphatic aldehydes and thiourea were used low yields of DHPMs were realized. Results and Discussion We herein report a one-pot synthesis of DHPMs using a catalytic amount of zeolite under solvent-free conditions. In our quest to bring about the Biginelli reaction, we attempted the reaction using zeolite

Synthesis of 2-substituted 9-oxa-guanines {5-aminooxazolo[5,4-d]pyrimidin- 7(6H)-ones} and 9-oxa-2-thio- xanthines {5-mercaptooxazolo[5,4-d]pyrimidin- 7(6H)-ones}

• Subrata Mandal,
• Wen Tai Li,
• Yan Bai,
• Jon D. Robertus and
• Sean M. Kerwin

Beilstein J. Org. Chem. 2008, 4, No. 26, doi:10.3762/bjoc.4.26

• below) with ammonia in methanol fails to afford 2a. The thiourea 6b and its analog 6a, which was prepared from aminooxazole 3a in 51% yield, were also subjected to cyclization in the presence of ethanolic KOH to afford the 5-mercaptooxazolo[5,4-d]pyrimidin-7(6H)-ones 7a,b (Figure 4). Further elaboration

Perhalogenated pyrimidine scaffolds. Reactions of 5-chloro- 2,4,6-trifluoropyrimidine with nitrogen centred nucleophiles

• Emma L. Parks,
• Graham Sandford,
• John A. Christopher and
• David D. Miller

Beilstein J. Org. Chem. 2008, 4, No. 22, doi:10.3762/bjoc.4.22

• , many pyrimidine derivatives have been used for various medicinal applications (Figure 1) [1][2][3]. Synthesis of pyrimidine rings most commonly involves cyclocondensation reactions of amidine, guanidine or thiourea derivatives with either 1,3-diketone or 1,3-diester systems [4][5]. However, many of

The first organocatalytic carbonyl- ene reaction: isomerisation- free C-C bond formations catalysed by H-bonding thio- ureas

• Matthew L. Clarke,
• Charlotte E. S. Jones and
• Marcia B. France

Beilstein J. Org. Chem. 2007, 3, No. 24, doi:10.1186/1860-5397-3-24

• of highly activated enophiles can be catalysed by H-bonding thio-ureas to give tertiary alcohols in high yields without extensive isomerisation side products. An asymmetric variant of this reaction was realised using a chiral thiourea but was limited by low enantioselectivity (up to 33% e.e.) and low

• was carried out (Scheme 2 and Table 1). N,N'-di [3,5-bis(trifluoromethyl)phenyl]thiourea 5,[18], emerged as by far the most active promoter for this reaction. The catalyst was used at 20 mol % loading and compared against a control reaction with no catalyst. Products were isolated by chromatography

• , but reactions run at both -20 and 0°C using 10 and 25 mol % catalyst respectively gave good yields and only ~30% e.e (Scheme 3 and Table 2). A reaction carried out with stoichiometric amounts of chiral thiourea also gave ~30% e.e. suggesting this is the true selectivity for this reaction with this

Efficient synthesis of 5-substituted 2-aryl- 6-cyanoindolizines via nucleophilic substitution reactions

• Eugene V. Babaev,
• Natalya I. Vasilevich and
• Anna S. Ivushkina

Beilstein J. Org. Chem. 2005, 1, No. 9, doi:10.1186/1860-5397-1-9

• achieved with ethyl mercaptoacetate in ethanolic sodium hydroxide. Interestingly, 2a reacted also with thiourea in refluxing butanol giving indolizinethione 6. The product 6 seems to be the result of decomposition of unstable isothiouronium salt, and the process resembles the known conversion of 2-chloro-3