Solution phase synthesis of short oligoribonucleotides on a precipitative tetrapodal support

• Alejandro Gimenez Molina,
• Amit M. Jabgunde,
• Pasi Virta and
• Harri Lönnberg

Beilstein J. Org. Chem. 2014, 10, 2279–2285, doi:10.3762/bjoc.10.237

• been elaborated. Novel 2'-O-(2-cyanoethyl)-5'-O-(1-methoxy-1-methylethyl) protected ribonucleoside 3'-phosphoramidites have been prepared and their usefulness as building blocks in RNA synthesis on a soluble support has been demonstrated. As a proof of concept, a pentameric oligoribonucleotide, 3

Second generation silver(I)-mediated imidazole base pairs

• Susanne Hensel,
• Nicole Megger,
• Kristina Schweizer and
• Jens Müller

Beilstein J. Org. Chem. 2014, 10, 2139–2144, doi:10.3762/bjoc.10.221

• shows silver(I)-mediated methylimidazole homo base pairs involving either 2-methylimidazole (top) or 4-methylimidazole (bottom), resulting in a shielded access to the silver(I) ions from the minor and major groove, respectively. The phosphoramidites required for automated DNA solid-phase synthesis were

• ) ions from minor and major groove, respectively. Synthesis of methylimidazole-based nucleosides and their corresponding phosphoramidites required for automated solid-phase DNA synthesis. a) 1. NaH, 2. Hoffer’s chloro sugar, CH3CN, 0 °C to ambient temperature, 3 h; b) aqueous NH3 (25%), CH3OH, ambient

Synthesis of phosphoramidites of isoGNA, an isomer of glycerol nucleic acid

• Keunsoo Kim,
• Venkateshwarlu Punna,
• Phaneendrasai Karri and
• Ramanarayanan Krishnamurthy

Beilstein J. Org. Chem. 2014, 10, 2131–2138, doi:10.3762/bjoc.10.220

• ) nucleic acid with bases directly attached to its linear backbone. IsoGNA exhibits (limited) base-pairing properties which are unique compared to other known flexible nucleic acids. Herein, we report on the details of the preparation of isoGNA phosphoramidites and an alternative route for the synthesis of

• nucleic acids; isoGNA; oligonucleotides; phosphoramidites; Introduction Acyclic nucleic acids have garnered a lot of attention and are becoming an important component in nucleic acid chemistry [1][2][3]. Lately, there has been an explosion in the number of investigated candidates [4][5][6][7]. We have

• known [10][11][12][13][14][15], the published synthetic routes and efficiencies of these vary widely and primarily depend on the nature of the nucleobase. Herein, we detail our synthetic efforts and the current improvements for the synthesis of all four isoGNA nucleosides and their phosphoramidites

A new building block for DNA network formation by self-assembly and polymerase chain reaction

• Holger Bußkamp,
• Sascha Keller,
• Marta Robotta,
• Malte Drescher and
• Andreas Marx

Beilstein J. Org. Chem. 2014, 10, 1037–1046, doi:10.3762/bjoc.10.104

• oligonucleotide synthesis was performed at 0.2 µmol scale (trityl-on mode) employing the standard phosphoramidites and 6 which was diluted in a mixture containing 10% CH2Cl2 in CH3CN to a final concentration of 0.12 M. 3000 Å LCAA-CPG support was used, derivatized with the respective 3'-nucleotide of the

• way that all branches have the same sequence and terminate with a free 3'-OH group required for processing by DNA polymerases. This was achieved by the employment of standard phosphoramidites until the incorporation of the branching unit 6. Afterwards, the inverse-phosphoramidite strategy was used for

• °C, 84%. Stepwise solid-phase synthesis for branched oligonucleotides. (I): The first oligonucleotide branch is synthesized in 3'–5' direction using standard phosphoramidites. (II): Incorporation of the branching point by usage of 6. (III): Simultaneous synthesis of the two remaining oligonucleotide

Synthesis of nucleotide–amino acid conjugates designed for photo-CIDNP experiments by a phosphotriester approach

• Tatyana V. Abramova,
• Olga B. Morozova,
• Vladimir N. Silnikov and
• Alexandra V. Yurkovskaya

Beilstein J. Org. Chem. 2013, 9, 2898–2909, doi:10.3762/bjoc.9.326

• derivative [27], we used the LPS strategy in combination with the phosphotriester approach for the oligonucleotide synthesis to obtain target conjugates 1–8. The phosphoramidite condensation in LPS usually leads to the lower yields in these reactions due to insufficient stability of active phosphoramidites

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• enantioselective versions of these two cycloadditions was actively pursued by several groups. The electronic similarity between phosphites and phosphoramidites suggested that chiral gold complexes of these highly modular monodentate ligands [65] could be good candidates to promote enantioselective variants of the

• π-acceptor ligands, such as phosphites or phosphoramidites favor the formation of the [4 + 2] adduct of type 15, DFT calculations indicated that the activation barriers for the ring-contraction process leading to these six-membered systems, and the 1,2-H shifts that retain that seven-membered ring

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• derived from DTBM-Segphos or, as recently demonstrated, with gold complexes derived from chiral phosphoramidites [88][89]. Also in 2007, L. Zhang and co-workers reported another formal intramolecular cycloaddition between alkenes and allenes, in particular a (3 + 2) cycloaddition between allenyl MOM

• shift) in the initially formed cycloheptenyl–gold carbene intermediate XXX (Scheme 28). Thus, the ligand at gold determines the fate of this carbene and hence the formation of the (4 + 3) (50) or (4 + 2) (53) cycloadducts. Based on the electronic similarity between phosphites and phosphoramidites, we

• also studied enantioselective variants of this cycloaddition using gold complexes derived from this highly versatile type of chiral ligand. We found that it was possible to obtain excellent enantioselectivities with gold complexes derived from bulky phosphoramidites with anthracenyl substituents at 3

Chiral gold(I) vs chiral silver complexes as catalysts for the enantioselective synthesis of the second generation GSK-hepatitis C virus inhibitor

• María Martín-Rodríguez,
• Carmen Nájera,
• José M. Sansano,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2011, 7, 988–996, doi:10.3762/bjoc.7.111

• gold(I) catalysts in this reaction was established by working with chiral phosphoramidites or with chiral BINAP. The best reaction conditions were used for the total synthesis of the hepatitis C virus inhibitor by a four step procedure affording this product in 99% ee and in 63% overall yield. The

• , generated from chiral phosphoramidites or BINAP as ligands, in order to prepare antiviral agent 2a. Results and Discussion The efficiency of the chiral phosphoramidite/silver(I) salts [25][26][29] and BINAP/Ag(I) salts [30][31] in 1,3-DC, following the general pattern shown in Scheme 1, has been

• -hexane:iPrOH 85/15, 0.1 mL/min, λ = 250 nm), tR,maj = 12.5 min, tR,min = 15.5 min. More active GSK HCV inhibitors. Chiral phosphoramidites tested in this study. Gibbs activation energy and main geometrical features of the computed ylide and transition structures (TS) corresponding to the 1,3-DC of the Au(I

Synthetic incorporation of Nile Blue into DNA using 2′-deoxyriboside substitutes: Representative comparison of (R)- and (S)-aminopropanediol as an acyclic linker

• Daniel Lachmann,
• Sina Berndl,
• Otto S. Wolfbeis and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2010, 6, No. 13, doi:10.3762/bjoc.6.13

• present in biopolymers and react selectively with each other in aqueous solutions. The “click” ligation can avoid the time-consuming synthesis of phosphoramidites as DNA building blocks which is especially important for brightly emitting fluorophores that are not compatible with the acidic, oxidative or

An exceptional P-H phosphonite: Biphenyl- 2,2'-bisfenchylchlorophosphite and derived ligands (BIFOPs) in enantioselective copper- catalyzed 1,4-additions

• T. Kop-Weiershausen,
• J. Lex,
• J.-M. Neudörfl and
• B. Goldfuss

Beilstein J. Org. Chem. 2005, 1, No. 6, doi:10.1186/1860-5397-1-6

• -catalyzed 1,4-additions of ZnEt2 to 2-cyclohexen-1-one, this P-H phosphonite (yielding 65% ee) exceeds even the corresponding phosphite and phosphoramidite. Keywords: phosphorus ligands; chirality; biaryls; asymmetric conjugate additions; phosphoramidites; phosphites; phosphonites; X-ray analyses

• ][13][14][15][16][17][18] Such asymmetric conjugate additions of diethylzinc to enones are often highly enantioselective, especially with phosphoramidites (amidophosphites) and phosphites. [2][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] These chiral

• ligands (L*) exhibit large steric demands and good metal to ligand back bonding abilities. Such ligands generate active R-CuI-L* catalysts and support the rate determining reductive elimination in the catalytic cycle (Scheme 1). [42][43][44][45][46][47] Common basis for diol-based phosphoramidites and

Mixtures of monodentate P-ligands as a means to control the diastereoselectivity in Rh-catalyzed hydrogenation of chiral alkenes

• Manfred T. Reetz and
• Hongchao Guo

Beilstein J. Org. Chem. 2005, 1, No. 3, doi:10.1186/1860-5397-1-3

• involves the use of additives, catalyst poisons or catalyst activators.[10][11] Based on the discovery that monodentate BINOL-derived phosphites,[12][13] phosphonites[14][15] and phosphoramidites [16][17][18] are excellent ligands in enantioselective Rh-catalyzed olefin-hydrogenation, we proposed in 2003 a

• generalized.[21][22][23] Following our initial discovery,[19] Feringa and deVries reported related results using BINOL-derived phosphoramidites.[24] In all of these studies it was found that the mixture, and consequently the hetero-combination MLaLb, is more active and more enantioselective than either of the