bluuebunny/crossref_metadata_2025_split huggingface dataset:
Syntheses of Bile Pigments. Part 17. Synthesis of a non‐racemizable urobilin derivative
Authors: Floch Lubomir , Nydegger Fredy , Gossauer Albert , Kratky Christoph 
Published: December 2004

AbstractThe optically active urobilin model compound 7 was synthesized, in which Me groups instead of H‐atoms are bound to the asymmetric centers, thus preventing loss of chirality by tautomerization. The key intermediate of the eleven‐step synthesis of 7 is the 1,4,5,10‐tetrahydro‐10‐hydroxy‐1‐oxo‐11H‐dipyrrin‐9‐carboxylate rac‐2, which could be resolved into enantiomers by fractional crystallization of the corresponding methyl N‐[1‐(naphth‐1‐yl)ethyl]carbamates 3 and 4. The absolute configuration of enantiomerically pure (−)‐2 was determined by X‐ray diffraction analysis of its camphor‐10‐sulfonate 5. As the CD spectrum of the urobilin analogue 7 obtained from (−)‐(R)‐2 displays a positive Cotton effect, the present results prove, in connection with previous work, that substitution of Me groups for the H‐atoms bound to the asymmetric centers of a chiral urobilin chromophore do not influence the relationship between absolute configuration of the latter and its helicity.
4,4‐Disubstituierte Imidazol‐Derivate aus der Umsetzung von 3‐Amino‐2H‐azirinen mit Salicylamid
Authors: Magirius Florian , Linden Anthony , Heimgartner Heinz 
Published: December 2004

4,4‐Disubstituted Imidazole Derivatives from the Reaction of 3‐Amino‐2H‐azirines with SalicylamideReaction of 3‐amino‐2H‐azirines 1a–c with salicylamide (7) in MeCN leads to imidazoles 10 and 11 in different rates, depending on the conditions. In the case of 1a and 1b, 11a and 11b, respectively, have been obtained as the main product at 50°; in reactions at 80°, 10a and 10b are the favored products (Tables 1 and 2). 2,2‐Dimethyl‐3‐(N‐methyl‐N‐phenylamino)‐2H‐azirine (1c) reacts with 7 in MeCN mainly to 2‐(2‐hydroxyphenyl)‐5,5‐dimethyl‐3,5‐dihydroimidazol‐4‐one (10a); in boiling toluene, 11c is formed with low preference (Table 3). The structure of the products has been established by spectroscopic means, and in the case of 10b and 11c, by X‐ray crystallography. Two different reaction mechanisms for the formation of the products are discussed (Scheme 2).
Novel Juvenoids of the 2‐(4‐hydroxybenzyl)cyclohexan‐1‐one Series
Authors: Wimmer Zdenêk , S̆aman David , Francke Wittko 
Published: December 2004

AbstractA series of insect juvenile hormone analogs (juvenoids) was synthesized and studied. The basic skeleton of these juvenoids contains three rings and a short aliphatic subunit and bears two or three chiral centers (depending on the appropriate structure; see 6–9). The chiral center located in the 1,2‐diphenoxypropane subunit has the configuration (RS), (R) (a series), or (S) (b series). The juvenoids were subjected to a biological screening, the preliminary results of which are briefly described.
Facile Synthesis of 2′‐Deoxyisoguanosine and Related 2′,3′‐Dideoxyribonucleosides
Authors: Seela Frank , Gabler Bert 
Published: December 2004

AbstractThe 2′‐deoxyisoguanosine (1) was synthesized by a two‐step procedure from 2′‐deoxyguanosine (5). Amination of silylated 2′‐deoxyguanosine yielded 2‐amino‐2′‐deoxyadenosine (6) which was subjected to selective deamination of the 2‐NH2 group resulting in compound 1. Also 2′,3′‐dideoxyisoguanosine (2) was prepared employing the photo‐substitution of the 2‐substituent of 2‐chloro‐2′,3′‐dideoxyadenosine (4). The latter was synthesized by Barton deoxygenation from 2‐chloro‐2′‐deoxyadenosine (3) or via glycosylation of 2,6‐dichloropurine (12) with the lactol 13. Compound 1 was less stable at the N‐glycosylic bond than 2′‐deoxyguanosine (5). The dideoxynucleoside 2 was deaminated by adenosine deaminase affording 2′,3′‐dideoxyxanthosine (17).
Oligosaccharides Related to Tumor‐Associate Antigens. Part 2. Conformational analysis of the trisaccharide α‐L‐Fucp‐(1→2)‐β‐D‐Galp‐(1→3)‐β‐D‐GalpNAc, epitope structure recognized by the MBr1 antibody
Authors: Toma Lucio , Ciuffreda Pierangela , Colombo Diego , Ronchetti Fiamma , Lay Luigi , Panza Luigi 
Published: December 2004

AbstractThe conformational space of the trisaccharide α‐L‐Fuc‐(1→2)‐β‐ D‐Gal‐(1→3)‐β ‐D‐GalNAc‐1‐OPr (2) and of its component disaccharide moieties α ‐L‐Fuc‐(1→2)‐β ‐D‐Gal‐1‐OMe (3) and β ‐D‐Gal‐(1→3)‐β‐ D‐GalNAc‐1‐OPr (4) was investigated with the aid of molecular‐mechanics energy minimizations and molecular‐dynamics simulations. These calculations suggested the occurrence of two conformations for each compound characterized by different ϕ and Ψ glycosidic angles. However, 1H‐NMR investigation of D2O solutions of 2–4 indicated a sure preference for one of the two conformers with a contribution of the other one ranging from negligible to low.
Large Water‐Soluble Cyclophanes with Convergent Intracavity Functionality
Authors: Diederich François , Carcanague Daniel R. 
Published: December 2004

AbstractNew tricyclic spacers, readily available through fourfold Mannich reaction of substituted dibenzyl ketones, were introduced into a series of ten H2O‐soluble cyclophanes with spacious preorganized cavity binding sites. These spacers provide H2O‐solubility with amine or crown‐ether functionality remote from the cyclophane cavity while directing functional groups such as keto or OH groups in a precise geometrical array inside the cavity. The cyclophanes were designed to include organic substrates via a combination of apolar and specific polar functional group interactions. The X‐ray crystal‐structure analysis of the tritopic receptor 18 with one potential neutral‐molecule and two cation‐binding sites showed a large rectangular open cavity with dimensions of roughly 9 × 14 Å and a spacing of 9.7 Å between the O‐atoms of two convergent CO groups. Despite the binding‐site preorganization, cyclophanes incorporating two of the new spacers did not show any substrate binding in aqueous solutions. The failure of these systems to function as receptors is mainly due to steric hindrance to important cyclophane aromatic ring‐guest interactions. Also, the favorable solvation of the intracavity functionality may prevent the formation of complexes. Hybrid receptors constructed from the novel spacers and diphenylmethane units were found to bind flat aromatic substrates as well as bulky [4.2]paracyclophanes. The observed large differences in stability (ΔΔG°> 2 kcal mol−1) of the complexes formed by three structurally closely related hybrid receptors with convergent CO, OH or CH2 groups and 6‐hydroxynaphthalene‐2‐carbonitrile as guest can be explained by a strong solvation effect of the convergent functional groups on apolar inclusion complexation.
Radical Anions of Polyalkylazulenes: An ESR and ENDOR Study
Authors: Bachmann Rainer , Burda Clemens , Gerson Fabian , Scholz Markus , Hansen Hans‐Jürgen 
Published: December 2004

AbstractProton‐hyperfine data are reported for the radical anions generated from azulene (1) and its alkyl derivatives 2–11 in 1,2‐dimethoxyethane both ‘chemically’ with K and electrolytically. The alkyl derivatives are 1,3‐dimethyl‐ (2), 5,7‐dimethyl‐ (3), 1,3,5,7‐tetramethyl‐ (4), 2‐methyl‐ (5), 4,6,8‐trimethyl‐ (6), 2,4,6,8‐tetramethyl‐(7), 1,3,4,6,8‐pentamethyl‐ (8), 1,3,4,8‐tetramethyl‐6‐propyl‐ (9), 6‐(tert‐butyl)‐1,3,4,8‐tetramethyl‐ (10), and 1,2,3,4,6,8‐hexamethylazulene (11). Alkyl substituents at the odd‐numbered centers μ = 1, 3, 5, and 7 partly shift the π‐spin population from the seven‐ to the five‐membered ring, whereas those at the even‐numbered centers μ = 4, 6, and 8 exert an opposite effect on the π‐spin distribution.
An Efficient Total Synthesis of Carbocyclic 2′‐Deoxyribonucleosides
Authors: Lang Hanspeter , Moser Heinz E. 
Published: December 2004

AbstractThe present work describes a new and efficient method for the preparation of either racemic or enantiomerically pure carbocyclic 2′‐deoxyribonucleosides 1. Key steps are the efficient assembly of the racemic carbocyclic 2′‐deoxyribose core (±)‐12, its enzymatic resolution, and a new approach to covalently link the purine and pyrimidine bases with the cyclopentane moiety via the cyclic sulfate (+)‐19. This total synthesis of enantiomerically pure and racemic carbocyclic 2′‐deoxyribonucleosides 1 represents one of the most efficient approaches reported to date. Starting from cyclopentadiene, the four carbocycles corresponding to the naturally occurring 2′‐deoxyribonucleosides could be prepared in 12 steps and 9–12% overall yield. For the corresponding racemic compounds, 10 steps were used with overall yields between 22 and 30%.
Preparation and Structural Analysis of Several New α,α,α′,α′‐Tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (TADDOL's) and TADDOL analogs, their evaluation as titanium ligands in the enantioselective addition of methyltitanium and diethylzinc reagents to benzaldehyde, and refinement of the mechanistic hypothesis
Authors: Ito Yoshio N. , Ariza Xavier , Beck Albert K. , Boháč Andrej , Ganter Camille , Gawley Robert E. , Kühnle Florian N. M. , Tuleja Juraj , Wang Yan Ming , Seebach Dieter 
Published: December 2004

AbstractPreparation and screening of twenty new ligands, all analogs of α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL), for the Ti‐catalyzed asymmetric addition of methyltri(isopropoxy)titanium and diethylzinc to benzaldehyde are described. These ligands have the dioxolane ring of the TADDOL's replaced by cyclobutane, cyclopentane, cyclohexene, cyclohexane, bicyclo[2.2.1]heptene and ‐heptane and bicyclo[2.2.2]octene and ‐octane moieties; several have H‐atoms or alkyl groups in place of the aryl groups, and nine of them have C2 symmetry. X‐Ray crystallography and molecular mechanics are used to analyze the structure of the ligands, and two structural features appear to correlate with selectivity: (i) the torsion angle for the chelating O‐atom and the ortho‐C‐atom of the axial Ph group (a small, ca. 19°, angle is optimum, Fig.8) and (ii) the “degree of perpendicularity” of the axial Ph group (Fig. 9). Competition experiments indicate that TADDOL 1a catalyzes both the methyltitanium and diethylzinc additions ≥ 50 times faster than the related dioxolane analogs 12a, 12c, and 12e (Scheme 7), indicating that both axial and equatorial aryl groups (see Footnote 6) are necessary for ligand‐accelerated catalysis of these reactions. A refined mechanistic hypothesis is presented (Fig. 10) to explain the selectivities observed for these new ligands. Our analysis suggests that a combination of structural features appear necessary for good catalytic efficiency and high selectivity. These features, especially the rather subtle conformational effects, appear to be optimized (among the ligands tested) in the TADDOL's.
Duplex Stabilization of DNA: Oligonucleotides containing 7‐substituted 7‐deazaadenines
Authors: Seela Frank , Thomas Horst 
Published: December 2004

AbstractThe oligonucleotide building blocks 4b–d derived from 7‐bromo‐, 7‐chloro‐, and 7‐methyl‐substituted 7‐deaza‐2′‐deoxyadenosines 3b–d were prepared. They were employed in the solid‐phase synthesis of the oligonucleotides 7–25. The dA residues of the homomer d(A12), the alternating d[(A‐T)6], and the palindromic d(G‐T‐A‐G‐A‐A‐T‐T‐C‐T‐A‐C) were replaced by 3b–d as well as by the parent 7‐deaza‐2′‐deoxyadenosine (3a). The melting profiles and CD spectra of oligonucleotide duplexes, showing this major groove modification, were measured, and the Tm values as well as the thermodynamic data were determined. It was found that small substituents such as Br, Cl, or Me introduced in the 7‐position of a 7‐deazaadenine residue increase the duplex stability compared to oligonucleotides containing adenine.
Synthesis of (+)‐Multifidene
Authors: Hemamalini Sundarababu , Scheffold Rolf 
Published: December 2004

Abstract(+)‐Multifidence ((+)‐1) has been synthesized starting from (R)‐(cyclopent‐2‐enyl)methanol ((+)‐2) via its chloroformate 4, Co‐mediated radical cyclization reaction to the lactone (+)‐6, and introduction of the olefinic side chains.
3‐(Prop‐2‐enylidene)azetidin‐2‐one Derivatives: Synthesis, structure, and formation of 3‐spiro‐β‐lactams via Diels–Alder reactions
Authors: Ruf Sabine , Otto Hans‐Hartwig 
Published: December 2004

AbstractReactions of 3‐silylated β‐lactams (1) with α,β‐unsaturated ketones give the propylidene‐β‐lactams 3 and the cycloalkenylidene derivatives 5. Structure and configuration are elucidated by spectroscopic methods, and the reactivity is discussed. While compounds 5 do not react with dienophiles, the (Z)‐isomers of 3 are the favored substrates for Diels‐Alder reactions yielding the spiro compounds 6 and 7.
Metal Complexes with Macrocyclic Ligands. Part XXXIX. Mono‐ and binuclear copper(II) complexes of a bridging bis[1, 4, 7‐triazacyclononane]
Authors: Behle Lutz , Neuburger Markus , Zehnder Margaretha , Kaden Thomas A. 
Published: December 2004

AbstractThe new bis‐macrocycle 1, 1′‐[(1H‐pyrazol‐3], 5‐diyl)bis(methylene)bis[1, 4, 7‐triazacyclononane] (1) was synthesized and its complexation with Cu2+ studied. Potentiometric and spectrophotometric titrations indicate that, in addition to the mononuclear species [Cu(LH2)]4+, [Cu(LH)]3+, [CuL]2+, and [Cu(LH−1)]+, binuclear complexes such as [Cu2L]4+, [Cu2(LH−1)]3+, and [Cu2(LH‐2)]2+ are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu2(LH−1)]3+ specifically reacts with an azide ion to give a ternary complex [Cu2(LH−1)(N3)]2+, the stability and structure of which were determined spectrophotometrically and by X‐ray diffraction, respectively. The two Cu2+ ions are in a square‐pyramidal coordination geometry. The axial ligand is one of the N‐atoms of the 1, 4, 7‐triazacyclononane ring, whereas at the base of the square pyramid, one finds the other two N‐atoms of the macrocycle, one N‐atom of the pyrazolide and one of the azide, both of which are bridging the two metal centres. In [Cu2(LH−1)(N3)]2+, a strong antiferromagnetic coupling is present, thus resulting in a species with a low magnetic moment of 1.36 B.M. at room temperature.
Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate in Supercritical Carbon Dioxide
Authors: Hunziker Richard , Sperandio David , Hansen Hans‐Jürgen 
Published: December 2004

Abstract1,3,4,6,8‐Pentamethylazulene (9), when heated at 100° in supercritical CO2 at 150 bar in the presence of 4 equiv. of dimethyl acetylenedicarboxylate (ADM), led to the formation of 16% of a 1:1 mixture of dimethyl 3,5,6,8,10‐pentamethylheptalene‐1,2‐dicarboxylate 12a) and its double‐bond‐shifted isomer 12b as well as 4% of the corresponding azulene‐1,2‐dicarboxylate 13 (Scheme 4). The formation of the [1 + 2] adduct 11 (cf. Scheme 2) was not observed. Similarly, benz[a]azulene (25) yielded in supercritical CO2 (150°/170 bar) in the presence of 4 equiv. of ADM dimethyl benzo[d]heptalene‐6,7‐dicarboxylate (29; 30%) and dimethyl benzo[a]cyclopent[cd]azulene‐1,2‐dicarboxylate (28; 22%; Scheme 5). The reaction of 5,9‐diphenylbenz[a]azulene (26) and ADM in supercritical CO2 (100°/150 bar) gave the corresponding benzo[d]heptalene‐6,7‐dicarboxylate 31 (22%) and dimethyl 5,9‐diphenyl‐4b,10‐etheno‐10H‐benz[a]azulene‐11,12‐dicarboxylate(30; 25%; Scheme 5).
Substituent Reactivity and Tautomerism of Isoguanosine and Related Nucleosides
Authors: Seela Frank , Wei Changfu , Kazimierczuk Zygmunt 
Published: December 2004

AbstractThe substituent reactivity and tautomerism of isoguanine nucleosides is studied. Benzoylation or tosylation of isoguanine nucleosides (pyridine, room temperature) yields the 2‐benzoyl derivatives 7c, 11, and 12 or the 2‐tosyl compounds 13 and 14. The isobutyrylation of the 6‐amino group which did not occur under these conditions was induced in the presence of Me3SiCl. In the absence of Me3SiCl, the reactivity of isoguanine substituents decreases in the order from 2‐oxo → 5′‐OH → 3′‐OH → 6‐NH2. From isoguanine nucleosides, the N1‐(2b), N3‐(17), N6‐(15a,b), and 2‐O‐alkylated (3b) derivatives were prepared. Their pKa values were determined and the UV and 13C‐NMR spectra compared with regard to the alkylation position. Also the tautomeric forms of isoguanine nucleosides were determined UV‐spectrophotometrically in aqueous and nonaqueous solution. Isoguanosine (1a), its 2′‐deoxy analogue 1b as well as the N6‐methyl‐ and 8‐substituted derivatives form lactam tautomers in aqueous solution, whereas the lactim form is present in dioxane.
Synthesis, Characterization, and Structural Properties of Luminescent Lanthanide Complexes
Authors: Paul‐Roth Christine O. , Lehn Jean‐Marie , Guilhem Jean , Pascard Claudine 
Published: December 2004

AbstractThe crystal structure of the macrobicyclic europium(III) complex [Eu3+ ⊂1]3Cl− incorporating a N,N′ ‐ dioxide unit has been determined. It confirms the cryptate nature of this species, the included cation being bound to six N‐ and two O‐sites. The efficient shielding of the bound Eu3+ ion may be related to the efficient luminescence of this cryptate and points to the role played by the N‐oxide sites. To further explore the effect of such binding groups, the two macrocyclic ligands 4 and 5 bearing two bipyridine N,N′ ‐dioxide lateral arms have been synthesized and their EuIII and TbIII complexes prepared.
Reactions of Diazo Compounds with Imines. Preliminary communication
Authors: Moran Mary , Bernardinelli Gérald , Müller Paul 
Published: December 2004

AbstractThe [Rh2(OAc)4]‐catalyzed addition of methyl diazoacetate to N‐benzylideneaniline (1a) afforded the imine cis‐2 in 35% yield. Under catalysis by chiral RhII catalysts, however, only racemic 1a was produced, and the yield was low. In the presence of dimethyl maleate, aziridine formation was suppressed, and an intermediate ylide 6 was trapped as cycloadduct 7. No aziridines were obtained, however, from 1b, 1c, and 3. The iminium salt 8 reacted with (trimethylsilyl)diazomethane in the absence of [Rh2(OAc)4] via dipolar cycloaddition followed by extrusion of N2 to 10.
10‐Alkyl‐10‐demethylcolchicines
Authors: Kouroupis Pavlos , Kessler Jacqueline , Hansen Hans‐Jürgen 
Published: December 2004

AbstractIt is shown that colchicine (4) can regiospecifically be transetherified at C(10) by heating in ROH in the presence of (RO)4M (M = Ti, Zr; cf. Scheme 2). (PrO)4Zr in PrOH gives better yields than (PrO)4Ti in PrOH, and also in the catalytic variant of the conversion is (PrO)4Zr more effective than (PrO)4Ti.
Theoretical Calculations of β‐Lactam Antibiotics. Part VII. Influence of the solvent on the basic hydrolysis of the β‐lactam ring
Authors: Frau Juan , Donoso Josefa , Muñoz Francisco , Gracia‐Blanco Francisco 
Published: December 2004

AbstractWe used semi‐empirical and ab initio calculations to investigate the nucleophilic attack of the OH− ion on the β‐lactam carbonyl group. Both allowed us to detect reaction intermediates pertaining to proton‐transfer reactions rather than the studied reaction. We also used the PM3 semi‐empirical method to investigate the influence of the solvent on the process. The AMSOL method predicts the occurrence of a potential barrier of 20.7 kcal/mol due to the desolvation of the OH− ion in approaching the β‐lactam carbonyl group. Using the supermolecular approach and a H2O solvation sphere of 20 molecules around the solute, the potential barrier is lowered to 17.5 kcal/mol, which is very close to the experimental value (16.7 kcal/mol).
New Addition Reactions of Organometal Compounds with 4,4‐Dimethyl‐1,3‐thiazole‐5(4H)‐thiones
Authors: Shi Junxing , Heimgartner Heinz 
Published: December 2004

AbstractAddition reactions of organometallic reagents with 4,4‐disubstituted 1,3‐thiazole‐5(4H)‐thiones were studied. Whereas the reactions with alkyllithium and alkyl Grignard reagents occurred in the thiophilic manner, the carbophilic addition was observed with allyllithium and allyl Grignard reagents. A radical reaction mechanism is proposed for rationalizing these observations (Scheme 5). A radical cyclization of the prepared 5‐allyl‐4,5‐dihydro‐1,3‐thiazole‐5‐thiol derivatives yielded 1,6‐dithia‐3‐azaspiro[4.4]non‐2‐enes (Table 4).
Synthesis of Highly Fluorinated Di‐O‐alk(en)yl‐glycerophospholipids and Evaluation of Their Biological Tolerance
Authors: Ravily Véronique , Gaentzler Sylvie , Santaella Catherine , Vierling Pierre 
Published: December 2004

AbstractThe syntheses of various fluorocarbon/fluorocarbon and fluorocarbon/hydrocarbon rac‐1,2‐ and 1,3‐di‐O‐alk(en)ylglycerophosphocholines and rac‐1,2‐di‐O‐alkylglycerophosphoethanolamines (see Fig.2), which may be used as components for drug‐carrier and delivery systems, are described together with some results concerning their biological tolerance. They were obtained by phosphorylation of perfluoroalkylated rac‐di‐O‐alk(en)ylgly‐cerols using POCl3, then condensation with choline tosylate or N‐Boc‐ethanolamine (2‐[(tert‐butoxy)carbonyl‐amino]ethanol) followed by Boc‐deportection (Schemes 6–8). The fluorcarbon/fluorocarbon 1,2‐di‐O‐alkylgly‐cerols were prepared by O‐alkylation of rac‐1‐O‐benzylglycerol using perfluoroalkylated mesylates, then hydrogenolysis for benzyl deprotection (Scheme 1). The two different hydrophobic chains in the mixed fluorocarbon/fluorocarbon and fluorocarbon/hydrocarbon 1,2‐di‐O‐alk(en)ylglycerols were introduced starting from 1,2‐O‐iso‐propylidene‐ then O‐trityl‐protected glycerols or from 1,3‐O‐benzylidene‐glycerol (Schemes 3 and 4). The perfluoroalkylated O‐alkenylglycerols were obtained by O‐alkylation of a glycerol derivative using an ω‐unsaturated alkenyl reagent, the perfluoroalkyl segment being connected onto the double bond in a subsequent step (Schemes 1) and 3. The perfluoroalkylated symmetrical and mixed 1,3‐di‐O‐alkylglycerols were synthesized by displacement of the Cl‐atom in epichlorohydrin by perfluoroalkylated alcohols, then catalytic (SnCl4) opening of the oxirane ring of the resulting alkyl glycidyl ethers in neat alcohols (Scheme 5). When injected intravenously into mice, acute maximum tolerated doses higher than 1500 and 2000 mg/kg body weight were observed for the fluorinated glycerophosphocholines, indicating a very promising in vivo tolerance.
Synthesis of (all‐E,2R,2′R)‐oscillol
Authors: Traber Bruno , Pfander Hanspeter 
Published: December 2004

AbstractOptically active (all‐E,2R,2′R)‐oscillol (= (all‐E,2R,2′R)‐3,4,3′,4′‐tetradehydro‐1,2,1′,2′‐tetrahydro‐ψ,ψ‐carotene‐1,2,1′,2′‐tetrol; 1) was synthesized according to the C10 + C20 + C10 = C40 strategy, applying the Wittig reaction to couple the synthons 4 and 6. The chiral centre was introduced by a Sharpless dihydroxylation of 3‐methylbut‐2‐enyl 4‐nitrobenzoate (8).
Nucleotides. Part XLVII. Synthesis of 3′‐Deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenylyl‐(2′–5′)‐3′‐O‐(2‐hydroxyethyl)adenosine and 3′‐Deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenylyl‐(2′–5′)‐3′‐O‐{2‐[(cholest‐5‐en‐3β‐yloxy)carbonyloxy]ethyl}adenosine: A New Type of (2′–5′)Adenylate Trimer Conjugate
Authors: Hörndler Cornelia , Pfleiderer Wolfgang 
Published: December 2004

AbstractA suitably protected adenosine derivative bearing an acetyl‐protected 2‐hydroxyethyl moiety in 3′‐O‐position was attached to the 2′‐terminus of a cordycepin (3′‐deoxyadenosine) dimer. Coupling was performed by phosphoramidite chemistry using two alternative approaches – condensation of 5′‐phosphoramidite 16 with 2′‐OH cordycepin dimer 18 and condensation of dimeric cordycepin phosphoramidite 19 with 5′‐OH adenosine derivative 15 – of which the latter synthesis worked best (→20). After cleavage of the acetyl protecting group (→21), cholesteryl carbonate was introduced into the OH function of the spacer (→24). Final deblocking of trimer 24 with, or trimer 21 without the cholesterol moiety afforded the modified cordycepin conjugates 25 and 23, respectively.