bluuebunny/crossref_metadata_2025_split huggingface dataset:
Palladium‐Catalyzed Syntheses of Polyethynyl‐Substituted 2,2′‐Bithiophenes
Authors: Dahlmann Uwe , Neidlein Richard 
Published: December 2004

AbstractThe syntheses of polyethynyl‐substituted 2,2′‐bithiophenes 2 and related 5,5′‐dicarbaldehyde derivatives 1 are described. The treatment of easily available polybrominated 2,2′‐bithiophenes 3 and 2,2′‐bithiophene‐5,5′‐dicarbaldehydes 4 with phenyl or (trimethylsilyl)acetylene in the presence of PdII and CuI in (i‐Pr)2NH yields substituted polyethynyl‐2,2′‐bithiophene compounds. The Me3Si protecting groups can be removed by protodesilylation under basic conditions to give the corresponding terminal ethynyl groups. These polyethynyl‐bithiophenes could be interesting precursors for the synthesis of macrocycles with interesting properties.
Synthesis and X‐Ray Structure of Bis{S‐(1‐lithio‐3,3‐diphenylprop‐2‐enyl)‐N‐methyl‐S‐phenylsulfoximine– Tetrahydrofuran (1/2)} Complemented by Model ab initio Calculations of α‐Lithiosulfoximines
Authors: Müller Jürgen F. K. , Spingler Bernhard , Zehnder Margareta , Batra Rohit 
Published: December 2004

AbstractThe gas‐phase structure of N,S,S‐trimethylsulfoximine 1 and of its monolithiated isomers 2–4 was calculated by ab initio methods. It was found that a LiCSN four‐membered chelate 2 is the most stable isomer. The second minimum 4 shows NLiO complexation and is only slightly higher in energy. Li‐Contacts with the C(α) atom and the sulfoximine O‐atom in 3 are energetically disfavored by 6.1 kcal/mol. The two transition states 5 and 6 suggest an interconversion mechanism of 2 to 3 with 4 as an intermediate. A comparison of 4 with the crystal structure of the THF solvate 7, which was prepared by the addition of BuLi to (±)‐S‐(3,3‐diphenylprop‐2‐enyl)‐N‐methyl‐S‐phenylsulfoximine (8) at low temperature in THF, demonstrates that the coordination geometry in the solid state is in good agreement with the calculated structure. The (1‐lithioallyl)sulfoximine 7 crystallized as a centrosymmetric dimeric aggregate featuring an eight‐membered ring with the atomic sequence (LiNSO)2. The O‐atoms of two THF molecules and the sulfoximine O‐ and N‐atoms are coordinated to the Li‐atom in a tetrahedral orientation. After metallation, a significant shortening of the SC(α) bond is observed. Remarkably, only one of the two possible diastereoisomeric enantiomer pairs is found in the solid state.
Isomerisierung von (all‐E)‐Cycloviolaxanthin Herstellung und Charakterisierung von (9Z)‐und (13Z)‐Cycloviolaxanthin
Authors: Molnár Péter , Deli József , Matus Zoltán , Tóth Gyula , Steck Andrea 
Published: December 2004

Isomerization of (all‐E)‐Cycloviolaxanthin. Preparation and Characterization of (9Z)‐ and (13Z)‐CycloviolaxanthinFrom (all‐E)‐cycloviolaxanthin (ex Capsicum annuum), (9Z)‐ and (13Z)‐cycloviolaxanthin were prepared in a highly pure state. The configuration of both isomers was determined by means of UV/VIS, NMR, and CD spectroscopy.
Synthesis of Glycosylrifamycins, a new type of semisynthetic rifamycins
Authors: Bartolucci Cecilia , Cellai Luciano , Martuccio Concetta , Rossi Andrea , Segre Anna Laura , Savu Simona Rizea , Silvestro Luigi 
Published: December 2004

AbstractGlycosylrifamycins, a new type of semisynthetic rifamycin derivatives, can be easily obtained by reaction of 3‐(2‐aminoethylthio)rifamycin SV (2) with a glycosyl compound carrying a coupling group, such as isothicyanate or carboxy. We prepared O‐acetylated and free glucopyranosyl and arabinopyranosyl derivatives of rifamycin S and SV (see 3–10). Additionally, derivatives with D‐saccharo‐1,4‐lactone and with shikimic acid were obtained (see 11–15). Glycosylrifamycins show an interesting inhibitory power on Gram‐positive bacteria (Table).
Crystal Structure and Packing of Isocyclosporin A
Authors: Pohl Ehmke , Sheldrick George M. , Bölsterli Johann J. , Kallen Jörg , Traber René , Walkinshaw Malcolm D. 
Published: December 2004

AbstractThe crystal structure of isocyclosporin A (1), a rearrangement product of the immunosuppressant drug cyclosporin A, has been determined at 193 (2) K. Crystals are orthorhombic with cell dimensions a = 26.684 (7), b = 26.936 (3) Å, c = 28.549 (7) Å, space group C2221. The structure was solved by direct methods and refined by full‐matrix least‐squares methods to a conventional R value of 0.110. In contrast to the structure of cyclosprin A in solution and in the crystal, isocyclosporin A (1) has no regular secondary structural elements. The backbone adopts an open, irregular conformation with cis amide bonds between residue 2 and 3, and 3 and 4, respectively. All the other amide bonds and the ester linkage are trans. Contrary to crystal structures of cyclosporin derivatives, this crystal structure is stabilized by two transannular and four intermolecular H‐bonds.
Synthesis and Structural Characterization of the Trimeric Furoxan (= Furazan 2‐Oxide) System, a New Potent Vasodilating Moiety
Authors: Gasco Andrea M. , Cena Clara , Di Stilo Antonella , Ermondi Giuseppe , Medana Claudio , Gasco Alberto 
Published: December 2004

AbstractThe synthesis, structural characterization, and NO donor properties of a series of terfuroxan (= terfurazan trioxide) derivatives 1a–h and 2a–j are reported (Schemes 1 and 2). Structural assignments were confirmed principally by mass and 13C‐ and 1H‐NMR spectroscopy. The extent and the initial rate of NO release in the presence of thiol cofactor was evaluated for each derivative. Vasodilator effects of all the terfuroxan derivatives were evaluated on endothelium‐denuded strips of rat aorta precontracted with noradrenaline. Concentration‐response curves were also evaluated in the presence of 10 m̈M oxyhemoglobin (HbO2), a well known NO scavenger. The whole series displays high vasodilating potency; the most active terfuroxans (1a, b, g and 2i) are 5–10 times as potent as glyceryl trinitrate taken as reference (see Table 3). The potency decrease observed in the presence of HbO2 agrees with the involvement of NO in the vasorelaxing action. The 4,3′:4′,4″ connection (series 1; furoxan numbering) gives rise to the most potent compounds. The conformational factors seem to play important roles in the activity. No clear relationship between physico‐chemical properties of the substituents and potencies of derivative emerges.
Stereoselective Formation of Ternary Copper(II) Complexes of (S)‐Amino‐acid Amides and (R)‐ or (S)‐Histidine and (R)‐ or (S)‐Tyrosine in Aqueous Solution
Authors: Dallavalle Francesco , Folesani Giuseppina , Leporati Enrico , Galaverna Gianni 
Published: December 2004

AbstractFormation constants of ternary complexes of CuII with (S)‐amino‐acid amides ((S)‐phenylalaninamide, (S)‐prolinamide, and (S)‐tryptophanamide) and (R)‐ or (S)‐histidine and (R)‐ or (S)‐tyrosine were determined potentiometrically in aqueous solution. Significant stereoselectivity was presented by all three amides towards histidine, the diastereoisomeric complexes with ‘heterochiral’ ligands being more stable than those with ‘homochiral’ ligands (see Table 3). The stereoselectivity observed with (S)‐phenylalaninamide and (S)‐tryptophanamide may be explained on the basis of hydrophobic stacking interactions between 1H‐imidazole and the aromatic side chain, favoured by the terdentate behaviour of histidine (see Fig.2), whereas repulsive effects seem to be prevalent with (S)‐prolinamide. Only (S)‐prolinamide and (S)‐phenylalaninamide show appreciable stereoselectivity with tyrosine, which is bidentate, probably on account of repulsive interactions. The present results on the stability of ternary complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination performed by CuII complexes of (S)‐amino‐acid amides added to the mobile phase in HPLC (reversed phase).
Reactions of 3‐(Prop‐2‐enylidene)azetidin‐2‐ones with 4,5‐Dihydro‐3H‐1,2,4‐triazole‐3,5‐diones
Authors: Ruf Sabine , Otto Hans‐Hartwig 
Published: December 2004

AbstractThe 3‐(2‐propenylidene)‐β‐lactams 1a–c react as semicyclic dienes with the dihydrotriazole‐diones 2 in a stereoselective fashion leading to the cycloadducts 3. The 3′,3′‐disubstituted derivative 4 gives no [4 + 2]‐cycloaddition products but forms the adducts 5 and 6. Sterochemistry and reaction pathways are discussed.
Synthesis of 4′‐C‐Acylated Thymidines
Authors: Marx Andreas , Erdmann Peter , Senn Martin , Körner Steffi , Jungo Tobias , Petretta Mario , Imwinkelried Petra , Dussy Adrian , Kulicke Klaus J. , Macko Ludwig , Zehnder Margareta , Giese Bernd 
Published: December 2004

AbstractTwo synthetic pathways towards 4′‐C‐acylthymidines are presented. These modified mononucleosides are precursors of the 2′‐deoxyribonucleotide 4′‐C‐radical. They were converted into their corresponding 3′‐O‐[(2‐cyanoethyl) N,N‐diisopropylphosphoramidites] 3a–c and incorporated in oligonucleotides by solid‐phase synthesis. The structure of some modified nucleosides was revealed by X‐ray crystal‐structure analysis.
Electrospray‐Ionization Mass Spectrometry. Part 2. Neighboring‐Group Participation in the Mass‐Spectral Decomposition of 4‐Hydroxycinnamoyl‐spermidines
Authors: Hu Wenqing , Reder Elke , Hesse Manfred 
Published: December 2004

AbstractThe three mono substituted N‐[(E)‐3‐(4‐hydroxyphenyl)prop‐2‐enoyl]spermidines 1–3 have been studied by positive‐ion electrospray‐ionization tandem mass spectrometry (ESI‐MS/MS). Because of the neighboring‐group participation, the MS/MS of [1 + H]+ and [2 + H]+ are essentially similar, while compound 3 can be easily distinguished from 1 and 2 because of the characteristic ions at m/z 218. However, with the source collision‐induced dissociation (source‐CID) MS/MS technique, the compounds 1 and 2 can be unambiguously distinguished by the signal of the pyrrolidinium ion (m/z 72) from their daughter ion (m/z 275). The source‐CID MS/MS of the labeled compound N‐(4‐aminobutyl)‐N‐(3‐aminopropyl)‐N‐[3‐(4‐ hydroxyphenyl)prop‐2‐en[15N]amide] ([15N(4)]‐2) provide more information on the decomposition mechanisms and proved the occurrence of a partial transamidation reaction 2→1 during the measurement.
Use of the Wolff Rearrangement of Diazo Ketones from Amino Acids as a synthetic method for the formation of oligonucleo‐peptides: A novel approach to chimeric biomolecules
Authors: Guibourdenche Christel , Seebach Dieter , Natt François 
Published: December 2004

AbstractPhotolysis and Ag‐benzoate‐catalyzed decomposition of the diazo ketones 2 and 4 derived from Z‐Ala‐OH and Z‐Ala‐Ala‐OH in the presence of oligonucleotide derivatives bearing at the 5′‐terminus an NH2 instead of the OH group, or an aminohexyl phosphate group lead to Z‐protected 3‐aminobutanoyl and to Z‐Ala‐β‐HAla derivatives, respectively (conjugates 12, 13, and 17‐23, Schemes 3‐5), In solution, this amide‐forming acylation reaction could be realized only with oligomers containing up to 8 unprotected nucleotide building blocks (Schemes 3 and 4). With the analogous polymer‐bound and protected oligonucleotide derivatives as amino nucleophiles, excellent yields were obtained with all chain lengths tested (up to 15mer Scheme 5), The products were purified by reversed‐phase HPLC and characterized by MALDI‐TOF mass spectrometry (Figs. 2–4, Table 2) and by capillary gel electrophoresis (Fig.2).
Oligonucleotides Containing Consecutive 2′‐Deoxyisoguanosine Residues: Synthesis, duplexes with parallel chain orientation, and aggregation
Authors: Seela Frank , Wei Changfu 
Published: December 2004

AbstractThe 2′‐deoxyisoguanosine phosphonates 3a and 4a and the phosphoramidites 3b and 4b were prepared as building blocks for solid‐phase oligonucleotide synthesis. The diphenylcarbamoyl (dpc) residue was introduced as 2‐oxo protecting group which stabilizes the N‐glycosylic bond against hydrolysis and prevents the molecule from side reactions. The dpc‐protected building blocks 4a, b were employed in solid‐phase synthesis and were found to be much more efficient than the unprotected compounds 3a, b. Oligonucleotides with alternating (11) or consecutive isoguanine residues (13–15) were synthesized. They form duplexes with parallel chain orientation. The aggregate d(T4‐iG4‐T4) (15) containing four consecutive 2′‐deoxyisoguanosine is shown to be a tetramer similar to that of d(T4‐G4‐T4).
Syntheses and Reactions of Alkylthio‐ and Arylthio‐Substituted 1,6‐Methano[10]annulenes
Authors: Bryant‐Friedrich Amanda C. , Neidlein Richard 
Published: December 2004

AbstractThe treatment of bromo‐substituted 1,6‐methano[10]annulenes with sodium thiolates in DMF provides easy access to alkylthio‐ and arylthio‐substituted 1,6‐methano[10]annulenes (Schemes 2‐4). These compounds are then brominated with N‐bromosuccinimide (NBS) to study their reactivity in electrophilic substitution reactions (Schemes 5 and 6). The resulting brominated thio‐1,6‐methano[10]annulenes are, in a subsequent reaction, subjected to Heck coupling with (4‐nitrophenyl)acetylene (13) to produce the alkynylated derivatives 14 in reasonable yield (Scheme 7).
Origin of diastereoselectivity in the thermal [4+2] cycloadditions of dienophiles derived from Oppolzer's sultams: Steric vs. Stereoelectronic Influences
Authors: Chapuis Christian , Laumer Jean‐Yves De Saint , Marty Maurus 
Published: December 2004

AbstractComparative semi‐empirical PM3 and ab initio STO 3‐21G calculations on bornanesultam‐derived dienophiles containing the structural moiety SO2NC(O)X(α) = Y(β) suggest that, among the conformers of low energy, the thermodynamically less stable SO2/C(O)‐syn,C(O)/X=Y‐s‐cis conformation is also reactive in terms of LUMO level and atomic coefficients. Furthermore, the X(α), Y(β) LUMO atomic coefficients are nonequivalent with respect to both X(α)‐re and X(α)‐si faces, and thus have, depending on the conformation, a matching or mismatching stereoelectronic influence with the co‐operative steric effect. This dissymmetry is believed to result from the generalized anemone effect of the N lone pair, itself anomerically stabilized and directed, in the absence of crucial steric interactions, by the pseudo‐axial anti‐periplanar SO bond. Five N‐acyl‐substituted bornanesultams arc discussed ((–)‐1a: N‐acryloyl, XCH, YCH2; (–)‐1b; N‐crotonoyl, XCH, YCHMe; (–)‐1c: N‐N′‐fumaroyl, XCH, YCH(C(O)‐bornanesultam); 2a: N‐glyoxyloyl, XCH, YO; 2b: N‐acylnitroso, XN, YO). In this context, differences with toluenesultams 3 are pointed out. A previous report on N‐(acylnitroso)‐bornanesultam 2b is revisited, and the diastereoselectivity observed is shown to result from thermodynamic control.
Partial Synthesis and Characterization of the Mono‐and Diepoxides of β‐Cryptoxanthin
Authors: Molnár Péter , Deli József , Matus Zoltán , Tóth Gyula , Steck Andrea , Pfander Hanspeter 
Published: December 2004

Abstractβ‐Cryptoxanthin (1) was acetylated and then epoxidized with monoperoxyphthalic acid. After hydrolysis, repeated chromatography, and crystallization, (3S,5R,6S)‐5,6‐epoxy‐β‐cryptoxanthin (3), (3S,5S,6R)‐5,6‐epoxy‐β‐cryptoxanthin (4), (3R,5′R,6′R)‐5′,6′‐epoxy‐β‐cryptoxanthin (5), (3S,5R,6S,5′R,6′S)‐5,6:5′,6′‐diepoxy‐β‐cryp‐toxanthin (6), and (3S,5S,6R,5′S,6′R)‐5,6:5′,6′‐diepoxy‐β‐cryptoxanthin (7) were isolated as main products and characterized by their UV/VIS, CD, 1H‐ and 13C‐NMR, and mass spectra. The comparison of the carotenoid isolated from yellow, tomato‐shaped paprika (Capsicum annuum var. lycopersiciforme flavum) with 3–5 strongly supports the structure of 3 for the natural product.
Radical Impurity Mechanisms for Helium Incorporation into Buckminsterfullerene
Authors: Patchkovskii Serguei , Thiel Walter 
Published: December 2004

AbstractRadical impurity mechanisms for incorporating He into C60 have been examined by semiempirical (MNDO) and density functional (BLYP/3‐21G) calculations. The key step in these mechanisms is the insertion of He into C60X or C60X2 intermediates generated by adding the impurity X to C60 (X = H, Me in our model study). Contrary to C60. several window‐type structures with one broken C,C bond exist as local minima on the MNDO potential surfaces of C60X and C60X2, but they are mechanistically irrelevant due to extremely facile ring closure. Effective activation barriers for the penetration of He through intact hexagons and various windows are reported for 65 different pathways in C60X and C60X2. Window‐type transition states are stabilized significantly when there is a CX bond involving a C‐atom from the broken C,C bond. The corresponding barriers in C60X and C60X2 are much lower than in C60, This provides some theoretical support for the suggested impurity mechanisms even though the computed barriers for X = H, Me are still higher than indicated by the experiment (X unknown).
Absolute Configuration of a Diterpene Lactone from Parinari capensis
Authors: Garo Eliane , Maillard Marc , Hostettmann Kurt , Stdeckti‐Evans Helen , Mavi Steven 
Published: December 2004

AbstractPhytochemical investigation of Parinari capensis (Chrysobalanaceae) led to the isolation of three diterpene lactones 1–3. The structures of these compounds have been established by NMR spectroscopy and X‐ray crystal‐structure analysis. Addition of bromine onto the exocyclic methylidene group of 1 yielded the brominated derivative 1‐Br. X‐Ray analysis of 1‐Br established unambiguously the absolute configuration, and 1 was then identified as the (4R, 9R)‐10‐hydroxy‐13‐methoxy‐9‐methyl‐15‐oxo‐20‐norkaur‐16‐en‐18‐oic acid γ‐lactone. Diterpenes 2 and 3 were identified as the C(13)‐demethoxylated and the C(13)‐demethylated derivatives of diterpene 1, respectively. Antifungal activity against Cladosporium cucumerinum was determined for 1–3.
Synthesis, Characterization, and Crystal Structure of Complexes of Lanthanide Picrates with N,N,N′,N′‐tetraphenyl‐3,6‐dioxaoctanediamide
Authors: Liu Shixia , Liu Weisheng , Tan Minyu , Yu Kaibei , Tan Ganzu 
Published: December 2004

AbstractLanthanide picrate complexes with the ligand N,N,N′,N′‐tetraphenyl‐3,6‐dioxaactanediamide (tdd): [Ln(Pic)3(tdd)] (Ln = La, Nd, Eu, Tb, Er) have been prepared in a nonaqueous medium and characterized by elemental analysis, conductivity measurements, IR, and 1H‐NMR spectra. The crystal structures of the complexes for Ln = Nd and Er were determined. The early lanthanide, NdIII, crystallizes as the nona‐coordinate complex [Nd(Pic)3(tdd)]. 2 CH3CN in the monoclinic space group P21n with a = 11.384(2), b = 18.805(4), c = 27.526(5) Å, β = 99.41(1)°, V = 5832(2) Å3, and Dc = 1.58 gcm−3 for Z = 4. The structure was refined to R = 0.0505, based on 4772 observed Deflections. The late lanthanide, ErIII, forms an octa‐coordinate complex [Er(Pic)3(tdd)]; crystals are triclinic, P1, with a = 12.449(2), b = 17.065(2), c = 26.243(4) Å, α = 72.12(1), β = 87.86(1), γ = 84.60(1)°, V = 5282(1) Å3, and Dc = 1.68 g cm−3 for Z, = 4. The structure was refined to R = 0.0469, based on 10666 observed reflections, The results reveal that tdd forms a ring‐like structure with its four O‐atoms, coordinating to the metal ions as multidentate ligand, together with one O‐atom of the bidentate picrate. The structure of the complexes is greatly affected by the ionic radius due to participation of the picrates in coordination.
Wechselwirkungen in Kristallen. 110. Mitteilung. Die Dimorphic von (2‐Pyridyl)(2‐pyrimidyl)amin
Authors: Bock Hans , Schödel Holger , Näther Christian , Butenschön Frauke 
Published: December 2004

Interactions in Crystals: The Dimorphism of (2‐Pyridyl)(2‐pyrimidyl)aminePreceding structural studies of 2‐aminopyridine derivatives prove that they form polymorphic H‐pair‐bonded dimmers, and, therefore, (2‐pyrimidyl)amine has been crystallized under different conditions. Two different monoclinic modifications are characterized by their crystal structures of the same space group P21/c: form I exhibits the well known herringbone motif and form II the sandwich‐herringbone one. Both modifications contain almost identical planar, H‐pair‐bridged molecular dimmers. Crystals of form I are readily obtained from any solvent, whereas those of form II result either on fast evaporation of a Et2O solution or by resolidification of the melt. Differential thermal analysis (DTA) and crystallization experiments at different temperatures prove, for both modifications, no transitions in the temperature range between −25° and the melting point at 152° and, therefore the system should be monotropic. The structural and thermodynamic aspects of the (2‐pyridyl)(2‐pyrimidyl)amine dimorphism are discussed in comparison to those of the trimorphism observed for di(2‐pyridyl)amine.
Synthesis and Photochromic Behaviour of Naphthopyrans, Pyranoquinolines, Pyranoquinazolines and Pyranoquinoxalines
Authors: Pozzo Jean‐Luc , Samat André , Guglielmetti Robert , Dubest Roger , Aubard Jean 
Published: December 2004

AbstractNew chromenes annulated with different six‐membered azaheterocycles were prepared, i.e., the 3H‐pyra‐no[3,2‐f]quinolines 9/10 and 14, the 8H‐pyrano[2,3‐h]isoquinoline 11, the 8H‐pyrano[3,2‐f]quinazolme 12, the 8‐H‐pyrano[3,2‐f]quinoxaline 13, and the 2H‐pyrano[2,3‐f]isoquinoline 15. The synthesis was achieved using conveniently substituted α,β‐unsaturated aldehydes and organotitanium intermediates arising from azaheterocyclic phenols. Their photochromic behaviour (photocolouration yield, UV/VIS spectrum of photomerocyanines, rate constant of thermal bleaching) were studied besides those of corresponding naphthopyrans. The heterocycle effect and the role of substituents in the pyran moiety were investigated quantitatively through the study of the photochromic properties and the solvent effects. Diaryl‐substituted azino‐fused chromenes, especially isoquinoline derivatives, exhibit increased colourabilities and bathochromically shifted spectra for photomerocyanines which open up new prospects for photochromic applications.
Nucleotides Part LI. Synthesis and biological activities of (2′‐5′)adenylate trimer conjugates with 2′‐terminal 3′‐O(ω‐hydroxyalkyl) and 3′‐O‐(ω‐carboxyalkyl) spacers
Authors: Hörndler Cornelia , Pfleiderer Wolfgang , Suhadolnik Robert J. , Suhadolnik Robert J. , Muto Nicholas F. , Henderson Earl E. , Henderson Earl E. , Guan Ming‐Xu 
Published: December 2004

AbstractAn efficient strategy for the synthesis of (2′‐5′)adenylate trimer conjugates with 2′‐terminal 3′‐O‐(ω‐hydroxyalkyl) and 3′‐O‐(ω‐carboxyalkyl) spacers is reported. Npeoc‐protected adenosine building blocks 37‐‐40 for phosphoramidite chemistry carrying a 3′‐O‐[11‐(levulinoyloxy)undecyl], 3′‐O‐{2‐[2‐(levulinoyloxy)ethoxy]ethyl}, 3′‐O‐[5‐(2‐cyanoethoxycarbonyl)pentyl], and 3′‐O‐{5‐[(9H‐fluoren‐9‐ylmethoxy)carbonyl]pentyl} moiety, respectively, were prepared (npeoc = 2‐(4‐nitrophenyl)ethoxycarbonyl). Condensation with the cordycepin (3′‐deoxyadenosine) dimer 1 led to the corresponding trimers 42, 43, 47, and 48. Whereas the levulinoyl (lev) and 9H‐fluoren‐9‐ylmethyl
(fm) blocking groups could be cleaved off selectively from the trimers 42, 43, and 48 yielding the intermediates 44, 45, and 49 for the synthesis of the 3′‐O‐(ω‐hydroxyalkyl)trimers 53, 54 and the cholesterol conjugates 59‐‐61, the 2‐cyanoethyl (ce) protecting group of 47, however, could not be removed in a similar manner from the carboxy function. Trimer 47 served as precursor for the preparation of the trimer 55 with a terminal 3′‐O‐(5‐carboxypentyl)adenosine moiety. The metabolically stable 3′‐O‐alkyl‐(2′‐‐5′)A derivatives were tested regarding inhibition of HIV‐1 syncytia formation and HIV‐1 RT activity. Only the conjugate 59 showed significant effects, whereas the trimers 53‐‐55 and the conjugates 60 and 61 were less potent inhibitors, even at 100‐fold larger concentrations.