bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

Optically 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

A 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.
Palladium‐Catalyzed Syntheses of Polyethynyl‐Substituted 2,2′‐Bithiophenes
Authors: Dahlmann Uwe , Neidlein Richard
Published: December 2004

The 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

The 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)‐Cycloviolaxanthin

From (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

Glycosylrifamycins, 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

The 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

The 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

Formation 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

The 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

Two 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

The 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.
Synthesis of Lipid Derivatives of Colchicine
Authors: Ducray Pierre , Lebeau Luc , Mioskowski Charles
Published: December 2004

The synthesis of glycero‐lipids linked to colchicine derivatives is reported. The lipid structures are designed to perform two‐dimensional crystallization experiments with tubulin, the structural subunit protein of microtubules.
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

Photolysis 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

The 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

The 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

Comparative 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

β‐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

Radical 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

Phytochemical 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

Lanthanide 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)amine

Preceding 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

New 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

An 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.
Methylated DNA: The influence of 7‐deaza‐7‐methylguanine on the structure and stability of oligonucleotides
Authors: Seela Frank , Chen Yaoming
Published: December 2004

The 7‐deaza‐2′‐deoxy‐7‐methylguanosine (2b) [9], which is the glycosylic‐bond‐stable, noncharged analogue of 2′‐deoxy‐7‐methylguanosine (1b), was incorporated in DNA by solid‐phase synthesis. As building blocks, the protected phosphonatc 3a and the phosphoramidite 3b were prepared. The 7‐methyl group of 2b stabilizes the B‐DNA duplex compared to 7‐deaza‐2′‐deoxyguanosine but does not induce a B‐Z transition as it is known from compound 1b. The stabilization by the 7‐deaza‐7‐methylguanine moiety is sequence‐dependent, and the nearest‐neighbor influence is different from that of 7‐deazaguanine. Homooligonucleotides of 2b show sigmoidal melting indicating a highly ordered single‐stranded structure. In general, Oligonucleotides containing 2b are very stable against hydrolysis with calf‐spleen phosphodiesterase (CS‐PDE, 5′ → 3′ exonuclease), while phosphodiester hydrolysis with snake‐venom phosphodiesterase (SV‐PDE, 3′ → 5′ exonuclease) is only slightly reduced.
Iridoid Glucosides with Free Radical Scavenging Properties from Fagraea blumei
Authors: Cuendet Muriel , Hostettmann Kurt , Potterat Olivier , Dyatmiko Wahjo
Published: December 2004

Four new iridoid glucosides 1–4, named blumeosides A–D, were isolated from the methanolic stem‐bark extract of Fagraea blumei G. DON. (Loganiaceae). They were accompanied by the benzyl‐alcohol derivative di‐O‐methylcrenatin (5) and the flavone C‐glucoside swertisin (6). The structures of 1–4 were established by spectroscopic methods, including FAB‐MS, and 1H‐ and 13C‐NMR, and by alkaline hydrolysis. Blumeosides A (1) and C (3) are 10‐O‐(2,5‐dihydroxytercphthalo) adoxosidic acid and 10‐O‐(2‐hydroxyterephthalo)adoxosidic acid, respectively. In blumeosides B (4) and D (2), both carboxylic groups of the terephthalic‐acid moiety are esterified by adoxosidic‐acid units, Blumeosides A–D (1–4) inhibited bleaching of crocin induced by alkoxyl radicals. Blumeosides A (1) and D (2) also demonstrated scavenging properties towards the 2,2‐diphenyl‐1‐picryl‐hvdrazvl (CDPPH) radical in TLC autographic and spectrophotometric assays.
Introduction of Amino Alcohols in the Ring‐Opening Reaction of 3‐bromo‐2,5‐dimethylthiophene 1,1‐dioxide. A short diastereoselective synthesis of substituted ‘tetrahydrobenzo[a]pyrrolizidines’ (= octahydro‐1H‐pyrrolo[2,1‐a]isoindoles) using L‐prolinol
Authors: Tsirk Anders , Gronowitz Salo , Hörnfeldt Anna‐Britta
Published: December 2004

Tetrahydrobenzo[a]pyrrolizidines (= octahydro‐1H‐pyrrolo[2,1‐a]isoindoles) and tetrahydrobenzo[a]indo‐lizidines, (= decahydropyrido[2,1‐a]isoindoles) were prepared stereoselectively in four steps through an amineinduced ring‐opening of 3‐bromo‐2,5‐dimethylthiophene 1,1‐dioxide (1) with L‐prolinol (9), piperidine‐2‐methanol (10), and piperidine‐2‐ethanol (11), yielding the dienes (2S)‐1‐[(2E,4Z)‐4‐bromohexa‐2,4‐dienyl]pyrrolidine‐2‐methanol (12), 1‐[(2E,4Z)‐4‐bromohexa‐2,4‐dienyl]piperidine‐2‐methanol (13), and 1‐[(2E,4Z)‐4‐bromo‐hexa‐2,4‐dienyl]piperidine‐2‐ethanol (14; Scheme2), which, after conversion into their α,β‐unsaturated esters, cyclized in a TiCl4‐catalyzed intramolecular Diets‐Alder reaction (Scheme3). A discussion on the mechanism of the ring opening reaction including semiempirical and ab initio calculations is also presented.
X‐Ray Structure Analyses of Alkyl‐Substituted N‐Acryloyl‐ and N‐Crotonoyltoluenesultams
Authors: Bernardinelli Gérald , Chapuis Christian , Kingma Arend J. , Wills Martin
Published: December 2004

The X‐ray crystal‐structure analyses of two N‐enoyl‐toluenesultam derivatives 1 are reported. The structural differences with their bornanesultam analogues 2 as well as stereochemical aspects with respect to their [4 + 2] and [3 + 2] cycloadditions are discussed.
Theoretical Parameters to Characterize Antioxidants. Part 1. The case of vitamin E and analogs
Authors: Migliavacca Eugenia , Carrupt Pierre‐Alain , Testa Bernard
Published: December 2004

The objectives of ibis work were (a) to evaluate parameters obtained by quantum‐mechanical calculations as predictors of antioxidant activities, and (b) to obtain information on the molecular mechanism(s) underlying the antioxidant effects of vitamin E and analogs. To this effect, we selected a large series of tocopherol analogs for which some experimental antioxidant activities were available in the literature (i. e., peak of oxidation potential, Ep, and rate constant of the reaction with a free radical log ks). AM1 Semi‐empirical calculations were performed, the results of which were validated by ab initio calculations on a subset of compounds. The quantum chemical descriptors considered here (HOMO, ΔHox and ΔHabs) were fairly well correlated with the experimental antioxidant activities (Ep and ks). Moreover, these theoretical parameters were intercorrelated, suggesting that vitamin E analogs may act by a dual mechanism of single‐electron transfer (SET) and direct H‐atom abstraction.
7‐Deazaguanine DNA: Oligonucleotides with hydrophobic or cationic side chains
Authors: Ramzaeva Natalya , Mittelbach Cathrin , Seela Frank
Published: December 2004

The phosphoramidites 6b and 9 as well as the phosphonate 6a derived from 7‐(hex‐1‐ynyl)‐ and 7‐[5‐(trifluoroacetamido)pent‐1‐ynyl]‐substituted 7‐deaza‐2′‐deoxyguanosines 1 and 10, respectively, were prepared (Scheme 1). They were employed in solid‐phase oligodeoxynucleotide synthesis of the alternating octamers d(hxy7c7G‐C)4 (12), d(C‐hxy7c7G)4 (13), and d(npey 7c7G‐C)4 (15) as well as of other oligonucleotides (see 22–25; Table 2; hxy = hex‐1‐ynyl, npey = 5‐aminopent‐1‐ynyl). The Tm values and the thermodynamic data of duplex formation were determined and correlated with the major‐groove modification of the DNA fragments. A hexynyl side chain introduced into the 7‐position of a 7‐deazaguanine residue (see 1) was found to fit into the major groove without any protrusion. The incorporation of the (5‐aminopent‐1‐ynyl)‐modified 7‐deaza‐2′‐deoxyguanosine 2 into single‐stranded oligomers of the type 24 and 25 did not lead to change in duplex stability compared to the parent oligonucleotides. The self‐complementary oligomer 15 with alternating npey7c7Gd (2) and dC units did not lead to a cooperative melting, either due to orientational disorder or interaction of the 5‐aminopent‐1‐ynyl moiety with a base or with phosphate residues nearby or on the opposite strand.
Boophiline, an antimicrobial sterol amide from the cattle tick boophilus microplus
Authors: Potterat Olivier , Hostettmann Kurt , Höltzel Alexandra , Jung GüNther , Diehl Peter‐Allan , Petrini Orlando
Published: December 2004

Boophiline (1), a new sterol amide was isolated from the cattle tick Boophilus microplus (Ixodidae). The structure was assigned as N‐[3‐(sulfooxy)‐25ξcholest‐5‐en‐26‐oyl]‐L‐isoleucine by detailed 2D NMR investigations in conjunction with FAB mass spectrometry and acidic hydrolyses. Complete assignment of the diastereotopic methylene protons of the ring system could be deduced from the NMR data. In agar dilution assays, 1 exhibited antifungal properties against Cladosporium cucumerinum and antibacterial activity against Bacillus subtilis and Escherichia coli.
Total synthesis of 2,6‐dimethylergolin‐8α‐amines
Authors: Waldvogel Erwin , Engeli Peter , Küsters Ernst
Published: December 2004

A stereoselective total synthesis of the racemic form of the 2,6‐dimethylergolin‐8ã‐amine derivative III, previously obtained semi‐synthetically from lysergic acid, is described. Starting from the commercially available tricyclic lactam 1, the 9,10‐didehydroergoline skeleton containing an angular Me group in position 3 (see 18) is built up in several steps applying a Woodward D‐ring annelation sequence. The introduction of the 8‐amino group is achieved with complete diastereoselectivity to give exclusively the 8ã‐derivative 22. Subsequently, a Wagner‐Meerwein‐type migration of the angular Me group yields the 2‐methylated 9,10‐didehydroergoline derivative 31. The feasibility of this key transformation was tested on the two model systems 4 and 7 prior to the evaluation of the total synthesis. A stereoselective Birch reduction to the trans‐fused ergoline, and deacetylation/acylation conclude the total synthesis of the racemic target compound 34.

In addition, the resolution of an early intermediate (see 3) by chromatography on a chiral stationary phase is presented which demonstrates that the described total synthesis could also be used for the preparation of the biologically active (5R,8S,10R)‐enantiomer III.
The enantioselective copolymerisation of allylbenzene, 1‐allyl‐4‐(trifluoromethyl)benzene, and 1‐allyl‐4‐methoxybenzene with carbon monoxide
Authors: Benedetto Silvia Di , Consiglio Giambattista
Published: December 2004

The olefins mentioned in the title were copolymerized with CO in the presence of palladium catalysts modified with dicyclohexyl{(R)‐1‐[(S)‐2‐(diphenylphosphino)ferrocenyl]ethyl}phosphine. Productivities up to 95 g/(gPd · h) were achieved. The obtained copolymers were recovered in the pure, regio‐ und stereoregular polyketone structures3. The isotactic poly[2‐benzyl‐1‐oxopropane‐1,3‐diyl] (3a) and its analogues 3b, c were found to isomerize to the corresponding spirocyclic poly[3‐(arylmethyl)tetrahydrofuran‐2,2‐5,5‐tetrayl‐2‐oxy‐2‐methylene]s 4 in a suspension in CHC13, thus indicating that the spiroketal structure is thermodynamically the most stable for these copolymers. However, the atactic material did not undergo any structural transformation. These results show that regularity at the centers of chirality in the main chain is a prerequisite for the conversion of the polyketone to the spiroketal structure.
Potassium Cryptate of a Macrobicyclic Ligand Featuring a Reducible hexakis(phenylthio)benzene electron‐acceptor site
Authors: Mayor Marcel , Lehn Jean‐Marie
Published: December 2004

The synthesis and structural characterization of the macrobicyclic ligand 1 containing a reducible hexakis‐(phenylthio)benzene electron‐acceptor site is described. It is based on the condensation of the tetraoxa‐diazamacrocycle 3 with a suitably functionalized derivative 4 of hexakis(phenylthio)benzene. Complexation of a potassium cation by 1 gives the corresponding cryptate 2, with a stability constant of ca. 4000 M−1 as determined by 1H‐NMR titration in CD3CN. The reduction potential of the hexakis(phenylthio)benzene electron‐acceptor site in 2 is shifted by 170 mV towards more positive values with respect to that in 1 by complexation of potassium.
Push‐Pull Butadienes: Evidence for a possible CH…︁S hydrogen bond in 4‐(methylthio)‐4‐nitro‐1‐(pyrrolidin‐1‐yl)buta‐1,3‐diene
Authors: Surange Sheetal S. , Kumaran Govindaraj , Rajappa Srinivasachari , Pal Debnath , Chakrabarti Pinak
Published: December 2004

X‐Ray crystal structure of 4‐(methylthio)‐4‐nitro‐1‐(pyrrolidin‐1‐yl)buta‐1,3‐diene (2b)

The C‐atoms of the butadiene chain have been numbered as shown in 1 and 2. These numbers have been retained throughout the discussion for the sake of clarity and consistency.

indicates the presence of a CH…︁S hydrogen bond. This might also explain the observed downfield shift of this proton in solution.
Synthesis and Odor of Chiral Partial Structures of Khusimone. Part 3. Short communication
Authors: Spreitzer Helmut , Pichler Andrea , Holzer Wolfgang , Schlager Claudia
Published: December 2004

Khusimone (1), one of the main odor‐donating compounds of vetiver oil, is subject of the following study on structure/odor relationship. The omittance of the methano bridge of the tricyclic khusimone should lead to the bicyclic partial structure (−)‐2. Unexpectedly, (−)‐2 could not be obtained since epimerization favored (−)‐16. The stereochemical key step of the synthesis of the hydrazulene nucleus is based on a highly diastereoselective conjugate addition to a chiral oxocyclopent‐1‐ene‐1‐carboxylate.
A Convenient Stereoselective Synthesis of (1R,2S,3R,4S)‐3‐(Neopentyloxy)isoborneol
Authors: Verdaguer Xavier , Marchueta Iolanda , Tormo Jordi , Moyano Albert , Pericàs Miquel A. , Riera Antoni
Published: December 2004

A convenient preparation of (1R,2S,3R,4S)‐3‐(neopentyloxy)isoborneol (= (1R,2S,3R,4S)‐3‐(2,2‐dimethyl‐propoxy)‐1,7,7‐trimethylbicyclo[2.2.1]heptan‐2‐ol; 1a), a valuable chiral auxiliary, is described. The synthesis involves six steps starting from the readily available camphorquinone (5) and gives 1a in 48% overall yield. The key step is the chemoselective hydrolysis of the less hindered 1,3‐dioxolane moiety in the camphorquinone di‐acetal 4.
Syntheses of O‐Methylasparvenone‐Derived Serotonin‐Receptor Antagonists
Authors: Bös Michael , Stadler Heinz , Wichmann Jürgen , Jenck François , Martin James R. , Moreau Jean‐Luc , Sleight Andrew J.
Published: December 2004

Based on O‐methylasparvenone (1), a N‐free 5HT2C antagonist with moderate affinity (pKi = 6.7), derivatives bearing dimethylamino (7), (dimethylamino)methyl (17, 18, 21, and 22), and aminomethyl substituents (26) in place of the benzylic OH group of 1 as well as pyrrolidine‐ (33) and piperidine‐fused derivatives (29, 43, and 45) were synthesized. In contrast to the lead structure 1, these new ligands were active in vivo in the rat. The tricycles 33 and 45 display high affinities for the 5HT2C receptor (pKi = 8).
Synthesis and Properties of Monodisperse Chiral Dendrimers (up to Fourth Generation) with doubly branched building blocks: An intriguing solvent effect
Authors: Murer Peter , Seebach Dieter
Published: December 2004

‘Fully chiral’ dendrimers, containing a stereogenic center at each and every branching point, have been prepared using a chiral core triol with aromatic elongating units (cf. 27) and chiral branch diols (cf. 8, 12, and 24) as building blocks. The biggest dendrimer prepared is of the 4th generation (33: 46 building blocks, 93 stereogenic centers, 1028 possible stereoisomers), and has been obtained by a convergent growth approach in 32 steps starting from the biopolymer poly[(R)‐3‐hydroxybutanoic acid] (P(3‐HB)). All compounds were shown to be monodisperse by MALDI‐TOF mass spectrometry. Spin‐lattice relaxation‐time (T1) measurements and size‐exclusion chromatography show typical features of structurally related achiral dendrimers. The influence of the chiral building blocks on the shape of the whole dendrimer has been investigated by chiroptical measurements: the specific rotation can be considered as average of all chiroptical properties of its constituent chiral units, independent of the solvent, the concentration, and the temperature. On the other hand, regularity in the circular dichroism (CD) spectra is completely lost with variation of the solvent (cf. Fig. 13).
A Novel Hydrocarbon, 8,10‐Dimethylidenetricyclo[7.1.1.02,7]undeca‐2,4,6‐triene: Synthesis of benzopinane skeleton via di‐π‐methane rearrangement of benzonorbornadiene system
Authors: Altundaş Aliye , Akbulut Nihat , Balci Metin
Published: December 2004

The [4 + 2] cycloadduct 17 of 2,3‐dimethylidene‐1,2,3,4‐tetrahydro‐1,4‐methanonaphthalene and 4‐phenyl‐4H‐1,2,4‐triazole‐3,5‐dione (PTAD) was subjected to a triplet‐sensitized di‐π‐methane rearrangement. Hydrolysis of the resulting urazol 18 gave the hydrocarbon 7. Hydrolysis of 18 at lower base concentrations led to isomeric stable semicarbazides 24 and 25, which were submitted NiO2 or MnO2 oxidation, to give the target compound 7, and oxidation products 26 and 27.
NMR Verification of Helical Conformations of Phycocyanobilin in Organic Solvents
Authors: Knipp Bernd , Müller Martin , Metzler‐Nolte Nils , Balaban Teodor S. , Braslavsky Silvia E. , Schaffner Kurt
Published: December 2004

Selective NMR decoupling and nuclearOverhausereffect (NOE) experiments with phycocyanobilin (PCB) show proton‐proton interactions between the terminal rings A and D,viz. the chiral C(2) methine center and the ethyl substituent at C(18), as a result of the helical conformation of this open‐chain tetrapyrrole in solution. Quantitative NOE measurements and a combination of force‐field and semiempirical calculations (FSC) afford inter‐proton distances across the helical gap of 4.2–4.6 (NOE) and 3.2–4.2 A° (FSC). The NOE and FSC, in conjuction with a qualitative evaluation of the steric interactions in the two optimized helices, suggest furthermore that, in solution, the helixMis somewhat more stable thanP. The coexistence of at least two diastereoisomers is corroborated also by the circular dichroism (CD) spectra of PCB in MeOH/EtOH which point to a temperature‐dependent equilibrium in solution, and by a considerable increase of this CD upon changing the solvent from the achiral alcohols to ethyl (−)‐(S)‐lactate which reflects a selective solvent‐induced CD differentiating between diastereoisomers.
Origin of the Stereoselectivity in (Ethoxycarbonyl)‐, Cyano‐, and Phenyl‐Substituted (Arylsulfinyl)methyl Radicals
Authors: Renaud Philippe , Bourquard Thierry , Carrupt Pierre‐Alain , Gerster Michéle
Published: December 2004

An explanation for the very high diastereoselectivity observed for the reactions of carbonyl‐substituted (arylsulfinyl)methyl radicals is presented, based on experimental results and semiempirical calculations. The influence of dipole‐dipole interactions, allylic 1,3‐strain (A1,3 strain), allylic 1,2‐strain (A1,2 strain), and coulombic interactions is discussed based on stereoselectivities observed with (alkoxycarbonyl)‐, cyano‐, and aryl‐substituted (arylsulfinyl)methyl radicals. In the second part, the effect of solvents and Lewis acids on the stereoselectivity of reactions of (arylsulfinyl)‐ and (alkylsulfinyl)benzyl radicals has been examined.
8‐Fluoro‐6‐(methoxymethoxy)quinoline: Synthesis and regioselective functionalization via reaction with organolithium compounds
Authors: Stadlwieser Josef , Barbier Pierre , Taylor Sven
Published: December 2004

8‐Fluoro‐6‐(methoxymethoxy)quinoline (1) was synthesized, and the reactivity of 1 against organolithium compounds was studied under different reaction conditions. With BuLi, directed ortho‐metalation (DoM) was accompanied by 1,2‐addition to the CN bond. 1,2‐Addition was exclusively observed with t‐BuLi. Selective ortho‐metalation was achieved with MeLi (Table). Based on these findings, a short and high‐yielding synthesis of the highly functionalized quinolines 12a–c was developed.
8‐Azaadenosine and Its 2′‐Deoxyribonucleoside: Synthesis and oligonucleotide base‐pair stability
Authors: Seela Frank , Münster Ingo , Lüchner Uwe , Rosemeyer Helmut
Published: December 2004

The synthesis of 8‐azaadenosine (1a; z8A) has been performed by SnCl4‐catalyzed glycosylation of 8‐azaadenine (4) with 1,2,3,5‐tetra‐O‐acetyl‐β‐D‐ribofuranose (5), followed by the separation of the regioisomers 6 and 7 and subsequent deacetylation. The ribonucleoside 1a as well as its 2′‐deoxy derivative 1b (z8Ad) were converted into oligonucleotide building blocks–the phosphonate 2 as well as the phosphoramidites 3 and 19. They were used to prepare the oligoribonucleotide (z8A‐U)6 and oligodeoxyribonucleotides. The Tm values and the thermodynamic data of duplex formation of the modified duplexes showed no significant changes compared to those containing Ad or A residues. This indicates that the stereoelectronic effect of the 8‐azaadenine base which was found for the monomeric nucleoside has only a minor influence on the duplex stability.
Hydrogen Isotope Effect on the Isomerization of Peroxynitrous Acid
Authors: Padmaja Sarojini , Kissner Reinhard , Bounds Patricia L. , Koppenol Willem H.
Published: December 2004

The kinetics of isomerization of deuterium and hydrogen oxoperoxonitrate, ONOOD and ONOOH, respectively, to trioxonitrate(1−), NO, and a deuteron or proton have been studied. Analysis of the pH‐rate profiles result in a normal equilibrium isotope effect (KH/KD) of 3.3. The kinetic deuterium isotope effect for the isomerization reaction is 1.6 ± 0.2 between 5 and 55°. The activation enthalpies of isomerization of ONOOD and ONOOH are identical within the error of the measurement, 86.2 ± 0.5 and 86.5 ± 0.5 kJmol−1, respectively. A secondary kinetic isotope effect of 1.6 is compatible with a mechanism of isomerization where the terminal peroxide O‐atom shifts to the N‐atom.
Isolation of Carotenoids with 3,5,6‐Trihydroxy‐5,6‐dihydro‐β‐end Groups from Red Paprika (Capsicum annuum)
Authors: Deli József , Molnár Péter , Matus Zoltán , Tóth Gyula , Steck Andrea , Pfander Hanspeter
Published: December 2004

6‐Epikarpoxanthin ((all‐E,3S,5R,6S,3′R)‐5,‐6‐dihydro‐β,β‐carotene‐3,5,6,3′‐tetrol, 5), 5,6‐diepikarpoxanthin ((all‐E,3S,5S,6S,3′R)‐5,6‐β,β‐carotene‐3,5,6,3′‐tetrol, 13), 5,6‐diepilatoxanthin ((all‐E,3S,5S,6S,3′S5′R,6′S)‐5,6′‐epoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,5,6,3′‐tetrol, 14), and 5,6‐diepicapsokarpoxanthin ((all‐E,3S,5S,6S,3′S,5′R)‐5,6‐dihydro‐3,5,6,3′‐tetrahydroxy‐β,κ‐caroten‐6′‐one, 15) were isolated from red spice paprika (Capsicum annuum var. longum) and characterized by their UV/VIS, CD, 1H‐ and 13C‐NMR, and mass spectra. Our investigations demonstrate that the configuration of the 3,5,6‐trihydroxy‐5,6‐dihydro‐β‐end group may differ depending on the biological source.