bluuebunny/crossref_metadata_2025 huggingface dataset:
A Facile Route to Some [n.1.1]Propellanes
Authors: Kreuzholz Rüdiger , Szeimies Günter
Published: July 2007

The 1,7‐disubstituted tricyclo[4.1.02,7]heptanes 1a and b could be synthesized using FeIII‐catalyzed cross coupling methods. The reaction of LDA with 1a and 1b afforded an equilibrium mixture of the organolithium compounds 6 and 7, respectively. Whereas 6a/7a cyclized to the stable [4.1.1]propellane 8 in a 40% yield, 6b/7b gave rise to a 59% yield of [6.1.1]propelladiene 9 which polymerized on attempted distillation.
Chiral Bifluorophoric Perylene Dyes with Unusually High CD Effects – a Simple Model for the Photosynthesis Reaction Center
Authors: Langhals Heinz , Gold Josef
Published: July 2007

The synthesis of a bifluorophoric perylene dye (4a) is described, in which the two chromophores are linked by a chiral binaphthyl unit. A strong exciton coupling of the two chromophores, a bathochromically shifted fluorescence and strong CD effects are observed. The structure of 4 is compared to the photosynthesis reaction center.
Stereoselective Synthesis of Some γ‐ and δ‐Fluoro‐α‐amino Acids
Authors: Kröger Stefan , Haufe Günter
Published: July 2007

(R)‐(−)‐2‐Amino‐4‐fluorobutyric acid (4c) (32% ee) and six of its homologues 9 have been synthesized by diastereoselective alkylation (54–72% yield) of (R)‐(+)‐camphor‐based glycine ester imines 1 with 1‐bromo‐2‐fluoro‐alkanes 6, at low temperature, followed by deprotection. Similarly 1‐bromo‐3‐fluoropropane was used for the preparation of (R)‐(−)‐5‐fluornorvaline (4d) (42% ee). With 1‐bromo‐2‐fluoropropane (6a) and its homologues (prepared by bromofluorination of 1‐alkenes) partial resolution occurs in the alkylation step, yielding mixtures of four diastereomers. Using (R)‐1‐bromo‐2‐fluoro‐4‐methylpentane two diastereomeric alkylation products are formed (58% de). The overall yield of the three‐step procedure varied from 10% to 32%.
Thermal Interconversions of the C16H10 Cyclopenta‐Fused Polycyclic Aromatic Hydrocarbons Fluoranthene, Acephenanthrylene and Aceanthrylene Revisited
Authors: Sarobe Martin , Jenneskens Leonardus W. , Wesseling Jolanda , Snoeijer Judith D. , Zwikker Jan W.
Published: July 2007

The thermal interconversion of the C16H10 cyclopenta‐fused polycyclic aromatic hydrocarbons (CP‐PAH) fluoranthene (1), acephenanthrylene (2) and aceanthrylene (3) has been studied using Flash Vacuum Thermolysis (FVT). In contrast to previously reported flow‐pyrolysis results, which gave the unexpected thermodynamic stability order 1 > 3 > 2, FVT temperature‐conversion data unequivocally show the expected order 1 > 2 > 3. These results are supported by independent FVT experiments with 9‐ethynylphenanthrene (4), 9‐ethynylanthracene (5) and 5‐(anthryl‐9′‐methylene)‐2,2‐dimethyl‐1,3‐dioxan‐4,6‐dione (6), which are precursors for acephenanthrylene (2) and aceanthrylene (3), respectively. The interpretation of the FVT results is corroborated by semiempirical AM1 calculations of the C16H10 potential energy surface.
Enzymatic Cleavage of N‐Phenylacetyl‐Protected Ethanolamine Phosphates
Authors: van Straten Nicole C. R. , Duynstee Howard I. , de Vroom Erik , van der Marel Gijsbert A. , van Boom Jacques H.
Published: July 2007

Immobilized penicillin‐G acylase mediated removal of the N‐phenylacetyl protective group in ethanolamine phosphates 7 and 9 furnished compounds 8 and 10, respectively. Deblocking of N‐phenylacetyl‐protected ethanolamine phosphate heptosyl disaccharide 22, a protected spacer‐containing fragment of the inner‐core lipopolysaccharide region of Neisseria meningitidis, immunotype L3 was readily accomplished with penicillin‐G acylase, yielding target dimer 2. Disaccharide 22 was accessible by elongation of ethyl 1‐thio‐L‐glycero‐α‐D‐manno‐heptopyranosyl donor 13 with acceptor 14 under the influence of N‐iodosuccinimide/triflic acid. Protective group manipulations, phosphorylation with the reagent 2‐cyanoethyl 2‐(phenylacetylamino)ethyl N,N‐diisopropylphosphoramidite (5) and deprotection furnished LD‐Hepp dimer 22.
Synthesis of Protected Hexp‐(1 → 4)‐β‐D‐GlcpNAc‐(1 → 2)‐α‐D‐Manp‐(1 → O)(CH2)7CH3 sequences (hex = β‐D‐Glc, 4‐deoxy‐4‐fluoro‐β‐D‐Gal, or 4‐deoxy‐β‐D‐Gal) Using a Glc–GlcNPhth Donor, Eventually Fluorinated or Deoxygenated at the Oligosaccharide Level
Authors: van Dorst Johannes A. L. M. , Voskamp Anton F. , Kamerling Johannis P. , Vliegenthart Johannes F. G.
Published: July 2007

Three trisaccharide derivatives of the type β‐D‐Hexp‐(1 → 4)‐β‐D‐GlcpNAc(1 → 2)‐α‐D‐Manp‐(1 → O)(CH2)7CH3 have been synthesized, with Hex being either glucose (15), 4‐deoxy‐4‐fluorogalactose (20), or 4‐deoxygalactose (27). These trisaccharides have been designed for the study of the acceptor specificity of glycosyltransferases involved in termination of N‐acetyllactosamine‐type N‐glycans. Allyl (2‐O‐acetyl‐3,6‐di‐O‐benzyl‐β‐D‐glucopyranosyl)‐(1 → 4)‐3,6‐di‐O‐benzyl‐2‐deoxy‐2‐phthalimido‐β‐D‐glucopyranoside (10) was synthesized by condensation of 2,4,6‐tri‐O‐acetyl‐3‐O‐benzyl‐α‐D‐glucosypanosyl trichloroacetimidate with allyl 3,6‐di‐O‐benzyl‐2‐deoxy‐2‐phthalimido‐β‐D‐glucopyranoside, followed by 4′,6′‐de‐O‐acetylation, 4′,6′‐O‐benzylidenation (8), and specific acetal ring opening. Acetylation or inverted fluorination of 10, followed by deallylation and imidation, gave suitable disaccharide donors which were each condensed with octyl 3,4,6‐tri‐O‐benzyl‐α‐D‐mannopyranoside (14) to afford the fully protected trisaccharides 15 and 20. Deallylation and imidation of 8, followed by coupling to 14 and subsequent specific acetal ring opening, triflation, halogenation, and reductive dehalogenation gave the protected 4″‐deoxytrisaccharide.
Reversible Redox Systems, LXII. 2,3‐Disubstituted 1,4‐Benzoquinones and Their N,N′‐dicyanimines: Syntheses, Physical Properties, and CT Complexes with TTF
Authors: Erk Peter , Hünig Siegfried , Klebe Gerhard , Metzenthin Tobias , Werner Hermann P. , von Schütz Jost‐ U.
Published: July 2007

Synthesis, redox potentials, and AM1 calculations for 2,3‐disubstituted 1,4‐benzoquinones 3a–3j are described together with those of N,N′‐dicyanimines (DCNQIs) 4. All data compare well with the corresponding 2,5‐disubstituted derivatives, except R1,R2 = OMe, SMe. The special effect of these groups is discussed on the basis of low energy out of plane conformers. All DCNQIs 4 occur as syn isomers with respect to the =NCN groups except 4d, where the five membered ring formed with R1,R2 = −[CH2]3– forms 20% anti‐4d in solution. All DNCQIs form CT complexes with TTF (derivatives) with powder conductivities of 10−1 to 10−3 Scm−1.
Synthesis of Thio‐Linked Analogues of Lewis X and Sialyl Lewis X
Authors: Eisele Thomas , Schmidt Richard R.
Published: July 2007

The synthesis of thio‐linked Lewis X and sialyl Lewis X‐derived epitopes 3–5 has been achieved using a small number of building blocks. The key building‐block was 1‐O‐silyl‐protected 4‐S‐acetyl‐2,6‐di‐O‐benzoyl‐3‐S‐(2,3,4‐tri‐O‐acetyl‐α‐L‐fucopyranosyl)‐3,4‐dithio‐β‐D‐glucopyranose (15), which was obtained from the fucosyl donor 6 together with 3‐thiogalactose 7 as the acceptor. Their acid‐catalyzed S‐glycosylation afforded the thio‐linked disaccharide 8 which was subsequently converted to the 4a‐O‐unprotected derivative 12. Conversion to the 4a‐triflate followed by treatment with KSAc in tetrahydrofuran led, under inversion of configuration, to 15 in good overall yield. Selective removal of the S‐acetyl group followed by base‐promoted S‐glycosylation with acetobromogalactose gave the acyl‐protected Lewis X analogue 25. Acetobromogalactose gave the acyl‐protected Lewis X analogue 25. Transformation into trichloroacetimidate 27, followed by acid‐catalyzed S‐glycosylation of heptylthiol and complete deacylation afforded target molecule 3. Similarly, acid‐catalyzed reaction of donor 27 and the 3b,4b‐O‐unprotected lactose derivative 31 as acceptor led to pentasaccharide 32, complete deacylation of which afforded target molecule 4. Transformation of 15 into the donor trichloroacetimidate 34, followed by acid‐catalyzed S‐glycosylation of heptylthiol afforded thioglycoside 35. Selective removal of the S‐acetyl group and subsequent base‐promoted S‐glycosylation with the known donor 37 furnished the thio‐linked tetrasaccharide 38. Cleavage of all the O‐acyl groups and hydrolysis of the methyl ester moiety afforded the sialyl Lewis X analogue 5.
Thermal and Electron‐Transfer Induced Reactions of Enediynes and Enyne‐Allenes, 9. Electron‐Transfer versus Acid Catalysis in Enediyne Cyclizations
Authors: Schmittel Michael , Kiau Susanne
Published: July 2007

Four novel aryl‐substituted enediynes 3 have been synthesized. While their cyclization to the Bergman products 4 could be accomplished at temperatures of 240–320°C, α‐functionalization rather than cyclization was observed during anodic oxidation and in the presence of one‐electron oxidants. In contrast, enediyne 1a was cyclized in the presence of two one‐electron oxidants to the indenone 2a as indicated in the literature; mechanistic investigations clearly indicate the occurrence of an acid‐catalyzed mechanism.
Improved Synthesis of Anhydrohexitol Building Blocks for Oligonucleotide Synthesis
Authors: De Bouvere Bart , Kerremans Luc , Rozenski Jef , Janssen Gerard , van Aerschot Arthur , Claes Paul , Busson Roger , Herdewijn Piet
Published: July 2007

The synthesis of the four building blocks used for the preparation of hexitol nucleic acids were optimized. The nucleoside analogues with a purine base moiety are best prepared by a nucleophilic substitution reaction, whereas the pyrimidine nucleosides can best be obtained using Mitsunobu‐type conditions.
Sulfurization of Thiones: 2,2,4,4‐Tetramethyl‐3‐thioxocyclobutanone
Authors: Huisgen Rolf , Rapp Jochen , Huber Helmut
Published: July 2007

By treatment with elemental sulfur and a catalytic amount of sodium thiophenolate in acetone at room temp., the title compound 9 is converted to the bis‐spiro derivatives of 1,2,4,5‐tetrathiane, 13, and 1,2,3,5,6‐pentathiepane, 14. The initial attack by the phenyl oligosulfide anion takes place at the C‐atom of the thiocarbonyl group. There is 13C NMR evidence for the twist conformation 15 of the tetrathiane ring; dynamic 1H NMR led to ΔG≠ = 15.9 ± 1.0 kcal mol−1 for the enantiomerization. For the pentathiepane 14, twelve coalescence phenomena in the 1H and 13C NMR spectra point to ΔG≠ = 13.4 ± 0.2 kcal mol−1; the process is interpreted as a stereomutation on the pseudorotation circuit for twist‐chair and chair. The MS of 13 reveals a diversity of fragmentation patterns with several “thiologous” sequences. By prolonged treatment with the thiophenolate catalyst, 13 and 14 are converted to a γ‐butyrodithiolactone 36 in a Baeyer‐Villiger type reaction.
Reactions of Uracils, 22. Synthesis of Pyrimido[5,4‐c]quinolizines
Authors: Wamhoff Heinrich , Kramer‐Hoß Vera
Published: July 2007

Several heterocyclization reactions of uracil derivatives are described. 1,3‐Dimethyl‐6‐(triphenylphosphoranylideneamino)uracil‐5‐acrylic ester (1) undergoes aza‐Wittig cyclization to give pyrido[2,3‐d]pyrimidine 2. In a special application of the tert‐amino effect, 6‐tert‐amino‐substituted uracil‐5‐ylmethylenemalodinitriles 8a–f are cyclized with ZnCl2/toluene to afford pyrimido[5,4‐c]quinolizines 10b, d–f, and 1,4‐oxazino[3,4‐a]pyrido[2,3‐d]pyrimidine 10c, while the corresponding diesters 12a, b and 13 could not be cyclized. Alternative reaction mechanisms involving 1,6‐ and 1,5‐H shifts are discussed.
A Butyrolactone → 1,3‐Diol Strategy for the Obtention of Tolypothrix Polyethers – Stereoselective Synthesis of a Key Lactone Precursor
Authors: Priepke Henning , Weigand Stefan , Brückner Reinhard
Published: July 2007

A novel access to 1,3,5,7,…︁‐polyols is developed. It follows – in the context of the planned synthesis of the natural permethylated 1,3,5,7,9‐pentaol 1a from the blue‐green alga Tolypothrix conglutinata – the strategy depicted in Scheme 4. The present paper concerns the enantioselective synthesis of the key building block syn‐9a. This γ‐lactone was derived from O‐tert‐butyldiphenylsilylglycidol (R−15) via a synthetic equivalent of the 6‐hydroxy‐4‐ketoester 12 (cf. Scheme 5). As such, we used the hydroxydiene 28 rather than the 2‐(5‐hydroxy‐3‐methylenepentyl)‐1,3‐oxazoline 26 or the (5‐hydroxy‐3‐methylenepentyl)‐substituted orthoester 27 because of its greater ease of preparation (cf. Scheme 7). A double ozonolysis of the hydroxydiene 28 provided the desired 6‐hydroxy‐4‐ketoester 12 itself (Scheme 8). The CO bond of this compound was reduced syn‐selectively (ds = 100:0) through successive additions of Et2B(OMe) and NaBH4 and anti‐selectively (ds = 80:20) through the addition of NaBH(OAc)3 (Scheme 9). The dihydroxy ester syn‐34 formed in the mentioned syn‐selective reduction was isolable or could be lactonized in the presence of acid so that the syn‐configured hydroxy lactone syn‐9a was obtained directly (Scheme 10).
Total Synthesis of the Tolypothrix Pentaether via A Bis(γ‐butyrolactone) → 1,3,7,9‐Tetraol Route
Authors: Allerheiligen Swen , Brückner Reinhard
Published: July 2007

A total synthesis of the permethylether 1 from Tolypothrix conglutinata via a bis(γ‐lactone) intermediate was achieved. It constitutes a methodological complement of our previous syntheses (summarized in Scheme 7) of the same ether via mono(γ‐lactones) as key intermediates. The readily available γ‐lactone 4 and the allyl‐bromide containing lactone cis‐13 derived from 4 as shown in Scheme 3 were combined by a cis‐selective alkylation to the bislactone cis,trans‐14 (Scheme 4). From this bislactone, we removed both carboxylic centers and replaced each of them by a hydroxy group to obtain a single 1,3,7,9‐tetraol. Without purification, this tetraol was protected as bis‐acetonide 15 (Scheme 4; 43% yield over the two steps). In the next three steps the bis‐acetonide olefin 15 was transformed into the bis‐acetonide alcohol 19 (Scheme 5). Compound 19 gave epoxide 21 (Scheme 6) with concomitant inversion of the configuration at the hitherto incorrectly configured stereocenter. Opening the epoxide 21 at the less hindered side with a higher‐order lithium vinyl cyanocuprate, acetonide cleavage, and permethylation of the obtained pentaol finished the synthesis of the target ether 1 (Scheme 6).
Synthesis of rac‐Bisabola‐3(15),10‐dien‐7‐ol
Authors: Weyerstahl Peter , Schlicht Volker
Published: July 2007

1‐Acetyl‐4‐methylenecyclohexane (6) was obtained from ethyl 4‐methylenecyclohexane carboxylate (2), by DIBAH reduction (→ 4), Grignard reaction (→ 5) and oxidation. A further Grignard reaction furnished the rac‐bisabola‐3(15),10‐dien‐7‐ol (1), which we isolated recently from Vetiver oil. Its odor is mainly aldehydic (fatty, floral).
Biologically Active Glycosides from Asteroidea, 37. Glycosphingolipids from the Starfish Luidia maculata, 1 Structure of A New Sulfatide Molecular Species
Authors: Kawatake Satoshi , Inagaki Masanori , Isobe Ryuichi , Miyamoto Tomofumi , Higuchi Ryuichi
Published: July 2007

A sulfatide molecular species [LMG‐1 (1)] have been obtained from the water soluble lipid fraction of the chloroform/methanol extract of the starfish Luidia maculata. On the basis of chemical and spectroscopic findings, the structure of 1 has been elucidated. Negative FAB mass spectrometry provided important information both on the structure of the sugar moiety and on the molecular mass of the sulfatide. 1 is, to the authors' knowledge, new sulfatide molecular species and first sulfatide obtained from starfish. In addition, 1 shows neuritogenic activity toward the rat pheochromocytoma cell line, PC‐12 cell.
Stereoselective Synthesis of the Core Structure of the Nephritogenoside Glycopeptide
Authors: Zhang Hong , Wang Yali , Thürmer René , Meisenbach Mark , Voelter Wolfgang
Published: July 2007

A new strategy for the construction of the O‐glycoside bond in the nephritogenoside unit using the phenylsulfenyl method is reported. The readily accessible phenylsulfinyl glycoside proved to be an excellent glycosyl donor, leading to high yields and good selectivity. The extremely mild conditions utilized in glycosylation reactions allow trityl and other sensitive protecting groups to be used for temporary protection. The fact that phenyl thioglycosides function as glycosyl acceptors during the coupling reaction and can easily be transformed into glycosyl donors by conversion to phenylsulfinyl glycosides, enables complex oligosaccharides to be prepared in a highly convenient manner.
Practical Syntheses of (S)‐4‐Hydroxytetrahydrofuran‐2‐one, (S)‐3‐Hydroxytetrahydrofuran and Their (R)‐Enantiomers
Authors: Yuasa Yoshifumi , Tsuruta Haruki
Published: July 2007

Optically active 4‐hydroxytetrahydrofuran‐2‐one (3) has been synthesized in good yield from optically active ethyl 4‐chloro‐3‐hydroxybutanoate (2) by refluxing with dilute hydrochloric acid. In a similar manner, optically active 3‐hydroxytetrahydrofuran (5) was prepared from optically active 4‐chloro‐1,3‐butanediol (4), which was derived from 2 by NaBH4 reduction. These new cyclizations proceed without racemization.
Synthesis of Thromboxane A2 Models from Glucose. II. Epoxidation Studies of Hex‐2‐enopyranosides
Authors: Cirelli Alicia Fernández , Moradei Oscar , Thiem Joachim
Published: July 2007

The synthesis of halohydrin 7, a potential precursor of the heterocyclic moiety of thromboxane A2 (TXA2) is described. Claisen‐Meerwein‐Eschenmoser rearrangement of hex‐3‐enopyranosides 4 and 8 yields the branched olefin sugars 5 and 9. Epoxidation studies with perbenzimidic acid (Payne's method) and m‐chloroperbenzoic acid (Anderson's method) were performed. Under treatment of the 2,3‐anhydrosugar 6 with LiBr, the epimeric halohydrins 7 and 10 were obtained in a ratio of 3:2.
Flexible Molecules with Defined Shape, VIII. Model Studies and Predictions for the Conformational Behavior of 2,4,6,n‐Polymethylated Alkane Derivatives
Authors: Hoffmann Reinhard W. , Göttlich Richard
Published: July 2007

Conformer equilibria of compounds having a single (6–8) or two (15–17) neighbouring dimethylpentane backbone segments have been studied. As in 2,4‐dimethylpentane, a biconformational situation prevails in each segment. The position of the local conformer equilibria were estimated from vicinal 3JH,H coupling constants between hydrogen atoms along the backbone. The position of the conformer equilibria were also calculated with the MM3* force field in good agreement with the experimental findings. A simple estimate of the position of the local conformer equilibria based on counting the number of the low energy diamond lattice type conformers available was used to discuss the conformer situation in molecules 18 and 19 possessing three adjacent dimethylpentane segments. The results were used to interprete the conformational behaviour of the more complex trimethoxyhexamethylpentadecene 2.
Interactions in Molecular Crystals, 123. Crystallization and Structure of Donor–Acceptor Complexes between Rigid or Conformationally Flexible Thio‐Crowns and Iodine
Authors: Bock Hans , Nagel Norbert , Seibel Andreas
Published: July 2007

Studies of π and σ interactions in molecular crystals of donoracceptor complexes have stimulated interest in the crystallization and structure determination of {1,3,5‐trithiane…︁I2}, {1,5,8,12‐tetrathiocyclotetradecane…︁I2} and {1,4,7,10,13,16‐hexathiocyclooctadecane…︁(I2)3} in order to detect structural changes. The II bond lengths are stretched by up to 0.16 Å relative to the gas‐phase value and prove iodine to be the acceptor species. Additional distance data >S…︁I2 and II from the Cambridge Structural Database establish a nonlinear correlation. In contrast, bond lengths and bond angles of the sulphide donors remain largely unperturbed on complexation, even when considerable conformational changes are observed. For example, on addition of four iodine molecules, the rather flexible 18‐thio‐crown‐6 with a C2‐symmetric bowl‐shape is flattened to a Cs‐symmetric rectangle. The structural results complement those reported for stronger acceptor effects of metal cations.
Non‐Ionic Template Synthesis of Amide‐Linked Rotaxanes: Olefinic and Aliphatic Axle Building Blocks
Authors: Jäger Ralf , Baumann Sven , Fischer Marco , Safarowsky Oliver , Nieger Martin , Vögtle Fritz
Published: July 2007

The first synthesis of amide‐linked rotaxanes with non‐arene axle building blocks is reported. The threading synthesis of rotaxane 8 with olefinic fumaryl chloride proves that arene moieties are not necessary for non‐ionic template syntheses. Mass spectroscopic evidence of a rotaxane bearing an aliphatic axle, derived from succinic acid, revealed that hydrogen bonding, rather than π,π interactions, is the predominant template binding force. 1H‐NMR titration studies on the threading synthesis of these mechanically bonded molecules were carried out. The association constants measured suggest that the incorporation of the corresponding monoamide monochloride (cf. 7), rather than the incorporation of the diacid dichloride (cf. 5), plays the key role in these rotaxane syntheses. The X‐ray structural analysis of a semi axle (14) reveals hydrogen bonding patterns characteristic of diamides.
Radical Additions of Alkyl 2‐Haloalkanoates and 2‐Haloalkanenitriles to Alkenes Initiated by Electron Transfer from Copper in Solvent‐Free Systems
Authors: Metzger Jürgen O. , Mahler Ralf , Francke Gerald
Published: July 2007

Alkyl 2‐iodoalkanoates 2, and 2‐iodoalkanenitriles 15 were added, with copper powder, to the 1‐alkenes 1a, e, f, and h, and to the alkenes 1b, c, d, and g with a 1,2‐dialkyl substituted double bond, to give, respectively, γ‐lactones and 4‐iodoalkanenitriles in very good yields. No solvent was used. The reaction is a free radical addition initiated by electron transfer from copper to the activated iodoalkane. Yields were lower using the respective bromo compounds. In situ formation of the iodo compounds, by addition of stoichiometric amounts of sodium iodide to the reaction mixture, gave improved yields. In the case of the methyl bromomalonates 6, the addition of sodium iodide proved to be unnecessary. The diastereoselectivity of the addition reaction by relative 1,3‐asymmetric induction was rationalized by consideration of the steric interactions of the substituents in the transition state which is formed in the process of iodine transfer to the chiral adduct radical.
Cytotoxic Triterpene Glycosides from Far‐Eastern Sea Cucumbers Belonging to the Genus Cucumaria
Authors: Drozdova Olga A. , Avilov Sergey A. , Kalinin Vladimir I. , Kalinovsky Anatoly I. , Stonik Valentin A. , Riguera Ricardo , Jiménez Carlos
Published: July 2007

New cytotoxic triterpene oligoglycoside disulfates, cucumariosides A3 (1) and A6‐2 (2), have been isolated from the sea cucumber Cucumaria japonica. The trisulfated cucumarioside A7‐3 (4) was found to be the major component in the glycoside fraction of Cucumaria miniata. The structures were assigned on the basis of extensive spectral data (NMR and MS), selective solvolysis of desulfated derivative 3 and other chemical evidence. The presence or absence of a carbonyl group at C‐16 of the aglycone and of sulfate groups at C‐6 of the glucose and 3‐O‐methylglucose units are interpreted in terms of the functional evolution of sea cucumbers in order to improve their defensive system. Both (1) and (2) are cytotoxic in vitro at IC50 = 1 μg/ml against a selection of five human and mice tumoral cell lines.
Diastereoselective Protonation of Chiral Enolates with Chelating Proton Donors under Reagent Control: Scope, Mechanism, and Applications
Authors: Krause Norbert , Ebert Sophia , Haubrich Andreas
Published: July 2007

Endocyclic keto‐enolates of type 2 can be protonated under reagent control with high diastereoselectivities when chelating proton donors with a salicylate structure are used. The stereochemical course of these protonations is hardly affected by the ring size, the substitution pattern, and the presence of additional stereogenic centers in the enolate. The substrates can be prepared by conjugate cuprate addition as well as deprotonation; in the latter case, good diastereoselectivities are obtained by removal of competing proton sources and the inclusion of transmetalation steps. The chelate complex A serves as a mechanistic model that makes the usual trial and error search for stereoselective protonating agents unnecessary. The method is applied to stereoselective syntheses of a precursor for methyl epijasmonate and of the insect pheromone (2S,3S)‐diprionyl acetate.
Total Synthesis of (+)‐3‐Oxacarbacyclin 1. Retrosynthesis and Asymmetric Olefination through Horner–Wadsworth–Emmons, Peterson and Martin Reactions
Authors: Gais Hans‐Joachim , Schmiedl Gerhard , Ossenkamp Rainer K. L.
Published: July 2007

The asymmetric Horner–Wadsworth–Emmons (HWE) reaction of the prochiral ketones 8a/b with the phosphonoacetates 10a, ent‐10a, 10b and rac‐16, which contain 8‐phenylmenthol, 8‐phenylnormenthol and trans‐2‐(triphenylsilyl)‐cyclohexanol, respectively, as chiral auxiliaries, were studied. The HWE reaction of 8a with the phosphonoenolates Li‐10a/b at low temperatures gave the esters 7a/b and 11a/b in high yields with diastereoselectivities up to 97:3. The (E)‐configured esters 7a/b serve as starting material for the total synthesis of (+)‐3‐oxacarbacyclin. Similarly, the reaction of 8b with ent‐Li‐10a gave the esters ent‐7b and ent‐11b in a ratio of 95:5 in 82% yield. The olefination of 8b with rac‐16 afforded a mixture of the esters rac‐17 and rac‐18, of yet unassigned configuration, in a ratio of 70:30. The HWE reactions of 8a/b with Li‐10a, ent‐Li‐10a and rac‐Li‐10b show linear temperature–diastereoselectivity relationships. The stereochemical course of the HWE reactions can be understood in terms of a selective addition of the chiral (E)‐configured phosphonoenolate from its least hindered side to the ketone 8 at the convex side. The asymmetric Peterson reaction of 8b with the silyl enolate Li‐20 gave the esters ent‐7b and ent‐11b in a ratio of 89:11. The diastereomerically pure β‐hydroxy esters 22, rac‐25 and 27, which contain 8‐phenyl‐menthol, trans‐2‐(triphenylsilyl)cyclohexanol and 3‐{[(3,5‐dimethylphenyl)phenylsulfonyl]amino}isoborneol, respectively, as chiral auxiliaries, were prepared by a highly selective addition of the enolates Li‐21, rac‐Li‐24 and Li‐26 to the ketone 8b. The asymmetric Martin dehydration of 22, rac‐25 and 27 with the sulfurane 23 proceeds with stereoselectivities ranging from 82:18 to 99:1. Interestingly, the HWE, Peterson and Martin reactions involving 8‐phenylmenthol as the chiral auxiliary all proceed with the same sense of asymmetric induction.
Transitions of Electron Demand in Pericyclic Reactions: Normal, Neutral, and Inverse Diels–Alder Reactions of Polyhalogenated Cyclopentadienes
Authors: Eibler Ernst , Höcht Peter , Prantl Bernhard , Roßmaier Henry , Schuhbauer Hans Markus , Wiest Hubert , Sauer Jürgen
Published: July 2007

Normal, neutral, and inverse‐type Diels‐Alder reactions can be observed in [4+2] cycloadditions of polyhalogenated cyclopentadienes 1a–1i with various aryl‐substituted cyclic and open‐chain dienophiles, and characteristic gradations of reactivity associated with the different mechanistic types are often displayed. Reaction rate constants and semiempirically derived HOMO and LUMO values for the reactants suggest that neutral [4+2] cycloadditions should be regarded as a transition between normal and inverse Diels‐Alder reactions.
Pheromone Synthesis, CLXXXVI. Synthesis of (1S,2R,5R)‐Bicolorin, the Aggregation Pheromone of Male Beech Bark Beetles (Taphrorychus bicolor), and Its (1R,2R,5S) Isomer
Authors: Takikawa Hirosato , Sano Satoshi , Mori Kenji
Published: July 2007

(−)‐Bicolorin [(1S,2R,5R)‐(−)‐2‐ethyl‐1,5‐dimethyl‐6,8‐dioxabicyclo[3.2.1]octane (1)], the male‐produced pheromone of Taphrorychus bicolor, and its (1R,2R,5S) isomer 2 were synthesized by starting from (S)‐limonene oxide (3), employing osmium tetroxide catalyzed dihydroxylation of 7b as the key step.
Isofulminic Acid – Phantom or Reality?
Authors: Maier Günther , Bothur Axel , Eckwert Jürgen , Reisenauer Hans Peter , Stumpf Thomas
Published: July 2007

The complex photochemistry of matrix‐isolated dihaloformoximes 8a, 8b, and 8c, which are transformed upon irradiation into the new hydrogen‐bonded complexes HalCN…︁HOHal 10a–c′, identified by their IR spectra, has been unveiled. An earlier assignment of the experimental IR absorptions to isofulminic acid HONC (4) must be withdrawn. A competitive reaction to the formation of complexes 10a–c′ produces the hydrogen‐bonded complexes HalNCO/HHal 12a–c′, which can be regarded as intermediates on the photochemical pathway to the final product isocyanic acid HNCO (1), and are tentatively identified by their IR absorptions. Our findings are supported by deuteration experiments and theoretical calculations using the density functional method BLYP/6‐311G*.
Structure, Conformation, and Thermochemistry of Dimesityl Methanethial S‐oxide (Dimesityl Sulfine)
Authors: Kappert Wilhelm , Sander Wolfram , Landgrafe Claudia
Published: July 2007

The structure of dimesityl sulfine in solution and in the solid state was determined by NMR spectroscopy and X‐ray crystallography, respectively. In the crystal the two mesityl groups are twisted by approximately 60°, while in solution an averaged conformation with Cs symmetry is observed, with the anti mesityl ring located in the CSO plane and the syn mesityl ring perpendicular to the CSO plane. From the coalescence temperature Tc at 303 K, the free energy of activation for the rotation of the mesityl rings was estimated to be 14 ± 0.7 kcal/mol. At higher temperatures (140–185°C) dimesityl sulfine yields up to 95% 5,7‐dimethyl‐1‐mesityl‐benzo[c]thiophene.
Addition and Cyclization Reactions in the Thermal Conversion of Hydrocarbons with an Enyne Structure, 4. Formation and Rearrangements of Bicyclic C10H8 Aromatics from 1‐Phenyl‐1‐buten‐3‐yne
Authors: Schulz Kathrin , Hofmann Jörg , Zimmermann Gerhard
Published: July 2007

The thermal conversion of 1‐phenyl‐1‐buten‐3‐yne (1) into the cycloisomerization products naphthalene (2), azulene (3), and 1‐methylene‐1H‐indene (4) has been studied at temperatures between 550 and 1000°C, a reaction time of approximately 0.3 s at 13 Torr (FVP) and at low partial pressures in a quartz flow system. The results obtained by FVP as well as in the presence of chemically modified diluent gases suggest a predominance of unimolecular cycloisomerizations to 2 and 3 which are, however, always accompanied by radical cyclization reactions to 2 and 4 even under FVP conditions if temperatures above 550°C are applied.
Methylamination of Some 3‐Nitro‐1,8‐naphthyridines with Liquid Methylamine/Potassium Permanganate
Authors: Woźniak Marian , Grzegoz̊ek Maria , Surylo Piotr
Published: July 2007

3‐Nitro‐1,8‐naphthyridines (1a–1h) are aminated, with a liquid methylamine solution of potassium permanganate (LMA/PP), to the corresponding 4‐methylamino‐substituted nitro compounds (3a–g). The intermediary 4‐methylamino‐σ‐adducts of some 3‐nitro‐1,8‐naphthyridines are detected by 1H‐NMR spectroscopy. Quantum chemical calculations show the reactions to be controlled by the interaction of the frontal molecular orbitals (FMO) of the reagents. Moreover, the heats of formation of the intermediary methylamino‐σ‐adducts of 1a and 1c–1h and transition states are calculated for the reactions studied. The agreement, between the calculated and observed results, is satisfactory for the reactions described.
Synthesis, Solvatochromism, and Molecular Structure of a New Pyridinium N+N− Betaine Dye
Authors: Milart Piotr , Stadnicka Katarzyna
Published: July 2007

Two methods for the synthesis of N‐[4‐(2,4,6‐triphenyl‐1‐pyridinio)phenyl]‐p‐toluenesulfonaminide (4), a new betaine dye with positive and negative charges at two nitrogen atoms separated by an aromatic ring, are described. 4 displays a negative solvatochromic effect slightly smaller than that observed for the standard betaine 1 [ET(30) scale]. X‐ray structure determination of crystals containing 4 and acetone solvate molecules in the molar ratio of 1:1 revealed that the geometry of the pyridinium moiety is strongly influenced by the negatively charged aminide nitrogen atom.
Morphology of the mammalian vestibulo‐ocular reflex: The spatial arrangement of the human fetal semicircular canals and extraocular muscles
Authors: Cox Philip G. , Jeffery Nathan
Published: July 2007

The vestibulo‐ocular reflex is the system of compensatory ocular movements in response to stimulation of the kinetic labyrinth seen in all vertebrates. It allows maintenance of a stable gaze even when the head is moving. Perhaps the simplest influence on the VOR is the spatial orientation of the planes of the semicircular canals relative to the extraocular muscles. It is hypothesized that the extraocular muscles are in parallel alignment with their corresponding semicircular canals in order to reduce the amount of neural processing needed and hence keep reflex times to a minimum. However, despite its obvious importance, little is known of this spatial arrangement. Moreover, nothing is known about any ontogenetic changes in the relative orientations of the extraocular muscles and semicircular canals. The morphologies of fetal and adult specimens of Homo sapiens were examined using magnetic resonance (MR) images. Three‐dimensional co‐ordinate data were taken from the images and used to calculate vector equations of the extraocular muscles and planes of best fit for the semicircular canals. The relative orientations of the muscles and canals were then calculated from the vectors and planes. It was shown that there are significant correlations between both the anterior and lateral semicircular canals and their corresponding extraocular muscles during ontogeny. In the case of the lateral canal with the medial rectus, the lateral canal with the lateral rectus, and the anterior canal with the inferior oblique, the trend is towards, though never reaching, alignment, whereas the anterior canal and the superior rectus muscle move out of alignment as age increases. Furthermore, it was noted that none of the six muscle‐canal pairs is in perfect alignment, either during ontogeny or in adulthood. It was also shown that the three semicircular canals are not precisely orthogonal, but that the anterior and posterior canals form an angle of about 85°, while the anterior and lateral canals diverge by ∼100°. Overall, it was shown that there is significant reorientation of the extraocular muscles and semicircular canals during ontogeny, but that, in most cases, there is little realignment beyond the fetal period. J. Morphol., 2007. © 2007 Wiley‐Liss, Inc.
Dynamic contrast‐enhanced magnetic resonance imaging of human melanoma xenografts with necrotic regions
Authors: Gaustad Jon‐Vidar , Benjaminsen Ilana C. , Ruud Else‐Beate M. , Rofstad Einar K.
Published: July 2007

Purpose

To investigate whether high‐resolution images of necrotic regions in tumors can be derived from gadopentetate dimeglumine (Gd‐DTPA)‐based dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) series.

Materials and Methods

E‐13 human melanoma xenografts were used as preclinical models of human cancer. DCE‐MRI was performed at a voxel size of 0.23 × 0.47 × 2.0 mm3 with the use of spoiled gradient recalled sequences. Tumor images of E · F (E is the initial extraction fraction of Gd‐DTPA and F is blood perfusion) and λ (the partition coefficient of Gd‐DTPA, which is proportional to extracellular volume fraction) were produced by subjecting DCE‐MRI series to Kety analysis, and these images were compared with histological preparations from the imaged slices.

Results

Strong correlations were found between fraction of necrotic tissue and fraction of voxels with λ > λL for λL values of 0.4 to 0.6. Binary λ images differentiating between λ values > λL and λ values < λL were found to mirror necrotic regions well in tumors with large necroses. However, necrotic foci that were small compared with the voxel size were not detectable.

Conclusion

Clinically relevant images of necrotic tumor regions can be obtained for E‐13 melanomas by subjecting Gd‐DTPA‐based DCE‐MRI series to Kety analysis. J. Magn. Reson. Imaging 2007;26:133–143. © 2007 Wiley‐Liss, Inc.
Solitary fibrous tumor of the pleura: Apparent diffusion coefficient (ADC) value and ADC map to predict malignant transformation
Authors: Inaoka Tsutomu , Takahashi Koji , Miyokawa Naoyuki , Ohsaki Yoshinobu , Aburano Tamio
Published: July 2007

Solitary fibrous tumors (SFTs) of the pleura are rare soft‐tissue tumors that are presumed to be of mesenchymal origin. Most SFTs are histologically benign, but up to 20% of SFTs may be malignant. In addition, malignant transformation may occur within histologically benign SFTs, though it is rare. However, it is difficult to diagnose malignant SFTs of the pleura by means of conventional computed tomography and magnetic resonance imaging (MRI). In this article we present the first case of malignant SFT of the pleura in an 81‐year‐old man in which the apparent diffusion coefficient (ADC) value and ADC map based on diffusion‐weighted MRI were very useful for identifying malignant transformation. J. Magn. Reson. Imaging 2007;26:155–158. © 2007 Wiley‐Liss, Inc.
Applications of multislice computed tomography in coronary artery disease
Authors: de Roos Albert , Kroft Lucia J.M. , Bax Jeroen J. , Geleijns Jacob
Published: July 2007

Multislice computed tomography (MSCT) provides high accuracy for noninvasive assessment of coronary artery disease (CAD). The introduction of the latest computed tomography (CT) technology allows comprehensive evaluation of various aspects of CAD, including the coronary calcium score, coronary artery stenoses, bypass patency, and myocardial function. Other applications, such as plaque characterization, first‐pass perfusion imaging, and viability imaging using delayed contrast enhancement, are still under development and may demonstrate clinical utility in the future. Further improvements in CT hardware and imaging protocols are expected that may result in improved coronary artery imaging, new applications, and a significant reduction of radiation dose. J. Magn. Reson. Imaging 2007;26:14–22. © 2007 Wiley‐Liss, Inc.
Improved transverse relaxation rate measurement techniques for the assessment of hepatic and myocardial iron content
Authors: Song Ruitian , Cohen Alan R. , Song Hee Kwon
Published: July 2007

Purpose

To develop and validate an optimized respiratory‐gated, gradient‐echo sampling of free induction decay and echo (GESFIDE) pulse sequence for the simultaneous measurement of R2, R2*, and R2′ in the liver or heart.

Materials and Methods

Fifteen subjects (12 thalassemia patients and three normal volunteers) were scanned using an optimized navigator‐gated GESFIDE pulse sequence for the measurement of R2, R2*, and R2′ in the liver and heart. For imaging the myocardium, dark‐blood preparation was used to suppress the blood signal to improve accuracy. The results were compared with those obtained from breath‐held GESFIDE and multi‐gradient‐echo (GRE) scans.

Results

Good agreement between breath‐held and navigator‐gated scans was found for R2, R2*, and R2′ values in the liver (slopes = 0.97–0.99, r = 0.997–0.998, P < 0.0001) and for R2* in the heart (slope = 1.02, r = 0.85, P < 0.0001). Both R2* and R2′ were closely correlated to R2 in the liver, with correlation factors of 0.998 and 0.994, respectively, but weaker correlations were observed in the heart (r = 0.72 for R2* vs. R2 and r = 0.51 for R2′ vs. R2).

Conclusion

The improved sequence enables free‐breathing measurements of transverse relaxation rates of the myocardium and liver. The method precludes the need for multiple breath‐held scans and possible misregistration issues, and may prove most beneficial for imaging young children and patients who may have difficulty with prolonged or repeated breath‐holds. J. Magn. Reson. Imaging 2007;26:208–214. © 2007 Wiley‐Liss, Inc.
T2mapping of hip articular cartilage in healthy volunteers at 3T: A study of topographic variation
Authors: Watanabe Atsuya , Boesch Chris , Siebenrock Klaus , Obata Takayuki , Anderson Suzanne E.
Published: July 2007

Purpose

To perform baseline T2mapping of the hips of healthy volunteers, focusing on topographic variation, because no detailed study has involved hips. T2mapping is a quantitative magnetic resonance imaging (MRI) technique that evaluates cartilage matrix components.

Materials and Methods

Hips of 12 healthy adults (six men and six women; mean age = 29.5 ± 4.9 years) were studied with a 3.0‐Tesla MRI system. T2measurement in the oblique‐coronal plane used a multi‐spin‐echo (MSE) sequence. Femoral cartilage was divided into 12 radial sections; acetabular cartilage was divided into six radial sections, and each section was divided into two layers representing the superficial and deep halves of the cartilage. T2of these sections and layers were measured.

Results

Femoral cartilage T2was the shortest (–20° to 20° and –10° to 10°, superficial and deep layers), with an increase near the magic angle (54.7°). Acetabular cartilage T2in both layers was shorter in the periphery than the other parts, especially at 20° to 30°. There were no significant differences in T2between right and left hips or between men and women.

Conclusion

Topographic variation exists in hip cartilage T2in young, healthy adults. These findings should be taken into account when T2mapping is applied to patients with degenerative cartilage. J. Magn. Reson. Imaging 2007;26:165–171. © 2007 Wiley‐Liss, Inc.
Priming effects in soil size fractions of a podzol Bs horizon after addition of fructose and alanine
Authors: Ohm Heike , Hamer Ute , Marschner Bernd
Published: July 2007

It is well known that the addition of easily available substrates to soils can affect microbial activity and thus the mineralization of soil organic carbon (SOC). Up to now, little is known about the processes leading to these priming effects and which fractions of organic matter (OM) are affected. The objectives of this study were to determine if SOC associated with isolated soil size fractions showed different susceptibility to priming effects, whether these pools are easily depleted, or whether the amount of substrate addition affects the extent of priming effects. In an incubation experiment, the effect of the uniformly 14C‐labeled substrates fructose and alanine on the mineralization of the SOC of a Bs horizon of a Haplic Podzol was investigated. The soil sample was fractionated into the three soil size fractions sand, silt, and clay by a mild sonication followed by sieving and sedimentation. Additionally, nonfractionated soil of the horizon was included in the experiment. Every soil sample received four substrate additions repeated at weekly intervals with 3.325 μg substrate‐C (mg SOC)–1 and a final addition of 13.3 μg substrate‐C (mg SOC)–1 after 4 weeks. The respiration was determined hourly and 14CO2 was analyzed every 2, 4, and 7 d after the respective substrate addition. After 56 d, between 42% and 58% of the added substrates had been mineralized. Both substrates strongly increased the mineralization of the OM in all fractions (positive priming effects). The priming effects were always higher after the addition of the high substrate dose than during the first 4 weeks when four small doses were added. In general, the priming effects increased with decreasing particle size. Alanine generally caused higher priming effects than fructose in the soil size fractions (up to 280% vs. 231%, respectively). This indicates that alanine serves not only as an energy substrate but also as a N source and, thus, also promotes microbial growth. The strong priming effects in the silt and clay fraction (133% and 125% with fructose, 172% and 168% with alanine) showed, that not only the labile pool of OM is affected, but also a more stable pool characterized by higher 14C ages. We assume that the stability of the OM in these fractions is not only due to recalcitrance or to interactions with the minerals, but that it may also be caused by a substrate limitation of the degrading microorganisms.
Simulated consumer use of a battery‐powered, hand‐held, portable diode laser (810 nm) for hair removal: A safety, efficacy and ease‐of‐use study
Authors: Wheeland Ronald G.
Published: July 2007

Background and Objectives

Safety, efficacy and ease‐of‐use of a hair removal diode laser for consumer use were evaluated.

Study Design/Materials and Methods

The treatment group consisting of 77 appropriate users measured safety and efficacy from three self‐administered treatments. The non‐treatment group consisting of 44 inappropriate users measured safety from delivery of a single laser pulse.

Results

The mean hair reduction was 61% 3 weeks after the first treatment, 70% 3 weeks after the second treatment, 60% 1 month after the third treatment, 24% 2 months after the third treatment, 6% 3 months after the third treatment, 41% 6 months after the third treatment, 31% 9 months after the third treatment, and 33% 12 months after the third treatment. The only observed side effect for appropriate users was transient erythema.

Conclusions

In simulated consumer use, the laser was highly effective at removing hair with minimal side effects for appropriate users. Lasers Surg. Med. 39:476–493, 2007. © 2007 Wiley‐Liss, Inc.
Synthesis of Arborescent Copolymers by a One‐Pot Method
Authors: Yuan Zhongshun , Gauthier Mario
Published: July 2007

A “grafting from” scheme was developed for the preparation of arborescent copolymers in one single reactor, by anionic copolymerization of styrene with 1,3‐diisopropenylbenzene and activation of the pendent isopropenyl moieties with sec‐butyllithium. Arborescent polystyrene‐graft‐poly(tert‐butyl methacrylate) copolymers were thus obtained by addition of tert‐butyl methacrylate to linear and G0 macroinitiators, respectively. Arborescent polystyrene‐graft‐[polystyrene‐block‐poly(2‐vinylpyridine)] copolymers were also synthesized by successive additions of styrene and 2‐vinylpyridine to the same macroinitiators. The copolymers were characterized by SEC‐MALLS and 1H NMR analysis.

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Mass Ratio of CdS/Poly(ethylene oxide) Controlled Photoluminescence of One‐Dimensional Hybrid Fibers by Electrospinning
Authors: Wang Cheng , Yan Eryun , Sun Zhiyao , Jiang Zijiang , Tong Yanbin , Xin Yi , Huang Zonghao
Published: July 2007

One‐dimensional high‐quality CdS/poly(ethylene oxide) (PEO) hybrid nanoparticle‐polymer fibers were fabricated by an electrospinning method, followed by self‐assemble technologies with co‐fed H2S atmosphere at 60 °C. The structural and spectral information of the resulting hybrid nanofibers was characterized by field emission scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy and X‐ray diffractometer. The diameters of CdS/PEO hybrid nanofibers ranged from 90 to 200 nm and the average dimension of CdS nanoparticle within fibers from 4 to 12 nm. An interesting aspect of the CdS/PEO nanofibers shown in photoluminescence spectra and fluorescence images is that the fluorescence peaks of CdS/PEO were shifted along with changing the mass ratio of CdS/Poly(ethylene oxide), and consequently the size and phase of nanocrystal CdS.

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Ethylene‐Norbornene Copolymerization by New Titanium Complexes Bearing Tridentate Ligands. Sidearm Effects on Catalytic Activity
Authors: Gao Mingli , Wang Cong , Sun Xiuli , Qian Changtao , Ma Zhi , Bu Shizheng , Tang Yong , Xie Zuowei
Published: July 2007

The Ti complexes containing tridentate [O−NSR] (R = Me, iPr) ligands with alkylthio sidearms were prepared. The methylthio ether complex (R = Me shown in the Scheme) exhibits an excellent activity for copolymerization of ethylene with norbornene upon activation with MMAO, which is 10 times more active than the corresponding phenylthio one (R = Ph).

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