bluuebunny/crossref_metadata_2025 huggingface dataset:
Enzymatic optical resolution of a synthetic pyrethroid alcohol. Enantioselective transesterification by lipase in organic solvent
Authors: Mitsuda Satoshi , Nabeshima Shigeyasu
Published: September 2010

To obtain (S)‐4‐methyl‐1‐heptyn‐4‐en‐3‐ol [(S)‐1a], enzymatic enantioselective esterification of (R,S)‐1a in organic solvent was examined. Pseudomonas lipase catalyzed the transesterification of (R,S)‐1a with vinyl acetate in n‐hexane, and gave (S)‐1a and the corresponding acetate of (R)‐1a with good enantioselectivity and high reaction rate. The reaction was accelerated by increasing the hydrophobicity of the organic solvent used as reaction medium and decreasing the water content of the reaction mixture. Under optimum conditions, (S)‐1a of 99% ee was obtained at a conversion ratio of 68.6%. A kinetic udy revealed that the enzymatic reaction proceeded under the ping‐pong mechanism involving the acyl‐enzyme as an intermediate.
Formation of a distibacyclooctane; X‐ray crystal structure of 1,5‐dichloro‐1,3,3,5,7,7‐hexamethyl‐9‐oxa‐1,5‐distibabicyclo[3.3.1]nonane hydrochloride
Authors: Tinga M. A. G. M. , Groeneveld M. K. , Akkerman O. S. , Bickelhaupt F. , Smeets W. J. J. , Spek A. L.
Published: September 2010

The reaction of methylantimony dichloride with (2,2‐dimethyl‐1,3‐propanediyl)bis(magnesium bromide) (1), followed by oxidation with sulfuryl chloride and partial hydrolysis, gave the title compound 7. No evidence could be obtained for the formation of a stibacyclobutane in this reaction. Crystals of the title compound were block shaped, space group Pl̄ with a = 8.901(1), b = 9.378(1), c = 12.084(2) Å, α = 80.61(1), β = 89.01(1), γ = 72.41(1)°. The structure was solved using standard Patterson and Fourier methods and refined by full‐matrix least‐squares techniques to a final R = 0.036 for 3356 observed reflections.
Iodonium ion‐promoted glycosidation of sugar 1,2‐thio‐orthoesters
Authors: Zuurmond H. M. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Sugar 1,2‐thio‐orthoesters could be condensed with terminal glycosidic acceptors using halonium ion sources (IDCP, NIS/TfOH, NCS/TfOH) as activators. IDCP or NIS/TfOH‐assisted glycosidation of sugar 1,2‐thio‐orthoesters with disarmed alkyl 1‐thioglycosides gave chemoselectively the 1,2‐disarmed orthoester or 1,2‐trans linked disaccharides, respectively.
Chiral catalysts for enantioselective carbenoid cyclopropanation reactions
Authors: Doyle Michael P.
Published: September 2010

Chiral copper(I) and rhodium(II) catalysts designed to achieve enantioselection in cyclopropanation reactions have recently been reported. These catalysts react with diazo compounds to form intermediate metal carbenes that subsequently react with alkenes, in both intermolecular and intramolecular transformations, to form cyclopropane derivatives. They are constructed with chiral ligands whose function is to orient carbene substituents and control olefin approach to the carbenoid center. Enantioselectivities that are greater than 95% have been achieved.

In this review, the major advances in chiral catalyst design and development are described, and a uniform mechanistic interpretation is advanced to explain the results accumulated in reported investigations. Focus is placed on chiral salicylaldimine and semicorrin/bis‐oxazoline copper catalysts and on the newest class of chiral catalysts for enantioselective carbenoid reactions, rhodium(II) carboxamides. Although early in their development, sufficient advances have been made to justify placement of this catalytic methodology among the most promising for enantioselective cyclopropanation reactions.
Solid‐phase synthesis of RNA via a silyl‐protecting‐group strategy
Authors: Dreef‐Tromp C. M. , van Dam E. M. A. , van den Elst H. , van den Boogaart J. E. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Ribonucleoside phosphoramidites have been prepared of which the exocyclic amino functions and 2′‐hydroxyl functions are protected with 2‐[(tert‐butyldiphenylsiloxy)methyl]benzoyl groups and tert‐butyldimethylsilyl groups, respectively. The N‐SiOMB/O‐TBDMS‐blocked nucleosides proved to be suitable building units in a solid‐phase synthesis of the RNA‐fragment 5′‐AGAGUACCU‐3′ via a phosphite triester approach.
Synthesis of 17‐(isocyanotosylmethylene) steroids: Precursors to pregnane derivatives
Authors: van Leusen Daan , van Leusen Albert M.
Published: September 2010

The synthesis is described of a series of twenty 17‐(isocyanotosylmethylene) steroids 5 from 17‐oxo steroids and 4‐tolylsulfonylmethyl isocyanide (TosMIC). Furthermore, nine analogous 17‐(isocyanosulfonylmethylene) steroids (15–21a) have been prepared using sulfonylmethyl isocyanides other than TosMIC. The synthesis of four new TosMIC analogues is described.
Reductive cleavage of the carbonphosphorus bond with alkali metals. II. Cleavage of mixed functionalized triarylphosphines; Birch reduction of arylphosphines
Authors: van Doom Johannes A. , Frijns John H. G. , Meijboom Nico
Published: September 2010

The reductive cleavage of mixed ortho‐ and para‐functionalized triarylphosphines with Na/NH3 and Li/THF depends strongly on the nature and positions of the substituents. Reduction occurs readily with phosphines PhAr2P (4, 6 and 9) and Ph2ArP 19 when the corresponding phosphine Ar3P is not reduced. Cleavage of para‐substituted compounds 7 and 9 leads to mixtures of secondary phosphines. By contrast, cleavage of mixed ortho‐substituted triphenylphosphines is very selective. The functionalized phenyl group is split off in high yield when it carries CH3, (CH3)2N and CH3O substituents (2, 3, 5, 6, 8, 10, 11, 13, 14, 17, 19, 24, 25). Reaction of 4 is not selective due to loss of methoxy groups. By contrast, the phenyl group is split off when the mixed phosphine contains phenoxide groups (1, 15, 16). The reactions of bis‐ and tris(diphenylphosphino)benzenes with Li/THF lead predominantly to cleavage of the diphenylphosphino group from the respective substrates.

In a number of cases, the product of a Birch reduction with an isolated diene system is formed in NH3 (1, 9, 12, 21, 23) via a phosphino‐stabilized cyclohexadienyl anion. This reduction does not occur in the aprotic solvent THF. Base‐catalyzed isomerization leads to a conjugated double‐bond system with a vinylphosphine moiety.

We also report interesting large aJ(PP) couplings in 1,3‐diphosphinobenzenes and complicated 13C resonances of para‐substituted phosphines.
Conformational analysis of longicyclene: A 600 MHz 1H‐NMR and molecular mechanics study
Authors: Lankhorst Peter P. , van Beek Teris A. , Haasnoot Cornells A. G.
Published: September 2010

The complete assignment of the 1H‐NMR spectrum of the fully saturated tetracyclic sesquiterpene hydrocarbon longicyclene is presented. The assignment was achieved using phase‐sensitive double‐quantum filtered COSY at 600 MHz, heteronuclear correlation spectroscopy and COLOC spectroscopy. Accurate vicinal 1H‐1H coupling constants involving the seven‐membered ring protons were obtained using extensive simulation of the ID spectrum.

Molecular mechanics calculations indicate that the title compound may adopt two conformations which differ mainly in the geometry of the seven‐membered ring. These geometries are best described as twist‐chair‐like conformations denoted TC11 and TC8, respectively. The energy of the TC11 conformer is predicted to be slightly lower (4.6 kJ/mol) than the energy of the TC8 conformer. The vicinal 1H‐1H coupling constants of these two conformers were predicted from a generalized Karplus equation. The predicted coupling constants agree well with the experimental coupling constants if it is assumed that, in solution, longicyclene is engaged in a conformational equilibrium between TC11 (86%) and TC8 (14%).
Polymer networks: Formation and structure
Authors: Du Šek Karel
Published: September 2010

The features of network‐formation processes, network‐formation theories and their applications to simple and more complicated systems are briefly reviewed. Network‐formation theories describe changes in structure as a function of an evolution parameter of the system. The existing theories can be grouped into two major categories: (a) off‐space graph models of structure growth (statistical simulation of the growth from units and kinetic simulation) and (b) simulation of the growth in space (percolation). However, models of group (a) can be modified to treat spatial correlations approximately. The applications of the network formation theories to various model systems important for testing network formation and rubber elasticity theories are briefly discussed.
Reactions of styrene and derivatives with sulfur trioxide; characterization and chemistry of the initial products
Authors: Schonk Ruud M. , Bakker Bert H. , Cerfontain Hans
Published: September 2010

The reactions of styrene derivatives 1a‐14a with sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 mol equiv. of dioxane as reactivity moderator. Reaction of styrene (1a) at low temperature yields the carbyl sulfate 1c as the only observable intermediate in the ultimate formation of (E)‐2‐phenylethene‐1‐sulfonic acid (1d). The (phenyl) substituted styrenes 3a‐5a clearly demonstrate the presence of the β‐sultones 3b‐5b as the sole initial products leading to the corresponding carbyl sulfates 3c‐5c. The initially formed β‐sultone b in the reaction of styrene derivatives 3a‐5a, 9a and 10a with 1.0 mol equiv. of SO3 disproportionates to yield equal amounts of the corresponding carbyl sulfate and the starting styrene. This is thought to indicate that there is an equilibrium between the β‐sultone and the starting styrene. The group of the 1‐methyl‐substituted styrenes 11a‐13a are an exception to the generally observed eventual conversion of the initial intermediates into the 2‐sulfonic acids d, since they give the corresponding 3‐sulfonic acids f.

Mechanisms for the formation of the various products are proposed.
Synthesis and biological evaluation of A‐ring analogs of the natural germination stimulant strigol
Authors: Mangnus E. M. , Zwanenburg B.
Published: September 2010

An A‐ring‐derived analog of the natural germination stimulant, Strigol (1), has been prepared from citral in an unambiguous manner. This analog, 2, a γ‐hydroxy aldehyde for which a high stimulant activity was claimed in the literature, has been re‐evaluated as a germination stimulant for seeds of parasitic weeds and was found to be inactive. It was also shown that analog 2 is rather stable in aqueous solution, in contrast to other reports.

In addition, some related A‐ and AB‐ring‐derived analogs have been prepared and biologically evaluated. The γ‐hydroxy acid 12 was obtained in one step from a mixture of α‐ and β‐cyclocitral in 58% yield. The dihydroxy analog 14 was prepared by reduction of the γ‐hydroxy ester 13. The AB‐ring analog 15 has been synthesized in five steps from ester 13 following published procedures. All analogs have been evaluated using Striga and Orobanche seeds; none of the compounds induced germination. It was concluded that the actiphore of strigol does not reside in the AB part of the molecule.
Competing concepts in electronic control of face selection
Authors: Li Haifang , Le Noble William J.
Published: September 2010

The addition of reagents to trigonal carbon to give tetrahedral centers and its reverse involve the stereogenetic aspect known as face selection, which has ramifications throughout organic chemistry. Some of the root factors of face selection (e.g., steric and conformational) have long been understood in principle, but the electronic contribution of substituents and skeletal changes is controversial. The principal models for the electronic basis of face selection are those of Felkin, Anh and Cieplak. It is argued that none of the three are either right or wrong, but that the contribution each can make, varies from case to case. Each of them may become dominant depending on the reaction at issue.
Computer tools for reaction retrieval and synthesis planning in organic chemistry. A brief review of their history, methods, and programs
Authors: Ott Martin A. , Noordik Jan H.
Published: September 2010

An overview is presented of computer programs designed to assist the synthetic organic chemist. Reaction retrieval, reaction prediction, and synthesis design programs are discussed, the development of these systems is outlined, and their aims and possibilities are described. Brief accounts of some representative systems are given.
Computer‐assisted synthetic analysis. Quantitative assessment of transform utilities
Authors: Corey E. J. , Long Alan K. , Lotto Gerald I. , Rubenstein Stewart D.
Published: September 2010

A novel scheme for assigning initial, or substrate‐independent, ratings for transforms (retroreactions) in the chemical knowledge base for the LHASA program for computer‐assisted synthetic analysis is described. The new rating scheme is based on keyword scales defined for eight rating criteria. Initial ratings are calculated as weighted averages of the ratings in the eight categories. Various applications of initial ratings in LHASA are outlined.
Calix[4]arenes as building blocks for molecular receptors
Authors: van Loon Jan‐Dirk , Heida Jan F. , Verboom Willem , Reinhoudt David N.
Published: September 2010

Molecular receptors for organic molecules are described in which calix[4]arene is used as a molecular platform rather than for its cavity. This is illustrated by the synthesis of a receptor for barbiturates, a calix[4]arene in a cone conformation containing two diaminotriazine moieties at the upper rim. This receptor (9) forms a molecular cleft in which phenobarbital complexes by hydrogen bonding both triazine rings. The association constant K is 520 M 1, when the self‐association of the barbiturate is taken into account.
Molecular recognition of barbiturates by a metalloreceptor
Authors: van Doorn Arie R. , Rushton David J. , van Straaten‐Nijenhuis Wilma F. , Verboom Willem , Reinhoudt David N.
Published: September 2010

Metallomacrocycle 2, possessing an immobilized Lewis‐acidic uranyl cation, was synthesized by reaction of aldehyde 9 with 1,2‐cis‐cyclohexanediamine in the presence of Ba2+ as a template cation and subsequent transmetallation with UO22+. Docking experiments with barbituric acid revealed that a ‐(CH2)6– spacer between the salen‐uranyl and 2,6‐diamidopyridine moieties of 2 is optimal. According to 1H NMR titration experiments, the barbituric acid complex of 2 is up to 2.7 kcal · mol−1 more stable than the complexes with five disubstituted derivatives. The flux of barbituric acid through a supported liquid membrane is enhanced 3.7 times by carrier 2 mediated transport.
Spectroscopy and photochemistry of a series of alkyl‐substituted o‐ and p‐benzoquinones and their mono‐oxime O‐methyl ethers
Authors: Stunnenberg Frank , Cerfontain Hans , Rexwinkel Roel B.
Published: September 2010

Following our previous reports on the spectroscopy and photochemistry of methyl ethers of cyclic α‐oxo oximes, we have now studied a number of o‐ and p‐benzoquinone mono‐oxime O‐methyl ethers and, for comparison, some corresponding o‐ and p‐benzoquinones. The ground‐state electronic structure of o‐benzoquinones is described satisfactorily by the sum of the two propenal fragments. The structure of the corresponding (E)‐ and (Z)‐mono‐oxime ethers can be described similarly as the sum of the propenal and (E)‐ or (Z)‐(methoxyimino)propene fragments. This method fails when used for the construction of the ground‐state electronic structure of the isomeric p‐benzoquinones and their mono‐oxime ethers.

The UV spectra of o‐benzoquinone mono‐oxime ethers are quite different from those of the parent o‐benzoquinones in that the free lying n+ π* absorption of the latter is, for the former, shifted to lower wavelength and apparently hidden under the long‐wavelength ππ* absorptions. For the p‐benzoquinone mono‐oxime O‐methyl ether 12, however, the long‐wavelength nπ* absorption remains visible.

Direct irradiation of the tert‐butyl‐substituted o‐benzoquinone mono‐oxime O‐methyl ethers (E)‐5–(E)‐7 dissolved in acetonitrile at λ 350 nm leads (in addition to E‐Z isomerization) to the formation of the (E)‐azobenzenes 16–19 by dimerization of the respective phenylnitrenes. However, in addition, the 2,4‐di‐tert‐butyl derivative (E)‐7 undergoes mainly γ‐hydrogen abstraction, probably from the S1(nπ*) state, leading to subsequent cyclization to the relatively stable dienol (E)‐14, which eventually isomerizes thermally to the enone (E)‐15. Evidence is presented that (Z)‐7 exhibits only Z‐E photoisomerization and no photocyclization, as has been observed previously with the saturated six‐membered ring analogue. Direct irradiation of the corresponding 3,5‐di‐tert‐butyl‐o‐benzoquinone (3) at 350 nm leads to decarbonylation with formation of cyclopentadienone 13. Sensitized irradiation of mono‐oxime O‐methyl ether (E)‐7, using 1‐acetylnaphthalene and 1‐fluorenone as triplet sensitizers and acetonitrile as solvent, leads to E‐Z isomerization only with eventual photo‐stationary state [E]/[Z] ratios of 0.78 and 0.88, respectively.

The p‐benzoquinone mono‐oxime O‐methyl ethers 11 and 12 are photostable against 254, 300 and 350 nm radiation; however, any occurring E‐Z isomerization escapes detection for symmetry arguments.
Reactions of alkenoic acids with sulfur trioxide; sulfonation and sulfo‐lactonization
Authors: Schonk Ruud M. , Bakker B. H. , Cerfontain H.
Published: September 2010

The reactions of the alkenoic acid derivatives 1a–19a with sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 equiv. of dioxane as reactivity moderator. The alkenoic acids 13a and 14a, having a ‐(CH2)4‐ and ‐(CH2)7‐ linkage between the C = C and CO2H moieties, respectively, react as simple alkenes; at low temperatures, they yield the β‐sultones 13d, 14c and 14d, which at 25°C are slowly converted into the corresponding carbyl sulfates 13h, 14g and 14h. Reactions of the alkenoic acids 4a–12a with 1.2 equiv. of SO3 at −60°C leads to the quantitative formation of the γ‐lactones 4e–9e and 11e, and in some cases to the γ‐lactones 10f and 12f. The stereochemistry of this sulfo‐lactonization is dependent on the SO3 concentration, which is clearly demonstrated for the reactions of (E)‐ (5a) and (Z)‐3‐hexenoic acid (6a) with 1.0 equiv. and 10.0 equiv. of SO3. For reactions of 5a and 6a with ≤ 1.0 equiv. of SO3, the β‐sultones 5c and 6c are the presumed sole initial products undergoing subsequent lactonization. Upon using an excess of SO3, in addition, the corresponding carbyl sulfates 5g and 6g will undergo sulfocyclization to give the cis‐ (6e) and trans‐γ‐lactones (5e), respectively.

Reaction of 5‐norbornene‐endo‐2,endo‐3‐dicarboxylic anhydride (15a) with 1.2 equiv. of SO3 at 25°C yields slowly but quantitatively the β‐sultone 15c. This β‐sultone is surprisingly stable and it is very slowly converted into the γ‐lactone 15e only in the presence of H2O. Reactions of the norbornenecarboxylic acids and derivatives 16a–19a with SO3 yield the γ‐lactones 16e, 18e and 19e. Mechanisms for the formation of the various products are suggested.
Diastereo‐ and enantio‐selective synthesis of trans‐3‐phenyl‐ and trans‐3‐styryl‐2‐azetidinones via zinc ester enolates and imines
Authors: Kleijn Henk , van Maanen Hendrik L. , Jastrzebski Johann T. B. H. , van Koten Gerard
Published: September 2010

Zinc enolates of phenyl‐ and trans‐styryl‐acetic acid methyl ester react with excellent diastereoselectivety and good enantioselectivety (e.e. 64 to 91.5%) with imines in high yields to trans‐2‐azetidinones. The corresponding lithium enolates reacted with much lower selectivity and yields.
Enantioselective cleavage of esters by histidine‐containing tripeptides in micellar solutions of various hexadecyltrialkylammonium bromide surfactants
Authors: Cleij Marco C. , Drenth Wiendelt , Nolte Roeland J. M.
Published: September 2010

Cleavage of chiral p‐nitrophenyl esters derived from the amino acid phenylalanine by histidine‐containing tripeptides has been studied in micellar solutions of four quaternary ammonium surfactants. Enzyme‐like enantioselectivities up to kI/kD = 131 (at 0°C) are observed. The enantioselectivity can be rationalized by assuming a hydrophobically driven stabilizing hydrogen bond between the I. enantiomer of the ester and the tripeptide in the transition state of the reaction. This hydrogen bond is absent in the reaction with the D enantiomer of the ester. The transition state has an amphipolar character and is stabilized by the micellar environment. The hydrophilic‐hydrophobic balance of the reactants, which affects the transition state, was optimized by varying the composition of the tripeptide and the length of the N‐protecting groups in the tripeptide and the substrate. The activities and enantioselectivities depend on the structure of the quaternary ammonium surfactant headgroup. Increasing the size of this headgroup leads to an increase in rate of hydrolysis of the L ester and hence to an increase in enantioselectivity. This effect is attributed to a change in the degree of ion‐pair formation with a carboxylate group that is present in the peptides. Compared to previous studies the results indicate that a chiral surfactant is not required for obtaining high enantioselectivities.
Formation and [4 + 2] cycloaddition reactions of 2,3‐dimethylene‐2,3‐dihydrothiophene
Authors: van den Berg Keimpe J. , van Leusen Albert M.
Published: September 2010

2,3‐Dimethylene‐2,3‐dihydrothiophene (1), the thiophene analog of o‐xylylene (o‐quinodimethane), was generatedin situfrom the (trialkylammoniomethyl)‐(trimethylsilylmethyl)thiophene iodides 4 or 5 by fluoride‐induced 1,4 climination, and was trapped by [4 + 2] cycloadditions with a series of dienophiles. The reaction of 1 with dimethyl fumarate was considerably faster than with dimethyl maleate. Unsymmetrical dienophiles gave mixtures of regio‐isomers. In the absence of dienophiles, 1 formed [4 + 2] spiro dimers, of which15ais the major component, as determined by1H‐NMR comparison with a tetradeutero analog of15a. The syntheses of the new precursors of1and dideutero‐1: compounds4, 5a,b, as well as the 3.4‐isomer of4, are described.
Molecular‐mechanics calculation on oligomers of tert‐butyl isocyanide
Authors: Huige Cornelis J. M. , Hezemans Alfons M. F. , Nolte Roeland J. M. , Drenth Wiendelt
Published: September 2010

The consistent force‐field method developed by Niketic and Rasmussen was applied in molecular‐mechanics calculations on the hexamer and hexadecamer of tert‐butyl isocyanide, [(CH3)3C‐N = C < ]n, n = 6 and 16. Due to the limitations of the computer programme, calculations on the latter oligomer required a united atom approximation for the methyl groups. From the results, it is concluded that a compact helical conformation with a backbone torsional angle of 78.6° and 3.76 units per turn is the energetically most favourable state of these oligomers.
A new convenient route for the synthesis of 4(5)‐(ω‐aminoalkyl)‐1 H‐imidazoles
Authors: Vollinga Roeland C. , Menge Wiro M. P. B. , Timmerman Hendrik
Published: September 2010

A new route for the synthesis of 4(5)‐(ω‐aminoalkyl)‐1 H‐imidazoles 1 on a preparative scale through C5 lithiation of a 1,2‐diprotected imidazole is described. When the described 1,2‐diprotected 5‐lithio‐imidazole is treated with a 1‐chloro‐ω‐iodoalkane 5, selective substitution of the iodo group takes place. The chloro group of the resultant 1.2‐diprotected 5‐(ω chloroalkyl)imidazole can be easily converted into an amino group, but obviously other functional groups can be introduced as well. Subsequent deprotection of the 5‐substituted imidazole affords 4(5)‐(ω‐aminoalkyl)‐1 H‐imidazoles 1, as precursors for a large range of histaminergic compounds, in good overall yields.
Structural analysis of κ‐opioid receptor agonists
Authors: Ijzerman Adriaan P.
Published: September 2010

In the last decade, much interest has been shown in the development of agonists selective for the κ‐opioid receptor, which are potentially useful as analgesics with fewer side effects than morphine. The prototype drug is the benzeneacetamide U 50488, which was used in the present study as a starting point for molecular modelling of newer congeners. The heat of formation corresponding to the recently reported crystal structure of U 50488 was minimized with the semi‐empirical molecular orbital program MOPAC. Similar minimization and subsequent superimposition of all compounds used in the study yielded a template that was used for further discussion and manipulation. From the template, it appeared that compounds conformationally less restrained than U 50488, such as ICI 199441, may better accommodate the receptor environment. In addition, the template was used to generate ideas for the design of novel compounds. Finally, the little resemblance of the template to older, only marginally selective compounds, such as ethylketocyclazocine and the endogenous peptide dynorphin, supports the biochemical/pharmacological hypothesis of the existence of different subtypes of κ‐opioid receptors.
Three bacteriorhodopsins with ring‐didemethylated 6‐s‐locked chromophores and their properties
Authors: Groesbeek M. , van Galen A. J. J. , Ippel J. H. , Berden J. A. , Lugtenburg J.
Published: September 2010

Three novel, 6‐s‐locked rigidified retinals, racemic all‐E 1,5‐didemethyl‐8,16‐methanoretinal, all‐E 1,1‐didemethyl‐8,18‐methanoretinal and all‐E 8a, 18‐didehydro‐1, 1‐didemethyl‐8, 18‐ methanoretinal were prepared in good yield in high purity on a 100‐mg scale. For the preparation of the key intermediate in the synthesis of 1,5‐didemethyl‐8,16‐methanoretinal, reductive cyanation of an unsaturated cyanohydrin to the corresponding conjugated nitrile was accomplished using triethylsilane and trifluoroacetic acid. The three locked retinals interact with bacterioopsin to form bacteriorhodopsin with about the same rate as the native chromophore. This work proves that steric interaction of the 1,1‐dimethyl group in the chromophore is an important factor in binding to bacterioopsin.
Binaphthyl metallomacrocycles for complexation of neutral molecules
Authors: Reichwein Arjen M. , Verboom Willem , Reinhoudt David N.
Published: September 2010

Binaphthyl salophen crown ethers 1 and 2, containing an immobilized electrophilic uranyl cation, were synthesized by cyclization of dialdehyde 10 with 1,2‐benzenediamine (14) or cis‐1,2‐cyclohexanediamine (15), respectively, in the presence of Ba2+ as a template ion and subsequent transmetallation with UO22+. Solid complexes of urea and 1 and 2 were isolated. Molecular‐mechanics calculations show that the geometry of 1 and 2 is suitable for the introduction of functional groups close to the cavity of the metallomacrocycles.
Dipole moments can be used to determine the conformation of calix[4]arenes
Authors: de Mendoza Javier , Prados Pilar , Campillo Nuria , Nieto Pedro M. , Sáchez Concha , Fayet Jean‐Pierre , Vertut Marie Claire , Jaime Carlos , Elguero José
Published: September 2010

Experimental dipole moments for nine calix[4]arenes of known conformation are reported. An additive model, based on MNDO calculations, has been used to discuss these values, as well as three reported other dipole moments. It appears that a combination of calculated dipole moments of the aromatic fragments and experimental values can be used to determine the preferred conformation of calix[4]arenes in solution.
Alkylation of the SCS linkage. Towards lipophilic mono‐ and ditopic heavy‐metal receptors containing trithiane building blocks. Molecular structure of cis‐2,4,6‐tribenzyl‐1,3,5‐trithiane
Authors: Edema Jilles J. H. , Hoogenraad Marcel , Schoonbeek Franck S. , Kellogg Richard M. , Kooijman Huub , Spek Anthony L.
Published: September 2010

Reaction of 1,3,5‐trithiane with BuLi in THF at ‐ 50°C, followed by reaction with an equivalent amount of alkyl halide [n‐hexyl (a), benzyl (b), n‐dodecyl (c)] affords the corresponding lipophilic alkyl trithianes in moderate to good yields (25‐75%). Reactions with xylylene dibromides (ortho, meta, para) proceeded analogously to afford potentially ditopic ligands in reasonable overall yields (30‐50%). Alkylation of 1,3,5‐trithiane with excess alkyl halide results in the stereoselective formation of all‐cis di‐ or trisubstituted trithianes.

Investigation of the complexation behavior of these alkylated trithianes with Ag+ was done by means of conductometric titrations of AgO3SCF3 in MeCN and THF. The molecular structure of 2,4,6‐tribenzyl‐1,3,5‐trithiane (4b) has been determined by X‐ray crystallography. Crystal data for 4b: trigonal, space group R‐3 with a = b = 13.2287(7), c = 20.9177(2) Å, Z = 6, R = 0.030 (Rw = 0.034) for 1564 reflections.
Preparation and catalytic hydrogenolysis of some ω‐halogenoalkyl β‐D‐fructopyranosides; a convenient route to simple alkyl β‐D‐fructopyranosides
Authors: Raaijmakers Harry W. C. , Eveleens Susan M. , Arnouts Esther G. , Zwanenburg Binne , Chittenden Gordon J. F.
Published: September 2010

The acid‐catalysed reactions of D‐fructose, sucrose and inulin with ω‐halogenoalkyl alcohols yield the corresponding β‐D‐fructopyranosides. Catalytic hydrogenolysis of these glycosides provides a simple route to some crystalline alkyl β‐D‐fructopyranosides of potential biological interest.
4‐Alkoxy‐3′‐(alkylthio)‐3,4′‐diquinolinyl sulfides and 4‐alkoxy‐3‐(alkylthio) quinolines
Authors: Maślankiewicz Andrzej , Boryczka Stanistaw
Published: September 2010

The reactions of thioquinanthrene (1) with sodium alkoxides derived from 23 alcohols followed by S‐alkylation gave the title 4‐alkoxy‐3′‐(alkylthio)‐3,4′‐diquinolinyl sulfides 3 (18.5–91.5%) and, in some cases, 1,4‐dihydro‐4‐oxo‐3′‐(alkylthio)‐3,4′‐diquinolinyl sulfides 4a (up to 31.5%). The effect of the solvent applied, counter‐cation used and type of the alkyl group of alkoxide ions was then studied by means of competitive reactions. Effective transformation of 4‐alkoxy‐3′‐(alkylthio)‐3,4′‐diquinolinyl sulfides 3 into some 4 alkoxy‐ and 4‐(alkylthio)‐3‐(alkylthio)quinolines (5,6) and a one‐pot preparation of 4‐alkoxy‐3‐(alkylthio)quinolines 5 starting from thioquinanthrene (1) and sodium alkoxides were also presented.
Selective lipase‐catalyzed 6‐O‐acylation of alkyl α‐D‐glucopyranosides using functionalized ethyl esters
Authors: de Goede A. T. J. W. , Benckhuijsen W. , van Rantwijk F. , Maat L. , van Bekkum H.
Published: September 2010

Alkyl α‐D‐glucopyranosides were selectively converted into their 6‐O‐acyl esters by lipase‐catalyzed transesterification with ethyl acrylate or ethyl 4‐chlorobutanoate. Comparison of six lipase preparations showed large differences in activity and selectivity. The addition of zeolite CaA for selective adsorption of ethanol and water, exerted profound effects on conversion and regioselectivity of the transesterification. A quantitative conversion with high selectivity was achieved using lipases from C. antarctica in the presence of zeolite CaA.
A note on the solid‐phase synthesis of oligosaccharides by the Danishefski approach
Authors: Timmers C. M. , van der Marel G. A. , van Boom J. H.
Published: September 2010

The ZnCl2‐mediated glycosidation of an α‐1,2‐epoxide, prepared by epoxidation of a glycal with 3,3‐dimethyldioxirane, with an incoming glycal acceptor is not a priori, as advocated by Danishefski et al, a stereospecific process.
Synthesis and characterization of rigid bidentate nitrogen ligands and some examples of coordination to divalent palladium. X‐ray crystal structures of bis (p‐tolylimino) acenaphthene and methylchloro [bis(o,o′‐diisopropylphenyl‐imino) acenaphthene] palladium (II)
Authors: van Asselt Rob , Elsevier Cornelis J. , Smeets Wilberth J. J. , Spek Anthony L. , Benedix Roland
Published: September 2010

The synthesis and characterization of the rigid bidentate nitrogen ligands bis‐(phenylimino)camphane (Ph‐BIC) and a series of bis(arylimino)acenaphthenes (Ar‐BIAN) is described. These ligands were synthesized by the reaction of camphorquinone or acenaphthenequinone with the corresponding (substituted) aniline in the presence of ZnCl2 or NiBr2, followed by removal of the metal salt in a subsequent step. NDDO calculations on p Tol‐BIAN showed that the electronic properties of this ligand are comparable to the open‐chain analogue Ph‐DAB (DAB = 1,4‐diaza‐1,3‐butadiene). The aromatic group on the imine N atom of Ar‐BIAN ligands is orientated out of the bis(imino)acenaphthene plane, leading to the formation of syn and anti isomers for the ortho‐substituted derivatives o‐MeC6H4‐BIAN and o‐i PrC6H4‐BIAN. In solution one isomer is observed for these ligands, but upon coordination to a Pd(Me)Cl fragment both syn and anti forms are present, as two isomers are formed. Furthermore, the attempted synthesis of bis(isopropylimino)cyclohexane is described, but it was found that a tautomeric imine‐enamine compound is formed which coordinates to palladium(II) in a monodentate fashion, which could not be converted to a chelating ligand. The structures of p Tol‐BIAN and Pd(Me)Cl(o,o′‐i Pr2C6H3‐BIAN) in the solid state were determined by X‐ray diffraction. p Tol‐BIAN is monoclinic, space group C2, a = 20.021(2), b = 8.7703(10), c = 5.5664(10) Å, β = 103.37(1)°, Z = 2, final R = 0.040 for 963 reflections with I > 2.5σ(I). Pd(Me)Cl(o,o′‐i Pr2C6H3‐BIAN) is orthorhombic, space group Pbca, a = 11.440(2), b = 21.250(3), c = 27.087(2) Å, Z = 8, final R = 0.043 for 2433 reflections with I > 2.0σ(I >).
Hybrid molecular assemblies in combinations of a synthetic peptide lipid with macrocyclic cyclophanes
Authors: Murakami Yukito , Hayashida Osamu , Nagai Yasuyuki
Published: September 2010

Hybrid molecular assemblies were prepared as combinations of a synthetic lipid, involving an L‐alanine residue interposed between an anionic head group and a hydrophobic double‐chain segment, with macrocyclic hosts, cage‐type cyclophanes having a rigid molecular framework and peptide cyclophanes bearing four flexible branches. Each host was completely incorporated into a relatively polar domain close to the vesicular surface, as confirmed by ultrasensitive differential‐scanning calorimetry and dynamic‐light‐scattering measurements as well as by gel‐filtration chromatography and electronic‐absorption spectroscopy. Perturbation effects of the hosts on the membrane structure were characterized on the basis of steady‐state fluorescence polarization, evaluated using a fluorescent probe, 1‐[4‐(trimethylammonio)phenyl]‐6‐phenyl‐1,3,5‐hexatriene iodide, and thermodynamic parameters associated with the phase transition between gel and liquid‐crystalline states. The cage‐type cyclophanes caused a disturbance of the orderly bilayer lipid membrane in the liquid‐crystalline phase due to their rigid conformational framework, while the peptide cyclophanes generated little effect on the lipid fluidity. The hybrid molecular assembly formed with the lipid and the cage‐type host exercised effective molecular recognition toward α‐amino acids with an aromatic moiety through hydrophobic, π‐π and chirality‐based interactions; L‐ and D‐tryptophan were strongly incorporated into the host cavities as confirmed by 1H‐NMR spectroscopy. On the other hand, the hybrid assembly showed no capacity to bind aliphatic guests, such as L‐methionine and L‐threonine.
Micellar and lyotropic behavior of three isomeric bola‐amphiphiles with pyridinium groups
Authors: Festag R. , Hessel V. , Lehmann P. , Ringsdorf H. , Wendorff J.H.
Published: September 2010

The micellar and lyotropic phase behavior of three isomeric bola‐amphiphiles 1, 2 and 3 based on para‐, meta‐ and ortho‐phenylene derivatives with hydrophilic pyridinium headgroups was investigated. The micellar behavior was characterized by surface‐tension and conductivity measurements: while the para‐substituted amphiphile 1 and the ortho isomer 3 aggregated to micelles, the meta‐substituted amphiphile 2 exhibited stepwise, but discontinous self‐association. This is explained by the mass‐action and phase‐separation model. The existence of “premicellar” aggregates and the discontinous aggregation of 2 is evidenced in addition by a difference‐spectro‐photometric measurement. The low surface activity and the calculated areas per molecule of 100–200 Å2 at the air‐water interface agree with a loop‐like conformation of all three bola‐amphiphiles 1–3.

Lyotropic mesophases were found in the high‐concentration regime only for the para isomer 1, while 2 formed crystalline‐isotropic phases and 3 isotropic phases only. The mesophase of 1 was characterized by X‐ray measurements as lamellar.

The addition of 1‐hexanol as a co‐surfactant led to the induction of a lyotropic mesophase for 2. The role of the cosurfactant consists of filling the wedge between the two hydrophobic chains, thus stabilizing the aggregates.
Dimethylsulfonio‐ and sulfo‐de‐hydrogenation on reaction of azuleno[2,1,8‐ija]azulene (isopyrene) with the dimethyl sulfoxide‐sulfur trioxide complex as reagent
Authors: Cerfontain Hans , Koeberg‐Telder Ankie , Vogel Emanuel , Wilmes Oswald
Published: September 2010

Reaction of azuleno[2,1,8‐ija]azulene (isopyrene, 1) with SO3 in the presence of an excess of DMSO leads mainly to mono‐“dimethylsulfonio‐de‐hydrogenation” with formation of 5‐(dimethylsulfonio)isopyrene, the amount of initial sulfonation being relatively small. Subsequently, the 5‐(dimethylsulfonio)isopyrene is relatively slowly sulfo‐de‐hydrogenated to yield 5‐(dimethylsulfonio)isopyrene‐10‐sulfonic acid.
Synthesis of LL‐di‐myo‐inositol‐1,1′‐phosphate: A novel inositol phosphate from Pyrococcus woesei
Authors: van Leeuwen S. H. , van der Marel G. A. , van Boom J. H. , Hensel R.
Published: September 2010

Synthesis of LL, DD and LD stereoisomers of di‐myo‐inositol‐1,1′‐phosphate (DIP) could be realised by phosphitylation of properly protected L‐ or D‐myo‐inositol derivatives. It was also established that naturally occurring (+)‐DIP has the LL‐configuration.
Synthesis and Properties of 1,2‐Dimethylene‐3,5‐cycloheptadiene
Authors: Oda Mitsunori , Kuroda Shigeyasu , Shimao Ichiro , Morita Noboru , Asao Toyonobu
Published: September 2010

The regioselective synthesis of dimethyl 1,3,5‐cyloheptatriene‐1,2‐dicarboxylate (4) was achieved by a ring expansion method, starting from dimethyl 1,3‐cyclohexadiene‐2,3‐dicarboxylate (5). The title compound 3 was obtained as an air‐sensitive oil by zinc‐copper reduction of 1,2‐bis(bromomethyl)cyclohepta‐1,3,5‐triene (10) to which the diester 4 was transformed.
Chiral induction in lanthanide(III)‐alkoxide‐catalysed Meerwein‐Ponndorf‐Verley reductions
Authors: Huskens Jurriaan , de Graauw Cornells F. , Peters Joop A. , van Bekkum Herman
Published: September 2010

The reduction of acetophenone using a chiral catalyst, prepared in situ by adding a chiral dihydroxy compound to a solution of a lanthanide(III) alkoxide, was studied. The highest enantiomeric excess (ee) (32%) was observed with La(O′Bu)3 as the catalyst and 1,2:5,6‐di‐O‐isopropylidene‐D‐mannitol as the chiral ligand. With pinacolone as the substrate, an ee of 22% was obtained.
1,3‐Dilithiobenzene and 1,4‐dilithiobenzene
Authors: Fossatelli M. , Den Besten R. , Verkruijsse H.D. , Brandsma L.
Published: September 2010

Using the method of iodine‐lithium exchange, 1,3‐ and 1,4‐dilithiobenzene have been generated in solution and isolated in a dry state for the first time. The dilithium compounds are not formed from the corresponding dibromobenzenes.
Observing individual generations in poly(propyleneimine) dendrimers with natural abundance 15N‐NMR spectroscopy
Authors: van Genderen Marcel H. P. , Baars Maurice W. P. L. , van Hest Jan C. M. , Meijer E.W. , de Brabander‐van den Berg Ellen M. M.
Published: September 2010

Natural abundance 15N‐NMR spectra of poly(propyleneimine) dendrimers are presented to show the usefulness of the technique in characterizing these highly branched and well‐defined macromolecules. Inverse‐gated decoupled measurements show the number and intensities of signals that reflect the generations in the dendrimers.
t‐Butyl alcohol‐assisted fission of the P‐P bonds in red phosphorus with lithium in liquid ammonia: A convenient preparative method for dialkylphosphanes
Authors: Arbuzova S.N. , Gusarova N.K. , Trofimov B.A. , Brandsma L.
Published: September 2010

Essentially complete fission of the P‐P bonds in red phosphorus can be effected by adding one equivalent of t‐butylalcohol to a mixture of red P and lithium in liquid ammonia. The reaction has been applied to synthesize some dialkylphosphanes.
Synthesis of thiophenes from allenyl sulfones involving α,β‐unsaturated sulfines as intermediates
Authors: van der Linden Johannes B. , van Asten Peter F. T. M. , Braverman Samuel , Zwanenburg Binne
Published: September 2010

The synthesis of thiophenes starting from allenyl sulfones, via intermediate formation of α,β‐unsaturated sulfines, is described. The allenyl sulfones were synthesized by a [2,3]‐sigmatropic rearrangement of appropriately substituted prop‐2‐ynyl sulfinates. Treatment of the allenyl sulfones with n‐butyllithium and chlorotrimethylsilane gave α‐silylated allenyl sulfones in almost quantitative yield, which, on heteroconjugate addition of organolithium reagents, gave the desired α‐silyl carbanions. These reacted with sulfur dioxide to give the α,β‐unsaturated sulfines, which underwent in‐situ rearrangement to 2‐sulfonylthiophenes. The yield of the thiophenes depends on the organolithium reagents used. The use of exocyclic allenyl sulfones was more troublesome, and a thiophene was obtained for only one example.
Dual‐wavelength spectrophotometric determinations of copper and its composition of the complex with eriochrome blue black R
Authors: Gao Hong‐Wen
Published: September 2010

Copper has been determined by a modified dual‐wavelength spectrophotometric (DWS) method, using the reaction of CuII with eriochrome blue black R (EBBR) at pH 12, which is sensitive and selective in the presence of both pentadecyltrimethylammonium bromide (PTMAB) and ascorbic acid. The modified DWS can completely eliminate the effect of excess EBBR in its CuII solution and give the real absorbance of the produced chelate of CuII with EBBR, with increased analytical sensitivity and decreased error. The composition of the complex of CuII with EBBR can be determined easily and accuratively. Beer's law is obeyed over the concentration range of 0‐1.60 mg Cu per 1 and the true molar absorbance of chelate Cu(EBBR)2 at 550 nm has been computed as 1.80 · 104 · mol−1 · cm−1. The detection limit of Cu is 0.04 mg. This method has been applied for the determination of trace amounts of copper in waste water with satisfactory results.
Enantioselective oxidation by non‐heme iron mono‐oxygenases from Pseudomonas
Authors: Wubbolts Marcel G. , Noordman Reinoud , van Beilen Jan B. , Witholt Bernard
Published: September 2010

Xylene oxygenase (XO), an enzyme system from Pseudomonas putida mt‐2, selectively oxidizes the methyl side group of toluene‐derived compounds. The enzyme is related to Pseudomonas oleovorans mono‐oxygenase (POM), which has been used to produce optically active epoxides from various alkenes at high enantiomeric excess.

We have introduced XO into Escherichia coli and produced variously substituted benzyl alcohols from toluene derivatives and optically active styrene epoxides from styrene, m‐ and p‐chlorostyrene and m‐ and p‐methylstyrene using this biocatalyst. The products of oxidation of styrene and styrene derivatives had enantiomeric excesses (ees) ranging from 37% to over 98%.

Similarly, Pseudomonas putida was engineered such that the hydroxylation of compounds by POM could be investigated independent of subsequent product degradation. The biocatalyst accepted a wide range of substrates and oxidized both linear and branched alkanes, and cyclic alkanes as well as alkylbenzenes to the corresponding alcohols.

In this review we describe the catalytic potential of engineered biocatalysts based on both XO and POM and discuss the structural and functional similarities of these non‐heme iron mono‐oxygenases.
Catalytic enantioselective alkylation of aldehydes using chiral hydrogen phosphoramidates and hydrogen phosphinamides and their thio analogs
Authors: Soai Kenso , Ohno Yoshiaki , Inoue Yukikazu , Tsuruoka Toshihiro , Hirose Yuji
Published: September 2010

Chiral (enantiomerically pure) hydrogen thiophosphoramidates and hydrogen phosphoramidates and their phosphinamide analogs derived from norephedrine and other chiral (enantiomerically pure) amino alcohols catalyze the enantioselective addition of dialkylzines to aldehydes. The presence of titanium tetraisopropoxide increases the enantioselectivity, providing enantiomerically enriched secondary alcohols with up to 98% ee. The enantioselectivities of thiophosphoramidates and thiophosphinamides are higher than those of the oxygen analogs. The phosphoramidates and thiophosphoramidates, without the hydroxyl group, also catalyze the addition of dialkylzinc to aldehydes in the absence of Ti(OiPr)4.
Asymmetric synthesis of solenopsins A, B and C
Authors: Solladié Guy , Huser Nathalie
Published: September 2010

Solenopsins A, B and C have been synthesized in enantiomerically pure forms from the corresponding anti‐1,5‐diols which have been obtained from glutaric anhydride by an asymmetric synthesis induced by chiral sulfoxides.
Enhanced enantiocontrol in catalytic metal carbene transformations with dirhodium (II) tetrakis[methyl 2‐oxooxazolidin‐4(S)‐carboxylate], Rh2(4S‐MEOX)4
Authors: Doyle Michael P. , Dyatkin Alexey B. , Protopopova Marina N. , Yang Chien I. , Miertschin Charla S. , Winchester William R. , Simonsen Stanley H. , Lynch Vincent , Ghosh Ratna
Published: September 2010

The synthesis, spectral characteristics, and X‐ray structures for dirhodium(II) tetrakis[methyl 2‐oxooxazolidin‐4(S)‐carboxylate], Rh2(4S‐MEOX)4, and the related dirhodium(II) tetrakis[methyl 5(R)‐methyl‐2‐oxooxazolidin‐4(S)‐carboxylate], Rh2(4S‐THREOX)4, are reported. Comparison is made between these 2‐oxooxazolidin‐ligated dirhodium(II) catalysts for metal carbene transformations and those with comparable 2‐oxopyrrolidine ligands, especially dirhodium(II) tetrakis[methyl 2‐oxopyrrolidine‐5(S)‐carboxylate], Rh2(5S‐MEPY)4. Structure‐selectivity comparisons reveal that Rh2(4S‐MEOX)4 provides higher enantiocontrol and, in some cases, higher diastereocontrol than Rh2(5S‐MEPY)4 in intramolecular carbon‐hydrogen insertion reactions of sterically demanding diazoacetates and diazoacetamides and is the catalyst of choice for highly enantioselective diazodecomposition of adamantyl diazoacetates and N‐(tert)butyldiazoacetamides. The structurally analogous Rh2(4S‐THREOX)4 is nearly identical with Rh2(4S‐ MEOX)4 in its overall effect on selectivity. The net advantage of Rh2(4S‐MEOX)4 lies in its wider openness for metal carbene transformations.
Asymmetric synthesis of anti‐α‐alkyl‐β‐amino carboxamides
Authors: Davies Stephen G. , Edwards Alison J. , Walters Iain A. S.
Published: September 2010

The alkylation reactions of enolates derived from the highly diastereoselective conjugate additions of lithium (R)‐N‐benzyl‐N‐α‐methylbenzylamide (R)‐1 to N, N‐dimethyl crotonamide 2 and N, N‐dimethyl cinnamide 3 have been investigated. The alkylations of enolates derived from 3 are shown to afford anti‐α‐alkyl‐β‐amino carboxamides with excellent stereocontrol: the stereochemistry is assigned with the aid of a single crystal X‐ray structure of (2R,3S,αR)‐N, N‐dimethyl 2‐benzyl‐3‐phenyl‐3‐(N‐benzyl‐N‐α‐methylbenzylamino)propanamide (2R,3S,αR)‐10. As a result of the difficulty encountered in hydrolysing these hindered β‐amino amides such as 10, an alternative procedure is developed involving conjugate addition‐alkylations with α,β‐unsaturated N‐acyloxazolidin‐2‐ones as substrates, giving selectively alkylated products which are susceptible to reductive cleavage.
The synthesis and properties of some mesogenic 3–O‐alkyl derivatives of D‐glucitol and D‐mannitol
Authors: Raaijmakers Harry W. C. , Arnouts Ester G. , Zwanenburg Binne , Chittenden Gordon J. F. , van Doren Henk A.
Published: September 2010

The synthesis of some 3‐O‐long‐chain alkyl ethers of D‐glucitol, D‐mannitol, and mixtures thereof, from readily available di‐O‐isopropylidene derivatives of D‐glucose and D‐fructose is described. Some physical characteristics including critical‐micellar‐concentration (CMC) values, Krafft temperatures, thermotropic and lyotropic liquid‐crystal behaviour are also reported.