bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐tech partnering leads to learning‐centered curricula for individuals with disabilities
Authors: Hurley Kathleen S.
Published: January 2003

A business advisory council provides essential support to workforce development programs, including one that serves individuals with disabilities.
Concluding observations on successful partnerships
Authors: Spangler Mary S.
Published: January 2003

The elements necessary for establishing a successful partnership with business and the community and the types of challenges faced by these relationships are drawn from the readings as general observations.
Sources and information: Partnerships with business and the community
Authors: Piegonski Fred
Published: January 2003

An annotated bibliography of successful partnerships in community colleges is provided, including explanations of how the partnerships developed, discussions on current collaborations, reviews of statewide reports, samples of handbooks, and an analysis of one statewide effort to conduct an outcome measurement of its programs.
Features of the Java Commodity Grid Kit
Authors: von Laszewski Gregor , Gawor Jarek , Lane Peter , Rehn Nell , Russell Mike
Published: January 2003

In this paper we report on the features of the Java Commodity Grid Kit (Java CoG Kit). The Java CoG Kit provides middleware for accessing Grid functionality from the Java framework. Java CoG Kit middleware is general enough to design a variety of advanced Grid applications with quite different user requirements. Access to the Grid is established via Globus Toolkit protocols, allowing the Java CoG Kit to also communicate with the services distributed as part of the C Globus Toolkit reference implementation. Thus, the Java CoG Kit provides Grid developers with the ability to utilize the Grid, as well as numerous additional libraries and frameworks developed by the Java community to enable network, Internet, enterprise and peer‐to‐peer computing. A variety of projects have successfully used the client libraries of the Java CoG Kit to access Grids driven by the C Globus Toolkit software. In this paper we also report on the efforts to develop serverside Java CoG Kit components. As part of this research we have implemented a prototype pure Java resource management system that enables one to run Grid jobs on platforms on which a Java virtual machine is supported, including Windows NT machines. Copyright © 2002 John Wiley & Sons, Ltd.
A CORBA Commodity Grid Kit
Authors: Parashar Manish , von Laszewski Gregor , Verma Snigdha , Gawor Jarek , Keahey Kate , Rehn Nell
Published: January 2003

This paper reports on an ongoing research project aimed at designing and deploying a Common Object Resource Broker Architecture (CORBA) (ww.omg.org) Commodity Grid (CoG) Kit. The overall goal of this project is to enable the development of advanced Grid applications while adhering to state‐of‐the‐art software engineering practices and reusing the existing Grid infrastructure. As part of this activity, we are investigating how CORBA can be used to support the development of Grid applications. In this paper, we outline the design of a CORBA CoG Kit that will provide a software development framework for building a CORBA ‘Grid domain’. We also present our experiences in developing a prototype CORBA CoG Kit that supports the development and deployment of CORBA applications on the Grid by providing them access to the Grid services provided by the Globus Toolkit. Copyright © 2002 John Wiley & Sons, Ltd.
MPI‐CHECK: a tool for checking Fortran 90 MPI programs
Authors: Luecke Glenn , Chen Hua , Coyle James , Hoekstra Jim , Kraeva Marina , Zou Yan
Published: January 2003

MPI is commonly used to write parallel programs for distributed memory parallel computers. MPI‐CHECK is a tool developed to aid in the debugging of MPI programs that are written in free or fixed format Fortran 90 and Fortran 77. MPI‐CHECK provides automatic compile‐time and run‐time checking of MPI programs. MPI‐CHECK automatically detects the following problems in the use of MPI routines: (i) mismatch in argument type, kind, rank or number; (ii) messages which exceed the bounds of the source/destination array; (iii) negative message lengths; (iv) illegal MPI calls before MPI_INIT or after MPI_FINALIZE; (v) inconsistencies between the declared type of a message and its associated DATATYPE argument; and (vi) actual arguments which violate the INTENT attribute. Copyright © 2003 John Wiley & Sons, Ltd.
GridSim: a toolkit for the modeling and simulation of distributed resource management and scheduling for Grid computing
Authors: Buyya Rajkumar , Murshed Manzur
Published: January 2003

Clusters, Grids, and peer‐to‐peer (P2P) networks have emerged as popular paradigms for next generation parallel and distributed computing. They enable aggregation of distributed resources for solving large‐scale problems in science, engineering, and commerce. In Grid and P2P computing environments, the resources are usually geographically distributed in multiple administrative domains, managed and owned by different organizations with different policies, and interconnected by wide‐area networks or the Internet. This introduces a number of resource management and application scheduling challenges in the domain of security, resource and policy heterogeneity, fault tolerance, continuously changing resource conditions, and politics. The resource management and scheduling systems for Grid computing need to manage resources and application execution depending on either resource consumers' or owners' requirements, and continuously adapt to changes in resource availability.

The management of resources and scheduling of applications in such large‐scale distributed systems is a complex undertaking. In order to prove the effectiveness of resource brokers and associated scheduling algorithms, their performance needs to be evaluated under different scenarios such as varying number of resources and users with different requirements. In a Grid environment, it is hard and even impossible to perform scheduler performance evaluation in a repeatable and controllable manner as resources and users are distributed across multiple organizations with their own policies. To overcome this limitation, we have developed a Java‐based discrete‐event Grid simulation toolkit called GridSim. The toolkit supports modeling and simulation of heterogeneous Grid resources (both time‐ and space‐shared), users and application models. It provides primitives for creation of application tasks, mapping of tasks to resources, and their management. To demonstrate suitability of the GridSim toolkit, we have simulated a Nimrod‐G like Grid resource broker and evaluated the performance of deadline and budget constrained cost‐ and time‐minimization scheduling algorithms. Copyright © 2002 John Wiley & Sons, Ltd.
Polyurethane/clay and polyurethane/POSS nanocomposites as flame retarded coating for polyester and cotton fabrics
Authors: Devaux Eric , Rochery Maryline , Bourbigot Serge
Published: January 2003

Polyurethane resins (PU) are widely used as coatings for textile fabrics in order to improve some properties (for example mechanical behaviour, water repellency and air impermeability). Two kinds of additives have been added to the polyurethane in order to provide flame retardancy to the coated textile structure: montmorillonite clay and polyhedral oligomeric silsesquioxanes (POSS) have been used to process PU nanocomposites. The paper presents some results obtained with PU/clay and PU/POSS coated polyester or cotton fabrics, using cone calorimetry and thermogravimetric analysis. The efficiency of the additive chosen is clearly demonstrated and discussed. In particular, the great potential of using POSS for fire retardant applications is highlighted. Copyright © 2002 John Wiley & Sons, Ltd.
PIPD, a new high‐modulus and high‐strength polymer fibre with exceptional fire protection properties
Authors: Northolt M.G. , Sikkema D.J. , Zegers H.C. , Klop E.A.
Published: January 2003

The development of the new high‐modulus and high‐strength fibre M5, made of poly{2,6‐diimidazo[4,5‐b:4′,5′‐e]‐pyridinylene‐1,4(2,5‐dihydroxy)phenylene} or PIPD, has resulted in an organic polymer fibre with exceptional fire protection properties when compared with PBO, Twaron, Kevlar and Nomex fibres. The PIPD as‐spun fibre with a modulus of 150 GPa and a tensile strength of 2.5 GPa is a crystal hydrate containing 21 wt% water. Cone calorimeter measurements yielded a fire performance index (FPI) 20 times higher than Nomex, with extremely low value for the specific extinction area (SEA) characterizing the smoke formation. The PIPD‐HT fibre (recrystallized in an after treatment into the anhydrous crystalline structure) with a modulus >300 GPa and a strength >5 GPa has a FPI value similar to PBO but shows much less smoke formation than this fibre. Copyright © 2002 John Wiley & Sons, Ltd.
Enhancing polymer flame retardancy by reaction with phosphorylated polyols. Part 2. Cellulose treated with a phosphonium salt urea condensate (proban CC®) flame retardant
Authors: Horrocks A. Richard , Zhang Sheng
Published: January 2003

Phosphorylation of cellulose flame retarded with an ammonia‐cured, polycondensed tetrakis(hydroxymethyl) phosphonium‐urea derivative (as Proban CC, Rhodia) with a polyol diphosphoryl chloride or phosphorochloridate like spirocyclic pentaerythritol di(phosphoryl chloride) or diphosphorochloridate, SPDPC can yield phosphorus levels in excess of 10% (w/w). Such high levels suggest up to 82% yields of reaction if phosphorylation of the free secondary amine groups present in the cross‐linked flame retardant is the assumed site.

The presence of substituted pentaerythritol phosphate moieties significantly increases char formation above 400°C and scanning electron microscopy indicates that the char has an intumescent structure. The char‐forming characteristic is not influenced by subjecting the phosphorylated flame retardant cellulose to boiling in a 1% detergent solution in water thereby suggesting that the product is durable. The potential of this reaction to create a durable, intumescent flame retardant for cellulose is discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Evaluation of the flammability of cotton bales
Authors: Wakelyn P.J. , Hughs S.E.
Published: January 2003

Bales of cotton were classified by the International Maritime Organization (IMO) code regulations as a flammable solid (Class 4.1), which required hazardous goods papers to accompany waterborne shipments. Various scientific investigations were conducted to evaluate the flammability hazard of bales of cotton to determine if this hazardous designation was valid. Cigarette (NFPA 261/ ASTM E1352), match (NFPA 705) and open flame (CA TB 129) tests were conducted; the potential for self‐heating and spontaneous combustion was evaluated; and the potential of cotton bales sustaining smouldering combustion in their interiors at various compression densities was studied. These studies showed that bales of cotton should not be required to have the hazardous designation, ‘flammable solid’, and led to the IMO and the US Department of Transportation (DOT) removing the designation for baled cotton [compressed to a density of 360kg/m3(22.4lb/ft3) or greater; meets ISO 8115], with effect from 1 January 1999. Published in 2002 John Wiley & Sons, Ltd.
Use of cone calorimetry to quantify the burning hazard of apparel fabrics
Authors: Nazaré Shonali , Kandola Baljinder , Horrocks A. Richard
Published: January 2003

UK fire statistics reveal that there are 60–80 clothing‐related burns fatalities each year and nightwear is the garment category which is more likely to cause deaths. Existing test methods for assessing the burning behaviour of apparel fabrics do not quantify the fabrics for their potential burn injury hazard. In the present work an oxygen consumption or cone calorimetric technique has been used to study the heat release parameters of apparel fabrics. Experimental fabrics selected for this study represent those typically used in manufacturing nightwear. Reproducibility and repeatability have been tested for both thermally thin and thick specimens in the form of single and multi‐layered fabrics, respectively. The effect of varying incident heat flux enabled the derivation of critical heat flux (CHF), peak heat release (PHRR) under zero incident heat flux and fire growth index (FIGRA). Ranking of fabrics for their potential burning hazard is discussed in terms of the relative magnitudes of these parameters. Copyright © 2002 John Wiley & Sons, Ltd.
A comparative analysis of protocols for measuring heat transmission through flame resistant materials: capturing the effects of thermal shrinkage
Authors: Crown E.M. , Dale J.D. , Bitner E.
Published: January 2003

Bench‐scale tests measuring the thermal protective performance of textile materials do not capture the effect of thermal shrinkage, primarily because of the planar geometry of the test device. The performance of single‐layer fabrics commonly used in protective garments is compared here following several protocols, including the use of a new cylindrical device as well as standard and modified ASTM, CGSB and ISO procedures, with and without a 6.35 mm air gap between the fabric and the sensor. Both the time to reach the second degree burn criterion and the time for the sensor to register a 24°C temperature rise were measured. Fabrics that shrink had reduced thermal protection when measured with the cylindrical device, compared with other tests. Two‐way analysis of variance indicated that, although the dependent measures differ significantly among fabrics, the nature and extent of those differences depend on the test used. One‐way analyses of variance indicate that each method differentiates among the fabrics. However, most tests in which the fabrics are in contact with the sensor rank heaviest fabrics as the most protective. Among the tests incorporating a space between the fabric and sensor, those using the cylindrical device differentiate best between lighter fabrics that shrink and those that do not. Regression analyses of data from bench scale tests with data from instrumented mannequin tests confirm the superiority of the cylindrical device in capturing the effects of both thermal shrinkage and fabric integrity. Copyright © 2002 John Wiley & Sons, Ltd
Pyrolysis and limiting oxygen indices of cotton fabrics graft copolymerized with oligomeric vinyl phosphonate and/or N‐methylolacrylamide
Authors: Masuko Fumi , Mitani Chizu , Sakamoto Munenori
Published: January 2003

Graft copolymerization of an oligomeric vinyl phosphonate (FYR) and/or N‐methylolacrylamide was made onto cotton fabrics by a pad‐dry‐steam method. The limiting oxygen indices (LOI) of the treated samples confirmed the P–N synergism. Simultaneous TG/DTA measurements indicated that an exothermic peak appeared at a temperature near that where the main decomposition ended for the samples of high LOI (>24) values, either prepared with FYR or with both monomers. The peak temperature, however, did not correlate directly with the LOI of the sample. Curie‐point pyrolysis at 590°C was extensively studied on the treated samples by GC and GC–MS. Most of the main degradation products of the untreated cotton included hydroxyacetaldehyde, 1‐hydroxypropan‐2‐one, ethyl methyl ketone and acrolein. The amounts (per unit weight of the cellulose fraction of the samples) of these carbonyl compounds were much reduced by the introduction of a small amount of phosphorus into cotton. The decrease in the amount (per unit weight of the treated sample) of acrolein correlated highly with the increase in LOI. Copyright © 2002 John Wiley & Sons, Ltd.
Heat resistance and flammability of high performance fibres: A review
Authors: Bourbigot Serge , Flambard Xavier
Published: January 2003

The heat and flame resistance of high performance fibres are reviewed according to the literature data. The performance is discussed considering the physical and chemical structure of the fibres. Some selected high performance fibres are then evaluated using the cone calorimeter as a fire model to provide realistic data on the fire behaviour of the fibres. They are also examined in terms of heat resistance using combined TGA/DSC. The results are discussed and compared with literature data. Heterocyclic rigid‐rod polymers (poly (p‐phenylene‐2,6‐benzobisoxazole or PBO (Zylon®) and poly(2,6‐diimidazo (4,5‐b:4′,5′‐e) pyridinylene‐1,4 (2,5‐dihydroxy) phenylene or PIPD (M5)) exhibit the best performance (little or contribution to fire, low smoke and good heat resistance) and offer a good combination between heat and flame resistance and mechanical properties. Copyright © 2002 John Wiley & Sons, Ltd.
Toxic gaseous products of thermal decomposition and combustion of natural and synthetic fabrics with and without flame retardant
Authors: Wesolek Dorota , Kozlowski Ryszard
Published: January 2003

The results of studies on the toxicity of the gas products of thermal decomposition and combustion of natural and synthetic fabrics, as well as the influence of flame retardants (FR) on the emission of toxic products from fabrics are presented.

Thermal decomposition and combustion were investigated according to the Polish standard PN‐88/B‐02855 that is not essentially different from the method described by the German standard DIN 53436.

These gas products evolved from untreated and FR‐treated fabrics were subject to quantitative analysis, in order to determine environmental toxicity. They included carbon monoxide and dioxide as well as nitrogen oxides, hydrogen cyanide, hydrogen sulphide and sulphur dioxide.

In order to evaluate the toxic properties of gas products emitted during thermal decomposition of the above fabrics, calculations were performed to determine specific emission of the toxic products as well as toximetric indices that relate results of analytical methods to those obtained by laboratories specializing in biological methods. Copyright © 2002 John Wiley & Sons, Ltd.
Possible phosphorus/halogen synergism in flame retardant textile backcoatings
Authors: Davies P.J. , Horrocks A.R. , Alderson A.
Published: January 2003

Selected phosphorus/halogen flame retardant synergisms on cotton fabric substrates have been modelled using simple salt mixtures (sodium bromide and diammonium phosphate) and backcoating formulations based on combinations of ammonium polyphosphate, melamine phosphate and cyclic phosphonate with decabromodiphenyl oxide and/or hexabromocyclododecane and utilizing a chlorinated binder system. The results obtained suggest that there is a possibility of synergism as observed by limiting oxygen index. Linear modelling of the results suggests that the optimum phosphorus mole fraction occurs in the region of 0.15 to 0.45. Linear regression of the data shows an improved regression fit with the inclusion of an interaction term suggesting that there is a synergistic interaction taking place. Copyright © 2002 John Wiley & Sons, Ltd.
Flexible fire barriers based on natural nonwoven textiles
Authors: Kozlowski R. , Mieleniak B. , Muzyczek M. , Kubacki A.
Published: January 2003

These studies aimed at the development of natural fibre containing nonwoven fabrics with limited flammability. For 100% cellulosic fabrics, the presence of a flame retardant was essential for good fire performance, while for blended wool/hemp fabrics, (Wo+Hemp), moderate flame retardant levels were achieved without the addition of chemical treatment. Using cone calorimetry and LOI methods, fire performances were determined and all burning samples emitted low amounts of CO, although noticeable levels of CO2 were evident. Copyright © 2002 John Wiley & Sons, Ltd.
An investigation into the mechanism of flame retardancy and smoke suppression by melamine in flexible polyurethane foam
Authors: Price Dennis , Liu Yan , Milnes G. John , Hull Richard , Kandola Baljinder K. , Horrocks A. Richard
Published: January 2003

The mechanism of flame retardancy and smoke suppression by melamine in flexible polyurethane foam has been investigated using cone calorimetry, TG, DSC and pyrolysis/GC/MS. The cone calorimetric results indicate that the addition of melamine into polyurethane foam was very effective at reducing heat release rates and suppressing smoke and CO production during the initial combustion stage. GC/MS analysis showed that the volatiles evolved from polyurethane foam, pyrolysed at 350°C in air, consisted mainly of the 2,6‐ and 2,4‐ isomers of toluene diisocyanate. Such species together with other aromatic compounds are accepted as being the main contributors to smoke released from polyurethane foam in a fire. Cone calorimetry, DSC and pyrolysis/GC/MS experiments indicated that interaction occurs between melamine and the evolved toluene isocyanate fraction arising from the decomposition of polyurethane foam. The resulting polymeric structures so formed will reduce the amount of aromatic smoke precursors evolved thus suppressing smoke in the event of a fire. This polymeric structure will also degrade to a char, reducing the amount of combustibles volatilized and hence the rate of heat release. The char would form a protective layer on the surface of the polyurethane foam. A mechanism for this important melamine–isocyanate interaction is proposed. Copyright © 2002 John Wiley & Sons, Ltd.
Technical note: Usability evaluation of the modified CIE1976 Uniform‐Chromaticity scale for assessing image quality of visual display monitors
Authors: Lee WookGee , Kim SeongHwan , Lee SunKyu , Kim SangSoo
Published: January 2003

White uniformity indicates the degree of uniform distribution of white color across the display screen and is one of the important inspection factors determining the image quality of a visual display unit (VDU). Experiments in which participants were confronted with 6 evaluation points embedded in 3 measurement groups on a VDU screen were conducted to gather the psychophysical data that include the levels of white uniformity obtained from participants and a colorimetric system (CA‐100). In an accuracy test, 37.12% of the participants showed the same conclusion led by the original CIE1976 criteria, and 62.88% of the participants showed the same conclusion led by the modified equation. In magnitude estimation evaluating the display's white uniformity, the magnitude score of the modified equation (0.36) was significantly larger than that of the original equation (0.32). It was concluded that the modified equation is more sensitive to the change of white uniformity. © 2003 Wiley Periodicals, Inc. Hum Factors Man 13: 85–95, 2003.
The α‐L‐Threofuranosyl‐(3′→2′)‐oligonucleotide System (‘TNA'): Synthesis and Pairing Properties
Authors: Schöning Kai‐Uwe , Scholz Peter , Wu Xiaolin , Guntha Sreenivasulu , Delgado Guillermo , Krishnamurthy Ramanarayanan , Eschenmoser Albert
Published: January 2003

Our studies of α‐L‐Threofuranosyl‐(3′→2′)‐oligonucleotides (‘TNA') are part of a systematic experimental inquiry into the base‐pairing properties of potentially natural nucleic acid alternatives taken from RNA's close structural neighborhood. TNA is an efficient Watson‐Crick base‐pairing system and has the capability of informational cross‐pairing with both RNA and DNA. This property, together with the system's constitutional and (presumed) generational simplicity, warrants special scrutiny of TNA in the context of the search for chemical clues to RNA's origin.
Evidence that the β‐Peptide 14‐Helix is Stabilized by β3‐Residues with Side‐Chain Branching Adjacent to the β‐Carbon Atom
Authors: Raguse Tami L. , Lai Jonathan R. , Gellman Samuel H.
Published: January 2003

Oligomers of β‐substituted β‐amino acids (‘β3‐peptides') are known to adopt a helical secondary structure defined by 14‐membered ring hydrogen bonds ('14‐helix'). Here, we describe a deca‐β3‐peptide, 1, that does not adopt the 14‐helical conformation and that may prefer an alternative secondary structure. β3‐Peptide 1 is composed exclusively of residues with side chains that are not branched adjacent to the β‐C‐atom (β3‐hLeu, β3‐hLys, and β3‐hTyr). In contrast, an analogous β‐peptide, 2, containing β3‐hVal residues in place of the β3‐hLeu residues of 1, adopts a 14‐helical conformation in MeOH, according to CD data. These results illustrate the importance of side‐chain branching in determining the conformational preferences of β3‐peptides.
Allylsilane‐Modified Amino Acids from the Claisen Rearrangement
Authors: Mohamed Mustafa , Brook Michael A.
Published: January 2003

The Claisen rearrangement of the N‐protected, silylated allyl glycinates 11 and 12 led to the formation of allyl/silyl‐functionalized amino acids 13 and 14 in yields up to 80%. The diastereoisomer ratio varied from 2 : 1 to 29 : 1 for 11mb, and from 2 : 1 to 46 : 1 (syn/anti) for 12mb, depending on reaction conditions, as shown by X‐ray crystallographic analysis of 14mb. The relationship between the size of the alkyl groups on the chlorosilane reagent (Me2R″SiCl, R″=Cl, Me, t‐Bu, Ph) used as an enolate trap and the observed stereoselectivity was investigated in the case of the Ireland–Claisen variant. Me3SiCl gave the best results. However, the size of the alkyl groups on the silylated ester (Me2R″Si, R=Me, t‐Bu, Ph, i‐Pr) did not exert a significant effect on the diastereoselectivity or yield of the rearrangement.
A Study of the Stereochemical Course of β‐Oxygen Elimination with a Rhodium(I) Complex
Authors: Murakami Masahiro , Igawa Hideyuki
Published: January 2003

The stereochemical course of β‐oxygen elimination of an organorhodium(I) complex was investigated through the Rh‐catalyzed addition of phenylboronic acid to a chiral propargyl acetate to produce an allene. The degree of chirality transfer suggests that the β‐oxygen elimination takes place in both syn and anti modes.
Enantioselective Synthesis of β‐Amino Acids, Part 13
Authors: Gutiérrez‐García Víctor Manuel , Reyes‐Rangel Gloria , Muñoz‐Muñiz Omar , Juaristi Eusebio
Published: January 2003

Inexpensive acryloyl chloride was converted in 91% overall yield to two derivatives of β‐alanine, (R,R,R)‐6 and (R,R,S)‐6, containing two chiral auxiliaries. C‐Alkylation of (R,R,R)‐ and (R,R,S)‐6 via a dianion derivative, was performed by direct metallation with 2.2 equiv. of lithium hexamethyldisilazane (LHMDS) in THF at −78°. C‐Alkylation of (R,R,S)‐6‐Li2 (‘matched' pair of chiral auxiliaries) afforded the mono‐alkylated products 8–11 in 29–96% yield and 54–95% stereoselectivity. Employment of LiCl as an additive generally increased stereoselectivities, whereas the effect of HMPA as a cosolvent was erratic. Chemical correlation of the major diastereoisomer from the alkylation reactions with (S)‐α‐alkyl‐β‐alanine (12–15) showed that addition of the electrophile preferentially takes place on the enolate's Si‐face. This conclusion is also supported by molecular‐modeling studies (ab initio HF/3‐21G), which indicate that the lowest‐energy conformation for (R,R,S)‐6‐Li2 presents the more sterically hindered Re‐face of the enolate. The theoretical studies also predict a determining role for NLiO chelation in (R,R,S)‐6‐Li2, giving rise to an interesting ‘ion‐triplet' configuration for the dilithium dianion.
A Novel Concept for Combinatorial Chemistry in Solution: Synthesis of Highly Substituted Pyrrolidines by Multicomponent Domino Reactions
Authors: Tietze Lutz F. , Evers Holger , Töpken Enno
Published: January 2003

The multicomponent domino Knoevenagel hetero‐DielsAlder hydrogenation process of N‐[(benzyloxy)carbonyl(Cbz)‐protected amino aldehydes with N,N‐dimethylbarbituric acid and the trimethylsilyl enol ethers 1–3 leads to the formation of the substituted pyrrolidines 12–15. Under the same conditions, reaction of the trimethylsilyl enol ether 4, obtained from acetophenone, gave the primary amines 18a,b probably due to a hydrogenolytic cleavage of the intermediately formed pyrrolidines. The zwitterionic products were obtained in high purity simply by precipitation with Et2O.
Study of Unusually High Rotational Barriers about SN Bonds in Nonafluorobutane‐1‐sulfonamides: The Electronic Nature of the Torsional Effect
Authors: Lyapkalo Ilya M. , Reissig Hans‐Ulrich , Schäfer Andreas , Wagner Armin
Published: January 2003

Slow rotation about the SN bond in N,N‐disubstituted nonafluorobutane‐1‐sulfonamides 1 can easily be detected by NMR measurements at room temperature. This effect causes magnetic nonequivalence of otherwise identical geminal substituents in symmetrical staggered ground‐state conformation A. The torsional barriers determined (62–71 kJ⋅mol−1) proved to be the highest ever observed for sulfonamide moieties. They are comparable to the values routinely measured for carboxylic acid amides or carbamates. The restricted rotation is interpreted as result (nNdS)‐π and of nNσ interactions, which develop substantial S,N double‐bond character in sulfonamides 1. The S,N binding interaction is increased by the highly electron‐withdrawing effect of the perfluorobutyl group. The anticipated symmetry of the ground‐state conformation A and the considerable shortening of the SN bond (1.59 Å) compared to the mean value in sulfonamides (1.63 Å) are confirmed by single‐crystal X‐ray study of N,N‐dibenzylnonafluorobutane‐1‐sulfonamide (1c).
New Results on the Stereoselective Alkylations of Malic Acid Derivatives Supported by Molecular Modeling
Authors: Sefkow Michael , Koch Andreas , Kleinpeter Erich
Published: January 2003

The stereoselectivity of the alkylation of dialkyl malates is dependent on steric hindrance of both ester alkyl groups. It was found that the two alkyl groups have opposite effects on diastereoselectivity. Increased steric hindrance at the C(1) carboxy group increases the anti‐selectivity, whereas increased steric hindrance at the C(4) carboxy group decreases it. The results are explained by comparing the structures of the enolates, which were obtained by molecular modeling. Alkylation at C(4′) of dioxolanones, derived from benzyl‐substituted malic acids, with an additional stereogenic center on the side chain is dependent on the stereogenic centers of the ring acetal and of the side chain. Alkylation at low temperatures occurs only with cis‐dioxolanones having an (R)‐configured side‐chain stereogenic center. The corresponding trans‐dioxolanone and the cis‐dioxolanone with a (S)‐configured side‐chain stereogenic center were recovered unchanged. A rationale is presented with models of monolithiated dioxolanones obtained by ab initio calculations.
Automated Solid‐Phase Synthesis and Structural Investigation of β‐Peptidosulfonamides and β‐Peptidosulfonamide/β‐Peptide Hybrids: β‐Peptidosulfonamide and β‐Peptide Foldamers are Two of a Different Kind
Authors: de Jong Remco , Rijkers Dirk T. S. , Liskamp Rob M. J.
Published: January 2003

Fmoc‐protected β‐aminoethane sulfonylchlorides can be employed for efficient automated solid phase synthesis of β‐peptidosulfonamides and β‐peptidosulfonamide/β‐peptide hybrids containing one or more β‐peptidosulfonamide residues. Thus, Fmoc‐protected β‐aminoethane sulfonylchlorides 5a–c led to the hexa‐β‐peptidosulfonamide 9 and the nona‐β‐peptidosulfonamide 10. In addition, the β‐peptidosulfonamide/β‐peptide hybrids 13 and 16, consisting of six and nine β‐residues, respectively, and containing a single β‐peptidosulfonamide unit in the middle, as well as the peptidosulfonamide/β‐peptide hybrid 15 with nine β‐residues, including an N‐terminal β‐peptidosulfonamide residue, were synthesized by automated solid‐phase synthesis. Both CD and NMR spectroscopic measurements did not indicate any helical secondary structure for 9 and 10. As was shown by CD‐measurements, the β‐peptidosulfonamide residue in the hybrids 13, 15, and 16 acts as a ‘helix breaker', especially when located in the middle of the hybrid chain (13 and 16), but, although to a lesser extent, also at the N‐terminus.
Trimetaphosphate‐Induced Addition of Aspartic Acid to Oligo(glutamic acid)s
Authors: Hill Aubrey , Orgel Leslie E.
Published: January 2003

When a solution containing 0.01M decaglutamic acid, 0.1–1.0M aspartic acid, 1.0M MgCl2, and 0.5M sodium trimetaphosphate is allowed to stand at temperatures in the range 0–50°, addition products containing up to ten aspartic acid residues are formed. Addition occurs to the side‐chain carboxy moieties, not to the terminal amine of the decaglutamic acid. A number of other amino acids including glutamic acid, glycine, and histidine fail to react with decaglutamic acid under the same conditions. We believe that the activation of aspartic acid leads to the formation of a cyclic anhydride that is the key intermediate in the reaction.
Hourglass‐Shaped Dendrimers on Surfaces: A Comparison of Different Scanning‐Tunneling‐Microscopy Approaches
Authors: Widmer I. , Hubler U. , Stöhr M. , Merz L. , Güntherodt H.‐J. , Hermann B. A. , Samorí P. , Rabe J. P. , Rheiner P. B. , Greiveldinger G. , Murer P.
Published: January 2003

Large molecules adsorbed on surfaces can be analyzed by scanning tunneling microscopy (STM) under various environmental conditions: on a dry surface in air or vacuum, and at the solid‐liquid interface. However, can measurements under dissimilar conditions be compared, e. g., when sample A was studied at the solid‐liquid interface and sample B in a dry environment? Only rarely can the same substance be examined with more than one approach, since completely different set‐up and preparations are necessary. Furthermore, few substances are suitable for several methods of sample preparation and characterization. We have chosen a large, flexible, nonplanar molecule, namely an alkoxy‐substituted second‐generation dendritic compound with a chiral core unit, which is peculiar for its ‘hourglass' conformation. The assembly properties have been explored by STM both in solution‐cast self‐organized monolayers (SOMs) and multilayer films, as well as at the solid‐liquid interface. The complexity and limits of the three approaches applied to our hourglass‐shaped dendritic compound are discussed. Depending on the approach and environmental conditions, several quality levels of image resolution could be achieved; measurements carried out at low temperatures led to highest resolution on the aromatic parts of the molecule. A comparison of equally sized images obtained under these varying conditions reveals not only different packing arrangements, but also spots of unlike shape. Therefore, when the approach, preparation, and/or environmental conditions are not the same, STM measurements of different compounds have to be compared with greatest care.
Theoretical Studies on the Diastereoselectivity in the Lewis Acid Catalyzed CarbonylEne Reaction: A Fundamental Role of Electrostatic Interaction
Authors: Yamanaka Masahiro , Mikami Koichi
Published: January 2003

Lewis acids affect reactivity, selectivity, and mechanism in the carbonyl‐ene reaction. The diastereoselectivity in the glyoxylate‐ene reaction depends on Lewis acids. While the SnCl4‐promoted reaction can be achieved with a high level of anti‐selectivity, the use of Al reagents leads to a high syn‐selectivity. The origin of the Lewis acid dependency of the diastereoselectivity in the carbonylene reaction of (E)‐but‐2‐ene with glyoxylate was theoretically studied (HF/6‐31G*) from the point of view of differences and similarities between the ene and the Diels–Alder reactions. Though it has been widely accepted that the endo‐preference would be less obvious in the ene reaction than in the Diels–Alder reaction, our ab initio molecular studies showed that the electrostatic interaction between carbonyl O‐atom lone pair and cationic allylic central C‐atom of ene component exists in the Lewis acid‐promoted carbonyl–ene reaction to affect the transition‐state conformation. It is illustrated that such an electrostatic interaction is essential to control the exo/endo‐selectivity, which provides the diastereoselectivity of the product in the transition state of the Lewis acid promoted carbonylene reaction.
Highly Diastereo‐ and Enantioselective Aziridination of α,β‐Unsaturated Amides with Diaziridine and Mechanistic Consideration on Its Stereochemistry
Authors: Ishihara Hiroyuki , Hori Kiyoto , Sugihara Hiroyasu , Ito Yoshio N. , Katsuki Tsutomu
Published: January 2003

During studies of aziridination of α,β‐unsaturated amides with diaziridine, we found that we could prepare both the cis‐ and trans‐aziridinecarboxamides by choosing an appropriately substituted diaziridine. While 3‐monosubstituted diaziridine 2 was suitable for the trans‐selective aziridination, employment of 3,3‐dialkyldiaziridine 1 resulted in the formation of cis‐aziridine carboxamides, irrespective of the geometry of the substrate (Scheme 1 and Tables 1 and 2). To elucidate the unique nonstereospecificity and to expand these aziridinations to asymmetric ones, several optically active diaziridines were newly prepared. Aziridination with an optically active 3‐monosubstituted diaziridine, 3‐cyclohexyl‐1‐[(1R)‐1‐phenylethyl]diaziridine 16, proceeded smoothly with high trans‐selectivity as well as excellent enantioselectivity (up to 98% ee; see Table 3). On the other hand, highly enantioselective cis‐aziridination was achieved (>99% ee) with optically active 3,3‐dimethyl‐1‐[(1R)‐1‐phenylethyl]diaziridine 15, though the yield was low (4%). This aziridination was considered to proceed stepwise by way of the enolate intermediate (Scheme 2). Careful inspection of the stereochemistry and its solvent‐dependence suggested that the diastereoselection of the reaction was kinetically controlled: the 1,4‐addition of N‐lithiated diaziridine was a crucial step for determination of the stereochemical course of the aziridination (Figs. 2–4).
Synthesis and Reactivity of π‐Electron‐Deficient (Arylsulfonyl)acetates
Authors: Alonso Diego A. , Nájera Carmen , Varea Montserrat
Published: January 2003

Different π‐electron‐deficient (arylsulfonyl)acetates 9 were synthesized (Scheme 1, Table 1), and their behavior as soft nucleophiles in the dialkylation reaction under phase‐transfer catalysis conditions was studied (Schemes 2 and 3, Tables 2 and 3). The [3,5‐bis(trifluoromethyl)phenyl]sulfonyl group was shown to be the best substituent for the stereoselective synthesis of (E)‐aconitates 18 via an alkylation hydro‐sulfonyl‐elimination integrated process under very mild phase‐transfer‐catalysis conditions (Scheme 5, Table 4). Sulfonylacetates 9h,i also underwent smooth Diels‐Alder reactions with acyclic and cyclic dienes via in situ formation of the appropriate dienophile through a Knoevenagel condensation with paraformaldehyde (Scheme 6). Reductive desulfonylation with Zn and NH4Cl in THF was shown to be an efficient method for removal of the synthetically useful sulfonyl moiety (Scheme 7).
Catalyzed Asymmetric DielsAlder Reactions of Benzoquinone. Total Synthesis of (−)‐Ibogamine
Authors: White James D. , Choi Younggi
Published: January 2003

The DielsAlder reaction of 1,4‐benzoquinone with 1,3‐dienes catalyzed by Mikami's [Ti{(S)‐binol(2−)}Cl2] complex (binol=[1,1′‐binaphthalene]‐2,2′‐diol) gives cycloadducts in good yield and in high enantiomer excess. A model is proposed to explain the observed absolute configuration of cycloadducts, and the reaction is used as the key step in an asymmetric synthesis leading to the alkaloid (−)‐ibogamine.
Steric and Electronic Effects on an Antibody‐Catalyzed Diels–Alder Reaction
Authors: Gozin Yael , Hilvert Donald
Published: January 2003

A series of substituted thiophene dioxides was tested as diene substrates for the antibody 1E9, which was elicited with a hexachloronorbornene derivative and normally catalyzes the inverse electron‐demand Diels–Alder reaction between 2,3,4,5‐tetrachlorothiophene dioxide (TCTD) and N‐ethylmaleimide (NEM). Previous structural and computational studies had suggested that the catalytic efficiency of this system derives in part from a very snug fit between the apolar active site and the transition state of this reaction. Nevertheless, replacing all the Cl‐atoms in the hapten with Br‐atoms leads to no loss in affinity (Kd=0.1 nM), indicating substantial conformational flexibility in the residues that line the binding pocket. Consistent with this observation, the 2,3,4,5‐tetrabromothiophene dioxide is a good substrate for the antibody (kcat=1.8 min−1, KNEM=14 μM), despite being considerably larger than TCTD. In contrast, normal electron‐demand Diels–Alder reactions between NEM and unsubstituted thiophene dioxide or 2,3,4,5‐tetramethylthiophene dioxide, which are much smaller or nearly isosteric with TCTD, respectively, are not detectably accelerated. These results show that the electronic properties of the 1E9 active site are optimized to a remarkable degree for the inverse electron‐demand Diels–Alder reaction for which it was designed. Indeed, they appear to play a more important role in catalysis than simple proximity effects.
Facile Preparation and Activation of High‐Productivity Single‐Site Nickel Catalysts for Highly Linear Polyethylene
Authors: Pickel Marco , Casper Thomas , Rahm Annette , Dambouwy Christian , Chen Peter
Published: January 2003

A easy‐to‐prepare series of nickel complexes are reported, which, upon activation with near‐stoichiometric alkylating agents, polymerize ethylene with turnover number (TON) of over 105, which brings the catalyst into the range of commercial single‐site catalysts based on early transition metals. However, in contrast to the usual metallocenes, the catalyst shows the same activity in coordinating solvents such as THF and dioxane as it shows in toluene. Moreover, the polymer produced is highly linear, which, together with the long catalyst lifetime, suggests that the combination of the nickel catalyst and a Lewis acid suppresses formation of nickel hydrides.
Cyclic RGD Peptides Containing Azabicycloalkane Reverse‐Turn Mimics
Authors: Belvisi Laura , Caporale Andrea , Colombo Matteo , Manzoni Leonardo , Potenza Donatella , Scolastico Carlo , Castorina Massimo , Cati Matilde , Giannini Giuseppe , Pisano Claudio
Published: January 2003

The Fmoc‐protected lactams 3 and 4 were used to prepare cyclo(Arg‐Gly‐Asp‐lactam) 1 and cyclo(Arg‐Gly‐Asp‐Phe‐lactam) 2, which contain the Arg‐Gly‐Asp (RGD) recognition motif. Their solid‐phase synthesis, conformational analysis, and binding to purified αVβ3 and αVβ5 integrins are reported. Compound 1 was found to act as an active and selective inhibitor of the αVβ5 integrin.
Regioselective Benzoylation of 6‐O‐Protected and 4,6‐O‐Diprotected Hexopyranosides as Promoted by Chiral and Achiral Ditertiary 1,2‐Diamines
Authors: Hu Guixian , Vasella Andrea
Published: January 2003

Monobenzoylation of triols (6‐O‐silylated glycopyranosides) or diols (4,6‐O‐benzylidenated glycopyranosides) with benzoyl chloride and triethylamine at −60° to 23° is promoted by catalytic amounts of ditertiary 1,2‐diamines. The regioselectivity depends mostly on the structure of the alcohols; it is modulated by the configuration and constitution of the diamines, as shown by comparing the effect of Oriyama's catalyst ((S)‐1 and (R)‐1), N,N,N′,N′‐tetramethylethylenediamine (TMEDA), N,N,N′,N′‐tetraethylethylenediamine (TEEDA), Et3N, and EtNMe2. The effect of the catalysts on the reactivity is impaired by their steric hindrance. In agreement with the modest enantioselectivity of the mono‐ and dibenzoylation of rac‐cyclohexane‐1,2‐diol in the presence of Oriyama's catalyst, the influence of these diamines on the regioselectivity is rather limited. While associated with procedural simplicity, these catalysts lead, in a few cases, to higher yields of a single benzoate than established methods, viz. in the preparation of the 3‐O‐benzoyl β‐D‐glucopyranoside 4, the 2‐O‐benzoyl α‐D‐galactopyranoside 22, the 3‐O‐benzoyl α‐D‐galactopyranoside 23, and the benzylidenated 2‐O‐benzoyl α‐D‐galactopyranoside 44. The regioselective benzoylation of the benzylidenated β‐D‐mannopyranoside 47, leading to 48, appears to be new.
Construction and Analysis of LifsonRoig Models for the Helical Conformations of α‐Peptides
Authors: Kemp Daniel S.
Published: January 2003

New forms of LifsonRoig algorithms are introduced for modeling stabilities of helices formed by polypeptides derived from α‐amino acids. The principles of constructing and generalizing these algorithms are developed, and their application to modeling of circular dichroism ellipticities and protection factors derived from H/D exchange of α‐peptide backbone amide residues are critically reviewed. With the aim of comparing the properties of structured conformations formed by α‐ and β‐peptides, the intrinsic limitations of LifsonRoig algorithms and their underlying assumptions are analyzed. LifsonRoig state sums that provide easy structural analysis are generated by new algorithms based on products of 8×8 and 16×16 matrices, and a simple protocol is introduced for generating new state sums that are tailored for specific purposes. The N‐ and C‐capping of highly helical α‐peptides by means of tailored helix‐stabilizing templates is shown to result in helical conformational manifolds that approach those of helical β‐peptides in conformational homogeneity.
Synthesis of a Conformationally Flexible β‐Hairpin Mimetic
Authors: Hoffmann Reinhard W. , Schopfer Ulrich , Müller Gerhard , Brandl Trixi
Published: January 2003

Rational conformation design led us to a synthesis of the ω‐amido‐undecenamide 4, which was shown by theoretical means (simulated annealing techniques) and by NMR and IR spectroscopy to have a high tendency to populate a conformation corresponding to a natural β‐II′‐type hairpin, despite possessing a conformationally fully flexible open‐chain backbone.
Designed Beta‐Turn Mimic Based on the Allylic‐Strain Concept: Evaluation of Structural and Biological Features by Incorporation into a Cyclic RGD Peptide (Cyclo(‐L‐arginylglycyl‐L‐α‐aspartyl‐))
Authors: Sukopp Martin , Marinelli Luciana , Heller Markus , Brandl Trixi , Goodman Simon L. , Hoffmann Reinhard W. , Kessler Horst
Published: January 2003

The (3R,5S,6E,8S,10R)‐11‐amino‐3,5,8,10‐tetramethylundec‐6‐enoic acid (ATUA; 1), which was designed as a βII′‐turn mimic according to the concepts of allylic strain and 2,4‐dimethylpentane units, was incorporated into a cyclic RGD peptide. The three‐dimensional structure of cyclo(‐RGD‐ATUA‐) (=cyclo(‐Arg‐Gly‐Asp‐ATUA‐)) 4 in H2O was determined by NMR techniques, distance geometry calculations and molecular‐dynamics simulations. The RGD sequence of 4 shows high conformational flexibility but some preference for an extended conformation. The structural features of the RGD sequence of 4 were compared with the RGD moiety of cyclo(‐RGDfV‐) (=cyclo(‐Arg‐Gly‐Asp‐D‐Phe‐Val‐)). In contrast to cyclo(‐RGDfV‐), which is a highly active αvβ3 antagonist and selective against αIIbβ3, cyclo(‐RGD‐ATUA‐) shows a lower activity and selectivity. The structure of the ATUA residue in the cyclic peptide resembles a βII′‐turn‐like conformation. Its middle part, adjacent to the CC bond, strongly prefers the designed and desired structure.
Synthesis and Reactions of New Dithiolopyrroles
Authors: Stachel Hans‐Dietrich , Eckl Eduard , Immerz‐Winkler Elisabeth , Kreiner Christine , Weigand Wolfgang , Robl Christian , Wünsch Ralf , Dick Stefan , Drescher Norbert
Published: January 2003

The title compounds were prepared starting from pyrrolinone 4. Nucleophilic‐displacement and ring‐closure reactions yielded the dithiolopyrrole 5a, which formed salts with electrophiles (7, 8) as well as with bases. The crystal structure of 5a was determined. Oxidation of the dithioles 5a and 6a led to S(2)‐oxides (10a, 11a) and the corresponding S(2)‐dioxides (10b, 11b) depending on reaction conditions. The thiosulfinate 10a was converted by a ring‐opening/ring‐closure reaction sequence to the bicyclic sulfinamide 12. The oxidative addition reactions of [Pt(η2‐C2H4) (PPh3)2] (14) with the disulfides 5a and 13 led to the dithiolatoplatinum(II) complexes 15 and 16, respectively. Complex 16 was characterized structurally. The sulfenato‐thiolato complex 17 was synthesized via reaction of 14 with the thiosulfinate 10a. The thiosulfonato PtII complex 18 was prepared by an oxidative insertion of Pt0 into the CS bond of the corresponding thiosulfonate 10b. Furthermore, complex 18 was characterized by single‐crystal X‐ray‐diffraction studies.