bluuebunny/crossref_metadata_2025_split huggingface dataset:
The stabilizing contribution of thymine in duplexes of (dA)24 with (dU)24, (dT)24, (dU12–dT12), (dU–dT)12, (dU2–dT2)6, or (dU3–dT3)4: Nearest neighbor and next‐nearest neighbor effects
Authors: Howard Frank B. 
Published: May 2005

AbstractUltraviolet melting curves are used to determine the effect of the pyrimidine 5‐methyl group on the stability of duplexes of (dA)24 with (dU)24, (dT)24, (dU12–dT12), (dU–dT)12, (dU2–dT2)6, and (dU3–dT3)4. Substitution of a T for a U results in an increase in stability, which is attributed to an increase in strength of dipole‐induced dipole and dispersion (van der Waals) interactions. Significant additional enhancement occurs when two T residues are adjacent. A further increase in the number of adjacent T's has a relatively slight effect on Tm. The sequence effect appears to be largely attributable to an increment in dispersion forces.The CD spectra of the duplexes are all closely similar except in the region between 260 and 290 nm. A band near 272 nm associated with the presence of U in the spectrum of (dA)24·(dU)24 decreases in intensity when T's are incorporated in the pyrimidine strand. The band is completely replaced in the spectrum of (dA)24·(dT)24 with a new maximum at 282 nm and a minimum at 268 nm, both of lower magnitude. The emergence of the two new bands is correlated with the presence of adjacent T's once more, and only two adjacent T's appear necessary for a major part of the change to occur.The degree of cation release on thermal dissociation of the oligomer dimers ranges from Δi = 0.14 to 0.16, about the same or slightly less than values reported for polynucleotide duplexes and less than predicted from theoretical calculations. © 2005 Wiley Periodicals, Inc. Biopolymers 78:221–229, 2005
Multiplex‐PCR‐Based Recombination as a Novel High‐Fidelity Method for Directed Evolution
Authors: Eggert Thorsten , Funke Susanne Aileen , Rao Nalam M. , Acharya Priyamvada , Krumm Holger , Reetz Manfred T. , Jaeger Karl‐Erich 
Published: May 2005

AbstractA new and convenient method for the in vitro recombination of single point mutations is presented. This method efficiently reduces the introduction of novel point mutations, which usually occur during recombination processes. A multiplex polymerase chain reaction (multiplex‐PCR) generates gene fragments that contain preformed point mutations. These fragments are subsequently assembled into full‐length genes by a recombination‐PCR step. The process of multiplex‐PCR‐based recombination (MUPREC) does not require DNase I digestion for gene‐fragmentation and is therefore easy to perform, even with small amounts of target DNA. The protocol yields high frequencies of recombination without creating a wild‐type background. Furthermore, the low error rate results in high‐quality variant libraries of true recombinants, thereby minimizing the screening efforts and saving time and money. The MUPREC method was used in the directed evolution of a Bacillus subtilis lipase that can catalyse the enantioselective hydrolysis of a model meso‐compound. Thereby, the method was proved to be useful in producing a reliable second‐generation library of true recombinants from which better performing variants were identified by using a high‐throughput electrospray ionization mass spectrometry (ESI‐MS) screening system.
Utilizing the Power of Microbial Genetics to Bridge the Gap Between the Promise and the Application of Marine Natural Products
Authors: Fortman J. L. , Sherman David H. 
Published: May 2005

AbstractMarine organisms are a rich source of secondary metabolites. They have yielded thousands of compounds with a broad range of biomedical applications. Thus far, samples required for preclinical and clinical studies have been obtained by collection from the wild, by mariculture, and by total chemical synthesis. However, for a number of complex marine metabolites, none of these options is feasible for either economic or environmental reasons. In order to proceed with the development of many of these promising therapeutic compounds, a reliable and renewable source must be found. Over the last twenty years, the study of microbial secondary metabolites has greatly advanced our understanding of how nature utilizes simple starting materials to yield complex small molecules. Much of this work has focused on polyketides and nonribosomal peptides, two classes of molecules that are prevalent in marine micro‐ and macroorganisms. The lessons learned from the study of terrestrial metabolite biosynthesis are now being applied to the marine world. As techniques for cloning and heterologous expression of biosynthetic pathways continue to improve, they may provide our greatest hope for bridging the gap between the promise and application of many marine natural products.
Highly Diastereoselective and Enantioselective Preparation of Homoallylic Amines: Application for the Synthesis of β‐Amino Acids and γ‐Lactams
Authors: Ramachandran P. Veeraraghavan , Burghardt Thomas E. 
Published: May 2005

AbstractReactions of N‐silyl‐ and N‐aluminoimines with B‐allyldiisopinocampheylborane in the presence of methanol, followed by oxidative workup furnished homoallylic amines in good yields and high ee. A 11B NMR spectroscopy study revealed that the reactions do not proceed, even at room temperature, unless a molar equivalent of water or methanol is added. The first reagent‐controlled asymmetric crotylboration and alkoxyallylboration of aldimines furnishing β‐methyl or β‐alkoxy homoallylic amines in very high diastereoselectivity and enantioselectivity are reported herein. Crotylboration and alkoxyallylboration of imines proceed only with the “allyl”‐boron “ate” complexes, instead of the “allyl”‐dialkylboron reagents used with aldehydes. The addition of methanol is necessary for these reactions as well. Application of this methodology for the conversion of representative nitriles to β‐amino acids in two steps has been described. Additionally, a procedure for the preparation of chiral δ‐amino alcohols and γ‐lactams from nitriles is also reported.
G–G Base‐Pairing in Nucleobase Adducts of the Anticancer Drug cis‐[PtCl2(NH3)(2‐picoline)] and Its trans Isomer
Authors: McGowan Geraldine , Parsons Simon , Sadler Peter J. 
Published: May 2005

Abstractcis‐[PtCl2(NH3)(2‐picoline)] (AMD473) is a sterically‐hindered anticancer complex with a profile of chemical and biological activity that differs significantly from that of cisplatin. Adducts of AMD473 with neutral 9‐ethylguanine (9‐EtGH) and anionic (N1‐deprotonated) 9‐ethylguanine (9‐EtG) as perchlorate and nitrate salts, and also a nitrate salt of the trans isomer (AMD443), were prepared and their structures determined by X‐ray crystallography: cis‐[Pt(NH3)(2‐pic)(9‐EtGH)2](ClO4)2 (1)⋅2 H2O⋅Me2CO, cis‐[Pt(NH3)(2‐pic)(9‐EtGH)2](NO3)2 (2)⋅2 H2O, cis‐[Pt(NH3)(2‐pic)(9‐EtGH)(9‐EtG)]NO3 (3)⋅3.5 H2O, trans‐[Pt(NH3)(2‐pic)(9‐EtGH)(9‐EtG)]NO3 (4)⋅8 H2O. In all cases, platinum coordination is through N7 of neutral (1, 2) and anionic (3, 4) guanine. In each complex, the guanine bases are arranged in the head‐to‐tail conformation. In complex 1, there is an infinite array of six‐molecule cycles, based on both hydrogen bonding and π–π stacking of the 2‐picoline and guanine rings. Platinum(II) coordinated at N7 acidifies the N1 proton of neutral 9‐ethylguanine (pKa=9.57) to give pKa1=8.40 and pKa2=8.75 for complex 2, and pKa1=7.77 and pKa2=9.00 for complex 4. In complexes 3 and 4, three intermolecular hydrogen bonds are formed between neutral and deprotonated guanine ligands involving O6, N1 and N2 sites. Unusually, both of the platinated guanine bases of complexes 3 and 4 participate in this triple GG hydrogen bonding. This is the first report of X‐ray crystal structures of nucleobase adducts of the promising anticancer drug AMD473.
Frequency of SOX Group B (SOX1, 2, 3) and ZIC2 antibodies in Turkish patients with small cell lung carcinoma and their correlation with clinical parameters
Authors: Vural Burcak , Chen Lin‐Chi , Saip Pinar , Chen Yao‐Tseng , Ustuner Zeki , Gonen Mithat , Simpson Andrew J. G. , Old Lloyd J. , Ozbek Ugur , Gure Ali O. 
Published: May 2005

AbstractBACKGROUNDExpression of neuroectodermal markers is a key feature of small cell lung carcinoma (SCLC). Although immune responses against a number of these proteins have been associated with paraneoplastic neuronal disease (PND), most patients with SCLC have anti‐neuroectodermal antibodies in the absence of PND. Whether these immune responses affect the clinical outcome in SCLC is critical in understanding the potential value of these proteins as cancer vaccine targets as well as in the pathogenesis of PND.METHODSThe authors investigated the frequency of immunoglobulin G autoantibodies against Sry‐like high‐mobility group box (SOX)1, 2, 3 and Zinc‐finger gene of the cerebellum (ZIC)2 proteins in stored serum samples from 90 patients utilizing the λ‐phage plaque assay. Data obtained from patient records were utilized to measure clinical correlates of seroreactivity.RESULTSAntibodies to SOX1 were present in 28% of patients and another 28% had anti‐ZIC2 antibodies, classifying these as some of the most frequent antibody responses observed in SCLC. None had autoimmune paraneoplastic disease. Antibody titers were frequently as high as ≥ 1:106 and were stable for ≤ 6 months after diagnosis. Seroreactivity against either SOX1 or ZIC2 correlated with younger age, lower lactate dehydrogenase levels, and better response to initial therapy.CONCLUSIONSThe frequent and stable presence of SOX Group B and/or ZIC2 antibodies in SCLC, but not in healthy individuals examined, indicates they are serological markers of SCLC. However, the correlation between known clinical parameters of less aggressive disease and seroreactivity suggests that these antibodies are indicators of better prognosis in SCLC and warrants further studies to clarify the nature of the underlying immune responses. Cancer 2005. © 2005 American Cancer Society.
Differential expression ofvasaRNA and protein during spermatogenesis and oogenesis in the gibel carp (Carassius auratus gibelio), a bisexually and gynogenetically reproducing vertebrate
Authors: Xu Hongyan , Gui Jianfang , Hong Yunhan 
Published: May 2005

AbstractThe RNA helicase Vasa is a germ cell marker in animals, and its homolog in vertebrates to date has been limited to bisexual reproduction. We cloned and characterizedCagVasa, a Vasa homolog from the gibel carp, a fish that reproduces bisexually or gynogenetically.CagVasa possesses 14 RGG repeats and eight conserved motifs of Vasa proteins. In bisexually reproducing gibel carp,vasais maternally supplied and its zygotic expression is restricted to gonads. By in situ hybridization on testicular sections,vasais low in spermatogonia, high in primary spermatocytes, reduced in secondary spermatocytes, but disappears in spermatids and sperm. In contrast,vasapersists throughout oogenesis, displaying low–high–low levels from oogonia over vitellogenic oocytes to maturing oocytes. A rabbit anti‐Vasa antibody (αVasa) was raised against the N‐terminalCagVasa for fluorescent immunohistochemistry. On testicular sections, Vasa is the highest in spermatogonia, reduced in spermatocytes, low in spermatids, and absent in sperm. In the ovary, Vasa is the highest in oogonia but persists throughout oogenesis. Subcellular localization ofvasaand its protein changes dynamically during oogenesis. The αVasa stains putative primordial germ cells in gibel carp fry. It detects gonadal germ cells also in several other teleosts. Therefore,Cagvasaencodes a Vasa ortholog that is differentially expressed in the testis and ovary. Interestingly, the αVasa in combination with a nuclear dye can differentiate critical stages of spermatogenesis and oogenesis in fish. The cross‐reactivity and the ability to stain stage‐specific germ cells make this antibody a useful tool to identify fish germ cell development and differentiation. Developmental Dynamics 233:872–882, 2005. © 2005 Wiley‐Liss, Inc.
Specific requirements of sonic hedgehog signaling during oligodendrocyte development
Authors: Oh Saeock , Huang Xi , Chiang Chin 
Published: May 2005

AbstractOligodendrocyte precursors (OLPs) in the developing spinal cord are generated from the same part of the ventral neuroepithelium as motor neurons, by inductive processes that include a temporal switch from neuronal to glial cell fate. Recent studies have implicated Shh as a key signal in the generation of both OLPs and ventral neurons. In this study, we used Shh−/−, Gli3−/−, and Shh−/−;Gli3−/− mutants to address the role of Shh signaling during oligodendrocyte development. We find that, in the absence of Gli3, Shh signaling is dispensable for the generation and maintenance of OLPs. However, Shh is required for OLPs to emerge at the appropriate developmental stages and for subsequent differentiation of OLPs into mature oligodendrocytes. The initial delay and reduction in OLP generation in Shh−/−;Gli3−/− mutants are accompanied by extended neurogenesis and persistent expression of Neurogenin 2 in the Olig2 progenitor domain, suggesting that Shh signaling influences the timing of neuron–glia fate switching. Thus, our studies suggest that Shh signaling plays multiple roles during development of oligodendrocytes. Developmental Dynamics 234:489–496, 2005. © 2005 Wiley‐Liss, Inc.
The Mechanism of Hydrolysis of Aryl Ether Derivatives of3‐Hydroxymethyltriazenes
Authors: Carvalho Emília , Francisco Ana Paula , Iley Jim , Rosa Eduarda 
Published: May 2005

Abstract1‐Aryl‐3‐aryloxymethyl‐3‐methyltriazenes hydrolyse to the corresponding anilines and phenols by specific‐acid‐catalysed, general‐acid‐catalysed and pH‐independent mechanisms. All compounds studied exhibit specific‐ and general acid catalysis, though for 5a general acid catalysis was not observed below a pH of approximately 4, while for compounds 5e,f, such catalysis was absent above a pH of approximately 5. The pH‐independent pathway is observed only for those compounds, 5d–f, that contain good aryloxy nucleofugic groups. The specific‐acid‐catalysed pathway is supported by a solvent deuterium isotope effect (SDIE) of 0.64, consistent with a mechanism involving protonation of the substrate followed by rate‐determining unimolecular decomposition of the protonated species. The kH+ values gave rise to a Hammett ρ value of –0.93, reflecting the competing effect of the substituents on the protonation of the substrate and the cleavage of the aryl ether. Correlation of kH+ with the pKa of the phenol leaving group affords a βlg of 0.3. Decomposition of the protonated intermediate proceeds via a triazenyliminium ion that can be trapped by methanol. The general‐acid‐catalysed process exhibits an SDIE of 1.43 and Hammett ρ values of 0.49, 0.84 and 1.0 for reactions catalysed by chloroacetic, formic and acetic acids, respectively. Correlation of kA with the pKa of the acid gave Brønsted α values that diminish from 0.6 for O‐aryl systems that are poor nucleofuges (5a,b) to 0.2 for the best nucleofuge (5f), reflecting the different extents of proton transfer required to expel each phenol. Compounds containing powerful nucleofuges exhibit a pH‐independent reaction that has an SDIE of 1.1, a Hammett ρ value of 3.4 and a Brønsted βlg value of 1.4. These imply a mechanism involving displacement of the aryloxide leaving group to form a triazenyliminium ion intermediate that again was trapped as a methyl ether. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Mechanism of the Reaction of Lawesson’s Reagent with N‐Alkylhydroxamic Acids
Authors: Przychodzeń Witold 
Published: May 2005

AbstractThe mechanism of the reaction under discussion has been established by investigating the products of the reaction between 2,4‐bis(4‐methoxyphenyl)‐1,3,2,4‐dithiadiphosphetane 2,4‐disulfide (Lawesson’s reagent, LR) and N‐alkylhydroxamic acids HAs 1. The primary intermediate is an adduct, O‐dithiophosphonylated hydroxamic acid 19, which decomposes to yield metathiophosphonate (AnsPOS), a sulfur atom, and an amide. At the same time, owing to the co‐existence of 19 and metadithiophosphonate (AnsPSS) in equilibrium, the carbonyl group is thionated. It has also been established that monomeric AnsPOS formed in both reduction and thionation processes does not undergo oligomerisation to cyclic trimer 5 and linear oligomers, which is typical for amides reacting with LR. Since there is unreacted HA 1 in the reaction mixture, AnsPOS takes part in a controlled transformation to form a dimer, the corresponding pyrothiophosphonate 3, together with the intermediate O‐thiophosphonylated hydroxamic acid 2. A hydrolysed product of AnsPOS, namely (4‐methoxyphenyl)thiophosphonic acid 4, participates in the last reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Efficient Routes to Acenaphthylene‐Fused Polycyclic Arenes/Heteroarenes and Heterocyclic Fluoranthene Analogues
Authors: Panda Kausik , Venkatesh Chelvam , Ila Hiriyakkanavar , Junjappa Hiriyakkanavar 
Published: May 2005

AbstractThe acenaphthenone‐derived α‐oxoketene dithioacetal 2 has been subjected to various [3 + 3] aromatic and heteroaromatic annulation and other heterocyclization reactions previously developed in our laboratory, providing short and efficient routes to a diverse range of known and unknown acenaphtho‐annulated linear and angular PAHs, heteroaromatics and five‐membered heterocycles in good yields. Thus, benzo‐ and naphthoannulation of 2 with various allyl and benzyl Grignard reagents afforded substituted fluoranthenes 4a–c and benzo[k]fluoranthene 8, respectively, in good yields. Similarly, the parent benzo[j]fluoranthene 15a and its substituted derivative 16b have been synthesized by base‐induced conjugate 1,4‐addition of arylacetonitriles to 2, followed by acid‐induced cyclization of the conjugate adducts 12a–b to give 13a–b and subsequent further transformations. The adducts obtained by 1,4‐addition of anions derived from acetophenone and acenaphthenone were subjected toheterocyclization in the presence of ammonium acetate to give 8‐arylacenaphtho[1,2‐b]pyridines 18a–b and bis(acenaphtho)‐annulated pyridine 20. Heterocyclization of 2 with bifunctional nucleophiles such as 2‐picolyllithium and guanidinium nitrate afforded the corresponding acenaphtho[1,2‐b]quinolizinium salt 23 and acenaphtho[1,2‐d]pyrimidine 24, respectively, in high yields. Finally, acenaphtho[1,2‐c]‐fused five‐membered heterocycles such as 7‐(methylthio)acenaphtho[1,2‐c]thiophene (25), 7‐(methylthio)acenaphtho[1,2‐c]furan (27) and 7‐(methylthio)acenaphtho[1,2‐c]pyrrole‐2‐carboxylic acid (30) were obtained in good yields by subjection of 2 to Simmons–Smith reaction conditions or by treatment with dimethylsulfonium methylide or glycinate dianion. Some of these newly synthesized PAHs or fused heterocycles were subjected to Raney Ni desulfurization to furnish sulfur‐free compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Novel Highly Efficient P‐Chiral Ferrocenylimino Diamidophosphite Ligands for Pd‐Catalysed Asymmetric Allylation
Authors: Tsarev Vasily N. , Lyubimov Sergey E. , Bondarev Oleg G. , Korlyukov Alexander A. , Antipin Mikhail Yu. , Petrovskii Pavel V. , Davankov Vadim A. , Shiryaev Alexei A. , Benetsky Eduard B. , Vologzhanin Pavel A. , Gavrilov Konstantin N. 
Published: May 2005

AbstractNovel P*‐chiral P,N‐bidentate ligands were synthesized by treatment of ferrocene‐based imino alcohols with chlorophosphites derived from (S)‐2‐anilinomethylpyrrolidine or (S)‐prolinol. Metal chelate complexes with the ligands – [Rh(CO)(PN)Cl] and [Pd(PN)(allyl)]+X– (X– = BF4–, Cl–, I–, CH12B11–) – were obtained and all new compounds were fully characterized by 1H, 13C, 31P NMR, IR, MS (EI, CI, FAB, ESI and plasma desorption techniques) and X‐ray analysis (imino alcohol 2d and complex 7). P*‐Chiral diamidophosphites gave up to 97 % ee in the Pd‐catalysed allylic substitution of 1,3‐diphenylallyl acetate with dimethyl malonate and para‐toluenesulfinate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis of Enantiomerically Pure Dissymmetric 2,2'‐Disubstituted9,9'‐Spirobifluorenes
Authors: Thiemann Frank , Piehler Torsten , Haase Detlev , Saak Wolfgang , Lützen Arne 
Published: May 2005

AbstractRacemic dissymmetric 2,2'‐dihydroxy‐9,9'‐spirobifluorene was prepared and resolved by clathrate formation with (R,R)‐(+)‐2,3‐dimethoxy‐N,N,N',N'‐tetracyclohexylsuccindiamide, giving rise to both enantiomers in very good yields. The absolute stereochemistry of the resolved material could be assigned by an X‐ray structure analysis of single crystals of the clathrate. Enantiomerically pure diols could be transformed into the corresponding ditriflates, which were then used as starting materials in different cross‐coupling procedures to provide a number of new enantiomerically pure spiro compounds bearing versatile functional groups suitable for further elaboration, as demonstrated by some examples. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Regioselective Synthesis of Functionalized Furans by Cyclization of 1,3‐Bis‐Silyl Enol Ethers with 1‐Chloro‐2,2‐dimethoxyethane
Authors: Bellur Esen , Görls Helmar , Langer Peter 
Published: May 2005

AbstractCyclization of 1,3‐bis‐silyl enol ethers with 1‐chloro‐2,2‐dimethoxyethane allowed an efficient, regio‐ and diastereoselective synthesis of a variety of 2‐alkylidene‐4‐methoxytetrahydrofurans. The TFA‐mediated elimination of methanol resulted in the formation of functionalized furans. Similarly, 2,3,3a,4,5,6‐hexahydro‐2,3‐benzofurans were prepared and transformed into 4,5,6,7‐tetrahydro‐2,3‐benzofurans by treatment with TFA. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Concise Synthesis of (4R,9Z)‐Octadec‐9‐en‐4‐olide, the Female Sex Pheromone of Janus integer
Authors: Mori Kenji 
Published: May 2005

Abstract(4R,9Z)‐Octadec‐9‐en‐4‐olide, the female sex pheromone of the currant stem girdler (Janus integer), was synthesized in gram quantities by employing Sharpless asymmetric dihydroxylation (AD) and Jacobsen hydrolytic kinetic resolution (HKR). Crystalline (R)‐hexadec‐7‐yne‐1,2‐diol (87 % ee), obtained by AD and purified by recrystallization, was converted into (R)‐1,2‐epoxyhexadec‐7‐yne (87 % ee), which was further purified to 96 % ee by HKR. The epoxide was converted into the target lactone in 14 % overall yield based on hex‐5‐en‐1‐ol (11 steps). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Enzyme‐Catalysed Transformations of ent‐Kaurane Diterpenoids
Authors: Monsalve Leandro N. , Rosselli Sergio , Bruno Maurizio , Baldessari Alicia 
Published: May 2005

AbstractSeveral acetyl derivatives of linearol, atractyligenin and atractylitriol were obtained through enzyme‐catalysed acetylation and deacetylation reactions. In most reactions lipases showed regio‐ and stereoselective behaviour, allowing a family of novel compounds to be prepared. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
New Highly Active and Selective Heterogeneous Catalytic System for the Synthesis of Unsymmetrical Organic Carbonates: A Green Protocol
Authors: Veldurthy Bhaskar , Clacens Jean‐Marc , Figueras François 
Published: May 2005

AbstractA green, efficient, and selective synthesis of unsymmetrical organic carbonates is realised in the liquid phase by direct condensation of an alcohol and diethyl carbonate, in an eco‐compatible route, in the presence of a recyclable heterogeneous solid‐base CsF/α‐Al2O3 catalyst. The catalyst displayed unprecedented activity after activation at 393 K for 4 h and produced quantitative yields with a greater rate compared with solid bases reported so far. The present process is a potential alternative to replace soluble bases in commercial synthesis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)