bluuebunny/crossref_metadata_2025 huggingface dataset:
1‐Azafagomine: A Hydroxyhexahydropyridazine That Potently Inhibits Enzymatic Glycoside Cleavage
Authors: Bols Mikael , Hazell Rita G. , Thomsen Ib B.
Published: July 2007

(3,4‐trans‐4,5‐trans)‐4,5‐dihydroxy‐3‐hydroxymethylhexahydropyrida‐zine (16) was synthesized in four steps from 2,4‐pentadienol (22) and 4‐phenyl‐triazolin‐3,5‐dione (18) in an overall yield of 32%. In the first step a Diels‐Alder reaction between 18 and 22 gave (π)‐2‐hydroxymethyl‐8‐phenyl‐1,6,8‐triazabicyclo[4.3.0]non‐3‐ene‐7,9‐dione (23c) in 88% yield. Epoxidation of 23c with trifluoromethyl(methyl)dioxirane, generated in situ, gave the trans epoxide 24c in 62% yield. Hydrolysis of the epoxide with perchloric acid gave stereoselectively (2,3‐trans‐3,4‐trans)‐3,4‐dihydroxy‐2‐hydroxy‐methyl‐8‐phenyl‐1,6,8‐triazabicyclo[4.3.0]‐nonane‐7,9‐dione (26) in 73% yield. In the fourth and final step, hydrazinolysis of 26 gave 16 in 84% yield. Pyridazine 16 was found to be a potent inhibitor of α‐and β‐glucosidase, isomaltase and glyco‐gen phosphorylase, while galactosidases and α‐mannosidase were not inhibited. The inhibition of β‐glucosidase is independent of pH, and was found to be due to unprotonated 16.
A Comprehensive Qualitative and Quantitative Molecular Orbital Analysis of the Factors Governing the Dichotomy in the Dinorcaradiene 1,6‐Methano[10]annulene system
Authors: Mealli Carlo , Ienco Andrea , Zoellner Robert W. , Hoyt Earle B.
Published: July 2007

The interconversion between the valence tautomers 1,6‐methano[10]‐annulene (1) and dinorcaradiene (2) was computationally investigated by qualitative extended Hückel molecular orbital methods (with CACAO visualization) and quantitative semiempirical and ab initio methods. The fundamental bonding interactions are described in terms of perturbation theory arguments for both tautomers, the influence of π‐acceptor or π‐donor substituents at the C11 position is rationalized, and bonding changes during the interconversion are monitored. The electronic molecular structural preferences can be modified by through‐space interactions, and residual C1–C6 σ bonding remains even at the >2.1 å separations of the annulenic structures. Hitherto unprecedented calculations of the geometries of C11 homo‐disubstituted derivatives of 1 and 2 have been carried out at semiempirical and ab initio levels to identify the more stable tautomer and find whether two stable minima may exist for each derivative. Searches at the AM 1 level to determine transition‐state structures for the interconversion of 1 to 2 and of their C11 homo‐disubstituted derivatives are also reported.
A New Family of Carbenerhodium(I) Complexes: Ligand Variation as The Key to Success
Authors: Werner Helmut , Schwab Peter , Bleuel Elke , Mahr Norbert , Steinert Paul , Wolf Justin
Published: July 2007

A synthetic methodology to obtain square‐planar carbenerhodium(I) complexes of the general composition trans‐[RhCl(CRR′)(L)2] where L is a tertiary phosphane, arsane, or stibane has been developed. The starting material trans‐[RhCl(C2H4)(SbiPr3)2] (3) reacts with diazoalkanes RR′CN2 [RR′ = Ph2, Ph(C6H4X), (C6H4X)2, Ph(CF3), C12H8] under mild conditions to give the compounds trans‐[RhCl(CRR′)(SbiPr3)2] (4–11) almost quantitatively. On treatment of 3 with EtO2CCHN2 and PhC(N2)C(O)R, the olefinrhodium and diazoalkanerhodium compounds trans‐[RhCl{(E)‐C2H2(CO2Et)2}(SbiPr3)2] (12) and trans‐[RhCl{N2C(R)C(O)Ph}(SbiPr3)2] (13, 14) are obtained instead of carbene complexes. Displacement of the SbiPr3 ligands in 4 (R = R′ = Ph) by PiPr3, PiPr2Ph, PiPrPh2, PPh3, PPh2Me, AsiPr3, and SbEt3 leads to the corresponding carbene complexes trans‐[RhCl‐(CPh2)(L)2] (15–21) in high yields. The results of the X‐ray crystal structure analyses of 4 and 15 (L = PiPr3) illustrate that the different donor—acceptor properties of SbiPr3 and PiPr3 have little influence on the RhC bond length. The reactions of 4 and 15 with CO and CNtBu afford, by metal‐assisted CC coupling, diphenylketene Ph2CCO (23) and the corresponding imine Ph2CCNtBu (26). On treatment of 4 and 15 with ethene, however, two different olefinic products, 3,3‐diphenyl‐1‐propene (31) and 1,1‐diphenyl‐1‐propene (32), are formed. Compound 15 reacts with KBr, NaOPh, and NaC5H5 by substitution of the chloride to give trans‐[RhBr(CPh2)‐(PiPr3)2] (33), trans‐[Rh(OPh)(CPh2)‐(PiPr3)2] (34) and [C5H5Rh(CPh2)‐(PiPr3)] (35), and with HCl by oxidative addition to yield [RhCl2(CHPh2)‐(PiPr3)2](36).
The Role of Backbone Oxygen Atoms in the Organization of Nucleic Acid Tertiary Structure: Zippers, Networks, Clamps, and C‐H…︁O Hydrogen Bonds
Authors: Berger Imre , Egli Martin
Published: July 2007

Tight packing between structural elements is a prerequisite for molecular recognition and catalysis. In proteins, α‐helices and β‐sheets present the amino acid side chains on the surface while the polar amide bonds are buried. The opposite is found in double‐ and polystranded nucleic acids, where negatively charged phosphates occupy the surface and the side chains are hydrogen bonded in the core. Thus the question arises: How do densely packed nucleic acid molecules achieve close approach, despite the repulsion between phosphates that would appear to preclude tight contacts? One obvious answer is by mediating interstrand contacts through coordinated cations that can screen the negative charges. In this contribution, however, we highlight a variety of alternative direct interactions involving atoms of the sugar‐phosphate backbone that can promote tight packing of RNA and DNA into functional molecules. We have analyzed the existing nucleic acid crystal structures in terms of the presence of close contacts between backbone regions. In RNA, ribose 2′‐hydroxyl groups were observed to mediate such contacts in the majority of cases. However, their absence in DNA does not prevent oligodeoxynucleotides from packing tightly, aided by various interactions between backbone atoms.
A Contribution to the Asymmetric Synthesis of 3‐Amino β‐Lactams: The Diastereoselective [2+2] Cycloaddition Reaction of Chiral Aminoketene Equivalents with Enolizable Aldehyde‐Derived Imines
Authors: Palomo Claudio , Aizpurua Jesus M. , Legido Marta , Mielgo Antonia , Galarza Regina
Published: July 2007

N‐[Bis(trimethylsilyl)methyl]imines 9 show unique chemical properties when compared with conventional imines. Their reaction with optically pure aminoketenes derived from dehydrochlorination of 14 and 15 affords the corresponding 3‐amino‐4‐alkyl‐β‐lactams 16 and 17 in good yields and high diastereoselectivities. The mild deprotection of bis(trimethylsilyl)methyl‐ and phenyloxazolidinone moieties with, respectively, cerium(IV) ammonium nitrate and lithium/ammonia or hydrogen/Pd(OH)2 allows the preparation of a variety of β‐lactam antibiotic building blocks.
A Square As4 and a Prismatic As6 Structure as Complex Ligands
Authors: von Hänisch Carsten , Fenske Dieter , Weigend Florian , Ahlrichs Reinhart , Ahlrichs R. , Weigend F.
Published: July 2007

[As7(SiMe3)3] reacts with [(Cp*CoCl)2] to give black crystals of the ionic compound [(Cp*Co)3As6][CoCl4] (1). The cation [(Cp*Co)3As6]2+ consists of an As6 prism, with squares capped by [Cp*Co] fragments. When [(CptBuCoCl)2] is used instead of [(Cp*CoCl)2] in the reaction, dark red crystals of [(CptBuCo)3As6][CoCl3(thf)]2 (2) and green–black crystals of [(CptBuCo)2As4][Co3Cl8(thf)2] (3) can be obtained. The cation in 2 shows a structure very similar to that of 1. The [(CptBuCo)2As4]2+ cations in 3 can be described as a triple‐decker sandwich complex with two [CptBuCo]+ fragments bridged by an As4 ligand. Density functional calculations reproduce the experimental data of 1 and 3 and allow an interpretation of molecular electronic structure and bonding in these and related compounds with As replaced by P and Co by Fe.
1′,5′‐Anhydrohexitol Oligonucleotides: Hybridisation and Strand Displacement with Oligoribonucleotides, Interaction with RNase H and HIV Reverse Transcriptase
Authors: Hendrix Chris , Rosemeyer Helmut , De Bouvere Bart , Van Aerschot Arthur , Seela Frank , Herdewijn Piet
Published: July 2007

Hexitol nucleic acids (HNAs) with four natural bases form stable and sequence‐selective duplexes with RNA. This was investigated by Tm determinations and gel shift experiments. The CD spectra of an HNA‐RNA duplex show similarities with the CD spectra of the A‐form of dsRNA. Single‐stranded HNAs are able to induce strand displacement in a double‐stranded RNA sequence. An HNA‐RNA duplex is a poor substrate for RNase H, and can inhibit the RNase H‐mediated cleavage of a natural DNA‐RNA substrate. The HNA‐RNA hybrid enhances the activity of HIV reverse transcriptase.
Investigation of the Formation Reaction and Structural Characterization of the „Platinum Grignard Reagent”︁ [Pt(MgCl)2(THF)x] by Extended X‐ray absorption fine structure (EXAFS) and Other methods
Authors: Aleandri Lorraine E. , Bogdanović Borislav , Dürr Christine , Huckett Sara C. , Jones Deborah J. , Kolb Uwe , Lagarden Martin , Rozière Jacques , Wilczok Ursula
Published: July 2007

The „platinum Grignard reagent”︁ [Pt(MgCl)2(THF)x] (2), obtained by the reaction of PtCl2 and Et2Mg in a 1:2 molar ratio, as well as finely divided platinum (Pt*)—a possible intermediate formed during the preparation of 2—have been investigated by EXAFS spectroscopy at the PtLII edge. Parallel investigations were carried out on Pt* obtained from PtCl2 and (9,10–dihydro‐9,10‐an‐thracenediyl)tris(tetrahydrofuran)magnesium (MgA), and on 2 obtained from Pt*, MgA, and MgCl2. The EXAFS results suggest that Pt* consists of extremely small particles (≈ 5–11 Å) with strongly reduced Pt–Pt distances compared to bulk Pt (≈ 0.09 Å). The EXAFS spectra of 2 indicate the presence of Mg shells in addition to Pt shells in the Pt environment; Mg atoms are at a bonding distance from Pt atoms (2.78–2.80 Å). These results suggest that 2 consists of very small Pt–Mg clusters and confirm their formation from organomagnesium reagents and PtCl2 or Pt*.
Electronic and Geometrical Structures of Dialuminoxane, Diboroxane, and Their Sulfur Analogues: Ab Initio Study of H2X‐Y‐XH2 (X = Al, B; Y = O, S) Compounds
Authors: Boiteau Laurent , Demachy Isabelle , Volatron François
Published: July 2007

The structures of H2XYXH2 compounds (X = B, Al; Y = O, S) have been studied by means of ab initio calculations at the MP4/6‐311 G**/MP2/6‐311G** level. The potential energy surface (PES) of the aluminoxane species H2AlOAlH2 is rather flat: the energy differences between the various located extrema are less than 1.5 kcal mol−1, and this shows that the observed geometrical preference is not due to electronic factors. For the sulfur analogues H2XSXH2 (X = B, Al), three minima are located on the PES: a planar C2v structure, a Cs structure in which one hydrogen atom bridges the two X atoms, and a C2v structure with two bridging hydrogen atoms. For H2AlSAlH2, the Cs structure is the most stable, and the planar C2v and the dibridged structures lie 3.2 and 6.7 kcal mol−1 higher, respectively. Qualitatively similar results are obtained for H2BSBH2: the Cs and planar C2v structures are nearly isoenergetic, and the dibridged minimum lies 19.4 kcal mol−1 above the planar C2v minimum. These results are rationalized by analyzing the ability of these systems to bend, depending on the nature (oxygen or sulfur) of the central Y atom. The conjugation in these species is also discussed, and calculations on model systems H2XYH (X = B, Al; Y = O, S) are presented.
A Study of the Gas‐Phase Reactivity of Neutral Alkoxy Radicals by Mass Spectrometry: α‐Cleavages and Barton‐type Hydrogen Migrations
Authors: Hornung Georg , Schalley Christoph A. , Dieterle Martin , Schröder Detlef , Schwarz Helmut
Published: July 2007

The reactivity of neutral alkoxy radicals in the absence of any interfering intermolecular interactions is investigated by means of the recently introduced method of neutral and ion decomposition difference (NIDD) spectra. These are obtained from quantitative analysis of the corresponding neutralization–reionization (NR) and charge reversal (CR) mass spectra. The following trends emerge: alkoxy radicals with short (C1C3) or branched alkyl chains give rise to α‐cleavage products, whereas longer‐chained alkoxy radicals undergo 1,5‐hydrogen migrations from carbon to oxygen, that is, Barton‐type chemistry. This facile rearrangement has been studied in detail for n‐pentoxy radicals by isotopic labeling experiments and computation at the Becke 3 LYP/6‐31 G* level of theory. Further, the NIDD spectra of 3‐methylpentoxy radicals permit for the first time the identification of the diastereoselectivity of the gas‐phase hydrogen migrations. The results from the NIDD method are compared to those from earlier studies in the condensed phase. This new mass spectrometric approach is suggested as a tool for the examination of intramolecular reactions of free alkoxy radicals which can usefully complement theoretical studies.
Drug Discovery by Combinatorial Chemistry—the Development of a Novel Method for the Rapid Synthesis of Single Compounds
Authors: Terrett Nicholas K. , Gardner Mark , Gordon David W. , Kobylecki Ryszard J. , Steele John
Published: July 2007

Through the advantages conferred in the speed of synthesis, combinatorial chemistry is making a significant impact on the process of drug discovery. The mix‐and‐split paradigm has been an effective method for the production of compound mixtures, although there is now a need for new, fast library approaches to generate well‐characterised single compounds. Having already demonstrated the successful preparation and application of library mixtures, we have now developed a novel combinatorial method for the production of single compounds.
Metallic Hydrogen at High Pressures and Temperatures in Jupiter
Authors: Nellis W. J.
Published: July 2007

Electrical conductivities of hydrogen were measured recently at 93–180 GPa (0.93–1.8 Mbar), 0.28–0.36 mol cm−3, and 2000–4000 K. Shock temperatures were measured up to values of 5200 K at 0.83 Mbar. The conductivities indicate a continuous transition from a semiconducting to metallic fluid at 140 GPa and 3000 K. The results indicate that hydrogen becomes metallic much closer to the surface of Jupiter than thought previously and that Jupiter has no core–mantle boundary.
Synthesis of Rotaxane Assemblies
Authors: Dünnwald Thomas , Jäger Ralf , Vögtle Fritz
Published: July 2007

The preparative syntheses of new nano‐sized rotaxane assemblies are described, namely, of the first tris[2]rotaxane,15, the first bis[2]rotaxane connected at the axles,4, and the first [3]rotaxane with two different axles,12(unsymmetrical “bis[2]rotaxane”). These syntheses were made possible by the directed incorporation of a sulfonamide group into the amide‐linked rotaxane building blocks. The sulfonamide moiety can be used as a functional group in alkylation reactions, allowing the further attachment of building blocks in good yields. The successful synthesis of these new rotaxane architectures demonstrates the synthetic potential of this sulfonamide strategy in the preparation of multirotaxane and dendritic rotaxane structures.
Clinical progression of hepatitis C virus–related chronic liver disease in human immunodeficiency virus–infected patients undergoing highly active antiretroviral therapy
Authors: Pineda Juan A. , García-García José A. , Aguilar-Guisado Manuela , Ríos-Villegas María J. , Ruiz-Morales Josefa , Rivero Antonio , del Valle José , Luque Rafael , Rodríguez-Baño Jesús , González-Serrano Mercedes , Camacho Angela , Macías Juan , Grilo Israel , Gómez-Mateos Jesús M.
Published: July 2007

Little is known about the natural history of liver disease in human immunodeficiency virus (HIV)/hepatitis C virus (HCV)-coinfected subjects under highly active antiretroviral therapy (HAART). The objectives of this study were to obtain information about the mortality, the incidence of hepatic decompensations, and the predictors thereof in this population. In a multicenter cohort study, the time to the first hepatic decompensation and the survival of 1,011 antiretroviral naïve, HIV/HCV-coinfected patients who started HAART and who were followed prospectively were analyzed. After a median (Q1-Q3) follow-up of 5.3 (2.9–7.1) years, 59(5.83%) patients developed a hepatic decompensation and 69 (6.82%) died, 30 (43%) of them because of liver disease. The factors independently associated [HR (95% CI)] with the occurrence of hepatic decompensations were age older than 33 years [2.11 (1.18–3.78)], female sex [2.11 (1.07–4.15)], Centers for Disease Control stage C [2.14 (1.24–3.70)], a diagnosis of cirrhosis at baseline [10.86 (6.02–19.6)], CD4 cell gain lower than 100/mm3 [4.10 (2.18–7.69)] and less than 60% of the follow-up with undetectable HIV viral load [5.23 (2.5–10.93)]. Older age [2.97 (1.18–7.50)], lack of HCV therapy [11.32 (1.44–89.05)], hepatitis D virus coinfection [16.15 (2.45–106.48)], a diagnosis of cirrhosis at recruitment [13.69 (5.55–34.48)], hepatic encephalopathy [62.5 (21.27–200)] and lower CD4 cell gain [3.63 (1.45–9.09)] were associated with mortality due to liver failure.

Conclusion:

End-stage liver disease is the primary cause of death in HIV/HCV-coinfected patients under HAART. Higher increase of CD4 cell counts, lack of markers of serious liver disease and therapy against HCV are factors associated with better hepatic outcome. (Hepatology 2007.)
Crime behaviours and distance travelled in homicides and rapes
Authors: Santtila Pekka , Laukkanen Manne , Zappalà Angelo
Published: July 2007

We explored (1) distances between home and offence in homicides and rapes; (2) whether these distances differed from each other; and (3) whether offence features were associated with distances. The sample consisted of solved homicides (N = 40) and rapes (N = 37) from Finland with co‐ordinates for offence and offender home locations and information on crime features. Empirical models of incident density as a function of distance were estimated using CrimeStat III (Levine, 2004). Most of the distances were short displaying distance decay. Homicide median distance was 0.85km (Inter Quartile Range (IQR) = 0.13–7.69km) and rape median distance 2.44km (IQR = 0.83–6.96km) from perpetrators' home location. These distances differed significantly (Mann‐Whitney U = 543.0, p < 0.045). It was possible to identify crime features that were correlated with distances in both offence types. Spatial Behaviour Indices combining crime feature information correlated rs = 0.77 with distance in homicides and rs = 0.72 in rapes. Identifying theoretical constructs for understanding links between different crime features instead of looking at them in isolation is important. Copyright © 2007 John Wiley & Sons, Ltd.
Neuartige Diterpenoide aus den Ritterlingen Tricholoma aurantium und T. fracticum (Agaricales)
Authors: Knops Liliana , Nieger Martin , Steffan Bert , Steglich Wolfgang
Published: July 2007

Novel Diterpenoids from the Toadstools Tricholoma aurantium and T. fracticum (Agaricales)

Herrn Professor Dr. Heinz G. Floss zum 60. Geburtstag gewidmet.

Two novel diterpenoids trichaurantin (1) and its 6‐O‐acetyl derivative 2 have been isolated from Tricholoma species. Their structures were established by spectroscopic methods and an X‐ray crystal analysis, 1 and 2 appear to be biosynthetically related to the neodolabellane and dolastane group of diterpenes and can be designated as 2,3‐seconeodolastane derivatives.
Strukturmodifizierte Isokalafungine und Isonanaomycine
Authors: Hoffmann Bernd , Lackner Helmut
Published: July 2007

Structurally Modified Isokalafungins and Isonanaomycins

The total synthesis of structural analogues of the unnatural, C‐6‐hydroxylated isokalafungins and isonanaomycins is described. The new compounds show improved antibiotic activity and support theories for a mechanism of action which base on the formation of reactive quinone methides. Calculations of the molecular structures show that the chromophore of the most active 9‐methyl derivatives 28 and 32 is bended off along its 5‐CO‐10‐CO axis. This corresponds to an unusual shifting of characteristic 13C‐NMR signals. Different experiments for the introduction of X‐CH2‐ or sugar residues into 1 (e.g. isolactoquinomycins) demonstrate the limits of the general synthetic pathway. Finally a short overview on significant structure/activity relationships in the (iso)nanaomycin D field is given.
Chiralitätsgesteuerte Strukturvarianten von Bis(sulfoximin)/Metall‐Komplexen
Authors: Zehnder Margareta , Bolm Carsten , Schaffner Silvia , Kaufmann Daniel , Müller Jürgen
Published: July 2007

Chirality‐Monitored Structural Variants of Bis(sulfoximine)/Metal Complexes

The coordination geometries of sulfoximine/metal complexes differ substantially depending on the metal and on whether optically active or racemic sulfoximines are used for their preparation. Two copper and two zinc complexes have been characterized by X‐ray diffraction analysis.
Reactivity of cyclopentenyl anion analogous heterocycles: 1,5‐electrocyclization of 2‐oxa‐, 2‐thia‐, 2‐aza‐ and 2‐phosphabicyclo[3.2.0]hept‐3‐ene. A sigmatropic [1,3] carbon shift
Authors: Klärner Frank‐Gerrit , Yaslak Salih , Drewes Rolf , Gesenberg Christoph , Peter Michael
Published: July 2007

Carbonyl ylide‐like intermediates are involved in the 1,5‐electrocyclization of the bicyclo[3.2.0]heptenes 3a–c. The activation barriers analyzed by the time‐ and temperature‐dependence of the exo ⇌ endo isomerization of specifically deuterated derivatives or of the racemization of optically active derivatives turned out to be higher by Δ ΔG≠ ≥ 11 kcal/mol than those determined for the corresponding bicyclo [3.1.0]hexenes 1a–c. This result can be considered as an evidence for the electrocyclic nature of these ring openings due to the diminished Walsh character of cyclobutane bonds compared to cyclopropane bonds. A stereochemical analysis of the fragmentation of 2‐oxabicyclo[3.2.0]heptene 3a to furan and ethene leads to the conclusion that a sigmatropic [1.3] carbon shift proceeding with inversion of the migarting carbon followed by stereospecific retro‐Diels‐Alder reaction is the major pathway for this reaction similar to the rearrangement and fragmentation of the corresponding carbocycle 3e.
Enantioselective synthesis of α‐branched α‐amino acids with bulky substituents
Authors: Studer Armido , Seebach Dieter
Published: July 2007

Enantiopure 5,5‐disubstituted t‐butyl 2‐t‐butyl‐3‐methyl‐4‐oxoimidazolidine‐1‐carboxylates readily available by diastereoselective double alkylation of the parent compound (Boc‐BMI) can be converted to α‐branched α‐amino acids with two bulky substituents (PhCH2/Et, PhCH2/i‐Pr, PhCH2/CH2C6H11) in four simple steps: hydrolysis to the amino acid amides, N‐benzoylation, cleavage of the amino acid amide group, and debenzoylation (Scheme 3, products 6–10, overall yields >50%). This procedure constitutes an extension of the scope of amino acid synthesis from (R)‐ and (S)‐Boc‐BMI.
Preparation of α‐chiral crotylsilanes by retro‐[1,4]‐brook rearrangements. A stereochemical study
Authors: Behrens Karin , Kneisel Boris O. , Noltemeyer Mathias , Brückner Reinhard
Published: July 2007

Treatment of alcohols cis‐22, cis‐23, and trans‐23 with PPh3/ Ph2S2 provided three mixtures of isomers of α, γ‐disubstituted allyl phenyl sulfides. They consisted of diastereomers and ‐except starting from trans‐23–of regioisomers. Each mixture was lithiated reductively by lithium naphthalenide at −78°C in THF. α, γ‐Disubstituted allyllithium compounds resulted which underwent retro‐[1,4]‐Brook rearrangements within 30–90 min. A high degree of stereocontrol by 1,3‐asymmetric induction was observed in the rearrangement starting from a 5:1 mixture of the tBuPh2Si‐containing sulfide regioisomers cis‐25 and iso‐25 (each regioisomer consisting of more than one diastereomer): The α‐chiral crotylsilane anti, trans‐26 was formed as a racemic mixture with ds = 93:7:0:0 in preference to isomer syn,trans‐26 which possesses the opposite configuration at the silicon‐bearing stereocenter and in preference to the corresponding cis isomers (Scheme 5). The rearrangements of the two other sulfide mixtures were much less stereoselective and exhibited ds = 49:44:4:3 starting from the two tBuPh2Si‐containing diastereomers of the isomeric sulfide trans‐25 (Scheme 5) and ds = 59:41 starting from the 3.5:1 mixture of the MePh2Si‐containing sulfide regioisomers cis‐24 and iso‐24 (each regioisomer consisting of more than one diastereomer; Scheme 9). The stereostructures of the rearrangement products were determined by chemical correlations, NMR analogies, and a crystal structure analysis of 27. It was proven that the stereochemical outcome of the retro‐[1,4]‐Brook rearrangements of the MePh2Si‐containing 3.5:1 mixture of sulfides cis‐24/iso‐24 is kinetically rather than thermodynamically controlled (Scheme 10). Mechanistic aspects are discussed in Schemes 11–13.
Modellsysteme zur artifiziellen Photosynthese – Synthese und Elektronentransferstudien neuartiger Sensibilisator‐Relais‐Einheiten
Authors: Seiler Martin , Dürr Heinz
Published: July 2007

Modell Systems for an Artificial Photosynthesis – Synthesis and Electron Transfer Studies of Novel Sensitizer‐Relais Assemblies

Syntheses and determination of electron transfer rates between sensitizers and electron acceptors for a novel class of bis(4,4′‐dimethyl‐2,2′‐bipyridine)[4,4′‐bis(alkoxymethyl)‐2,2′‐bipyridin]ruthenium(II) complexes 6–8 are described. We report on the formation of supramolecular complexes between the dialkoxybenzene‐tethered bisheteroleptic Ru(II)‐bipyridine complexes 5, 8 and 1,1′‐dimethyl‐4,4′‐bypiridinium (MV2+) and cyclo‐[bis(1,1′‐p‐xylylene‐4,4′‐bipyridinium)] (BXV4+), respectively. Evidence for the formation of supramolecular sensitizer‐relais assemblies is taken from the viologen radical and hydrogen production rates in sacrificial model systems for artificial photosynthesis.
Thermal rearrangements of 1,2‐dialkoxybenzenes by flash vacuum pyrolysis
Authors: Gröschl Dieter , Meier Herbert
Published: July 2007

Flash vacuum pyrolysis of 1,2‐dialkoxybenzenes 1a‐c leads to the liberation of alkanes from the interacting side chains. A rearrangement of the skeleton yields the o‐hydroxy carbonyl compounds 2 and 4. The generation of phenol 3 can be rationalized by a decarbonylation. The latter reaction is the sole process which can be observed for the bicyclic starting compound 9.
Nickel‐catalyzed cross‐coupling reactions of bicyclo[1.1.0]butylmagnesium bromide and bicyclo[1.1.0]butyllithium derivatives with alkynyl chlorides and bromides
Authors: Stephen A. , Hashmi K. , Vollmer Antje , Szeimies Günter
Published: July 2007

Several alkynylbicyclo[1.1.0]butanes are prepared by coupling of bicyclo[1.1.0]butylmagnesium bromide with alkynyl chlorides. Severe side reactions, which take place with alkynyl bromides, are not observed. Bridgehead‐lithiated bicyclo[1.1.0]butanes are also effective components in these reactions. The coupling occurs by nickel catalysis as shown by control experiments, an uncatalyzed nucleophilic substitution at the acetylenic carbon atom not being a major reaction path. Alkyl‐ and aryllithium compounds could also be coupled with alkynyl chloride 13c, but in the case of alkynyllithium reagents side reactions decreased the synthetic value of this alkynylic coupling procedure.
Substituted metallotriazolehemiporphyrazines: Synthesis and characterization by FAB‐MS
Authors: Fernández‐Lázaro Fernando , Schäfer Wolfram , Torres Tomás
Published: July 2007

Novel triazolehemiporphyrazines 3a, 4a, and 5a, substituted on the isoindole units and soluble in organic solvents, have been synthesized by condensation of 3,5‐diamino‐1,2,4‐triazole with the corresponding 1,3‐diiminoisoindoline. First‐row transition‐metal complexes 3b–e, 4b–e, and 5b–e have also been prepared by reaction of the free ligands 3a, 4a, and 5a with the appropriate metal(II) salt. A FAB mass spectrometric study of this kind of metallomacrocycles is reported. Triazolehemiporphyrazines 3–5 show electrical conductivities in the range of 10−12‐10−9 Scm−1.
Kinetische Untersuchungen zur Ligandenhydrierung in Katalysatorvorstufen für die asymmetrische Reduktion prochiraler Olefine
Authors: Heller Detlef , Kortus Karin , Selke Rüdiger
Published: July 2007

Kinetic Investigations of the Hydrogenation of Ligands in Catalyst Precursors for Asymmetric Reduction of Prochiral Olefines

Herrn Professor Kurt Madeja zum 70. Geburtstag gewidmet.

The comparison of chiral rhodium(I) complex catalysts of the type [Rh(L)PP*]A (L = cyclic diolefin; PP* = chiral bis(phosphane) and A = anion like BF) regarding their hydrogenating activity against prochiral substrates is hampered by the induction period in the hydrogen consumption which can be attributed to the formation of the catalytically active species from the diolefin precatalyst. The competing hydrogenation of diolefin [e.g. cis,cis‐cycloocta‐1,5‐diene (COD), norborna‐2,5‐diene (NBD)] and prochiral substrate may cause a maximum of the hydrogenation rate, which is characteristic for different catalyst/substrate/solvent systems. Michaelis‐Menten rate constants for the hydrogenation of COD and NBD were determined for different chiral catalysts by stoichiometric and catalytic hydrogenations. The rate constants differ for one selected diolefin up to a factor of 40. The hydrogenation of NBD is generally 5–8 times faster than the COD hydrogenation. In the special case of precatalysts based on he‐xopyranoside bis(phosphinites) the rate constants for the NBD hydrogenation in comparison with those for COD are higher up to a factor of 48. In some cases the hydrogenation of the mono‐ene is faster than that of the diolefin (e.g. COD, NBD). The high hydrogenation rate reported in the literature for some precatalysts in the asymmetric hydrogenation of prochiral olefins is caused in part by the relatively fast diolefin hydrogenation which facilitates the complete formation of the catalyst. The influence of substrate, solvent, and some experimental conditions on the induction period will be discussed.
Synthesis of trifluoromethyl‐containing monomers for the preparation of piezoelectric polymers
Authors: Hübel Marcus , O'Hagan David
Published: July 2007

The synthesis of the novel β‐hydroxy acid 3 in six steps is described, starting from the commercially available trifluoromethyl ketone 6.
Spirostanol glycoside from the tuber of Ophiopogon japonicus
Authors: Branke Jürgen Thomas , Haslinger Ernst
Published: July 2007

A steroidal saponin isolated from the tuber of Ophiopogon japonicus. The structure of the saponin was elucidated by several one‐ and two‐dimensional NMR experiments to be (25S)‐1‐O‐β‐D‐fucopyranosyl‐3‐O‐α‐L‐rhamnopyranosylrus‐cogenin.
The effect of pressure on the trimerization and Diels‐Alder reaction of cyanoacetylene. Synthesis and reactivity of 2,3,5‐tricyanobicyclo[2.2.0]hexa‐2,5‐diene („tricyano Dewar benzene”︁)
Authors: Breitkopf Volker , Hopf Henning , Klärner Frank‐Gerrit , Witulski Bernhard , Zimny Bernd
Published: July 2007

The trimerization of cyanoacetylene (1a) and the Diels‐Alder reaction of 1a with 1,3‐cyclohexadiene (2) show a powerful pressure‐induced acceleration which allows the reaction temperature to be reduced from 160°C at 1 bar to 40°C at 12 kbar or from 100deg;C at 1 bar to room temperature at 7 kbar. At high pressure thermally unstable intermediates like the tricyano Dewar benzene 12 generated in the trimerization of 1a or the primary adduct 3a formed in the Diels‐Alder reaction of 1a with 2 were isolated.
Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, II. Analysis of radicals and carbenes from ethynylbenzene
Authors: Guthier Klaus , Hebgen Peter , Homann Klaus‐Heinrich , Hofmann Jörg , Zimmermann Gerhard
Published: July 2007

The pyrolysis of ethynylbenzene (1) in helium was studied in a tubular flow reactor at 10.7 mbar/1030°C and reaction times ranging from 5 to 30 ms. Reactive intermediates such as radicals and carbenes were scavenged with dimethyl disulfide (DMDS), Qualitative and quantitative analysis of the scavenging products and of the stable pyrolysis products were carried out by GC‐MS analysis. – The radicals phenyl (2a), o‐, m‐, and p‐ethynylphenyl (1c, d, e), 2‐ and 1‐phenyl‐vinyl (1a, b) 1‐ and 2‐naphthyl (3a, b), methyl, hydrogen atoms, and radicals resulting from the addition of phenyl and ethynylphenyl radicals to the triple bond of ethynylbenzene were detected. Carbenes, such as phenylvinylidene, occur only in small traces and obviously play no role in the overall pyrolysis. Concentration profiles of the radicals and of some important pyrolysis products are presented and discussed. Based on the detected radicals, a reaction scheme for the pyrolysis of ethynylbenzene is proposed. Results of pyrolyses of mixtures of ethynylbenzene and ethyne show that naphthalene (3), acenaphthylene (12), and other compounds are produced by a sequence of ethyne addition and cyclization reactions.
First total synthesis of the 2,7‐naphthyridine alkaloid neozeylanicine and unexpected formation of isoquinolines from ethoxyvinyl pyridines
Authors: Bracher Franz , Mink Kathrin
Published: July 2007

The 2, 7‐naphthyridine alkaloid neozeylanicine (6) was prepared starting from 3‐bromo‐4‐picoline (1) by side‐chain methoxycarbonylation, Pd‐catalyzed ring acetylation and one‐pot ring anellation in 32% overall yield. Condensation of the intermediate pyridyl enol ether 3 with dimethylformamide diethyl acetal to the enamine 7 was followed by spontaneous electrocyclization to give the isoquinoline 8. On treatment with acid or base 3 was cyclized to the 6(2H)‐isoquinolinone 10.
Synthesis of new substituted 1‐(3‐pyridyl)pyridinium salts and 3,4‐diamino‐2(1H)‐pyridinones
Authors: Gewald Karl , Rehwald Matthias , Müller Heike , Bellmann Peter
Published: July 2007

2‐[(Chloroacetyl)amino]acrylonitriles 1 and 3‐[(chloroacetyl)‐amino]propionitriles 4 were allowed to react with pyridine to form the 1‐(4‐amino‐3‐pyridyl)pyridinium salts 3 and 1‐(4‐amino‐5,6‐dihydro‐3‐pyridyl)pyridinium salts 6. Dehydrogenation of 6 with bromine in glacial acetic acid afforded 1‐(4‐amino‐3‐pyridyl)pyridinium bromides 7. Treatment of 3 and 7 with hydrazine hydrate yielded the 3,4‐diamino‐2(1H)‐pyridinones 8. Analogously to other ortho‐diamines, the substituted [1,2,5]thiadiazolo[3,4‐c]pyridin‐4‐one 10, [1,2,5]selenadiazolo[3,4‐c]pyridin‐4‐one 11, and further derivatives were obtained from 8. N‐(Chloroacetyl) derivatives of acetylacetoneimide 13 and 3‐oxo‐3‐phenyl‐2‐(phenylhydrazono)propionamide 17 were treated with pyridine to give 1‐(3‐pyridyl)‐pyridinium salts 14 and 18, respectively.
Solvent dipolarity/polarizability (SPP) of alcoholic solvents
Authors: Catalán Javier , López Vicenta , Pérez Pilar
Published: July 2007

The positive solvatochromism exhibited by 2‐(dimethylamino)‐7‐nitrofluorene (DMANF) and 2‐fluoro‐7‐nitrofluorene (FNF) was used to determine the solvent dipolarity/polarizability (SPP) of 29 saturated aliphatic alcohols, four unsaturated alcohols, an aromatic alcohol, a triol, and water. The SPP values for the alcohols lie at the top of the SPP solvent polarity scale. The SPP values for n‐alkanols decreases with increasing chain length, in contrast to the behavior of n‐alkanes. On the other hand, the polarity of n‐alkanols, like that of n‐alkanes, increases on cyclization. The polarity of m‐cresol (1.0) and of 1,1,1,3,3,3‐hexafluoro‐2‐propanol (1.007) places these solvents at the top of the SPP scale.
Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, 3 A mechanistic study of the thermal cycloisomerization of 1,4‐diphenyl‐1‐buten‐3‐yne
Authors: Hofmann Jörg , Zimmermann Gerhard , Homann Klaus‐Heinrich
Published: July 2007

The gas‐phase pyrolysis of 1,4‐diphenyl‐1‐buten‐3‐yne (1) was investigated in the temperature range between 600 and 800°C and in the presence of different carrier gases (N2, N2/toluene, H2). By a detailed analysis (GC, GC/MS, GC/FTIR) all volatile reaction products were identified and quantitatively determined. Besides several fragmentation products (substituted benzenes C7–C10) and some carbon‐rich deposits the main products are benzene (4), naphthalene (5) as well as 1‐ (2) and 2‐phenylnaphthalene (3). Under similar conditions 4‐(4‐fluorophenyl)‐1‐phenyl‐1‐buten‐3‐yne (1a) furnished mainly fluorobenzene (4a), naphthalene (5), 1‐ (2a) and 2‐(4‐fluorophenyl)naphthalene (3a). – If sufficient H atoms are available in the reactive gas phase the conversion of 1/1a is predominantly controlled by radical processes. The cycloisomerization of 1/1a presumably starts with previously formed vinyl radicals, which might initiate a multi‐step reaction cascade involving a 1,x‐H shift and homoallyl reactions. However, if the reaction system is poor in H atoms (or other chain carrier radicals), a cycloisomerization path via vinyl‐idene carbene species and their subsequent stabilization by intramolecular 1,6‐C,H insertion into 3/3a obviously dominates the reaction events. It is concluded that the 1,2‐dihydro‐2‐phenyl‐1‐naphthyl radicals 19/19a and the 1,2‐dihydro‐1‐phenyl‐2‐naphthyl radicals 21/21a are important intermediates which are not only precursors of the aromatics 2/2a and 3/3a but also thought to be key intermediates for the most important degradation products 4/4a and 5.
Asymmetric synthesis of β‐amino acids and α‐deuterated β‐amino acids via conjugate addition of homochiral amidocuprates
Authors: Sewald Norbert , Hiller Klaus D. , Helmreich Brigitte
Published: July 2007

Conjugate addition of homochiral amidocuprates based on N‐[(R)‐1‐phenylethyl]trimethylsilylamine or bis[(R)‐1‐phenylethyl]amine to α,β‐unsaturated esters provides an efficient methodology for the asymmetric synthesis of β‐amino acids. Trapping of the intermediate enolate with D2O yields α‐deuterated β‐amino acids with excellent stereoselectivity.
Synthetic microbial chemistry, XXVIII. Synthesis and absolute configuration of (−)‐koninginin A
Authors: Mori Kenji , Abe Kaoru
Published: July 2007

The absolute configuration of the microbial metabolite (−)‐koninginin A (2‐hexyloctahydro‐2H‐3,9a‐epoxy‐1‐benzoxe‐pine‐6,9‐diol, 1) is shown to have the configuration 2S,3S,6R,9S by its synthesis employing the Sharpless asymmetric dihydroxylation.
Unsaturated hetero chains, IV. Synthesis, structure, and protonation of 1‐oxa‐3‐azahexatrienes
Authors: Moldenhauer Jens‐Peter , Möller Manfred H. , Rodewald Ute , Würthwein Ernst‐Ulrich
Published: July 2007

Differently substituted 1‐oxa‐3‐azahexatrienes3were synthesized either by acylation ofN‐silyl‐1‐azabutadienes1or by a four‐step‐one‐pot procedure starting from the nitriles5, involving a Wittig‐Horner‐Emmons‐type olefination as the key step. Both methods allow the isolation of the highly reactive compounds3.The configuration and conformation of31in the crystalline state by X‐ray diffraction were determined, indicating an (E) configuration of the CC bond and agaucheconformation of the CNCO subunit. The reactivity of compounds3towards tetrafluoroboric acid was studied. Protonation takes place exclusively at the nitrogen atom leading to the 1‐oxa‐3‐azoniahexatriene salts10.Quantum‐chemical ab initio model calculations for all possible structures of the parent substances C4H5NO9and C4H6NO+14–16were performed in order to obtain quantitative data regarding the structural and dynamic behavior of these highly flexible molecules in the gas phase.
Regioselective ring opening of oxetanes by hydrogenolysis. – A convenient method for the carbohydroxylation of enol ethers
Authors: Bach Thorsten
Published: July 2007

Hydrogenolysis of the 2‐aryl‐3‐(silyloxy)oxetanes 1, 2, 5, and 9 in the presence of Pd(0) catalysts (Pd/C) yields 1,2‐diols as ring‐opened products almost quantitatively (82–98% yield). In combination with the preceding photocycloaddition it facilitates the regio‐ and stereoselective carbohydroxylation of silyl enol ethers (total yield: 43–74%). In the case of β‐substituted silyl enol ethers (R1 = alkyl) the reaction sequence leads to a single diastereomeric product (4, 6, 10) in a simple two‐step procedure. Acid‐sensitive substrates such as the dioxolane 1g or the dihydrofuran‐derived oxetane 11 are mildly cleaved in the presence of Pd(OH)2. As demonstrated by selected examples (13, 16, 18) the produced 1,2‐diol remains silyl‐protected if Pd(OH)2 is employed as a catalyst for the hydrogenolysis. In the latter case the silyl protective group stays at the tertiary hydroxy group to which it has been attached in the oxetane, but silyl migration may intervene as was found in the case of the sterically congested oxetane 18.
Bildungsenthalpie und Stabilisierungsenergie des Pentamethylcyclopentadienyl‐Radikals
Authors: Roth Wolfgang R. , Hunold Frank
Published: July 2007

Heat of Formation and Stabilization Energy of the Pentamethylcyclopentadienyl Radical

From the thermolysis of 1 in the presence of 1–60 bar oxygen between 70 and 100°C the activation energy for its dissociation is found to be 27.9 kcal · mol−1. Combining this result with the enthalpy of formation of 4 and a forcefield value for 1 leads to DH° (Me5C5‐H) = 74.1 kcal · mol−1 and ΔH (2) = 16.1 kcal · mol−1, which differs by 5.4 kcal · mol−1 from a value published recently by Walton[1]. The low dissociation enthalpy of 1 is caused only by the relieve of 28 kcal · mol−1 of strain. With an intrinsic radical stabilization energy (IRSE) of 17.3 kcal · mol−1 for 2 there is no justification for an extra stabilization due to cyclic conjugation.
Metabolic products of microorganisms, 271. Momofulvenone A and B, new benzo[b]fluorene quinones from Streptomyces
Authors: Volkmann Corinna , Rössner Ellen , Metzler Monika , Zähner Hans , Zeeck Axel
Published: July 2007

From the cultures of Streptomyces diastatochromogenes (strain Tü 2895) two novel benzo[b]fluorene quinones, named momofulvenone A (1) and B (2), were isolated. Difficulties in their spectroscopic characterization due to salt effects were overcome by fermentation in the presence of ammonium acetate. The structures were established by a detailed spectroscopic analysis. The polyketide origin of 1 and 2 was verified by feeding [1,2‐13C2]acetate to the growing cultures of Tü 2895. The momofulvenones represent the nitrogen‐free parent compound of the kinamycin family of antibiotics.
Preparation and reactions of silyl nitronates derived from 2,2,2‐trifluoronitroethane. Diastereoselective synthesis of trifluoromethyl‐substituted aminoethanols and ‐propanols
Authors: Marti Roger E. , Heinzer Josef , Seebach Dieter
Published: July 2007

Silyl nitronates of 2,2,2‐trifluoronitroethane and of 1,1,1‐trifluoro‐2‐nitropropane [SiMe3, SiMe2(tBu), SiMe2CMe2‐CHME2] were prepared and their reactions studied. – The TBDMS nitronate of the nitroethane is present at the (E) and (Z) isomer (2.3:1 at room temperature; EA = 9.3 kcal mol−1 for their isomerization). BU4NF‐catalyzed silyl nitro aldol additions to aldehydes show reasonable selectivities for the formation of the syn diastereoisomers of 5–13 (a. 4:1; with the non‐fluorinated analogs anti isomers prevailing!). The anti epimers (5–9, 12, 13, 17–20) in the trifluoromethyl series can be prepared by diastereoselective protonation of the corresponding O‐silyl lithium nitronates (ca. 9:1, Scheme 3). Careful reduction of the NO2 groups (H2/Raney nickel) gives trifluoroamino alcohol derivatives (22–30, Scheme 4). –The trimethylsilyl nitronates are also used for 1,3‐dipolar cycloadditions (to 1‐hexene, styrene, methyl vinyl ketone, and acrylates) to give N‐(silyloxy)isoxazolidines (2–40; Scheme 5). The configuration of the major products (2,3‐cis, 3,5‐trans) was derived from NMR measurements, X‐ray structure determinations, and thermal equilibration studies. The major course of reactions was thus derived to be an exo approach of the dipolarophiles to the (Z)‐silyl nitronates (Scheme 8).– Some conversions of the N‐(silyloxy)isoxazolidines (treatment with acid, base, and Raney nickel) are also described (products 42–51).
Synthesis and conformational studies of calixarene‐analogous trihydroxy[3.3.3]metacyclophanes and their O‐alkylated derivatives
Authors: Yamato Takehiko , Doamekpor Louis Korbla , Koizumi Ken‐Ichiro , Kishi Kumi , Haraguchi Mitsuteru , Tashiro Masashi
Published: July 2007

Tri‐tert‐butyltrihydroxy[3.3.3]metacyclophane 13 was prepared in 6 steps from p‐tert‐butylanisole in 25% overall yield by using the TosMIC method, followed by Wolff‐Kishner reduction and demethylation with boron tribromide. AlCl3/MeNO2‐catalyzed trans‐tert‐butylation of 13 in benzene gave the desired metacyclophane 14 in 85% yield, along with tert‐butylbenzene (15). Weak intramolecular hydrogen bonding was observed in the triols 13 and 14.–6,15,24‐Tri‐tert‐butyl‐9,18,27‐trihydroxy[3.3.3]MCP 13 was tri‐O‐alkylated with alkyl halides (RX: R = Et, Pr, and Bu) in the presence of Cs2CO3 to yield partial‐cone confomer 12b‐d in quantitative yield. Ring inversion by oxygen‐through‐the‐annulus rotation is allowed for triethoxy derivative 12b (coalescence temperature ca. 90°C) but inhibited for the tripropoxy‐12c and the tributoxy derivative 12d. The reaction of the triol 13 with ethyl bromoacetate in the presence of Cs2CO3 yielded cone and partial‐cone 12e, respectively. In contrast, a significant amount of cone conformer 12f resulted when NaH was used as base. Only when the template metal can hold the ester or amide group(s) and the oxide group(s) on the same side of the [3.3.3]MCP is the conformation immobilized to the cone.–Titration of cone amide cone‐12f with KSCN monitored by 1H NMR clearly demonstrates that a 1:1 complex is formed which is stable on the NMR time scale, and the original C3 symmetry is retained after the complete metal cation complexation.–The stability of multimembered carbon skeletons permits the interconversion of functional groups without special regard to ring‐opening side reactions as was observed for homotrioxacalix[3]arenes with ethereal linkages. For example, the introduction of nitro groups was accomplished on the upper rim by direct threefold ipso‐nitration of tert‐butyltrimethoxy derivative 12a.
Synthesis and characterization of water‐soluble and photolabile 10‐arylisoalloxazines: Tools for studying the mechanism of action of flavin‐type antimalarials
Authors: Kirsch Peer , Schönleben‐Janas Annette , Schirmer R. Heiner
Published: July 2007

Isoalloxazine derivatives such as 1a‐d are promising anti‐malarial agents which act as inhibitors of the antioxidant enzyme glutathione reductase and possibly of other proteins. The molecular mechanism of the pharmacological effects has not been studied in detail because compounds 1a‐d are poorly soluble in aqueous solutions of physiological pH. In the present study we introduce two new types of isoalloxazine derivatives with improved solubility properties: The 10‐aryl‐3‐carboxymethylisoalloxazines 2a‐d, and the isomeric 3‐methyl‐10‐(N‐methylpyridiniumyl)isoalloxazine salts 3 and 4. In addition, for the purpose of photoaffinity labeling experiments, the 10‐aryl‐8‐azido‐3‐methylisoalloxazine 5 was designed. The syntheses and characterizations of these new flavins as well as an alternative synthetic approach to the known antimalarials 1a‐d are described.
Synthesis of (+)‐ and (−)‐hydroxysedamine and (+)‐N‐methylpseudoconhydrine from (S)‐glutamic acid via homochiral acyliminium ion
Authors: Herdeis Claus , Held Walter A. , Kirfel Armin , Schwabenländer Franz
Published: July 2007

Efficient syntheses of (+)‐N‐methylpseudoconhydrine (5) and (−)‐hydroxysedamine (10) are described starting from the readily available (2RS,5S)‐Methyl 5‐(tert‐butyldimethyl‐silyloxy)‐2‐ethoxypiperidine‐1‐carboxylate (1) and proceeding via homochiral acyliminium ion as an intermediate. Compounds 5 and 7b were obtained in 32 and 34%, resp., overall yield from 1. After deprotection of the OH function of 3a, b the diastereomeric mixture of 6a, b was separated and converted to pseudoconhydrine 7b and epi‐pseudoconhydrine 7a, respectively. Reduction of the urethane moiety of 3a, b followed by treatment with hydrochloric acid provided enantio‐ and diastereopure 5. Reaction of 1‐phenyl‐1‐(trimethylsiloxy)ethene with 1 afforded 8a and 8b in a ratio of 1:9. Deprotection of 8a, b and separation of the diastereomers give after diastereoselective reduction of the ketone function and conversion of the urethane moiety into the methyl group natural (−)‐hydroxysedamine (10). Starting from 8b, deprotection and inversion of the OH function furnished 12 as a single homochiral diastereomer which was converted to ent‐10.