bluuebunny/crossref_metadata_2025 huggingface dataset:
Darstellung von aliphatisch und cycloaliphatisch verbrückten Porphyrin‐Chinonen als Modellverbindungen zur Untersuchung der lichtinduzierten Ladungstrennung in der Photosynthese
Authors: von Gersdorff Jörg , Kirste Burkhard , Kurreck Harry
Published: July 2007

Synthesis of Porphyrin Quinones with Aliphatic and Cycloaliphatic Bridges as Model Compounds for Studying the Light‐Induced Charge Separation in Photosynthesis

Covalently linked porphyrin quinones (P–Qs) are well‐suited as biomimetic model compounds in studying the light‐induced charge separation occuring in primary processes of photosynthesis. We report on a synthetic strategy which leads to P–Qs with the porphyrin donor covalently linked to the quinone acceptor via aliphatic and cycloaliphatic spacers. Preparation of two diastereomeric cyclohexylene‐bridged P–Qs 1 and 2 and of 3 bearing a butylene spacer is described. Structures, including the spatial arrangements of the donor, bridge and acceptor, are determined by various NMR techniques. These data are compared with those deduced from simple force‐field calculations using the molecular modelling program ALCHEMY II (Tripos Associates) and MNDO (MOPAC‐6) calculations.
Transition Metal‐catalyzed Oxidations, 6. – Total Synthesis of Hallachrome and Related 1,2‐anthraquinones
Authors: Krohn Karsten , Khanbabaee Karamali
Published: July 2007

9,10‐Anthraquinones 3b–3k are prepared by Diels‐Alder reaction of juglone (5a) and 7‐methyljuglone (5b) with the dienes 4a and 4b, then reduced to the corresponding 1‐anthracenols 2b–2d, 2f and 2i that are immediately oxygenated to the ortho‐anthraquinones 1b–1d, 1f and 1i with [MoO(O2)2]·py·HMPT. The 1,2‐anthraquinones dimerize in solution or upon BBr3 treatment. The naturally occurring 1,2‐anthraquinone hallachrome (1a) is prepared by selective protection of the bisphenol 3h as monosilyl ether 3i, oxygenation to the silylated ortho‐anthraquinone 1i and fluoride‐mediated deprotection to 1a.
Natural Product Chemistry, 161. – Oxidation of (±)‐Almeine with Aqueous Potassium Permanganate
Authors: Reisch Johannes , Iding Marlies
Published: July 2007

Treatment of (±)‐almeine (3) with aqueous potassium permanganate affords the dihydrofuro[3,2‐c]quinolin‐4(2H)‐ones 4 and 5.
Oxidative Rearrangement of 2′‐Acetamidochalcones with Thallium(III) Nitrate: A New Route to 3‐Aryl‐4(1H)‐quinolones
Authors: Tökés Adrienne L. , Antus Sándor
Published: July 2007

A convenient synthesis of the 3‐aryl‐4(1H)‐quinolones (azaisoflavones) 8 and 10 has been achieved by oxidative rearrangement of the 2′‐acetamidochalcones 2 and 4, respectively.
Synthesis and Spectroscopic Characterization of New NIR Absorbing (2‐Thienyl)‐ and (4‐Dialkylaminoaryl)‐substituted Croconic Acid Dyes
Authors: Keil Dietmar , Hartmann Horst , Reichardt Christian
Published: July 2007

By condensation of croconic acid (7) with 2‐(dialkylamino)‐thiophenes6a–dand with 3‐(dialkylamino)phenols9a–cthe deeply colored, sparingly soluble croconic acid dyes (“croconines”)8a–dand10a–c, respectively, have been prepared. These croconines have been characterized by UV/Vis, IR, and1H‐NMR spectrometry. They exhibit strong electronic absorption bands in the near infrared (NIR) region (λmax≈ 750–850 nm; cf. Table 1).
Preparative Bioorganic Chemistry, XVII. – Reduction of a Prochiral Diketone, 9‐Methyl‐trans‐decalin‐1,8‐dione, with Baker's Yeast
Authors: Mori Kenji , Takayama Shuichi , Yoshimura Seiji
Published: July 2007

Reduction of 9‐methyl‐trans‐decalin‐1,8‐dione (1) with baker's yeast affords (8S,9R,10R)‐8‐hydroxy‐9‐methyl‐trans‐1‐decalone (8) as the major product in 47% yield. Its (8S,9S,10S)‐isomer (9, 14% yield) and (1S,8S)‐9‐methyl‐trans‐decalin‐1,8‐diol (10, 7% yield) are obtained as minor products. Baker's yeast cannot reduce 9‐methyl‐cis‐decalin‐1,8‐dione (2).
Tmob Side Chain‐protected S‐Cysteine‐ and homo‐S‐Cysteinesulfonamides, their Nα‐Protected and Nω‐Aminoethylated Derivatives
Authors: Videnov Georgi , Aleksiev Boris , Stoev Mincho , Paipanova Tamara , Jung Günther
Published: July 2007

The 2,4,6‐trimethoxybenzyl (Tmob) group is very suitable for temporary protection of the aminosulfonyl group of S‐cysteine‐ and homo‐S‐cysteinesulfonamides. Both the introduction and removal of the Tmob‐protecting group can be achieved in high yields. 2‐Aminoethyl derivatization of the aminosulfonyl group of S‐cysteine‐ and homo‐S‐cysteinesulfonamides has been carried out, and various derivatives useful for peptide synthesis with Z, Boc and Fmoc as Nα‐protecting groups have been prepared. In all cases, a racemic mixture of S‐cysteine‐ or homo‐S‐cysteinesulfonic acid has been used and subsequent enantiomer resolution has been achieved by treatment with Bacillus subtilis alkaline protease.
New Studies and a Reinvestigation on [4+2] Cycloadditions of (−)‐Thebaine: Asymmetrical Diels‐Alder Reactions with a Conformationally Fixed Chiral Diene
Authors: Pindur Ulf , Keilhofer Diana
Published: July 2007

Some novel Diels‐Alder reactions of the opium alkaloid (−)‐thebaine (1) as an electron‐rich diene and a reinvestigation of its reactions with cyclic and acyclic dienophiles are described. The π‐facial selectivity has been studied on the basis of structural analyses of the cycloadducts. Some related results on [4 + 2] cycloaddition reactions of 1‐methoxy‐1,3‐cyclohexadiene (11) are also reported.
Studies on Ketoses, 7 – 5‐(α‐D‐Glucosyloxymethyl)furfural: Preparation from Isomaltulose and Exploration of Its Ensuing Chemistry
Authors: Lichtenthaler Frieder W. , Martin Dierk , Weber Thomas , Schiweck Hubert
Published: July 2007

An effective, practical, large‐scale adaptable procedure has been developed to selectively dehydrate the fructose portion of isomaltulose [glucosyl‐α(1→6)‐fructose] (6): heating in DMSO in the presence of a strongly acidic ion‐exchange resin generates α‐D‐glucosyloxymethylfurfural (“α‐GMF”, 3), isolable in yields up to 70%. A variety of ensuing reactions have been exploited concerning the generation of products with industrial application profiles such as aldol‐type additions to the dicyanovinyl (16), nitrovinyl (20), and benzoylvinyl (21) derivatives, or to the polymerizable unsubstituted vinyl compound (25) and the GMF‐acrylic acid (22). Oxidation to GMF‐carboxylic acid (11) and reductive amination to GMF‐amine 8 can be carried out without affecting the hydroxyl groups in the glucosyl portion; esterification of 11 with long‐chain alcohols and N‐acylation of 8 with fatty acid chlorides provide novel surfactants in which hydrophilic and hydrophobic parts of the molecule are separated by a heteroaromatic spacer.
Synthese, Struktur und Reaktionen von α‐Campholenepoxiden
Authors: Schulze Klaus , Habermann Anne‐Kathrin , Uhlig Holger , Weber Lutz , Kempe Rhett
Published: July 2007

Synthesis, Structure and Reactions of α‐Campholenic Epoxides

The epoxidation of α‐campholenic compounds 3, 4 is described, besides the rearrangement of the epoxides 5 and 6 into the hydroxy‐β‐campholenic system 7, 8, the reduction to the tertiary alcohols 11a, 12a, the alkylation reaction to 11b and 12b and the conversion of 7 into the diketone 10 are reported. The stereochemistry and the odour of the new compounds are also described.
Synthesis and Reactions of Pyridinethiones
Authors: Köditz Jens , Rudorf Wolf‐Dieter , Hartung Helmut , Heinemann Frank
Published: July 2007

The push‐pull systems 1 and 7 undergo regioselective cyclization with cyanothioacetamide 2 leading to pyridinethiones 3 and 8. Subsequent S‐alkylation affords the alkylthio derivatives 5 and 10. Thieno[2,3‐b]pyridines 6 and 11 are formed by using an α‐CH‐acidic halogen compound as alkylating agent, followed by Thorpe‐Ziegler reaction. The cyano group in 6d and 11d can be converted into an imidazoline ring by treatment with 1,2‐diaminoethane hydrate and carbon disulfide. Structures are supported by spectral data as well as by X‐ray analysis of 5d.
Diterpenoid Total Synthesis, XXX. Synthesis of the Racemic Form of Tripterifordin, a Novel Anti‐HIV Diterpene Lactone from Tripterygium wilfordii
Authors: Mori Kenji , Aki Shinji
Published: July 2007

The pentacyclic diterpene ketone (±)‐3, which had been prepared by a total synthesis from naphthalene, was methylenated and hydrated to give (±)‐tripterifordin [(±)‐1], the racemate of a new kaurane‐type diterpene lactone with anti‐HIV activity recently isolated from the roots of Tripterygium wilfordii.
Antibiotics from Gliding Bacteria, LIV. Isolation and Structure Elucidation of Soraphen A1α, a Novel Antifungal Macrolide from Sorangium cellulosum
Authors: Bedorf Norbert , Schomburg Dietmar , Gerth Klaus , Reichenbach Hans , Höfle Gerhard
Published: July 2007

From the myxobacterium Sorangium cellulosum, strain So ce26, a novel group of highly active antifungal metabolites was isolated. Large‐scale production of the basic compound soraphen A1α (1) was achieved by fermentation in the presence of the adsorber resin XAD‐16, extraction and crystallization. The 18‐membered macrolide structure of 1 was determined by spectroscopic methods. X‐ray crystal structure analysis revealed the absolute configuration of the ten asymmetric centers. According to proton coupling constants and difference NOE measurements the solution conformation in CDCl3 and [D6]DMSO is very similar to that in the crystal structure.
Chemie und Stereochemie der Iridoide, XIX. Zwei einfache EPC‐Synthesen mit chemischem Beweis der absoluten Konfiguration von (+)‐Mitsugashiwa‐Lacton aus (S)‐(−)‐Citronellol und Aucubin
Authors: Weinges Klaus , Ziegler Hans Jürgen , Maurer Wolfgang , Schmidbauer Stefan B.
Published: July 2007

Chemistry and Stereochemistry of Iridoids, XIX. – Two Straightforward EPC Syntheses with Chemical Evidence of Absolute Configuration of (+)‐Mitsugashiwa Lactone from (S)‐(−)‐Citronellol and Aucubin

Enantiomerically pure (+)‐Mitsugashiwa lactone (9) was prepared in eight steps from (S)‐(−)‐citronellol (1), whereas only four steps were required for the conversion of hexaacetylaucubin (10) into 9. Both starting materials are readily available in large quantities. The synthesis of 9 from 1 establishes the absolute configuration at C‐7 in 9. Conversely, the synthesis of 9 from 10 confirms the absolute configuration at C‐4a and C‐7a in 9.
Strukturaufklärung eines Azadirachtinderivates aus dem Marrangobaum Azadirachta excelsa durch NMR‐Spektroskopie
Authors: Kalinowski Hans‐Otto , Ermel Klaus , Schmutterer Heinrich
Published: July 2007

NMR Spectroscopically Structure Elucidation of an Azadirachtin Derivative from the Marrango Tree Azadirachta excelsa

The structure of marrangin, a new limonoid from the Marrango tree Azadirachta excelsa (Jack), has been established as 3 by 1D‐ and 2D‐1H and 13C‐NMR spectroscopy.
Regio‐ and Stereoselective Reduction of 3,5‐Disubstituted 3a,6a‐Dihydro‐4H‐pyrrolo[3,4‐d]isoxazole‐4,6(5H)‐diones with Sodium Borohydride
Authors: Konopíková Marta , Fišera L'Ubor , Prónayová Nada , Ertl Peter
Published: July 2007

The reduction of condensed imides 1 with sodium borohydride proceeds regio‐ and stereoselectively to yield the hydroxylactams 2, 3 and 4. AM1 calculations of the reactants and products reveal that the regiochemistry of the reductions seems to be controlled by both electronic and steric effects. The regio‐ and stereoselectivity of the reductions are dramatically improved by the presence of magnesium perchlorate. This is interpreted in terms of a chelate complex formation between the carbonyl group, isoxazoline oxygen atom and magnesium ion. The presence of p‐toluenesulfonic acid (p‐TsOH) also improves the regioselectivity, but lowers the chemoselectivity.
Synthesis and Application of a New Fluorescein Derivative for Fluorescent Labelling of Oligonucleotides and as a Novel Tool for Non‐radioactive DNA Sequencing
Authors: Holletz Torsten , Möller Uwe , Knaf Andrea , Reinhardt Richard , Cech Dieter
Published: July 2007

The synthesis of 4(5)‐(bromomethyl)fluorescein, which can be used as its 3′,6′‐dibenzoyl derivative 7 for the labelling of nucleosides is described. Pyrimidine nucleosides such as 3′‐and/or5′‐protected 2′‐deoxyuridine and thymidine are labelled by 7 at N3 of the heterocyclic base. The resulting base‐labelled 3′‐benzoyl‐5′‐dimethoxytrityl nucleosides may, on the one hand, be converted, after cleavage of the protective dimethoxytrityl group, into the 5′‐phosphoramidite 11 by normal phosphorylation; on the other hand, 5′‐triphosphates 13 are prepared by phosphorylation with 2‐chloro‐4H‐1,3,2‐benzodioxaphosphorin‐4‐one and pyrophosphate. The phosphoramidites 11 were sucessfully used for the fluorescent labelling of oligonucleotides during automatic DNA synthesis. The oligonucleotides can be used as primer in automatic non‐radioactive DNA sequencing. The 5′‐triphosphates 13 are potential substrates for DNA polymerases or terminal transferase.
Absolute Configurations of Three Naturally Occurring Acetylenic Spiroacetal Enol Ethers
Authors: Wurz Gerald , Hofer Otmar , Sanz‐Cervera Juan F. , Marco J. Alberto
Published: July 2007

The absolute configurations of three 6,7‐oxygenated acetylenic spiroacetal enol ethers were determined by using the kinetic method of Horeau. The results were confirmed by the circular dichroism of the compounds in correlation with the corresponding 6,7‐epoxide.
Amphiphilic Carbohydrate‐based Mesogens, IX. Mesogenic 4‐O‐Alkyl‐D‐glucoses via Methyl 4,6‐O‐Alkylidene‐D‐glucopyranosides
Authors: Dahlhoff Wilhelm V. , Riehl Klaus , Zugenmaier Peter
Published: July 2007

The 4,6‐O‐alkylidene derivatives (hexylidene–decylidene, 2a–e) are prepared by condensation of methyl α‐ or β‐D‐glucopyranoside 1 with alkanals in the presence of pyridinium tosylate. O‐diethylborylation of 2 gives 3 which are allowed to react firstly with bromodiethylborane and subsequently with sodium triethylhydroborate to yield methyl 4‐O‐alkyl‐D‐glucopyranosides 5 after deborylation. Acid hydrolysis of 5 gives mesogenic 4‐O‐alkyl‐D‐glucopyranoses 6a–e. The amphiphilic 6 exhibit the smectic A liquid crystalline phase on melting.
Terpenes and Terpene Derivatives, XXXII. New Cadinene and Bisabolene Derivatives from the Essential Oil of Pulicaria gnaphalodes
Authors: Weyerstahl Peter , Wahlburg Hans‐Christian , Marschall Helga , Rustaiyan Abdolhossein
Published: July 2007

From the essential oil of Pulicaria gnaphalodes growing near Tehran some new cadinene derivatives were isolated. The structures of 1,8‐oxidocadin‐4‐enes (6, 7, epimers at C‐10), 1(10),4‐cadinadien‐8α‐ol (1), 4,10(14)‐cadinadien‐ and 4,10(14)‐muuroladien‐8‐ols (2–5) could be verified by their 1H‐ and 13C‐NMR spectra. Furthermore, the 8α‐epimer 9 of the known α‐copaen‐8β‐ol (10), (Z)‐γ‐curcumen‐12‐ol (13a) and the esters (Z)‐13b–e could be identified.
Synthese und konformative Flexibilität von 4,9‐Dihydroindolo[3,2‐d][1,2,4]triazolo[4,3‐a]benzazepinen
Authors: Kunick Conrad
Published: July 2007

Synthesis and Conformational Flexibility of 4,9‐Dihydroindolo[3,2‐d][1,2,4]triazolo[4,3‐a]benazepines

Herrn Prof. Dr. P. Nickel zum 60. Geburtstag gewidmet

Indolotriazolobenzazepines 6 are prepared by cyclisation of thiolactam 4 with acylhydrazides 5. The influence of the 1‐ substituent on the barrier of ring inversion of the new ring system 6 is studied by dynamic 1H‐NMR spectroscopy.
Ringtransformationen heterocyclischer Verbindungen, VI. 3‐Nitrobenzonitrile aus 2,4,6‐Triarylpyryliumsalzen und Nitroacetonitril
Authors: Zimmermann Thomas , Pink Maren
Published: July 2007

Ring Transformations of Heterocyclic Compounds, VI. – 3‐Nitrobenzonitriles from 2,4,6‐Triarylpyrylium Salts and Nitroacetonitrile

2,4,6‐Triarylpyrylium salts 1 react with nitroacetonitrile in the presence of sodium acetate, triethylamine, triethylamine/acetic acid or piperidine acetate to give 3‐nitrobenzonitriles 2. In the course of this 2 6‐[C5 + C] pyrylium ring transformation a nitro group is shifted to C‐3 of the benzene ring formed. Structural elucidation of the reaction products 2 is based on an X‐ray structure determination of the methoxyphenyl derivative 2c.
Derivate des Imidazols, VII. 2,3‐Dihydro‐1,3,4,5‐tetramethyl‐2‐methylen‐1H‐imidazol als Kupplungsreagens. Die Kristallstruktur von Bis(1,3,4,5‐tetramethyl‐2‐imidazolyl)methylium‐iodid
Authors: Kuhn Norbert , Bohnen Hans , Kratz Thomas , Henkel Gerald
Published: July 2007

Imidazole Derivatives, VII. – 2,3‐Dihydro‐1,3,4,5‐tetramethyl‐2‐methylen‐1H‐imidazole as Coupling Reagent. The X‐ray Structure of Bis(1,3,4,5‐tetramethyl‐2‐imidazolyl)methylium Iodide

2,3‐Dihydro‐1,2,3,4‐tetramethyl‐2‐methylen‐1H‐imidazole (1) reacts with 1,3,4,5‐tetramethyl‐2‐(methylthio)imidazolium iodide (4) in the presence of pyridine to give bis(1,3,4,5‐tetramethyl‐2‐imidazolyl)methylium iodide (5) which is also formed by the reaction of 4 and methyl lithium in the ratio 2:3. The X‐ray structure of 5 is reported.
Stereoselective Synthesis of Alcohols, XLIII. Asymmetric Induction on the Intramolecular Allylboration Reaction of (8‐Oxo‐2‐octenyl)boronates
Authors: Hoffmann Reinhard W. , Sander Thomas
Published: July 2007

The cyclization of (8‐oxo‐2‐octenyl)boronates having methyl substituents in the chain linking the two functional groups proceeds with complete simple diastereoselectivity and with induced diastereoselectivity of 85 to > 98% to give methylsubstituted 2‐vinylcyclohexanols.
Stereoselective Synthesis of Alcohols, XLIV. Cyclization of Benzyloxy‐substituted (8‐Oxo‐2‐octenyl)boronates
Authors: Sander Thomas , Hoffmann Reinhard W.
Published: July 2007

The cyclization of (8‐oxo‐2‐octenyl)boronates having benzyloxy substituents in the chain linking the two functional groups gives benzyloxy‐substituted 2‐vinylcyclohexanols. High asymmetric induction is found for the 4‐ or 6‐benzyloxy‐(Z)‐octenylboronates 12a and 12c, whereas cyclization of the other isomers studied proceeded in a stereorandom fashion. Possible reasons for this unexpected behavior are discussed.
Cholesteno‐Indole, I – Synthese von 1′H‐5α‐Cholest‐2‐eno[3,2‐b]indolen
Authors: Samu János , Botyánszki János , Duddeck Helmut , Snatzke Günther
Published: July 2007

Cholesteno Indoles, I. – Preparation of 1′H‐5α‐Cholest‐2‐eno[3,2‐b]indoles

1′H‐5α‐Cholest‐2‐eno[3,2‐b]indole (1a), the corresponding N‐methyl, N‐acetyl, and N‐formyl compounds 1b–d, as well as the respective methoxy derivatives 2b–5d have been synthesized as model compounds for intended CD investigations. Application of the Fischer indole synthesis afforded the compouds 1a–5a which were N‐methylated to 1b–5b, N‐acetylated to 1c–5c, and N‐formylated to 1d–5d.
Studies on Isocyanides and Related Compounds. A Facile Synthesis of Imidazo[1,5‐a]imidazoles
Authors: Bossio Ricardo , Marcaccini Stefano , Pepino Roberto
Published: July 2007

The Ugi four‐component condensation between 1,1‐diethoxy‐2‐isocyanoethane (2), cycloketones 1, amine hydrochlorides 4, and potassium thiocyanate (3a) or selenocyanate (3b) affords spiroimidazoles 5, which are cyclized to spiroimidazo[1,5‐a]imidazole‐5‐thiones (or selenones) 6.
Bildung von Enolether‐Epoxiden durch Einwirkung von (9S,10E,12Z)‐Hydroperoxyoctadecadiensäure auf Plasmalogene
Authors: Scheick Cordula , Spiteller Gerhard
Published: July 2007

Formation of Enol Ether Epoxides by Reaction of (9S,10E,12Z)‐Hydroperoxyoctadecadienoic Acid with Plasmalogens

(9S,10E,12Z)‐Hydroperoxyoctadecadienoic acid (8a) oxidizes enol ethers (e.g. 2 and neutral plasmalogens 3) under physiological conditions (pH = 6.6, room temperature). The reaction products, unstable enol ether epoxides 9a and 10a, react as recently demonstrated with methanol to α‐hydroxyaldehyde dialkyl acetals 11a or with 1,2‐ethanedithiol to 2‐(α‐hydroxyalkyl)dithiolans 13a which can be detected by GC/MS after trimethylsilylation. If [18O2]‐(9S,10E,12Z)‐hydroperoxy‐octadecadienoic acid (8b) is used instead of 8a one atom of 18O is incorporated into the enol ether epoxide and found in the α‐hydroxy group of the aldehyde derivatives 11 and 13.
Plasmalogenepoxide als biologische Vorstufen von α‐Hydroxyaldehyden
Authors: Dudda Angela , Spiteller Gerhard
Published: July 2007

Plasmalogen Epoxides as Biological Precursors of α‐Hydroxyaldehydes

Cell damage produces hydroperoxides which in turn are able to oxidize plasmalogens 1 to plasmalogenepoxides 2. These are masked α‐hydroxyaldehydes, which can be detected after appropriate derivatization. The detected α‐hydroxyaldehydes could also be generated during the preparation procedure of tissue. Experiments carried out with 18O2 demonstrate no incorporation of 18O2 in α‐hydroxyaldehydes. Consequently, they are already present in tissue. – Further experiments proved that α‐acyloxyplasmalogens 3, recently suggested to be the source of α‐hydroxyaldehydes[1,2], do not occur in tissue.
Antarctic Marine Metabolites: New Polyhydroxylated Steroidal Glycosides from the Starfish Odontaster validus
Authors: Vázquez M. Jesús , Quiñoá Emilio , Riguera Ricardo , Martin Aurelio San , Darias José
Published: July 2007

Two new asterosaponins, validosides A and B, were isolated from the butanolic extract of the starfish Odontaster validus and their structures established as (24S)‐24‐O‐[2,4‐di‐O‐methyl‐β‐xylopyranosyl‐(1→2)‐α‐arabinofuranosyl]‐5α‐cholestane‐3β,4β,6α,8,15β,24‐hexaol 6‐O‐sodium sulfate (1) and (24S)‐24‐O‐(3‐O‐methyl‐β‐xylopyranosyl)‐5α‐cholestane‐3β,6α,8,15β,24‐pentaol 2′‐O‐sodium sulfate (2) on the basis of extensive spectroscopic investigations and chemical correlations. Validoside A and B are extremely rarely occurring saponins due to the presence of a sulfated group at C‐6 of the aglycone in 1 and at C‐2′ of a pyranose in 2. The absolute configuration at C‐24 was found to be S by the application of the Trost‐Mosher methodology.
Pheromone Synthesis, CLVIII. New Synthesis and Revision of the Absolute Configuration of the Hemiacetal Pheromone of the Spined Citrus Bug Biprorulus bibax
Authors: Mori Kenji , Amaike Masayasu , Watanabe Hidenori
Published: July 2007

The enantiomers and the racemate of (3R,4S,1′E)‐3,4‐bis(1′‐butenyl)tetrahydro‐2‐furanol (1) were synthesized by employing Ireland's ester enolate Claisen rearrangement of 5 as the key reaction to provide the corresponding lactone 3 via 4. Optically active 3 was prepared by employing either chemical asymmetric reduction [12 → (S)‐8b] or lipase‐mediated asymmetric hydrolysis (9→10) and acetylation (meso‐2 → ent‐10) as the key transformations. The absolute configuration of the naturally occurring 1 was revised as (3R,4S) on the basis of the chemical asymmetric synthesis of (3S,4R)‐3 by starting from (S)‐8b of known stereochemistry.
Ring Transformations of Oxazoles and Their Derivatives. – Synthesis of 2,3‐Dihydro‐2‐(2‐hydroxyphenylimino)‐4‐methylthiazoles by Reaction of 2‐(2‐Oxopropylthio)benzoxazoles with Amines
Authors: Kalcheva Veneta , Tosheva Madlena , Hadjieva Petia
Published: July 2007

Treatment of 2‐(2‐oxopropylthio)benzoxazoles 1a–d with an excess of primary amines in acetic acid or in perchloric acid affords 3‐substituted 2‐(2‐hydroxyphenylimino)‐4‐methylthiazoles 4a–q. Interaction of thiazoles 4a,i with diazomethane leads to the corresponding O‐methyl derivatives. The structure of compounds 4a–q is confirmed by an X‐ray analysis of compound 4d.
Untersuchungen mit selektiven Abspaltungsreagenzien für ADPOC‐geschützte Aminosäuren und Peptide
Authors: Voelter Wolfgang , Kalbacher Hubert
Published: July 2007

Investigations with Selective Deblocking Reagents for Adpoc‐Protected Amino Acids and Peptides

Selective reagents for the removal of the Adpoc group have been developed. For this purpose several peptides containing tryptophan and Nϵ‐Boc‐lysine have been synthesized. Among several acidolytic reagents, 0.1 N HCl/TFEt/CHCl3 (1:9:1) and 50% HCOOH/TFEt/CHCl3 (1:9:1) show high selectivity especially for the Nϵ‐tert‐butyloxycarbonyl group of lysine. Cleavage rates are determined by HPLC and TLC.
Synthese und polarographisches Verhalten neuer Isoindole. – 1‐Aryl‐ und 1‐Styryl‐2H‐isoindol‐4,7‐dione
Authors: Schubert‐Zsilavecz Manfred , Michelitsch Astrid , Likussar Werner , Gusterhuber Dagmar
Published: July 2007

Synthesis and Polarographic Behaviour of Novel Isoindoles. – 1‐Aryl‐ and 1‐Styryl‐2H‐isoindole‐4,7‐diones

Reactions of quinones 4a–c and sarcosine (2) with seven differently substituted aldehydes 1 yield – via the azomethine ylides 3 – the isoindolediones 5 and 6. The structures of all compounds were elucidated from spectral data, mainly by mass and NMR spectra.
Synthese der Theonelladine A, B, C, D und von Niphatesin A
Authors: Teubner Achim , Gerlach Hans
Published: July 2007

Syntheses of the Theonelladines A, B, C, D and of Niphatesine A

The pyridine alkaloids theonelladine A–D (1–4) and niphatesine (5) of marine origin have been synthesized starting either from 3‐(4,4‐dibromo‐3‐butenyl)pyridine (6) or from 3‐pyridinecarbaldehyde. Reaction of 6 with two equivalents of BuLi gave the lithiated derivative of the alkyne 7, which could be alkylated with 1‐bromo‐10‐(tetrahydro‐2‐pyranyloxy)decane (8) to yield the alkynol 9 after methanolysis. Selective hydrogenation of 9 with Lindlar palladium catalyst gave (Z)‐14‐(3‐pyridyl)‐11‐tetradecan‐1‐ol (11). – Addition of the Grignard reagent of 12‐(benzyloxy)‐1‐bromododecane (13) to 3‐pyridinecarbaldehyde gave 17, which was first oxidized (Swern) to give 18 and then reduced (Wolff‐Kishner) to give 14. Hydrogenolysis of the benzyl ether 14 yielded 15. The alcohol group in 9, 11, and 15 was converted into the tosyloxy group by reaction with tosyl chloride/pyridine. Subsequent reactions of the tosylates 10, 12, and 16 either with an excess of methylamine/ethanol or of ammonia/ethanol gave the pyridine alkaloids 1–5 in high yields as p‐toluenesulfonates.
Solanum Alkaloids, 126. Degradation of Solasodine to 16β,22‐Epoxy‐23,24‐dinorchol‐5‐ene‐3β,22β‐diol and Partial Synthesis of (23s)‐23‐Hydroxysolasodine
Authors: thi Quyen Le , Ripperger Helmut , Adam Günter , Schreiber Klaus
Published: July 2007

(22R,23S,25R)‐N‐Chloro‐22,26‐epiminocholest‐5‐ene‐3β,16β,23‐triol (11) and its 3,16,23‐O‐triacetyl derivative 15 were prepared from solasodine (1). Treatment of 11 or 15 with sodium methanolate yielded the 22,23‐secoaldehyde 16 as major product (Grob fragmentation) and (23S)‐23‐hydroxysolasodine (2) as minor product (Ruschig reaction). Hydrolysis of 16 with methanolic hydrochloric acid afforded 16β,22‐epoxy‐23,24‐dinorchol‐5‐ene‐3β,22β‐diol (17) and its 22‐O‐methyl derivative 18, the 3‐O‐acetate 19 of which was oxidized to the known acetyldiosgenin lactone (20), thus confirming the structures of 16–19. Compound 2 was shown to be identical in every respect with a rare spirosolane alkaloid, recently isolated from some Solanum species. Photolysis of (22R,23S,25R)‐3β,16β‐diacetoxy‐N‐chloro‐22,26‐epiminocholest‐5‐en‐23‐ol (10) yielded also via 22,23‐carbon‐carbon cleavage (20S)‐3β,16β‐diacetoxypregn‐5‐ene‐20‐carbaldehyde (21) as major product, which was converted by treatment with methanolic hydrochloric acid into the compound 18.
Synthesis and Stereochemistry of 7,9‐Disubstituted 3‐Azabicyclo[3.3.1]nonanes
Authors: Nemes Peter , Janke Frank , Scheiber Pál
Published: July 2007

The azabicyclic endo compound 3 was synthesized by reaction of enamine 1 with 2‐benzoyl‐1,3‐dichloropropane (2). The thermodynamically more stable exo isomer 4 was obtained by epimerization of 3 with sodium methoxide. The reduction of 3 and 4 was carried out with different reducing agents. The syn/anti isomeric amino alcohols 7a/7b and 8a/8b were separated either by fractional crystallization of their fumarate salts or by column chromatography. The relative configurations at C‐7 and C‐9 and the conformations of the molecules were determined by chemical and/or NMR spectroscopic methods.
Synthesis of β‐Glycosidically Linked Deoxydisaccharides in the L‐Ribo Series
Authors: Sajus Henry , Thiem Joachim
Published: July 2007

By Fischer glycosylation, alkylidenation, methylation, and subsequent reaction with dibromomethyl methyl ether L‐rhamnose 2 was converted into the L‐gluco‐configurated glycosyl bromide 5. According to classical routes 2 was transformed into the 2,6‐dideoxy compound 7 and further into the acceptor derivative 9 with arabino‐configuration. Glycosylation with 5 gave predominantly the β‐1 → 4‐linked disaccharides 11. After deacylation and simultaneous Mitsunobu inversion at C‐3 and C‐3′ the D–B disaccharide unit of kijanimicin was obtained.
Pheromone, 89 – Wittig‐Synthese alkylverzweigter und cyclischer Analoger von (Z)‐5‐Decenylacetat, dem Sexualpheromon von Agrotis segetum (Lepidoptera: Noctuidae)
Authors: Albores Martha , Bestmann Hans Jürgen , Döhla Bodo , Hirsch Hans‐Ludwig , Rösel Peter , Vostrowsky Otto
Published: July 2007

Pheromones, 89, – Wittig Syntheses of Alkyl‐Branched and Cyclic Analogs of (Z)‐5‐Decenyl Acetate, the Sex Pheromone of Agrotis segetum (Lepidoptera: Noctuidae)

By means of (Z)‐selective Wittig olefination alkyl‐branched and cyclic analogs of (Z)‐5‐decenyl acetate, the sex pheromone of the turnip moth, Agrotis segetum (Lepidoptera: Noctuidae), have been synthesized.
Antibiotika aus Gleitenden Bakterien, L – Chemische Modifikation von Sorangicin A und Struktur‐Wirkungs‐Beziehung II: Derivate aus Reduktions‐, Oxidations‐ und Umlagerungsreaktionen
Authors: Schummer Dietmar , Irschik Herbert , Höfle Gerhard
Published: July 2007

Antibiotics from Gliding Bacteria, L. – Chemical Modification of Sorangicin A and Structure‐Activity Relationship II: Derivatives Obtained by Reduction, Oxidation and Rearrangement Reactions

The synthesis of 38 derivatives of sorangicin A (1) with modifications of the three hydroxyl groups and the conjugated triene is described. By oxidation and reduction reactions 21‐desoxy‐21‐oxo sorangicin (8), 21‐epi‐sorangicin (9) and 21‐desoxysorangicins 14, 15 were obtained. With protection of the 21,22‐diol the 24,25‐didehydro‐25‐desoxysorangicin (18), 25‐desoxy‐25‐oxosorangicins 21, 22 and 25‐epi‐sorangicins 23, 24 were prepared. Further, the 25‐oxo derivatives 21, 22 were transformed into the oximes 25–28 and the 25‐desoxy‐25,25‐difluoro sorangicin (31). Catalytic reduction of sorangicin A (1) gave the 37,43‐dihydro derivative 35, thermolysis the cyclohexadienes 36, 37 and fluoride‐induced isomerisation the 36,38,40‐trienol ethers 38, 39. – Activities against Staphylococcus aureus, Escherichia coli, and in vitro inhibition of RNA polymerase of selected derivatives were examined. With most compounds a reduced biological activity was observed, some derivatives retained their activity (23–28, 31) and three were improved for certain strains (18, 21, 22) although they showed reduced enzyme inhibition activity.
Kondensierte Dithiole, III. Synthese von 1,2‐Dithiolo‐furanen
Authors: Stachel Hans‐Dietrich , Zoukas Thomas , Hußlein Manfred , Nienaber Julyane , Schorp Matthias
Published: July 2007

Ring‐Fused 1,2‐Dithioles, III. – Synthesis of 1,2‐Dithiolo‐furans

A series of 1,3‐dithiino‐furans 4/9 has been synthesized by starting with the β‐ketoester 5a or the cyclic ketone 5b. The dithiines undergo oxidative ring contraction to give the corresponding 1,2‐dithiolo‐furans 3/14. The ester function of 3h is easily removed to give 2, the oxaanalog of the antibiotic thiolutine. In general, the lactone group is the most sensitive part in compounds 3, 4 and 14. In marked contrast the dithiine 9a is cleaved by amines at the thioketale site forming the tetronic acid derivatives 10a/b.
Totalsynthese von Isokalafunginen und Isonanaomycinen
Authors: Hoffmann Bernd , Schönebaum Andreas , Lackner Helmut
Published: July 2007

Total Synthesis of Isokalafungins and Isonanaomycins

The total synthesis of isokalafungins (2) and isonanaomycins (12), the first members of a nonnatural group of benzoisochromanquinone antibiotics hydroxylated only at C‐6, is described. Pathway A (Scheme 1) yields the separated (±)‐cis and ‐trans diastereomers of 2 and 12 and is especially suited for modifications of the dihydropyrane ring. On pathway B the chirality of C‐1 is preformed by using 3,4,6‐trideoxy‐α‐L‐glycero‐hex‐3‐enopyranosid‐2‐ulose (22) as a main building block, for the first time synthesized from L‐fucose (Scheme 2). According to Scheme 3, condensation of 22 with the intermediate 23 gives the new 6‐hydroxylated variants (1S,3S,4S)‐isonanaomycin D (30) and (1R,3R,4R)‐isokalafungin (2). Pathway B favours modifications of the phenolic ring, which can strongly influence the spectrum of activity. Unexpectedly, the shifting of the hydroxy group from C‐9 to C‐6 changes the antibacterial properties unessentially.
1,2,3‐Triazine, IV Synthese von 1,2,3‐Triazincarbonsäureestern
Authors: Neunhoeffer Hans , Bopp Ralf , Diehl Werner
Published: July 2007

1,2,3‐Triazines, IV. – Synthesis of 1,2,3‐Triazinecarboxylates

1,2,3‐Triazinecarboxylates 5 have been prepared by rearrangement of the cyclopropenyl azides 6 as well as by oxidation of the 1‐aminopyrazoles 9, 10. Reaction of 1‐aminopyrazole‐5‐carboxylates 10 with triethyl orthoformate (19) and ammonia affords pyrazolo[3,2‐f][1,2,4]triazin‐4‐ones 18.
Pheromone Synthesis, CXLIX. Synthesis of (2E,4E,6R,10S)‐4,6,10‐Trimethyl‐2,4‐dodecadien‐7‐one – the Major Component of the Sex Pheromone of the Maritime Pine Scale (Matsucoccus feytaudi) – and its Three Stereoisomers
Authors: Mori Kenji , Harashima Susumu
Published: July 2007

(2E,4E,6R,10S)‐4,6,10‐Trimethyl‐2,4‐dodecadien‐7‐one (1) – the major component of the sex pheromone of the maritime pine scale – and its three stereoisomers were synthesized by starting from (R)‐ or (S)‐citronellol (4) and employing the asymmetric epoxidation (9 → 10) and the palladium‐catalyzed reductive cleavage of the epoxy ring (13 → 14) as the key steps.
Radikalische Cyclisierung von Dienen, V. Substratkontrollierte asymmetrische Synthese von (−)‐Hirsuten und (−)‐3‐Hydroxyhirsuten aus (R)‐(−)‐Carvon
Authors: Weinges Klaus , Reichert Hans , Huber‐Patz Ursula , Irngartinger Hermann
Published: July 2007

Radical‐Type Cyclization of Dienes, V. – Substrate‐Controlled Asymmetric Synthesis of (−)‐Hirsutene and (−)‐3‐Hydroxyhirsutene from (R)‐(−)‐Carvone

(3aR,6aR)‐(−)‐6a‐Methyl‐3,3a,4,6a‐tetrahydro‐2H‐cyclopenta‐ [b]furan‐2‐one (6) and (1R,4S)‐(−)‐3‐[4‐(but‐3‐inyl)‐3‐methyl‐cyclopent‐2‐enyl]‐2,2‐dimethylpropan‐1‐ol (11) are key compounds in the synthesis reported in this paper. Enantiomerically pure 6 was obtained in five straightforward steps from the inexpensive precursor (R)‐(−)‐carvone (1). Compound 11 was prepared from 6 via an SN2′ reaction, by analogy with the synthesis reported by Curran et al. The linear triquinanes 13 and 15 were obtained in gram quantities in two additional steps. The utilisation of (S)‐(+)‐carvone (ent‐1) allows access to the other enantiomeric forms. X‐ray analysis of 15a confirmed the structure of 15 and, by correlation, that of 13.
Metabolic Products of Microorganisms, 266. Serpentene, a Novel Polyene Carboxylic Acid from Streptomyces
Authors: Ritzau Michael , Drautz Hannelore , Zähner Hans , Zeeck Axel
Published: July 2007

From the culture filtrate of Streptomyces sp. a novel, bright yellow polyene carboxylic acid, named serpentene (1), was isolated by chemical screening methods. The structure elucidation of 1 is described. Remarkably, the C20 skeleton contains an ortho‐substituted benzene ring bearing a dienoic acid and a nonatetraenyl residue. Concerning its structure and biosynthetic origin 1 is a unique secondary metabolite.
A Convenient Synthesis of Centperazine, an Antifilarial Candidate Drug
Authors: Sengupta Sreela , Sahu Devi Prasad , Chatterjee Sunil Krishna
Published: July 2007

7‐Ethyl‐octahydro‐2‐methyl‐6H‐pyrazino[1,2‐c]pyrimidin‐6‐one (centperazine) (1), an antifilarial candidate drug, currently undergoing phase II clinical trials, has been synthesized by a more economically viable alternative route. Condensation of N,N′‐dibenzylethylenediamine (2) with 3,4‐dibromobutyronitrile (3) gives 2‐(1,4‐dibenzyl‐2‐piperazinyl)acetonitrile (4), which, on catalytic reduction, debenzylation, cyclocarbamation and N‐alkylation yields the target molecule 1 in 10.1% overall yield.
Amination and Synthesis of Some Nitronaphthyridines
Authors: Woźniak Marian , Tomula Maria
Published: July 2007

3‐Nitro and 3,6‐dinitro‐1,8‐naphthyridines 1, 4 and 5 are dehydroaminated with a liquid ammonia solution of potassium permanganate to the corresponding 4‐amino‐substituted compounds 3, 8 and 9. The intermediate 4‐amino σ‐adducts 2, 6 and 7 of the nitro‐1,8‐naphthyridines are detected by 1H‐NMR spectroscopy. The syntheses of some nitro‐substituted naphthyridines are described.
Synthesis of Fluorescent 7,8,9‐Tri‐O‐acetyl‐N‐acetyl‐ and 4‐O‐Acetyl‐N‐acetylneuraminic Acid α‐Thioketosides
Authors: Roth Andreas , Faillard Hans
Published: July 2007

Two new fluorescent regioselective O‐acetylated N‐acetylneuraminic acid (Neu5Ac) thioketosides, 2α‐[4‐(dansylamino)phenylthio]‐7,8,9‐tri‐O‐acetyl‐N‐acetylneuraminic acid {2α‐[4‐(dansylamino)phenylthio]‐Neu5,7,8,9Ac4} (3) and 2α‐[4‐(dansylamino)phenylthio]‐4‐O‐acetyl‐N‐acetylneuraminic acid {2α‐[4‐(dansylamino)phenylthio]‐Neu4,5Ac2} (9) were synthesized. The synthesis of both derivatives started with the peracetylated benzyl ester 1 as precursor. The 7,8,9‐tri‐O‐acetylated compound was prepared by partial deacetylation of 1 with sodium methoxide or with hydrazine hydrate, followed by catalytic benzyl ester hydrogenolysis. – Complete Zemplén deacetylation of 1 gave the Neu5Ac benzyl ester thioketoside 4, which was converted into the 8,9‐isopropylidene‐protected compound 5. By carefully performed regioselective 4‐O‐acetylation with acetic anhydride/pyridine in dichloromethane we obtained the desired fluorescent 4‐O‐acetyl derivative 6 and the nonfluorescent sulfonacetamide 7 as byproduct. Acidic 8,9‐deprotection of 6 and finally catalytic hydrogenolysis of the benzyl ester 7 terminated this synthetic route, yielding 2α‐[4‐(dansylamino)phenylthio]‐Neu4,5Ac2 (9). – The 4‐O‐acetylated derivative 9 could not be de‐O‐acetylated by influenza‐C virus esterase. However, the virus esterase transformed the tri‐O‐acetylated derivative 3 in small amounts into the Neu5Ac thioketoside 10.
Studies on the Constituents of the Stems of Tinospora tuberculata, IV. Isolation and Structure Elucidation of the Five New Furanoid Diterpene Glycosides Borapetoside C–G
Authors: Fukuda Naomichi , Yonemitsu Michiko , Kimura Takeatsu
Published: July 2007

Five new furanoid diterpene glycosides, named borapetoside C (1), D (2), E (3), F (4), and G (5), were isolated from the stems of Tinospora tuberculata Beumée (Menispermaceae). The structures of 1–5 were elucidated by chemical and spectroscopic methods.
First Synthesis of the Cytotoxic and Antifungal C14‐Amine (2S,3E,5Z)‐2‐Amino‐3,5,13‐tetradecatriene Isolated from the New Zealand Ascidian Pseudodistoma novaezelandiae
Authors: Enders Dieter , Finkam Michael
Published: July 2007

The synthesis of (2S,3E,5Z)‐2‐amino‐3,5,13‐tetradecatriene [(S‐1)] with high enantiomeric purity in excellent overall yield is described. In the crucial step the stereogenic center was generated by nucleophilic addition of tert‐butyl carbamate to a planar‐chiral tetracarbonyliron(1 +) complex.
Ein selektiver Abbau der Exomethylengruppe von Vitamin D. – Ein einfacher Zugang zu 10‐Oxo‐19‐norcholecalciferol und 10‐Oxo‐19‐norergocalciferol
Authors: Reischl Wolfgang
Published: July 2007

A Selective Degradation of the Exomethylene Group of Vitamin D. – A Simple Entry to 10‐Oxo‐19‐norcholecalciferol and 10‐Oxo‐19‐norergocalciferol

Nitrile oxides, generated in situ from nitroalkanes, add exclusively to the exomethylene group of (Z)‐ and (E)‐vitamin D3 acetates (1a, 12a) and D2 acetates (1b, 12b). The so generated spirocyclic isoxazoline derivatives are transformed through a Mo(CO)6‐induced fragmentation into (5Z,7E)‐ and (5E,7E)‐(3S)‐3‐acetoxy‐19‐nor‐9,10‐secocholesta‐5,7‐dien‐10‐one (20a, 22a) as well as (5Z,7E,22E)‐ and (5E,7E,22E)‐(3S)‐3‐acetoxy‐19‐nor‐9,10‐secoergosta‐5,7,22‐ trien‐10‐one (19a, 21a). The discribed method allows the synthesis of 19‐nor‐10‐oxo vitamin D derivatives without partial isomerisation of the Δ5‐double bond.
4‐disubstituted furans, 5. Regiospecific mono‐ipso‐iodination of 3,4‐bis(trimethylsilyl)furan and regiospecific ipso‐iodination of tris[(4‐alkyl‐ or ‐aryl)furan‐3‐yl]boroxines to 4‐substituted 3‐(trimethylsilyl)furans and unsymmetrical, 3,4‐disubstituted furans
Authors: Song Zhi Zhong , Wong Henry N. C.
Published: July 2007

4‐Iodo‐3‐trimethylsilylfuran (2), obtained through the regio‐Specific iodination of 3,4‐bis(trimethylsilyl)furan (1), underwent either palladium‐ or nickel‐catalyzed cross‐coupling reactions with terminal alkenes, terminal alkynes, areneboronic acids, bis(p‐methoxycarbonylbenzyl)zinc and Grignard reagents to give 4‐substituted 3‐(trimethylsilyl)furans 3–7, which were converted into boroxines 8. Regiospecific iodination of 8 gave iodofurans 9, which afforded in the usual way unsymmetrical 3,4‐disubstituted furans 10. Boroxines 8 gave also 3,4‐disubstituted furans 11 via palladium‐catalyzed cross‐coupling reactions with piperonyl chloride and vinyl bromide. magnified image
Synthesis of (3R,25R)‐3,25‐dihydroxyhexacosyl α‐D‐glucopyranoside, the heterocyst glycolipid of the marine cyanobacterium Nodularia harveyana
Authors: Mori Kenji , Qian Zhao‐Hui
Published: July 2007

(3R,25R)‐3,25‐Dihydroxyhexacosyl α‐D‐glucopyranoside (1a), the heterocyst glycolipid of Nodularia harveyana, was synthesized by starting from D‐glucose, (S)‐malic acid (4), 1‐octadecyne (5) and ethyl (R)‐3‐hydroxybutanoate (6). magnified image
Synthesis of sphingosine relatives, XIV. A new synthesis of symbioramide, a Ca++‐ATPase activator from Symbiodinium sp.
Authors: Mori Kenji , Uenishi Keiji
Published: July 2007

Symbioramide [(2S,2′R,3R, 3′E)‐N‐(2′‐hydroxy‐3′‐octadecenoyl)dihydrosphingosine, 1] was synthesized from D‐erythro‐dihydrosphingosine (19) and (R, E)‐2′‐tert‐butyldimethylsilyloxy‐3′‐octadecenoic acid (14), which was prepared from (E)‐2‐octadecen‐1‐ol (4) by employing the Sharpless asymmetric epoxidation. The (2S,2′S,3R,3′E)‐isomer 28 of 1 was also synthesized to further confirm the structure of 1. magnified image
Indium‐assisted allylation in carbohydrate chemistry: A convenient route to D‐glycero‐D‐galacto‐ and D‐glycero‐L‐galacto‐heptose
Authors: Prenner Reinhard H. , Binder Wolfgang H. , Schmid Walther
Published: July 2007

Starting with unprotected D‐pentoses 1–4 we achieved a chain elongation reaction by utilizing indium‐assisted allylation. After acetylation, the polyol derivatives 1a–4a were transformed into the corresponding α,β‐unsaturated aldehydes 1b–4b. Protection of the carbonyl group yielded the diethyl acetals 1c–4c. Subsequent dihydroxylation of the double bond by catalytic osmylation followed by acetylation of the newly introduced hydroxyl functions gave a mixture of diastereomeric products. However, only those diastereomers could be easily separated by column chromatography which were derived from 1c and 2c, giving access to D‐glycero‐D‐galacto and D‐glycero‐L‐galacto precursor 5 and 7, respectively. Final deprotection yielded the title aldoheptoses 6 and 8. magnified image
Synthesis of sphingosines, 9. Synthesis of phytosphingosine derivatives
Authors: Birk Rolf , Jung Karl‐Heinz , Schmidt Richard R.
Published: July 2007

Reaction of the lithium acetylide prepared from bromooctene 2 with 2,4‐O‐benzylidene‐D‐threose (1) yielded the epimeric dodec‐5‐ynetetrol derivatives 3a, b. Reaction of the Grignard reagent of bromooctene 2 with 1 gave (E,Z)‐dodec‐5‐ene‐tetrol derivatives (E,Z)‐12a,b. From these precursors D‐ribo‐phytosphingosine derivatives 7b, (E)‐18, and (Z)‐18, respectively, were obtained. Also interesting anhydro derivatives, for instance 3,4‐epoxides 11a and (E)‐21, and 1,4‐anhydro phytosphingosine derivatives 9a, 10a, and (E)‐23, respectively, were synthesized. A very useful method is described for the assignment of the configuration at C‐4 of the 1,3‐O‐benzylidene‐1,2,3,4‐tetrol derivatives 3a, 3b, (E,Z)‐12a, and (E,Z)‐12b by means of NMR spectroscopy. magnified image
Konformation und Bromierung von Bicyclo[3.3.1]nonan‐2,6‐dion sowie Dehydrobromierung der Bromketone. – Verbesserte Synthese von Bicyclo[3.3.1]nona‐3,7‐dien‐2,6‐dion
Authors: Quast Helmut , Becker Christian , Geißler Evelyn , Knoll Katja , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: July 2007

Conformation and Bromination of Bicyclo[3.3.1]nonane‐2,6‐dione and Dehydrobromination of the Bromo Ketones. – Improved Synthesis of Bicyclo[3.3.1]nona‐3,7‐diene‐2,6‐dione

Bromination by copper(II) bromide of bicyclo[3.3.1]nonane‐2,6‐dione (1) affords the epimeric α‐bromo diketones exo‐and endo‐5 and, eventually, the α, α′‐dibromo diketones exo‐ and endo‐7 (3:7) in high yield. Dehydrobromination of the mixtures of bromo diketones by calcium carbonate in dimethylacetamide yields the unsaturated diketones 6 (30%) and 2 (72%), respectively. Bromination of 1 by molecular bromine is less selective and furnishes mixtures of brominated diketones consisting of exo‐ and endo‐7, 8 and the tetrabromo diketone 10. An excess of bromine yields pure 10. – The ethylene acetal 12 is brominated by pyridinium perbromide to produce the α,α′‐dibromo acetal 13 which is very reluctant towards 1,2‐dehydrobromination by potassium tert‐butoxide. Thus, with an excess of potassium tert‐butoxide in tetrahydrofuran, 1,2‐dehydrobromination is achieved only on one side to afford 14. In contrast, potassium tert‐butoxide in dimethyl sulphoxide induces a transannular dehydrobromination leading to the diacetal 15 of 3‐bromonoradamantane‐2,6‐dione. – The conformations of 1,10, and 13 in the solid state are determined by X‐ray diffraction analyses. From torsional angles, vicinal proton coupling constants are calculated with the aid of the Karplus equation and compared to those determined from solutions by high‐field NMR spectroscopy. The reasonable agreement provides the basis for the assessment of the configuration and conformation for exo‐ and endo‐7. magnified image
Regioselective aectylations of sialic acid α‐ketosides
Authors: Reinhard Bernd , Faillard Hans
Published: July 2007

Various partially acetylated sialic acid α‐ketosides were obtained without expensive protecting group techniques by using trimethyl orthoacetate or dimethylacetamide dimethyl acetal as acetylating agents or by performing a partial Zemplén de‐O‐acetylation. Using trimethyl orthoacetate as acetylating agents we synthesized 9‐O‐acetylated, 8‐O‐acetylated, and 8,9‐di‐O‐acetylated sialic acid α‐ketoside benzyl ester derivatives. The acetylation with dimethylacetamide dimethyl acetal yielded 9‐O‐acetylated, 8‐O‐acetylated, 4, 9‐di‐O‐acetylated, 8,9‐di‐O‐acetylated, and 4,8,9‐tri‐O‐acetylated sialic acid α‐ketoside benzyl ester derivatives. The partial Zemplén de‐O‐acetylation permitted the synthesis of 7,8,9‐tri‐O‐acetylated sialic acid α‐ketoside benzyl ester derivatives. After catalytic hydrogenation the 8‐O‐acetylated derivatives 2e and 3d were not stable and were completely converted into the 9‐O‐acetylated sialic acid α‐thioketoside 2k. The N‐acetyl‐8,9‐di‐O‐acetylneuraminic acid α‐aminophenylthioketoside 21 showed a migration of the acetyl group from position 8 to position 7 in polar solvents, yielding a mixture of the 8,9‐di‐O‐ and the 7, 9‐di‐O‐acetylated derivatives 21 and 2m in a molar ratio of approximately 1:1. The 7, 9‐di‐O‐acetylated derivative 2m could be separated and was completely stable in methanol. Using the isopropylidene protecting group we could also prepare the 4‐O‐acetylated sialic acid α‐thioketoside 2o. Treatment of the 9‐O‐acetylated derivative 2k with fluorescein isothiocyanate gave the fluorescent derivative 5. magnified image
Synthesis of 4‐nitro‐1‐(trialkylsilylalkyl)imidazoles
Authors: Földeák Sándor , Molnár Mária , Lǒkös Magdalena
Published: July 2007

1‐(2‐Hydroxyethyl)‐2‐methyl‐5‐nitroimidazole (1) reacts with haloalkyltrialkylsilanes [Hal(CH2)nSiMe2R] to give 4‐nitroimidazole derivatives 3 and acetaldehyde. This process involves at least two reaction steps, N‐alkyl quaternization and elimination of the hydroxyethyl group. magnified image