bluuebunny/crossref_metadata_2025 huggingface dataset:
Gezielte Funktionalisierung des Pimarangerüstes, II. Aufbau des D‐Ringes zur Synthese höherer Terpene
Authors: John Michael , Haslinger Ernst
Published: July 2007

Directed Functionalization of the Pimarane Skeleton, II. — Formation of the D‐Ring for the Synthesis of Higher Terpenes

The conversion of the pimarane skeleton 1 into the tetracyclic compound 3 is described. The synthetic route includes the formation of the D‐ring and the stereoselective introduction of an angular methyl group at C‐14. D‐ring construction has been achieved by selective oxidation of the double bond systems of 2 which lead via 14 to compound 18. This was alkylated to 19 and subsequently converted into 20. Further oxidation gave 21 and the ester 24 which upon treatment with potassium tert‐butoxide formed 25. The angular methyl group was introduced using a organocopper ragent: 26. After decarboxylation and hydrogenation 3 was obtained. It can be used as building unit for the construction of higher terpenes (e.g., tirucallanes 4).
Transannulare Wechselwirkung der funktionellen Gruppen in Tetracyclo[6.3.0.04,11.05,9]undec‐6‐en‐2‐on. — Abnormaler Verlauf einer Ketalisierungsreaktion
Authors: Ipaktschi Junes , Sang Bernd
Published: July 2007

Transannular Interaction of Functional Groups in Tetracyclo[6.3.0.04,11.05,9]undec‐6‐en‐2‐one. — Unexpected Course of a Ketalization Reaction

The reaction of polycyclic enones 1 with ethylene glycol yielded beside the ketal 2 as main product unexpectedly the cyclic polyether 3. The structure of 3 was established by spectroscopic analysis and independent synthesis starting from 10a and 12a. The analogous synthesis of polyether 17 is described.
Oxidation of Palmitoyl‐ and Benzoylascorbate. — A 13C‐NMR Study
Authors: Berger Stefan , Otten Martina G. , Steinbach Klaus
Published: July 2007

Ascorbic acid (1a), the 6‐benzoate and 6‐palmitate ester (1b, c) were oxidized by iodine both in D2O and in [D6]DMSO solution. The reactions were followed by 13C‐NMR spectroscopy. It was shown for the 6‐esters 1b, c, that, with the exclusion of water, monomeric dehydroascorbic acid esters 6b, c could be detected.
Synthesis of Segments of the GnRH‐Associated Peptide
Authors: Somlai Csaba , König Wolfgang , Knolle Jochen
Published: July 2007

The 56 amino acid containing GnRH‐associated peptide (GAP) may be prepared by a combination of fragment condensation and solid‐phase peptide synthesis (SPPS). The solution‐phase synthesis of the fragments 1–9 is described. Furthermore, we report on the selective cleavage of benzyl esters by catalytic hydrogenation in the presence of the 9‐fluorenylmethyloxycarbonyl (Fmoc) protecting group. The C‐terminal 15 amino acid containing fragment of GAP (10) was synthesized by SPPS.
Chemo‐enzymatische Synthese von Kohlenhydraten: Die Herstellung von L‐Xylose und 2‐Desoxy‐L‐xylo‐hexose
Authors: Schmid Walther , Heidlas Jürgen , Mathias John P. , Whitesides George M.
Published: July 2007

Chemo‐Enzymatic Synthesis of Carbohydrates: The Preparation of L‐Xylose and 2‐Deoxy‐L‐xylo‐hexose

A synthetic approach to L‐xylose (6) and 2‐deoxy‐L‐xylo‐hexose (8) has been developed. The strategy utilizes achiral starting materials and employs two enzymatic reactions to introduce the desired chiral centers. Rabbit muscle aldolase (RAMA)‐catalyzed condensation of (3‐phenylthio)propanal (1) with dihydroxyacetone phosphate (DHAP) affords the C‐6 skeleton 2 with D‐threo configuration between C‐3 and C‐4. Diastereoselective reduction of 2 with sorbitol dehydrogenase (SDH) introduces the final stereocenter of the tetrahydroxy derivative 3. After oxidation of sulfide 3 to the corresponding diastereotopic sulfoxides 4, L‐xylose (6) is obtained by thermal elimination of phenylsulfenic acid followed by ozonolysis. 2‐Deoxy‐L‐xylo‐hexose (8) is yielded from 4 by a Pummerer rearrangement and subsequent reductive deprotection (DI‐BAL‐H) of the rearrangement product 7.
Synthetische und spektroskopische Studien an Nb‐substituierten Hexahydrocanthin‐6‐olen und deren Säure‐katalysierte Dimerisierung
Authors: Achenbach Hans , Düthorn Berthold , Waibel Reiner
Published: July 2007

Synthetic and Spectroscopic Studies with Nb‐Substituted Hexahydrocanthin‐6‐ols and Their Acid‐Catalyzed Dimerization

Hexahydrocanthin‐6‐ol (1) constitutes with its carbinolamine group the reactive structural element of some alkaloids of the eburnamine/vincamine group. In acidic medium, the title compounds undergo a dimerization reaction by linkage between the D‐rings. Dimerization products caused by electrophilic substitution of the aromatic system have not been observed under the conditions applied.
D‐Galacturonsäurederivate, VI. D‐Galacturonsäurederivate mit flüssigkristallinen Eigenschaften
Authors: Vogel Christian , Jeschke Udo , Vill Volkmar , Fischer Hartmut
Published: July 2007

D‐Galacturonic Acid Derivatives, VI. — D‐Galacturonic Acid Derivatives with Liquid Crystalline Properties

Esters, thioesters, and amides of D‐galacturonic acid have been synthesized from alcohols, thioalcohols, and amines having long alkyl chains. Key intermediate of the reaction with the different nucleophiles was the 1,2;3,4‐di‐O‐isopropylidene‐α‐D‐galactopyranuronosyl chloride (3). Deisopropylidenation of the protected esters, thioesters, and amides was achieved by trifluoroacetic acid. The investigation of the liquid crystalline properties was carried out with a polarizing microscop, DSC measurements, and X‐ray diffraction. Molecules with three long alkyl chains can be obtained by reaction of amides 5h and 5i with thioalcohols. MM2 calculations voted a Y‐shaped structure of the mercaptals 8a and 8b which do exhibit thermotropically a columnar hexagonal mesophase (Dhd) as we have proved by X‐ray diffraction.
Base‐Mediated Ring Expansion Reactions, III. A New Route from Dihydroisoquinolines to 2‐benzazepines
Authors: Groth Ulrich , Richter Lutz , Schöllkopf Ulrich , Zindel Jürgen
Published: July 2007

The substituted 2‐benzazepines 4, 5 and 12 were prepared by a base‐mediated ring expansion reaction of mesylates 1a–e, which were synthesized in 4 to 5 steps by starting from benzolactams 6.
Pheromone Synthesis, CXLIV. A Synthesis of (1R,5S)‐(+)‐Frontalin from (S)‐(—)‐2‐Hydroxyparaconic Acid
Authors: Mori Kenji , Fukamatsu Kunio
Published: July 2007

(—)‐2‐Hydroxyparaconic acid (1a) was converted into (1R,5S)‐frontalin (10) via dimethyl (R)‐citramalate (4), and shown to possess the absolute configuration S.
Biosynthesis of Natural Products with a PC Bond, X. Incorporation of D‐[1‐2H1]Glucose into 2‐Aminoethylphosphonic Acid in Tetrahymena thermophila and into Fosfomycin in Streptomyces fradiae. — the Stereochemical Course of a Phosphoenolpyruvate Mutase‐Catalyzed Reaction
Authors: Hammerschmidt Friedrich , Kählig Hanspeter
Published: July 2007

2‐Aminoethylphosphonic acid and fosfomycin produced on feeding D‐[1‐2H1]glucose to Tetrahymena thermophila and Streptomyces fradiae, respectively, indicate that the phosphoenolpyruvate mutase catalyzes the stereospecific transfer of the phospho group of (Z)‐phosphoenol‐[3‐2H1]pyruvate from oxygen to carbon from the si face. 2H‐NMR spectroscopy was used to determine the configuration at C‐1 of biosynthetically formed 2‐amino‐[1‐2H1]ethylphosphonic acid after derivatization with (—)‐camphanoyl chloride and diazomethane.
Synthesis of a Spiro[tetrahydroquinoline‐[1,3,4]thiadiazole] Derivative
Authors: Somogyi László , Batta Gyula , Tokés Adrienne L.
Published: July 2007

The synthesis of 2‐phenyl‐1,2,3,4‐tetrahydroquinolin‐4‐one thiosemicarbazone (2c) and subsequent cyclization to the title compound (3e, R = H) under acetylating conditions are described Their structure was determined by IR‐, 1H‐ and 13C NMR, as well as mass spectral data.
Enzym‐katalysierte Reaktionen, 13. Eine neue, effiziente Synthese von Fagomin
Authors: Effenberger Franz , Null Volker
Published: July 2007

Enzyme‐Catalyzed Reactions, 13. — A New, Efficient Synthesis of Fagomine

2‐Deoxy‐L‐threo‐5‐hexulosonitrile (4) is obtained in excellent chemical yield by yeast transketolase (EC 2.2.1.1)‐catalyzed reaction of racemic 3‐hydroxy‐4‐oxobutyronitrile [(R/S)‐2] with lithium hydroxypyruvate (3). Catalytic hydrogenation of 4 exclusively gives fagomine (7).
Synthese von Plagiochin A und B, zwei macrocyclische Bis(bibenzylether) aus Plagiochila acantophylla
Authors: Kametler László , Keseru György M. , Nógrádi Mihály , Mezey‐Vándor Gabriella , Vermes Borbála , Kajtár‐Peredy MÁRia
Published: July 2007

Synthesis of Plagiochins A and B, Macrocyclic Bis(bibenzyl) Ethers from Plagiochila acantophylla

Plagiochins A (1) and B (2), macrocyclic bis(bibenzyl) ethers with a 16‐membered ring, are synthesized. The key steps are the Pd(0)‐catalyzed C—C coupling of an areneboronic acid (18) with an aryl bromide with formation of a biphenyl (13), Ullmann ether synthesis of a diphenyl ether (23), Wittig reaction to connect the two components 13 and 23, and a modified Wurtz reaction to close the ring. The latter reaction is accompanied by an unusual transformation of a C‐benzyloxy to a C‐benzoyl group.
Reaction of 3‐Acetyl‐7,12‐dihydro‐2‐methyl‐6H‐indolo[2,3‐a]quinolizinium Chloride with Aromatic Aldehydes Forming “Dimers” under Kinetic Control; Stereoselective Acetal versus Aldol Ring Closure
Authors: Teuber Hans‐Joachim , Quintanilla‐Licea Ramiro , Bats Jan Willem
Published: July 2007

3‐Acetyl‐7,12‐dihydro‐2‐methyl‐6H‐indolo[2,3‐a]quinolizinium chloride (1) forms “dimers” (5a, b) by condensation with benzaldehyde and by means of kinetically controlled acetal ring closure (piperidine catalysis). In 5a, b the two quinolizinium units are connected by intercalation of a hydrogenated chroman system whose reactivity is attributed to the presence of a pyranoid hemiacetal structure. On standing or heating of their solution 5a, b are converted via the intermediate 4 and aldol ring closure into the thermodynamically more stable diastereoisomers 2a, b with a bicyclo[3.3.1]nonadiene system. All the ring closures occur with diastereofacial selectivity. In the case of the condensation of 1 with salicylaldehyde the Schiff base of this aldehyde with aniline replaces the aldehyde moiety as well as the piperidine catalyst and yields 10a, b under kinetically controlled conditions. By sodium tetrahydridoborate reduction in methanol 5a is converted into 7, the X‐ray structural analysis of which confirms structure and stereochemistry.
1,3‐Dipolare Cycloaddition elektrophiler Azide an cyclische Keten‐N,X‐acetale. — Stickstoff‐Extrusion und Ringerweiterung der [3 + 2]‐Cycloaddukte
Authors: Quast Helmut , Ach Manfred , Peters Eva‐Maria , Peters Karl , Peters Karl , von Schnering Hans Georg
Published: July 2007

1,3‐Dipolar Cycloaddition of Electrophilic Azides to Cyclic Ketene N,X‐Acetals. — Extrusion of Molecular Nitrogen and Ring Expansion of the [3 + 2] Cycloadducts.

The electrophilic azides 2 react with cyclic ketene N,X‐acetals of type 7, e.g. 13, 15, 18, 21, 23, 25, and with the alkylidene‐dihydroindoles 28 as well, to produce, besides molecular nitrogen, ring‐expanded products of type 11 and 12, e.g. 14, 16, 19, 22, 24, 26, and 29 (path A), and/or N‐sulfonylimines 10, viz. 17, 20, 27, and 31, besides diazo compounds (path B). The configurations of 16b, 19, 24a, and 26a are elucidated by means of X‐ray diffraction analyses. The envelope conformations of the hetero rings of 19, 29 undergo ring inversion with rates in the range of the 1H NMR time scale [19: ΔG#c (285 K) = 54.8 kJmol−1, 29; ΔG#c (301 K) = 61.4, ΔG#c (314 K) = 60.7]. The formation of the ring‐expanded products 11 and 12 is interpreted in terms of an initial [3 + 2] cycloaddition leading to unstable spiro compounds 8. Opening of their dihydro‐1,2,3‐triazole ring generates the zwitterions 9 which lose molecular nitrogen with concomitant ring expansion by a 1,2‐shift of the more soft one of the atoms N and X.
What is the Structure of Peptide Antibiotic Tü 1718 B? Previously Proposed Structure Disproved by Synthesis
Authors: Postels Hans‐Thomas , König Wilfried A.
Published: July 2007

Two stereoisomers (1a and 1b) of N‐(L‐valyl)‐2′,5‐dihydroxyhomoproline, the proposed structure of the dipeptide antibiotic Tü 1718 B, were synthesized by starting from natural (2S,4R)‐hydroxyproline. The 1H‐ and 13C‐NMR spectra of 1a and 1b clearly differ from the corresponding spectra of the natural product. From both synthetic stereoisomers characteristic mass spectra were obtained after esterification and trifluoroacetylation. Isomer 1a is present as a mixture of two stable conformers, as indicated by peak splitting in the1H‐NMR spectra, which disappears at higher temperature, while 1b exits as a single conformer. Both synthetic stereoisomers are antibiotically inactive.
Iodocyclization of Homoallylic Hydroxylamines Derived from D‐Glyceraldehyde
Authors: Dhavale Dilip D. , Gentilucci Luca , Piazza Maria Giulia , Trombinl Claudio
Published: July 2007

The reaction of allylmagnesium chloride with nitrone 1 derived from D‐glyceraldehyde affords two diastereoisomeric homoallylic hydroxylamines 2a and 3a which, after separation and O‐silylation, are subjected to iodocyclization using N‐iodosuccinimide. The stereochemical outcome of the cyclization reaction was found to be different; thus, the hydroxylamine 2b is converted into a mixture of cis‐ and trans‐isoxazolidines 10 and 11 in which the trans product prevails, whereas 3b is stereoselectively converted into the cis product 12. The final 5‐(iodomethyl)isoxazolidines 10–12 may be easily subjected to further studies; for example they undergo iodine displacement by treatment with azide, phthalimide, and acetate ions to give 13–16, formal precursors of deoxy‐amino‐hexitols. As an example, 1‐O‐acetyl‐3,4‐dideoxy‐5,6‐O‐(1‐methylethylidene)‐4‐[(phenylmethyl)amino]‐D‐lyxo‐hexitol (17) is synthesized.
Synthesis of Sphingosine Relatives, XII Synthesis and Absolute Configuration of the Two Epimeric Aliphatic Amino Alcohols [5E, 7E)‐2‐Amino‐5,7‐tetradecadien‐3‐ols] Isolated from a Sponge, Xestospongia sp.
Authors: Mori Kenji , Matsuda Hiroyuki
Published: July 2007

(2S, 3S, 5E, 7E)‐ and (2S, 3R, 5E, 7E)‐2‐Amino‐5,7‐tetradecadien‐3‐ol [(S)‐1a and (S)‐1b], which were proposed as the structures of epimeric amino alcohols isolated from a marine sponge, and their two enantiomers were synthesized from (S)‐ and (R)‐alanine, respectively. The high‐field 1H‐NMR spectra of the diacetyl derivatives of 1a, b were identical with those of the derivatives of naturally occurring amino alcohols. However, the absolute configurations of the natural products were corrected as (2R) by comparing the optical rotations of natural products with those of the synthetic products.
Synthesis of Novel HMG‐CoA Reductase Inhibitors, I. Naphthalene Analogs of Mevinolin
Authors: Novák Lajos , Rohály JáNos , Poppe László , Hornyánszky Gábor , Kolonits Pál , Zelei István , Fehér Imre , Fekete Jenö , Szabó Éva , Záhorszky Uwe , Jávor András , Szántay Csaba
Published: July 2007

The title compounds 2 and their corresponding (6 S) epimers 18 are prepared in several steps by starting with chiral formyl ester 5, and α‐tetralones 10: (1) coupling reaction with the ylide generated from 11 to yield unsaturated ester 13, (2) reduction to the corresponding alcohol 14, (3) addition of the Grignard reagent derived from 14 to formyl ester 5 to afford the hydroxy esters 16 and 17, and (4) lactonization. This procedure is also used to synthesize the β‐naphthyl analogs 29 and 30. Some results obtained from HMG‐CoA reductase inhibitor screening are also reported.
Chirale Porphyrine mit C‐verknüpften Menthyl‐Resten
Authors: Marx Thomas , Breitmaier Eberhard
Published: July 2007

Chiral Porphyrins with C‐Connected Menthyl Residues

Chiral porphyrins 9 and 10 with C‐connected (—)‐menthyl residues are prepared starting from (—)‐menthol 1 in eight steps, finally involving cyclization of 3‐formyl‐β‐(p‐menth‐3‐yl)styrene (6) with pyrrole (7) or the 2,2′‐dipyrrylmethane 8.
Regioselectivity in Cyclofunctionalization of Olefinic Alcohols with Benzeneselenenyl Halides at Different Temperatures[1 – 4]
Authors: Konstantinovic Stanimir , Bugarčič Zorica , Milosavljevič Slobodan , Schroth Gerhard , Mihailovič Mihailo Lj.
Published: July 2007

The regioselectivity in cyclofunctionalization of some acyclic olefinic alcohols with benzeneselenenyl halides (PhSeCl and PhSeBr) at different temperatures (−78°C, O°C and room temperature) is investigated. It has been found that Δ4‐ and Δ5‐ alkenols are converted into five‐ and/or six‐membered cyclic phenyl selenoethers, the yield of which decreases with increasing reaction temperature. PhSeCl has been found to be more efficient than PhSeBr in the cyclization reactions.
Terpenes and Terpene Derivatives, XXVIII. New Monoterpene Derivatives from the Essential Oil of Artemisia salsoloides
Authors: Weyerstahl Peter , Wahlburg Hans‐Christian , Kaul Vijay K. , Lochynski Stanislaw
Published: July 2007

From the essential oil of Artemisia salsoloides the oxygenated monoterpenes 1, and 3–8 could be isolated. The easy formation of the hydroperoxide 2 from 1 suggests a biogenetic pathway from geraniol/nerol to 3. By comparison, the synthesized 8 exhibits mushroom and celery odor, typical of fractions of the A. salsoloides oil containing 8.
Synthese von Chlorinen aus dem roten Blutfarbstoff Hämin
Authors: Haake Gerold , Meier Axel , Montforts Franz‐Peter , Scheurich Gerhard , Zimmermann Gottfried
Published: July 2007

Synthesis of Chlorins from the Red Blood Pigment Heme

Hydroxyalkylporphyrins rac‐8h, k and rac‐9h, k prepared from the readily accessible red blood pigment heme can be transformed into the geminally dialkylated chlorins rac‐10–13 upon reaction with N,N‐dimethylacetamide dimethyl acetal. The chlorins are promising candidates for application in Photodynamic Tumor Therapy (PDT). The reported synthetic method should be useful for the synthesis of natural hydroporphyrins containing geminally dialkylated structural parts.
Synthesis of 4,7‐Dihydroxyperhydroisobenzofuran‐1‐one and Comparison with Zwergal's Structure of “garlicin”
Authors: Nour Reema Abdel , Schneider Karin , Urban Ernst
Published: July 2007

The Diels‐Alder reaction of 2‐(benzoyloxy)furan (2) with maleic anhydride leads to the adduct 3 which, on hydrogenation, affords the exo anhydride 4a (71%) and endo anhydride 4b (2.4%). The regioselective reduction of 4a and 4b with NaBH4 leads to the lactones 5a and 5b, respectively. Base‐catalyzed cleavage of 5a gives the keto lactone 6 or dimethyl acetal 7, depending on the reaction conditions. Catalytic hydrogenation of keto lactone 6 results in the diastereoselective formation of the title compound 8a which has been converted into the acetate 8b and trifluoroacetate 8c. The structure and properties of the dihydroxylactone 8a are discussed in comparison with garlic compound “garlicin”.
Irreversible Desaktivierung von menschlicher β‐Hexosaminidase A mit dem alkylierenden Pseudodisaccharid (3,4,6/5)‐6‐(2‐Acetamido‐2‐desoxy‐β‐D‐glucopyranosylthio)‐3,4‐epoxy‐5‐hydroxycyclohexen
Authors: Kuhn Cai‐Steffen , Lehmann Jochen , Sandhoff Konrad
Published: July 2007

Irreversible Deactivation of Human β‐Hexosaminidase A with the Alkylating Pseudodisaccharide (3,4,6/5)‐6‐(2‐Acetamido‐2‐deoxy‐β‐D‐glucopyranosylthio) ‐3,4‐epoxy‐5‐hydroxycyclohexene

(3,4,6/5)‐6‐(2‐Acetamido‐2‐deoxy‐β‐D‐glucopyranosylthio)‐3,4‐epoxy‐5‐hydroxycyclohexene (8b) has been synthesised and found to deactivate irreversibly human β‐D‐hexosaminidase from lysosomes. Deactivation did not take place in the presence of the competitive inhibitor (3,6/4,5)‐6‐(2‐acetamido‐2‐deoxy‐β‐D‐glucopyranosylthio)‐4‐bromo‐3,5‐dihydroxy‐cyclohexene (5a/b).
Pheromone Synthesis, CXXXVII. A New Synthesis of (+)‐Grandisol
Authors: Mori Kenji , Fukamatsu Kunio
Published: July 2007

The natural and (+)‐enantiomer of grandisol [1, (1R,2S)‐(+)‐2‐isopropenyl‐1‐methylcyclobutaneethanol] has been synthesized from (R)‐(—)‐carvone (2) by employing the intramolecular alkylation of 8 to give 9 as the key step.
Stereochemie der Addition von Phenylmetall‐Reagenzien an Bicyclo[3.3.0]octandione und ‐octadiendione. — Synthese phenylsubstituierter Bicyclo[3.3.0]octadiene
Authors: Quast Helmut , Carlsen Jürgen , Herkert Thomas , Janiak Rolf , Röschert Horst , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: July 2007

Stereochemistry of the Addition of Phenylmetal Reagents to Bicyclo[3.3.0]octanediones and ‐octadienediones. — Synthesis of Phenyl‐Substituted Bicyclo[3.3.0]octadienes

Conjugate addition of dilithium diphenylcyanocuprate is observed only on one side of the dienedione 4b, affording the enedione 5b, but on both sides in the presence of boron trifluoride yielding the diphenyldione 6b. Likewise, the latter reagent gives rise to the formation of 6a from 4a. Phenylcerium(III) dichloride is much superior to phenyllithium and phenylmagnesium bromide in the 1,2 addition reaction to encumbered, enolizeable bicyclo[3.3.0]octanediones. Thus, a mixture of the diols exo,exo‐8, exo,endo‐8, and endo,endo‐8 is formed in almost quantitative yield from the 3,7‐dione 7. Furthermore, the diphenyldione 6a is transformed into the tetraphenyldiol 14 in this way and in high yield. The 2,6‐dione 11b adds phenylcerium(III) dichloride affording a mixture of the hydroxyketone endo‐16, which is inert towards an excess of the reagent, and the diol exo,endo‐12b. The inertness of endo‐16 is attributed to the formation of the cyclic hemiacetal 20 which eventually is trapped quantitatively by O‐silylation with chlorotrimethylsilane in the presence of pyridine. The hydroxyketone endo‐16 is dehydrated to give the enone 17 which subsequently is treated with phenylcerium(III) dichloride to form exo‐ and endo‐19. A solution of sulfuric acid in acetic acid dehydrates the tertiary benzyl alcohols 8 (→9 + 10), endo,endo‐12a (→ 13a), exo,endo‐12b (→ 13b), 14 (→ 15), endo‐16 (→ 17), and 19 (→ 13b) in high yields. The same results are achieved even more conveniently with a solution of chlorotrimethylsilane in dichloromethane in the absence of a base. The oxanortwistane 18 is obtained as a byproduct in the dehydration of exo,endo‐12b with both reagents. The gross structures of all compounds are based on spectroscopic evidence, in particular NMR spectra. Concentration‐independent IR and low‐field NMR absorptions of two equivalent hydroxy groups are indicative of intramolecular hydrogen bonds and hence the endo,endo configuration of the diols endo,endo‐8, endo,endo‐12a, and 14. Eventually, the configurations of 5b, 6b, endo,endo‐8, endo,endo‐12a, exo,endo‐12b, 14, 15, endo‐16, and the structure of 18 as well, are established by X‐ray diffraction analyses. In the solid state, the bicyclo[3.3.0]‐octanols endo,endo‐12a, exo,endo‐12b, 14, and endo‐16 adopt conformations that allow the phenyl groups the occupation of quasi equatorial positions. The optimized procedures described open high‐yield routes to phenyl‐substituted bicyclo‐[3.3.0]octadienes starting from readily available bicyclooctanediones.
Synthesis of α‐Arabinose Nucleosides from 6‐Substituted Uracils
Authors: Jørgensen Per T. , El‐Barbary Ahmed A. , Pedersen Erik B.
Published: July 2007

The reaction of silylated 6‐substituted uracils 5 with methyl 2,3,5‐tri‐O‐benzoyl‐α‐D‐arabinofuranoside (3) in the presence of trimethylsilyl trifluoromethanesulfonate (TMS triflate) afforded a mixture of the corresponding protected N1,N3‐bis(arabinofuranosyl)uracils 6 and the 6‐substituted 2,3,5‐tri‐O‐benzoyl‐α‐D‐arabinofuranosyluracils 8. Deprotection of 6 and 8 gave the corresponding α nucleosides 7 and 9. The reaction of silylated 6‐ethyl‐ and 6‐methylthiouracil with 3 afforded a mixture of S‐ and N3‐glycosides 10 and 11. The glycosides 10 were deblocked by treatment with methanolic ammonia to obtain the deprotected α nucleosides 12.
Some Synthetic Studies Related to Perylenequinones
Authors: Zhao Chen , Zhang Xu‐Sheng , Zhang Pang
Published: July 2007

Two closely related routes to dimethyl 3,10‐dihydro‐2,11‐dihydroxy‐4,6,7,9‐tetramethoxy‐3,10‐dioxo‐1,12‐perylenediacetate (10), one involving Ullmann phenol coupling and the other by double oxidative coupling are described. Regioselective demethylation of 10 followed by methylation or vice versa yields dimethyl 3,10‐dihydro‐4,9‐dihydroxy‐2,6,7,11‐tetramethoxy‐3,10‐dioxo‐1,12‐perylenediacetate (22) which, except for its side chains, structurally resembles some of the natural perylenequinones.
Stereochemie von Aldolreaktionen mit 3‐Hexulose‐Phosphat‐Synthase
Authors: Brockamp Hans‐Peter , Steigel Alois , Kula Maria‐Regina
Published: July 2007

Stereochemistry of Aldol Reactions with 3‐Hexulose Phosphate Synthase

The enzymic reaction between ribulose‐5‐phosphate (1) and formaldehyde or acetaldehyde catalyzed by hexulose phosphate synthase (HPS) from Methylomonas M 15 DSM 580 yielded D‐arabino‐3‐hexulose‐6‐phosphate (2) and two new 7‐deoxy‐4‐heptulose‐1‐phosphates (4, 6). By various NMR‐spectroscopic methods, especially NOED, the configuration of the dephosphorylated products was established as (5R,6S) and (5R,6R). The configuration of two earlier described 7,8‐dideoxy‐4‐octulose‐1‐phosphates (8, 10) synthesized likewise by HPS catalysis must be corrected.
Refunctionalization of Homoallylic Alcohols Containing a Vinylic Chlorine Atom
Authors: Hoffmann Reinhard W. , Giesen Volker , Fuest Marcus
Published: July 2007

The chlorine atoms in Z‐substituted vinyl chlorides 1, 5, 7 and 14 have been replaced by alkyl, vinyl and (trimethylsilyl)methyl groups to give the alkenes 3, 4, the dienes 9, 10, 15, or the allylsilanes 8. The latter have been transformed stereoselectively into tri‐ and tetrasubstituted tetrahydrofurans 18 and 20. The vinyl chlorides 1 have been converted into the corresponding Z‐vinylsilanes 13 and 23. These serve as starting compounds for the stereoselective generation of trisubstituted 5,6‐dihydro‐2H‐pyrans 25, 26, 28, and 30. Derivatives 31 and 34 of the vinyl chlorides 1 have been subjected to stereoselective free‐radical cyclizations giving substituted tetrahydropyrans 33 and 35. The vinyl chlorides 1 may readily be converted to the alkynes 37.
Easy and General Method for the Preparation of m‐ and p‐Acylbenzoic Acids: A New Synthesis of rac‐Suprofen
Authors: Camps Pelayo , Giénezm Silvia , Farrés Xavier , Mauleón David , Carganico Germano
Published: July 2007

A method for the preparation of m‐ and p‐acylbenzoic acids 3 based on the Claisen condensation of isophthalic or terephthalic diesters 1 with α‐methylenecarboxylic esters 2 is described. p‐Propionylbenzoic acid p‐4 (R = Me) is used in a new synthesis of rac‐suprofen (11).
Pheromone Synthesis, CLI. Synthesis of Chlorinated Steroids Related to the Structures Proposed for Blattellastanosides A and B, the Aggregation Pheromone of the German Cockroach, Blattella germanica L.
Authors: Mori Kenji , Fukamatsu Kunio , Kido Masaru
Published: July 2007

Remote functionalization of 5α‐stigmastan‐3β‐ol (5) to yield eventually 5α‐stigmast‐9(11)‐en‐3α‐ol (8) was employed for the syntheses of 9α‐chloro‐5α‐stigmastane‐3β,11β‐diol (13) and 12α‐chloro‐9α,11α‐epoxy‐5α‐stigmastan‐3β‐yl β‐D‐glucopyranoside (3). The former (13) was the aglycone part of the structure 2 originally proposed for blattellastanoside B, and the latter (3) was exactly the structure proposed for blattellastanoside A, the components of the aggregation pheromone of the German cockroach, Blattella germanica L. The present work disproved the structures 1–4 proposed for blattellastanosides A and B.
Synthetic Microbial Chemistry, XXV. Synthesis of the Enantiomers of Differolide [4‐(2′,5′‐Dihydro‐2′‐oxo‐3′‐furanyl)‐3a,4,5,6‐tetrahydro‐1(3H)‐isobenzofuranone], a Microbial Bioregulator for the Formation of Aerial Mycelium and Spores of Streptomyces glaucescens
Authors: Mori Kenji , Tomioka Hiroki , Fukuyo Emiko , Yanagi Kazunori
Published: July 2007

Both the enantiomers of differolide [4‐(2′,5′‐dihydro‐2′‐oxo‐3′‐furanyl)‐3a,4,5,6‐tetrahydro‐1(3H)‐isobenzofuranone (1)] were synthesized by starting from the known lactone rac‐2. The key step was the optical resolution of hemiacetal rac‐3 by acetal formation with (+)‐ or (−)‐menthol. A single crystal X‐ray analysis of acetal (−)‐4a established its absolute configuration. Since the natural product was known to be racemic, the present synthesis of both (+)‐ and (−)‐1 with known absolute configuration provided molecular probes to examine the enantioselectivity at the receptor site of Streptomyces glaucescens.
Synthesis of 2,3‐Dihydro‐7‐hydroxymethyl‐1H‐pyrrolizin‐1‐one, the Alkaloid Loroquine
Authors: Röder Erhard , Bartkowski Jan‐Pit Barko , Bourauel Thomas
Published: July 2007

The title compound 4 is synthesized in 8 steps by cyclization of N‐tosylglycinate 5 with vinyl ketone 6. After elimination of water and sulfinic acid the pyrrolecarboxylate 9 is obtained which, on N‐alkylation with ethyl acrylate, Dieckmann cyclization, saponification and decarboxylation, yields methylloroquine 12. The reaction with chlorotrimethylsilane/sulfuric acid in acetic anhydride and subsequent saponification give loroquine (4) in 2.1% overall yield.
Epoxides of Phytosphingosine and Derivatives, Potential Inhibitors of Sphingosine Biosynthesis
Authors: Birk Rolf , Sandhoff Konrad , Schmidt Richard R.
Published: July 2007

2,4‐O‐Benzylidene‐D‐threose (1) was treated with the Grignard reagent obtained from n‐octyl bromide to afford the epimeric tetrol derivatives 3a, b. Regioselective 2‐O‐mesylation and subsequent azido group introduction furnished azidophytosphingosine derivatives 5a, b. Ensuing 4‐O‐mesylation, acidcatalyzed benzylidene group removal and then treatment with NaH as a base provided preferentially the desired 3,4‐epoxide derivatives 8a, b; subsequent azido group reduction with triphenylphosphane/water yielded the target molecules 9a, b possessing D‐ribo and L‐lyxo configuration, respectively.
Stereoselective Synthesis of Alcohols, XLII. Stereoselective Cyclization of (8‐Oxo‐2‐octenyl)boronates to cis‐ or trans‐2‐Vinylcyclohexanol
Authors: Hoffmann Reinhard W. , Sander Thomas , Hense Achim
Published: July 2007

Intramolecular allylboration reactions of (8‐oxo‐2‐octenyl)boronates proceed with excellent diastereoselectivity: the E‐isomer 1d leads to the trans‐2‐vinylcyclohexanol (2) with 99.5% d.s., the corresponding Z‐isomer 3d cyclizes to give the cis‐isomer with a diastereoselectivity exceeding 99.8%.
Acetogenic Isoquinoline Alkaloids, L. The Synthesis of All Possible Isomeric 6,8‐Dioxygenated 1,3‐Dimethyl‐1,2,3,4‐tetrahydroisoquinoline Methyl Ethers – Useful Chiral Building Blocks for Naphthylisoquinoline Alkaloids
Authors: Bringmann Gerhard , Weirich Ralf , Reuscher Hehnut , Jansen Johannes R. , Kinzinger Lioba , Ortmann Thomas
Published: July 2007

The practicable synthesis of all imaginable isomeric heterocyclic moieties 8–11 and ent‐8–ent‐11 of the naphthylisoquinoline alkaloids is described. The stereoinformation at C‐3 is induced by asymmetric reductive amination, using 1‐phenylethylamines of either enantiomeric series as chiral auxiliaries. The key step of the stereocontrolled construction of the stereocenter at C‐1 is the diastereoselective reduction of the corresponding dihydroisoquinolines, as obtained by Bischler‐Napieralski synthesis, or the regio‐ and stereoselective Pictet‐Spengler reaction of arylisopropylamines with acetaldehyde, respectively.
Herstellung von (R,R)‐ oder (S,S)‐2‐Amino‐3‐hydroxycarbonsäuren (allo‐Threonin‐Analoge) durch Acylierung/Reduktion von 2‐t‐Butyl‐3‐methyl‐4‐oxoimidazolidin‐1‐carbonsäure‐t‐butylester (Boc‐BMI)
Authors: Blank Stefan , Seebach Dieter
Published: July 2007

Preparation of (R,R)‐ or (S,S)‐2‐Amino‐3‐hydroxycarboxylic Acids (allo‐Threonine Analogs) by Acylation/Reduction of t‐Butyl 2‐t‐Butyl‐3‐methyl‐4‐oxoimidazolidine‐1‐carboxylate (Boc‐BMI)

While there are numerous methods of preparing threonine analogs by aldol additions of chiral glycine derivatives to aldehydes, only few general routes leading to the epimers with C,C‐bond formation are presently available. This paper describes the acylation of the title compound 1 with acyl chlorides (→ trans products 2–9), the subsequent reduction with LiBHEt3 in THF (→ hydroxyalkylated BMI derivatives 10–14), and acidic hydrolysis to the free allo‐threonines 18–22. The first two steps are totally stereoselective (by NMR analysis), and the overall yields from BocBMI are in the order of 30–60%. Only allo‐threonines without branching in the γ‐position are accessible by this method. In one case we have also applied this sequence of steps to prepare an α‐branched allo‐threonine derivative 26. – The 5‐acyl‐BocBMI derivatives 2–9 are remarkably stable to epimerization at the center between the two carbonyl groups. Possible reasons for this are discussed and are partially supported by an X‐ray crystal structure analysis of the phenacetyl derivative 6.
Synthesis of 11‐Membered Enediyne Ketones by the Intramolecular Nicholas Reaction
Authors: Maier Martin E. , Brandstetter Tilmann
Published: July 2007

An efficient route to 11‐membered enediyne ketones 13 and 22 was developed. This route is based on an intramolecular Nicholas reaction of 11 and 20, respectively. In the course of the preparation of the cyclization substrates 11 and 20, it was important to use the acetylenic alcohols 6 and 15 as building blocks for the construction of the cis‐enediynes 8 and 17, respectively, instead of the corresponding ketones which were converted into unstable acyclic enediynes. Some transformations of enediyne ketone 22 were also studied. For example, 22 could be transformed into the 2‐formyl compound 26 via the silyl enol ether 24. In addition, 24 was used for the preparation of the 2‐amino ketone 29.
Chemie der Ginkgolide, VI. Herstellung von 1,10‐Dihydroxy‐ und 1,7,10‐Trihydroxyginkgolid aus 1,3,7,10‐Tetrahydroxyginkgolid
Authors: Weinges Klaus , Rümmler Matthias , Schick Hartmut
Published: July 2007

Chemistry of the Ginkgolides, VI. – Preparation of 1,10‐Dihydroxy‐ and 1,7,10‐Trihydroxyginkgolide from 1,3,7,10‐Tetrahydroxyginkgolide

1,3,7,10‐Tetrahydroxyginkgolide (“ginkgolide C”, 1) which can be isolated in large quantities from the terpene fraction of Ginkgo leaves, can be converted into 1‐(tert‐butyldiphenylsilyloxy)‐3,7,10‐trihydroxyginkgolide (2) in 95% yield. 2 was converted via straightforward reactions into 1,7,10‐trihydroxyginkgolide (“ginkgolide M”, 9) and into the until now unknown 1,10‐dihydroxyginkgolide (15). 15 can also be obtained from 1,3,10‐trihydroxyginkgolide (“ginkgolide B”, 10). The intermediate products 14‐epiginkgolides 8 and 14 were epimerized to the ginkgolides with natural configuration at C‐14 by reaction with 4‐(dimethylamino)pyridine in acetonitrile. The title compounds are of interest for their possible activity as antagonists of the platelet activating factor (PAF).
De‐novo Synthesis of Enantiomerically Pure Deoxy‐ and Aminodeoxyfuranosides
Authors: Gräf Silke , Braum Manfred
Published: July 2007

(R)‐3‐Hydroxy‐4‐pentenoic acid (2), readily available by an aldol addition of doubly deprotonated (R)‐2‐hydroxy‐1,2,2‐triphenylethyl acetate (1) to acrolein, functions as a key intermediate for the synthesis of enantiomerically pure deoxy‐and aminodeoxyfuranosides 8–13. Iodolactonization of the acid 2 enables the generation of the second stereogenic center and provides the furanone skeleton of 6a which is submitted to reduction and various functional‐group manipulations. Whereas the halogen atom of 7a is easily replaced by lithium azide in an SN2‐type reaction to deliver 10a, a free‐radical substitution pathway is suitable for the conversion of 7b into the glycoside 8a. The latter compound serves as an intermediate in a formal synthesis of 3′‐azido‐2′,3′‐dideoxythymidine (AZT). On the other hand, the triflate 7c is converted into the diazide 12 by a twofold nucleophilic substitution. The novel aminodeoxy‐furanosides 11 and 13 are available in enantiomerically pure from upon catalytic hydrogenation of the azides 10 and 12.
Proton Acid‐induced Rearrangements of α‐Alkynylestradiol Methyl Ethers
Authors: Pindur Ulf , Schall Thomas
Published: July 2007

When subjected to proton catalysis, the α‐alkynylestradiol methyl ethers 1a and 1b furnish the Rupe or Meyer‐Schuster rearrangement products 2, 4, and 5a. In the presence of sulfuric acid, α‐ethynylestradiol 3‐methyl ether (1a) is converted into the D‐homosteroid 3a. The use of deuterated acids gives rise to the formation of the corresponding deuterated steroids 2b, 2c, 3b, and 5b. Some mechanistic implications of these results are also discussed.
Steroidal Cyclobutanones, IV. Heterocyclic Spiroannulation of 5α‐Cholestan‐3‐one. Stereospecific Beckmann Rearrangement of Steroidal 3‐Spirocyclobutanone Oximes
Authors: Blaszczyk Krzysztof , Paryzek Zdzislaw
Published: July 2007

Diastereomeric 5α‐cholestane‐3,3′‐spiro‐2′,2′‐dichlorocyclobutanones 1 and 2 served as starting materials for the synthesis of related heterocyclic spirane derivatives. Thus, diastereomeric 5α‐cholestane‐3,3′‐spiropyrrolidin‐5′‐one (10, 11), ‐3′‐spiro‐γ‐lactone (12, 16), and ‐3′‐spirotetrahydrofuran (14, 18) are described. The spirocyclobutanone oximes (E)‐4 and (Z)‐5 and their O‐acetyl and O‐benzoyl derivatives 6, 7 and 8, 9 are also prepared. It has been shown that the Beckmann rearrangement of the spirocyclobutanone oximes 4 and 5 proceeds stereospecifically with exclusive anti migration. The stereochemistry of the spiro compounds is assigned on the basis of the 1H‐ and 13C‐NMR spectral data.
(1→4)‐β‐D‐Galaktosyltransferase läßt sich durch photolabile Liganden im Akzeptor‐Bindebereich spezifisch kovalent modifizieren
Authors: Lehmann Jochen , Petry Stefan
Published: July 2007

The Acceptor Binding Area of (1→4)‐β‐D‐Galactosyltransferase Can Be Covalently Modified by Photoaffinity Labelling in the Presence of Photolabile Ligands

Three spacer‐modified oligosaccharides (SMOs) 2, 3, and 4, consisting of two nonreducing GlcNAc end groups, O‐linked by an acyclic 10‐membered spacer carrying azi groups in positions 2, 3, or 5, proved to be acceptor substrates for (1→4)‐β‐D‐Galactosyltransferase (Gal‐T) and models of the natural biantennary core heptasaccharide of N‐glycoproteins. Photoaffinity labelling with each compound takes place with different efficiencies. This is an indication of regioselective chemical modification of the enzyme's extended binding area, because the reactive carbene in each case is placed in a different chemical surrounding. A radioactive SMO was used to prove the irreversible chemical modification of the acceptor binding site.
Total Synthesis of rac‐Silandrin, an Antihepatotoxic Flavanolignan
Authors: Antus Sándor , Baitz‐Gács Eszter , Gottsegen Agnes , Kovács Tibor , Szunyog József , Tóth Tamás S. , Wagner Hildebert
Published: July 2007

The first synthesis of racemic silandrin (rac‐1), which shows significant antihepatotoxic activity, has been accomplished via the key intermediate 9 prepared from the readily available starting materials caffeic acid ethyl ester (4) and coniferyl alcohol (5).
Reactions of 7‐(Methoxyimino)‐4‐methyl‐2H‐chromene‐2,8(7H)‐dione with Phosphorus Ylides. Synthesis of 2‐Substituted 6‐Methyl‐8H‐benzopyrano[7,8‐d]oxazol‐8‐ones
Authors: Bezergiannidou‐Balouctsi Catherine , Litians Konstantions E. , Malamidou‐Xenikaki Elizabeth , Nicolaides Demetrios N.
Published: July 2007

7‐(Methoxyimino)‐4‐methyl‐2H‐chromene‐2,8(7H)‐dione (3) reacts with phosphonium salts 1a–c, 8a, b under phasetransfer catalysis conditions to afford the title 2‐substituted 6‐methylbenzopyranooxazol‐8‐ones 5a–c, 10a, b, respectively, along with compound 6, instead of the expected Wittig reaction products. However, the reaction of 3 with the stable phosphorus ylides 11a–c in addition to the corresponding benzopyranooxazoles 12a–c and compound 6 affords in the last case compound 16 as well according to a sequence involving an initial Wittig reaction between 11c and 3.
Pheromone Synthesis, CLVII. Synthesis of the Enantiomers of syn‐4‐Methyl‐5‐nonanol to Determine the Absolute Configuration of the Naturally Occurring (4S,5S) Isomer Isolated as the Male‐produced Pheromone Compound of Rhynchophorus vulneratus and Metamasius hemipterus
Authors: Mori Kenji , Kiyota Hiromasa , Malosse Christian , Rochat Didier
Published: July 2007

The enantioselective synthesis of both (4R,5R)‐ and (4S,5S)‐4‐methyl‐5‐nonanol (1) was achieved by starting from an optically active epoxide 5. A GC comparison on a chiral stationary phase of the synthetic enantiomers of 1 with the naturally occurring 1 was executed, and (4S,5S)‐1 was shown to be identical with the natural 1 isolated as the male‐produced pheromone compound of the weevils Rhynchophorus vulneratus and Metamasius hemipterus.
Studies on Heterocyclic Enaminonitriles, XIV. Preparation of Dihydrothiophenium‐1‐bis(ethoxycarbonyl)methylides and Their Recyclization with a Base
Authors: Yamagata Kenji , Takaki Mikiko , Ohkubo Kimiko , Yamazaki Motoyoshi
Published: July 2007

The reaction of 4,5‐dihydro‐2‐morpholino‐(2‐pyrrolidino and 2‐piperidino)‐3‐thiophenecarbonitriles 1–3 with bis‐(ethoxycarbonyl)carbenoid afforded stable dihydrothiophenium‐1‐bis(ethoxycarbonyl)methylides 4–6. The recyclization of compounds 4–6 with bases gave the corresponding diethyl 2,2(3H)‐thiophenedicarboxylates 7 and ethyl 2‐thiophenecarboxylates 7a′, 8, 9. The starting compounds 1–3 were synthesized by the reaction of 2‐amino‐4,5‐dihydro‐3‐thiophenecarbonitriles with morpholine, pyrrolidine, and piperidine.
Homochirale 2,4‐disubstituierte 1,3‐Dioxane aus (S)‐(−)‐Äpfelsäure: Stereoselektive Synthese und Untersuchung der NMDA‐Rezeptoraffinität aller vier Stereoisomerer
Authors: Wünsch Bernhard , Diekmann Heike , Höfner Georg
Published: July 2007

Homochiral 2,4‐Disubstiuted 1,3‐Dioxanes from (S)‐(−)‐Malic Acid: Stereoselective Synthesis and Investigation of the NMDA Receptor Affinity of All Four Stereoisomers

Starting from a single enantiomerically pure compound, (S)‐(−)‐malic acid, all four stereoisomeric 4‐dimethylaminomethyl‐2‐phenyl‐1,3‐dioxanes (S,S)‐15 (S,R)‐16, and (R,S)‐16 are prepared: Transacetalisation of benzaldehyde dimethyl acetal (6b) with (S)‐(−)‐methyl 2,4‐dihydroxybutyrate (7a), which is obtained by chemoselective BH3 reduction of (S)‐(−)‐malic acid monoester 8b, yields the diastereomeric 1,3‐dioxane derivatives (S,S)‐10 and (R,S)‐11 in a 85:15 ratio. LDA deprotonation of (S,S)‐10 followed by protonation leads to C‐4 epimerisation [(S,S)‐10:(S,R)‐11 = 30:70]. The thermodynamically controlled 88:12 equilibrium of (R,R)‐10 and (S,R)‐11 is reached by treatment of (S,R)‐11 with acid. Aminolysis with dimethylamine and subsequent LiAlH4 reduction transform the four stereoisomeric esters (S,S)‐10, (R,R)‐10, (S,R)‐11 and (R,S)‐11 to give the amines (S,S)‐15, (R,R)‐15, (S,R)‐16 and (R,S)‐16, respectively. In the 3H‐(+)‐MK 801 displacement experiment (S,S)‐15, (R,R)‐15, (S,R)‐16 and (R,S)‐16 show a very little affinity to the phencyclidine binding site in the cation channel associated with the NMDA receptor.
Synthesis of the Hydroxyamino Sugar of Calicheamicins
Authors: Rainer Hildegard , Scharf Hans‐Dieter
Published: July 2007

Methyl 6‐deoxy‐2,3‐O‐isopropylidene‐4‐O‐mesyl‐α‐D‐galactopyranoside (6) was prepared from D‐galactose in six steps. 6 was subjected to a nucleophilic displacement reaction with sodium azide as the nucleophile to yield methyl 4‐azido‐4,6‐dideoxy‐2,3‐O‐isopropylidene‐α‐D‐glucopyranoside (7) in 75% yield. Reduction of the azido group with NaBH4 afforded the amino sugar 8 (81%) which was adsorbed on silica gel and subsequently oxidized with ozone to methyl 4,6‐dideoxy‐2,3‐O‐isopropylidene‐4‐nitro‐α‐D‐glucopyranoside (10, 80%). This crystalline and stable compound 10 was reduced with Zn/NH4Cl to yield the desired methyl 4,6‐dideoxy‐4‐hydroxy‐amino‐2,3‐O‐isopropylidene‐α‐D‐glucopyranoside (11, 85%), which is unstable to air and therefore has to be transferred to its N,O‐diacetate derivate 12. No chromatographic purification was necessary.
Aminosäuren, 17 – Eine neue Synthese von Didehydrodipeptiden und Didehydrotripeptiden
Authors: Effenberger Franz , Kühlwein Jürgen , Hopf Martin , Stelzer Uwe
Published: July 2007

Amino Acids, 17. – A New Synthesis of Didehydro Dipeptides and Didehydro Tripeptides

Esters of N‐phthaloyl‐protected (R)‐ or (S)‐didehydro dipeptides 5–7 were obtained in good yields by the perrhenate‐catalyzed decomposition of 2‐azidocarboxylates 1 with N‐phthaloyl‐protected (R)‐ or (S)‐amino acid chlorides 2 in presence of at least equimolar amounts of N‐methyl‐2‐pyridone (4) as acylation catalyst. Esters of didehydro tripeptides 16 were obtained in a comparable procedure from the optically active amino acid chlorides 2 and 2‐(2‐azidoacyl)amino acid esters 15, which were prepared from 2‐azidocarboxylic acids 12 or the corresponding chlorides 13 with 2‐amino acid ester hydrochlorides (S)‐14. – As an example, the unprotected (S)‐alanly‐didehydrovalin 20 was prepared from the didehydro dipeptide 18a without any racemization by hydrolysis of the benzyl ester and subsequent hydrogenolytic removal of the N‐phthaloyl group.
Indolalkaloide, II. – Synthese von 4‐Amino‐tetrahydrocarbazol‐1‐on‐Derivaten
Authors: Patir Süleyman , Götz Peter H.
Published: July 2007

Indole Alkaloids, II. – Synthesis of 4‐Amino‐tetrahydrocarbazol‐1‐one Derivatives

Treatment of 1,2,3,4‐tetrahydrocarbazol‐1‐one with 1,2‐ethanedithiol gave the tetrahydrocarbazole 2 which was oxidized with DDQ to compound 3. It was converted into the imine 6 by treatment with n‐butylamine and ZnCl2. The imine was directly reduced with NaBH4 to give the amine 7, which was acetylated with benzoyl chloride to yield amide 8. Treatment of 8 with mercury(II) oxide and Et2O·BF3 gave 9.
F‐Säure‐haltige Phospholipidmoleküle in Zuckerrohrzellen
Authors: Scheinkönig Josef , Spiteller Gerhard
Published: July 2007

F Acid‐Containing Phospholipids in Sugar Cane Cells

Heterotrophic suspension cultures of sugar cane (Saccharum spec.) cells contain the F acids 1b–f. These acids are bound preferably to phosphatidylethanolamine 3 and phosphatidylcholine 4. Structures of F acid‐containing phospholipid molecular species 3b–d, 4b and 4c were established by enzymatic positional hydrolysis and GC/MS analysis of the respective (trimethylsilyl)diacylglycerol derivatives 5.
Neue Synthesen mit 1,3‐ambident‐nucleophilen Phosphor‐Yliden, VII. Heterocyclische Triphenylphosphonium‐chloride, Triphenylphosphonio‐olate, acyclische Triphenylphosphonio‐thiolate und ihre Wittig‐Derivate
Authors: Capuano Lilly , Drescher Stefan , Huch Volker
Published: July 2007

Syntheses with 1,3‐Ambident‐Nucleophilic Phosphorus Ylides, VII. – Heterocyclic Triphenylphosphonium Chlorides, Triphenylphosphonio‐Olates, Acyclic Triphenylphosphonio‐Thiolates and Their Wittig Derivatives

Under mild conditions, benzoylmethylenetriphenylphosphorane (1b) reacts readily with oxalyl chloride to give the unstable 4‐(4,5‐dihydro‐4,5‐dioxo‐2‐phenyl‐3‐furyl)triphenylphosphonium chloride (3b). This undergoes rapid hydrolysis to afford the triphenylphosphonium chloride 4 of benzoylpyruvic acid. Thermolysis of 3b or 4 results in the formation of 2‐(triphenylphosphoranyliden)indan‐1,3‐dione (10), the structure of which was established by X‐ray diffraction analysis. – With phenylmalonyl chloride, the title compounds 1a, b, d react by formation of the triphenylphosphonio‐olates 7 of pyridine‐, pyran‐ and thiopyran‐dione, respectively. – The (thioaroylmethylene)triphenylphosphoranes 1e, f react with benzonitrile imine 12 to give the red hydrazonotriphenylphosphoniothiolates 16, the structures of which have been elucidated by an X‐ray diffraction analysis. Under rigorous conditions, compounds 16 undergo an intramolecular Wittig‐type reaction leading to pyrazoles 14.