bluuebunny/crossref_metadata_2025 huggingface dataset:
C‐glycoside syntheses, IV. Henry condensation of nitroethane and nitropropane with 4,6‐O‐benzylidene‐D‐glucopyranose
Authors: Wang Xiaojing , Gross Paul H.
Published: July 2007

The condensation of 4,6‐O‐benzylidene‐D‐glucopyranose (1) with nitroethane gave the diastereomeric α‐nitroethyl

„α”︁ refers to C‐1 of the alkyl substituent; see 2 in Scheme 1.

β‐C‐glucosides 2 (minor), and 6. The latter was only obtained pure by an acetylation‐deacetylation procedure and was reduced by a mixture of elemental Fe0/Ni0 in aqueous THF under CO2 to α‐aminoethyl β‐C‐glucoside 7, with retention of the 4,6‐O‐benzylidene blocking group. Acetylation of 2 produced an open‐chain compound 3. An oxime derivative 5 was separated as a byproduct from the acetylation. The condensation of 1‐nitropropane with 1, followed by acetylation, similarly gave diastereomers 8 and 9. Deacetylation of 8 gave 10.
Total Synthesis of (±)‐20‐epiapotacamine and its conversion into (±)‐apotacamine by the Polonovski‐Potier reaction
Authors: Lounasmaa Mauri , Belle David Din , Tolvanen Arto
Published: July 2007

(±)‐20‐Epiapotacamine (8) was synthesized in two steps from aldehyde 6 and was converted into the indole alkaloid (±)‐apotacamine (2) by the Polonovski‐Potier reaction.
Pheromone synthesis CLXIX. Improved synthesis of the racemate of the hemiacetal pheromone of the spined citrus bug Biprorulus bibax
Authors: Amaike Masayasu , Mori Kenji
Published: July 2007

The racemate of (3R,4S,1′E)‐3,4‐bis(1′‐butenyl)tetrahydro‐2‐furanol (1) was synthesized by employing Ireland's ester enolate Claisen rearrangement of (±)‐5 as the key step. The synthesis was efficient enough to provide 23.7 g of (±)‐1 in 41% overall yield based on (±)‐7 (8 steps) without having recourse to such a toxic solvent as HMPA in the key step.
A facile synthesis of 1‐hydroxypyrazole by oxidation of pyrazole
Authors: Reuther Wolfgang , Baus Ulf
Published: July 2007

The oxidation of sodium pyrazolate with dibenzoyl peroxide is the first direct route to 1‐hydroxypyrazole (2a). The reaction may be also applied to substituted pyrazoles.
Cyclization of ethyl (E)/(Z)‐[2‐(1‐cyclohexen‐1‐yl)cyclohexylidene]cyanoacetate to 10‐amino‐1,2,3,4,5,6,7,8‐octahydrophenanthrene‐9‐carboxylic acid — a route to 1,2,3,4,5,6,7,8‐octahydrophenanthrene derivatives
Authors: Wilamowski Jaroslaw , Krasodomski Wojciech , Nowak Barbara , Sepioł Janusz J.
Published: July 2007

Cyclization of ethyl (E)/(Z)‐[2‐(1‐cyclohexen‐1‐yl)cyclohexylidene]cyanoacetate (2) in cold concentrated sulfuric acid affords 10‐amino‐1,2,3,4,5,6,7,8‐octahydrophenanthrene‐9‐carboxylic acid (4) and 3,5,6,7,8,8a‐hexahydro‐3‐oxospiro‐[1H‐2‐benzopyran‐1,1′‐cyclohexane]‐4‐carbonitrile (5). The o‐amino acid 4 is employed in the synthesis of several 1,2,3,4,5,6,7,8‐octahydrophenanthrene derivatives: the carboxylic acid 6, o‐hydroxy carboxylic acid 7, and the amine 8. The lactone 5 undergoes decarboxylation on heating yielding a mixture of unsaturated nitriles 9 and 10 which are cyclized to the amine 8.
Hydrogen bonding of benzenesulfonamides in molecular recognition processes
Authors: König Burkhard , Möller Oliver , Jones Peter G. , Ahrens Birte
Published: July 2007

Benzenesulfonamides represent a hydrogen donor‐acceptor moiety that is changed to a bisacceptor by deprotonation. The dimerization constant of N‐tosyl‐n‐butylamine (7) and N‐tosyl‐L‐alanine (9‐H) in CDCl3 and the binding constant of the tetrabutylammonium salt 7·NBu4 to urea in DMSO were determined by 1H‐NMR titration methods. The X‐ray structure analysis of 9‐H is reported.
Synthesis of β,γ‐unsaturated phenyl esters by aluminium chloride initiated reactions of allylsilanes with aryl chloroformates
Authors: Mayr Herbert , Gabriel Andreas O. , Schumacher Ralf
Published: July 2007

Phenyl chloroformate (1) reacts with the allylsilanes 2a–h in the presence of aluminium chloride to give the β,γ‐unsaturated phenyl esters 3a–h in 50–90% yield. While these reactions proceed in the usual manner with allylic inversion, (1,1‐dimethylallyl)trimethylsilane (2i) reacts with allyl retention to yield the 2,2‐dimethyl‐3‐butenoate 3i. Attempts to use 1 for the phenoxycarbonylation of arenes were not successful.
A new approach to C‐branched monosaccharides by the stereoselective hydrodesulfurization of methyl 4,6‐O‐benzylidene‐3‐[bis(methylthio)‐methylene]‐3‐deoxy‐α‐D‐erythro‐hexopyranosid‐2‐ulose
Authors: Peseke Klaus , Thiele Gabriela , Michalik Manfred
Published: July 2007

The stereoselective reduction of methyl 4,6‐O‐benzylidene‐3‐[bis(methylthio)methylene]‐3‐deoxy‐α‐D‐erythro‐hexopyranosid‐2‐ulose 1 with sodium tetrahydridoborate and tributyltin hydride, respectively, to (Z)‐configured 4 is described. The increased reactivity of 4 compared to 1 is reflected in several substitution reactions resulting in the displacement of the methylthio group by different N nucleophiles. The substitution products 6–8 were stereoselectively obtained as (Z) isomers. Pyrano[3,4‐c]pyrazole derivatives 3 and 10 were prepared by treatment of 1 and 4, respectively, with hydrazine hydrate.
A facile synthesis of 5H‐1‐thia‐3,5,6,8‐tetraazaacenaphthylenes
Authors: Tumkevičius Sigitas
Published: July 2007

Ethyl 5‐substituted 7‐(methylthio)‐5H‐1‐thia‐3,5,6,8‐ tetra‐azaacenaphthylene‐2‐carboxylates (5a‐f) representing a new heterocyclic system were prepared by acid‐catalyzed cyclocondensation of ethyl 5‐amino‐4‐(substituted amino)‐2‐(methylthio)thieno[2,3‐d]pyrimidine‐6‐carboxylates (3a‐f) with triethyl orthoformate. Compounds 3 were obtained by aminolysis of 4,6‐dichloro‐2‐(methylthio)pyrimidine‐5‐carbonitrile (1) affording 2 followed by base‐promoted cyclization with sodium ethyl thioglycolate.
Cyclodehydrogenation of 2′‐hydroxychalcones with hypervalent iodine reagent: A new synthesis of flavones
Authors: Litkei György , Gulácsi Katalin , Antus Sandor , Blaskó Gábor
Published: July 2007

A new synthesis of chrysin (1) and luteolin (4) was accomplished by the cyclodehydrogenation of the appropriately substituted 2′‐hydroxychalcones 21 and 22 in the presence of iodosobenzene diacetate/potassium hydroxide in methanol. The scope and limitation of this transformation is discussed.
Azepines by photochemical ring enlargement of 9‐azidopodophyllotoxin‐ and 9‐azido‐9′ ‐demethylepipodophyllotoxin derivatives
Authors: Laatsch Hartmut , Erns Bernd Peter , Hoffmann Dieter
Published: July 2007

The azepines 5a‐5c were obtained by photochemical nitrene rearrangement of the azides 1e/1f and 4b/4c in cyclohexene, but not in other solvents. They are ring expansion products of podophyllotoxin (1a) and resemble steganacin (9), but show only low biological activity. The triazenes 7a/8a and the aziridine 8b are also less active than 1a.
Azo bridges from azines, XVI. 1,2,3‐oxadiazolidines by intramolecular [3 + 2] cycloaddition
Authors: Hünig Siegfried , Schmitt Michael
Published: July 2007

Olefinic bonds and an azoxy group held in a rigid parallel position in systems of type I undergo smooth thermal [3 + 2] cycloadditions which can be strongly catalyzed by acids. Double bonds of a bicycloheptene (norbornene) moiety are ca. 10 times more reactive than those of a bicyclooctene system. The newly formed cage compounds of type K are the first stable derivatives of the so far unknown 1,2,3‐oxadiazolidine.
Synthesis of novel HMG‐CoA reductase inhibitors, II. Heterocyclic analogs of mevinolin
Authors: Novák Lajos , Hornyánszky Gábor , Rohály János , Kolonits Pál , Szántay Csaba
Published: July 2007

The indole (1) and chroman analogs (2) of mevinolin and their 6S diastereomers 15c and 25d were synthesized in several steps starting with methyl (R)‐3‐[(tert‐butyldimethylsilyl)oxy]‐4‐formylbutyrate (12) and 2‐(indol‐3‐yl)ethanol (3) or 6‐methoxychroman‐4‐one (16), respectively. Compounds 1 and 2 inhibited moderately the HMG‐CoA reductase. The diastereomers 15c and 25d were shown to be inactive.
Total synthesis of angucyclines, 7. Hydroaromatic angucyclines of the SF‐2315 type
Authors: Krohn Karsten , Khanbabaee Karamali , Jones Peter G.
Published: July 2007

Osmylation of the Diels‐Alder adduct 3 afforded the cis‐diol 4, which was dehydrated by acid treatment to the phenol 6. Reaction with tetrafluoroboric acid converted the diol 4 by intramolecular acyl shift into the acetate 7. The relative stereochemistry of 7 was determined by single‐crystal X‐ray analysis. Photooxygenation of 4 afforded the C‐1 carbonyl compound 8 and treatment with sulfuric acid the silanol 9. Functionalization of C‐6 was achieved by treatment of 4 with methanolic KOH to yield the cis‐methyl ether 11.
Geminal substituent effects, 11. The anomeric effect in orthoesters — the concept of geminal pairwise interactions for the interpretation of standard enthalpies of formation
Authors: Rakus Klaus , Verevkin Sergey P. , Peng Wei‐Hong , Beckhaus Hans‐Dieter , Rüchardt Christoph
Published: July 2007

New enthalpies of formation ΔH(g) are provided for the series of orthoesters 2a‐2f, 3 and 4 from their enthalpies of combustion ΔH and their enthalpies of vaporization ΔH or enthalpies of sublimation ΔH. From these data and from literature data the following new thermochemical increments were calculated [kJ · mol−1]: CH[O3] – 106.4, C[O3, C] ‐103.7, and C[O3, Ph] ‐124.5. In addition the increment C[O4] – 167.1 was calculated from literature data for ΔH(g) of the orthocarbonates 9a and 9b. The anomeric stabilization derived from these results and from previous results for acetals and ketals are reported in Table 3. – A new concept of additive structural increments for the quantitative analysis of the group increments of hydrocarbons, ethers, acetals, and ketals is proposed. It is shown that the increments for CH3, CH2, CH, and C groups with their different neighboring atoms (see Table 4) are determined by the number of hydrogen atoms in the group and by the number of pairwise geminal interactions between all atoms attached to the central carbon atom. – Using this procedure for orthoesters and orthocarbonates, deviations from additivity for the geminal interaction between oxygen atoms, i.e. the anomeric effect, are observed.
New 2,5‐dihydroimidazole‐1‐oxyls with functional side groups (N, O, S donors)
Authors: Hintermaier Frank , Volodarsky Leonid B. , Polborn Kurt , Beck Wolfgang
Published: July 2007

A series of functionalized 2,5‐dihydro‐1‐hydroxy‐2‐R1‐2‐R2‐4‐R3‐imidazoles were prepared by cyclocondensation of α‐oxo hydroxylamines with ketones R1R2C = O in the presence of ammonia (R1 = R2 = 2‐pyridyl, 4,5‐diazafluoren‐9‐ylene, R3 = Me; R1 = CH2OCOMe, CH2OCOPh, 2‐thienyl, CH2OH, CO2K, R2 = R3 = Me; R1 = Py, R2 = Me, R3 = Ph; R1 = R2 = CH2OCOPh, CH2OH, R3 = Me) and oxidized to the corresponding nitroxide radicals. The structures of 2′,5′‐dihydro‐1′‐hydroxy‐4′,5′,5′‐trimethylspiro[4,5‐diazafluoren‐9,2′‐imidazole] (2) and of 2‐(acetoxymethyl)‐2,5‐dihydro‐2,4,5,5‐tetramethylimidazole‐1‐oxyl (14) were determined by X‐ray diffraction. In the crystal 2 forms one‐dimensional chains through hydrogen bonding between N atoms of the hydroxylamine and imidazoline groups.
Bifunctional Catalysis of Ester Aminolysis – A Computational and Experimental Study
Authors: Wang Li‐Hsing , Zipse Hendrik
Published: July 2007

Various pathways for the reaction of methylamine with methyl acetate catalyzed by 2(1H)‐pyridone have been investigated at the Becke3LYP/6–31G**/HF/6–31G** level of theory. The most favorable pathway consists of a one‐step reaction, in which all bond‐forming and ‐breaking processes occur in concert. These modeling studies also show the pyridone to function as an acid, which led to the investigation of several substituted pyridones. 4‐Cyano‐, 3‐cyano‐6‐methyl‐, and 3‐cyano‐2(1H)‐pyridone have indeed been shown to provide better catalysis in the ester aminolysis reaction by ab initio modeling at the Becke3LYP/6–31G**/HF/3–21G level. In order to verify the theoretical results, the catalytic activities of various substituted 2‐pyridones in the reaction of n‐butylamine with p‐nitrophenyl acetate in chlorobenzene solution have been determined. The observed catalytic rate constants are indeed in agreement with the theoretical predictions. Other catalyst characteristics such as solubility and state of aggregation are, however, also of paramount importance in this reaction.
Synthesis of HR 916 K: An Efficient Route to the Pure Diastereomers of the 1‐(Pivaloyloxy)ethyl Esters of Cephalosporins
Authors: Defoßa Elisabeth , Fischer Gerd , Gerlach Uwe , Hörlein Rolf , Isert Dieter , Krass Norbert , Lattrell Rudolf , Stache Ulrich , Wollmann Theo
Published: July 2007

HR 916 K (5), the 1‐(S)‐(pivaloyloxy)ethyl prodrug ester of the cephalosporin cefdaloxime, exhibits a significantly higher oral bioavailability than the 1‐(R) diastereomer HR 916 J. An efficient synthesis of HR 916 K was developed. The separation of the diastereomers was achieved by precipitation of the 1‐(R)‐hydrochloride 9 followed by crystallization of the 1‐(S)‐amine 10 (de > 96%). The 1‐(R) diastereomer 9 was recycled by acidic saponification or enzymatic cleavage to AMCA (7). The amine 10 was acylated with mercaptobenzothiazole thioesters or mixed anhydrides, prepared from carboxylic acids 13 and 14, in almost quantitative yield. Deprotection of the oxime and formation of the tosylate proceeded in one step. Using thioester 18, we obtained HR 916 K (5) from AMCA (7) in 42% yield.
Asymmetric Alkylation of Chiral 2‐Azapentadienyl Metal Compounds: Diastereoselective Synthesis of Alkyl‐Substituted N‐Allylimines (2‐Aza‐1,4‐pentadienes)
Authors: Stakemeier Hubertus , Würthwein Ernst‐Ulrich
Published: July 2007

N‐Allylimines (2‐aza‐1,4‐pentadienes) 3 bearing a chiral auxiliary group at C‐1 were prepared by a three‐step sequence involving condensation of pivaloyl chloride with allylamine, chlorination and reaction with a chiral amine (SMP or SMEMP) as an auxiliary group. Deprotonation of 3 by treatment with butyllithium in tert‐butyl methyl ether as solvent at ‐20°C afforded the chiral 2‐azapentadienyllithium compounds 4. Transmetalation of 4a with MgBr2 · Et2O gave the corresponding magnesium bromide 5. Alkylation with primary alkyl halides is predominantly kinetically controlled and leads to the 3‐substituted N‐allylimines 6. Secondary and tertiary alkyl halides, however, preferentially give 5‐substituted 2‐aza‐1,3‐pentadienes 7. The diastereoselectivity of the alkylation reaction may be increased by transmetalation from the lithium compound to the corresponding magnesium bromide or by exchange of the SMP group for the stronger chelating SMEMP group. The halide ion of the alkylating agent strongly influences the configuration of the newly formed stereogenic center. Thus, the chlorides lead to the opposite stereochemistry compared to the bromides. The effect of different solvents on the regio‐ and diastereoselectivity of the alkylation reactions was studied. Semiempirical calculations (PM3, MNDO) were used to design a stereochemical model for the metalated intermediates in order to rationalize the stereochemistry observed in the experiments.
Synthetic Applications of Conjugated Nitrones, 5 A Novel Entry to the 13‐Azasteroid System
Authors: Lopez‐Calle Eloisa , Höfler Johannes , Eberbach Wolfgang
Published: July 2007

A synthetic approach to 13‐azasteroid and C‐nor‐13‐azasteroid derivatives (type 17/18) as well as to the 4,13‐diaza analogues 27/28 is described. For the construction of the tetracyclic compounds precursors with preformed rings A, B and D containing a conjugated nitrone system were used (16/26). These were prepared from the annulated cyclohexenones 10/20a, b in six steps according to slightly modified standard procedures. The failure in obtaining the terminal silyl alkynes 15b by Michael addition of the enolate of 14b to nitrostyrene is explained on the basis of a strong Si–O complexation. After replacement of the trimethylsilyl substituent by the sterically more demanding triisopropylsilyl group the formation of 15c was accomplished as expected. Upon thermally induced 1,7‐cyclization of the nitrones 16/26 a multistep rearrangement of the primary cycloallenic intermediates takes place resulting in the formation of the corresponding 6,6,6,5‐ and 6,6,5,5‐ring steroids (17/27 and 18/28) in 55–86% yield.
Derivatives of Natural Tetrapyrroles for Photodynamic Therapy, 4. Oxidative Degradation Studies: Direct Analysis and Determination of Ether and Ester Linkages in Porphyrin Dimers and Oligomers of Hematoporphyrin Derivative (HPD),
Authors: Risch Nikolaus , Hesse Ulrike , Josephs Andrea , Gauler Rainer
Published: July 2007

Oxidative degradation studies of dimeric porphyrins provide valuable information about the individual linkages between the porphyrin units. MS and NMR data of the degradation products of hematoporphyrin derivative furnish unambiguous evidence of ester and ether linkages in the di‐ and oligomeric compounds of HPD.
Azo Bridges from Azines, XXIII. 1,5‐Laticyclic Conjugation Between Parallel Azo and o‐Phenylene Bridges. Structure Dependence of [6 + 2] Photocycloadditions
Authors: Beck Karin , Brand Uwe , Hünig Siefried , Martin Hans‐Dieter , Mayer Bernhard , Peters Karl , von Schnering Hans Georg
Published: July 2007

Examples were synthesized of the four systems 1, 3, 5, and 7, in which rigid parallelo o‐phenylene and azo bridges are connected to five‐ and/or six‐membered carbocyclic moities. The o‐phenylene bridge was introduced by two routes: (A) starting from precursors already containing that bridge (24, 29) and assembling the azo bridge in consecutive steps (→ 3a, 3b, 5c, 5d, 5e, 5f, 5g); (B) starting from the systems with parallel CC/NN bridges (9a, 11a, 13a, 42) and completing the dihydro‐o‐phenylene ring by tetrachlorothiopene dioxide. Dyotropic hydrogen transfer of the azo bridge enhances the dehydrogenation of the intermediate dihydro‐o‐phenylene derivatives (22, 3cH2, 25). This mechanism was proved by the domino hydrogen transfer 44 → 45 → 5h. Via route B, systems 1a, 1b, 3c, 3d, 5a, 5b, 5h, and 43 were obtained. In sharp contrast to the smooth [2 + 2] photocycloaddition of systems 9, 11, 13, and 15 (CC/NN bridges), [6 + 2] photocycloaddition occurs only with systems 1 and (5C/5N) and 3 (6C/5N) but not with systems 5 (5C/6N) and 7 (6C/6N). These differences are not caused by slightly varying distances of the two bridges (X‐ray data) but by the higher n_ ionization energy of the azo group incorporated into a 2,3‐diazabicyclo[2.2.1]hept‐2‐ene (DBH) instead of a 2,3‐diazabicyclo[2.2.2]oct‐2‐ene (DBO) moiety, the hypsochromicity of the corresponding DBH n‐π* state and the higher ground‐state energy of DBH compared to DBO.
Pheromone Synthesis, CLXXVII. Synthesis of the Enantiomers of 2‐Methyl‐4‐heptanol and 2‐Methyl‐4‐octanol, the Pheromone Components of the West Indian Sugarcane Borer
Authors: Takenaka Motonobu , Takikawa Hirosato , Mori Kenji
Published: July 2007

Both the enantiomers of 2‐methyl‐4‐heptanol (1) and 2‐methyl‐4‐octanol (2), the components of the male‐produced aggregation pheromone of the West Indian sugarcane borer (Metamasius hemipterus), were synthesized by starting from the enantiomers of leucine.
Enantioselective Total Synthesis and Absolute Configuration of the Natural Norsesquiterpene 7‐Demethyl‐2‐methoxycalamenene by a Silane‐Terminated Intramolecular Heck Reaction
Authors: Tietze Lutz F. , Raschke Thomas
Published: July 2007

The total synthesis of the norsesquiterpene 7‐demethyl‐2‐methoxycalamenene (1) by a newly developed enantioselective silane‐terminated Heck reaction is described. The Pd0‐catalyzed transformation of the allylsilane 7, obtained from 3‐(3‐methoxyphenyl)propanol (2) in 7 steps, provides the tetralin 8 in 91% yield and with 92% ee in the presence of (R)‐BINAP. Transformation of 8 via 14 and 15 gives 1. The absolute configuration of 1 which has previously not been known was deduced from a single‐crystal X‐ray analysis of 10, obtained from the cyclization product 8 by hydroboration and acylation with camphanic acid chloride.
Chemical Reactions of the Stable Carbene 1,3,4‐Triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene
Authors: Enders Dieter , Breuer Klaus , Runsink Jan , Henrique Teles J.
Published: July 2007

The title compound 1,3,4‐triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene (1), a stable carbene, is chemically characterized via its reactivity towards a multitude of organic substrates. Its behaviour in insertion, addition and cycloaddition reactions allows its classification as a typical representative of nucleophilic carbenes.
Concave Reagents, 21. Selective Acylations of Primary and Secondary Alcohols by Ketenes
Authors: Schyja Wolfgang , Petersen Sönke , Lüning Ulrich
Published: July 2007

Concave pyridines 1 were used to catalyze the addition of primary and secondary alcohols to ketenes 4, and the kinetic data of these catalyses were determined. In inter‐ and intramolecular competitions the use of 1e–g led to improved selectivities for the acylation of primary alcohols in comparison with secondary alcohols. All primary alcohols react at comparable rates. Observed rate constants were correlated with Taft's Es values. The starting materials and products were fully characterized.
Molecular Ribbons Containing Pyridine Rings
Authors: Breidenbach Stefan , Ohren Stefan , Herbst‐Irmer Regine , Kotila Sirpa , Nieger Martin , Vögtle Fritz
Published: July 2007

The first synthesis of the ribbon‐like compounds 6–10 is described. The new building block diethyl 2,6‐bis(bromomethyl)pyridine‐3,5‐dicarboxylate 1 was prepared and characterized. Single‐crystal X‐ray structure analyses indicate that these ribbon‐like molecules arrange in a folded conformation, with the pyridine and benzene units being folded in a face‐to‐face manner, and the tosyl units of 8–10 pointing outwards. The “intramolecular self‐assembly” (folding) of these molecular ribbons is primarily attributable to the energetically more favourable syn conformation of both the [3.3]metacyclophanes and the pyridinophanes.
Configuration of Enolates of β‐Ketocarboxylic Acid Esters — Carbocation‐Carbanion Salts
Authors: Meier Herbert , Buß Monika , Adam Martin
Published: July 2007

Deprotonation of (Z)‐ or (E)‐3‐hydroxy‐2,3‐dimesitylpropenoic acid methyl ester (1a) with tetrakis(dimethylamino)‐methane (3) led to stable salt (E)‐2a, which belongs to a very rare species of salts that consist of a heteroatom‐stabilized carbocation and a heteroatom‐stabilized carbanion. An analogous guanidinium salt (E)‐2bwas formed in the reaction of 3‐oxo‐2,3‐diphenylpropanoic acid methyl ester (1b) and3. The molecular structures of these enolates were studied by NMR spectroscopy and an X‐ray analysis of (E)‐2a{MC[N(CH3)2]3} and compared with those of the corresponding alkali enolates.
Zur Rekombinationsenthalpie von Radikalen — Thermochemie der Ringöffnung von Cyclophanen
Authors: Roth Wolfgang R. , Hopf Henning , de Meijere Armin , Hunold Frank , Börner Sabine , Neumann Martin , Wasser Thorsten , Szurowski Jörg , Mlynek Cornelia
Published: July 2007

Radical Recombination Enthalpy. — Thermochemistry of the Ringopening of Cyclophanes

By thermolysis of the cyclophanes 1, 5, 8, 11, 14, 18, and 21 in the presence of NO or O2 the enthalpy profiles for the ring opening were determined from the temperature, NO, or O2 dependance of the trapping rates of the intermediate diradicals. The experimental enthalpy wells, which varied between 3 and 12 kcal · mol‐1, can be simulated well with a reaction forcefield making use of the EVBH method of Malrieu et al. This result gives confidence that also meaningful recombination barriers of radicals can be obtained by this method.
The Structure of Benzimidazole Cyanine Dyes, Their Spectroscopy and Their Performance in Photographic Emulsions
Authors: Peng Zheng‐Hong , Geise H. J. , Zhou Xiang‐Feng , Peng Bi‐Xian , Carleer R. , Dommisse R.
Published: July 2007

The multi‐step synthesis of two benzimidazole trimethine cyanines as possible green sensitizing dyes (Gs3‐1, Gs3‐2) is reported. Compounds were characterized from UV‐Vis, mass spectroscopic and NMR data. The charge density distributions of the two compounds, calculated using the semi‐empirical MOPAC 93 package, are in agreement with assignments in NMR spectroscopy. Sensitizing properties of the cyanine dyes were evaluated in actual photographic T‐grain emulsions.
Addition and Cycloaddition Reactions of Arenediazonium Ions with 1,3‐Dienes: A Shift From a Concerted to a Stepwise Mechanism
Authors: Hartnagel Manfred , Grimm Klaus , Mayr Herbert
Published: July 2007

Arenediazonium ions 1 undergo [2+ + 4] cycloadditions with (E)‐1,3‐pentadiene (2a), 2,3‐dimethylbutadiene (2b), and (E)‐2‐methyl‐1,3‐pentadiene (2c) to give dihydropyridazines or pyridazinium salts. While highly electrophilic diazonium ions and the unsymmetrical dienes 2a and 2c predominantly yield those regioisomers that are expected for a stepwise cycloaddition process, the opposite regioselectivity is found in the cycloadducts of less electrophilic diazonium ions. Kinetic investigations and product studies indicate that all cycloaddition reactions proceed concertedly. The dienes 2d and 2e, in contrast, undergo ordinary azo coupling reactions in acetonitrile/methanol with formation of the hydrazones 17 and the azo compounds 18, respectively. It is demonstrated that the linear free enthalpy relationship lgk = s (N + E) can also be used to roughly estimate the rates of ionic cycloaddition reactions.
Synthesis of Bromo‐iodo‐hydroquinone Monoalkyl Ethers
Authors: Höger Sigurd
Published: July 2007

Two methods for the preparation of 2‐bromo‐5‐iodo‐p‐alkoxyphenols and the isomeric 5‐bromo‐2‐iodo‐p‐alkoxyphenols are reported in detail. In both cases the key to successful synthesis is the use of the difference in ortho‐directing power of phenols, phenolethers and phenolesters. During the bromination of 2‐iodo‐4‐propyloxyphenyl acetate (5) an unexpected “iodo‐effect” was observed, which can be attributed to the high polarisibility of iodine.
A Tandem Claisen‐Decarboxylation‐Aldol Reaction – Facile Access to The Fredericamycin A Core
Authors: Baskaran Sundarababu , Nagy Edgar , Braun Manfred
Published: July 2007

A tandem reaction of doubly deprotonated indanecarboxylic acid 3 with ethoxyphthalide 5 leads to the formation of the spirocyclic diastereomers 6a and the 6b in a ratio of 9:1. They are converted to the spirodiketone core 2 of fredericamycin A (1).
Pheromone Synthesis, CLXXVIII. – Synthesis of (−)‐exo‐Isobrevicomin and Its (−)‐endo Isomer, the Components of The Male‐Produced Volatiles of the Mountain Pine Beetle, Dendroctonus ponderosae
Authors: Mori Kenji , Takikawa Hirosato , Nishimura Yutaka , Horikiri Hiromasa
Published: July 2007

(–)‐exo‐Isobrevicomin {(1S,5R,7S)‐(–)‐5‐ethyl‐7‐methyl‐6,8‐dioxabicyclo[3.2.1]octane (1)} and its (–)‐endo isomer [(1S,5R,7R)‐2] were synthesized by employing the acetylenic acetal 7 as the common intermediate and by using the Sharpless asymmetric dihydroxylation and lipase‐catalyzed acetylation as the key reactions.
Regiospecific Synthesis of 3,4‐Disubstituted Furans and Thiophenes
Authors: Ye Xin‐Shan , Yu Pe , Wong Henry N. C.
Published: July 2007

The regiospecific synthesis of 3,4‐disubstituted furans and thiophenes is reviewed. Our initial approach used 3,4‐bis(tri‐n‐butylstannyl)furan as a building block, which led to many structurally diverse 3,4‐disubstituted furans. Another avenue was explored by using 3,4‐bis(trimethylsilyl)furan and 3,4‐bis(trimethylsilyl)thiophene as precursors. A variety of unsymmetrically 3,4‐disubstituted furans and thiophenes were prepared in this way. The advantages of our strategy lie in its stepwise manner as well as its prospect of yielding 3,4‐disubstituted furans and thiophenes with rather different substitution pattern.
New Sesquiterpene Lactones and Other Constituents from Centaurea paui
Authors: Cardona Luz , García Begoña , Muñoz M. Carmen , Navarro Francisca I. , Pedro José R.
Published: July 2007

Aerial parts of Centaurea paui afforded, in addition to several known sesquiterpene lactones, the two new elemanolides 2–4, the new elemane derivative 5 as well as the five new heliangolides 14–18. Their structures were elucidated by spectroscopic methods, especially high‐field NMR spectroscopy. The structure of the heliangolide 12 previously isolated from this plant, has been confirmed by X‐ray diffraction.
Diastereoselective Synthesis of 1‐Hydroxy‐Substituted Benzo[b]quinolidines and 11‐Hydroxy‐Substituted Azepino[1,2‐b]isoquinolines via Hetero‐Ene Cyclization
Authors: Monsees Axel , Laschat Sabine , Kotila Sirpa , Fox Thomas , Würthwein Ernst‐Ulrich
Published: July 2007

(L)‐Phenylalanine 4 can be converted to N‐(4‐methyl‐3‐pentenyl)tetrahydrosisoquinoline‐3‐carbaldehyde 10 and the corresponding homologous aldehyde 19 in 4 and 5 steps, respectively, by employing the Pictet–Spengler reaction as the key step. After Lewis acid catalyzed cyclization of 10 and 19 the cis‐configured 1‐hydroxybenzo[b]quinolizidine 21a and 11‐hydroxyazepino[1,2‐b]isoquinoline 22a were obtained with high diastereoselectivities. Compound 21a, which was characterized by X‐ray structure analysis, displays a fishbone pattern of endless zig‐zag chains connected via intermolecular hydrogen bonds in the solid state.
1,4,5,8‐Tetraazafulvalenes – A Convenient One‐Pot Synthesis and Their Conversion to Fused Ring Systems
Authors: Käpplinger Christian , Beckert Rainer , Günther Wolfgang , Görls Helmar
Published: July 2007

Cycloacylation of formamidine with bisimidoyl chlorides of oxalic acid yields the new 1,4,5,8‐tetraazafulvalenes 4 via dimerization of carbenoid intermediates. The high symmetry of the stable heterofulvalenes as well as their dye character is confirmed by NMR and UV/Vis spectral data. Whereas methylation of these substrates leads to a mixture of diastereomeric tetramethyl derivatives 9a, b, cyclization with thiophosgene or triethyl orthoformate gives mainly the fused‐ring derivatives of 2H‐imidazole 10 and 12a, b, respectively. In the case of 12a, the X‐ray crystal structure reveals the approximately ideal planarity of the central tetraazafulvalene subunit.
Flexible, Long‐Chain Alkanediamines as Building Blocks for Catenanes – Steric Hindrance of Circumrotation by Derivatization
Authors: Baumann Sven , Jäger Ralf , Ahuis Friedrich , Kray Bernd , Vögtle Fritz
Published: July 2007

New catenanes of the amide‐linked type, such as 11 with one macrocycle containing two (CH2)12 chains are synthesized from long‐chain alkanediamines in yields of up to 21%. Consequently, the preorganization afforded by fixed and angular building units – so far considered essential – proves not to be necessary. The new sulfonamide catenanes exhibit high conformational flexibility. However, the circumrotation of one of the macrocycles can be hindered by substitution with bipyridine units at the sulfonamide nitrogen.
Intramolecular Heck Reaction for the Synthesis of Isochromanes under Ambient and High pressure
Authors: Tietze Lutz F. , Burkhardt Olaf , Henrich Marielouise
Published: July 2007

The iodoarenes 9 and 10, bearing (E)‐ and (Z)‐alkene moieties, respectively, easily prepared by alkylation of the corresponding alcohols 7a–c and 8a–c with 2 iodobenzyl iodide, undergo intramolecular Heck reactions to give the isochromanes 12–15a–c in good yields. The selectivity of the reaction depends on the size of the substituent R in 9 and 10; increasing bulkiness of R leads to a decrease in diastereoselectivity and an increase in regioselectivity. High‐pressure experiments confirm the proposed mechanism and show that bromoarenes such as 11, which tend to be unreactive at ambient pressure, give good results when the cyclisation is performed under high pressure.
Secondary Metabolites by Chemical Screening, 36. Ulupyrinone and Ulufuranol: New Heteroaromatic Metabolites from Streptomyces spina
Authors: Henne Petra , Grabley Susanne , Thiericke Ralf , Zeeck Axel
Published: July 2007

Chemical Screening with extracts of Actinomycetes strains resulted in the detection, isolation, and structural elucidation of two new heteroaromatic secondary metabolites, named ulupyrinone (1) and ulufuranol (2), from Streptomyces spina (strain FH‐S 2144). The absolute configuration of ulufuranol (2) was determined by analysis of the CD spectra of its dibenzoate, 3, using the dibenzoate chirality rule.
Synthesis of an Epoxide‐ and Carbonate‐Containing 6‐/10‐Membered Bicyclodienediyne Analogue of the Neocarzinostaitin Chromophore
Authors: Ferri Fabiola , Brückner Reinhard
Published: July 2007

The monocyclo‐diendiyne → bicyclo‐trienediyne strategy for obtaining dienediyne models of the antitumor antibiotic neocarzinostatin chromophore (1) was extended from generating 6‐/11‐membered bicyclotrienediynes (e.g. 2 → 4) to generating the 6‐/10‐membered bicyclotrienediyne 5. In the preparatory steps (Scheme 2), the bistriflate 10 was successively coupled with alkynes 9 and 11. Via the dienediynediol and its subsequent oxidation with the Dess‐Martin periodinane, we obtained the monocyclic dienediyne keto aldehyde 13. Cyclization of 13 with low‐valent titanium afforded the bicyclotrienediyne 5 in 42% yield (Scheme 3). Compound 5 was converted in five steps – namely ketal cleavage, monosilylation of the resulting diol 14, asymmetric Sharpless epoxidation, desilylation and carbonate formation – into the dienediyne epoxycarbonate 3. The structure of the latter is more closely related to the neocarzinostatin chromophore than our earlier analogues.
Carbocyliccis‐[1.1.1]‐Tris‐σ‐homobenzenes – Syntheses by Triple Epoxide → Cyclopropane Conversions, Structural Data, [σ2s+σ2s+σ2s] Cycloreversions
Authors: Rücker Christoph , Müller‐Bötticher Hermann , Braschwitz Wolf‐Dieter , Prinzbach Horst , Reifenstahl Uwe , Irngartinger Hermann
Published: July 2007

By triple epoxide → cyclopropane transformation starting fromcis‐benzene trioxide the 3α,6α,9α‐tris(TIPS‐ethynyl) (1b), ‐tris(alkoxycarbonyl) (1d, e), ‐tricyano (1f), and ‐tris(ammoniomethyl) (1j) derivatives of the still elusive parentcis‐[1.1.1]‐tris‐σ‐homobenzene (1a) have been synthesized. Out of a number of carbon nucleophiles tested, a weakly basic mixed cyanocuprate of Li‐TIPS‐propyne proved the reagent of choice: Eliminations were largely avoided, thescyllo

Descriptorsscyllo, chiro, allo, cisare used as in inositol nomenclature; TIPS– =iPr3Si–.

‐2,4,6‐tris(TIPS‐propargyl)cyclohexane‐1,3,5‐triol (13a), obtained in a stereoselective one‐pot threefold epoxide opening (up to 69%), allowed the pertinent functional group manipulations. The selectivity of the base‐induced triple cyclopropane ring closure in the flexible cyclohexane precursors strongly depends on the activating groups and is promoted by fixation of the“all‐axial”conformation as an adamantoid orthophosphate. The ΔG≠values determined for the generally neat 3σ → 3π isomerizations [28.5 (1e), 29.0 (1f), 22.6 (1j) kcal mol−1] are in line with concerted reaction courses ([σ2s+σ2s+σ2s]). For the trinitrile1fan X‐ray structure analysis confirmed a nearly planar cyclohexane ring and a relatively large cyclohexane/cyclopropane interplanary angle (113°).
Reaction of α‐Hydroxyamino Ketones with Dicarbonyl Compounds – Synthesis of Imidazoline Nitroxides with a Functional Group in a Side Chain
Authors: Reznikov Vladimir A. , Volodarsky Leonid B.
Published: July 2007

The reaction of α‐hydroxyamino ketones 1 with diacetyl, acetyl acetone or acetoacetic ester in the presence of ammonium acetate results in the formation of 3‐imidazoline derivatives 2, which are precursors for the synthesis of stable nitroxides 8, 9, 14, 16, 17, 23–24 with various functional groups in the side chain at the 2‐position of the heterocycle.
Chemical, Enzymatic and Structural Studies in Molecular Glycobiology
Authors: McGarvey Glenn J. , Wong Chi‐Huey
Published: July 2007

Carbohydrates are increasingly appreciated for their critical roles in biological functions. Driving these studies addressing the molecular basis of carbohydrate‐mediated events is the availability of natural and unnatural carbohydrates. Recently, new methods of enzymatic synthesis have been developed that now afford rapid access to complex, structurally diverse oligosaccharides on large scales. This methodology has been essential to gaining insight into the molecular details of important carbohydrate recognition phenomena that are associated with many signaling processes. This review summarizes recent chemical studies examining selectin/sialyl Lewisxbinding, a key event in inflammation and metastasis, and describes the development of carbohydrate mimetics that may offer leads to new therapeutic agents. In addition, combinatorial synthesis has been used to prepare carbohydrate mimetics to neomycin B, an aminoglycoside that binds RNA involved in HIV infection, and chemoenzymatic methodology has been applied to the design and synthesis of mechanism‐based inhibitors of glycoprocessing enzymes.
Saturated Heterocycles, 252. Synthesis and Stereochemistry of Stereoisomeric 6‐Methyl‐Substituted Pyrimido[6,1‐a]Isoquinolines
Authors: Fülöp Ferenc , Tari János , Bernáth Gábor , Sohár Pál , Dancsó András , Argay Gyula , Kálmán Alajos
Published: July 2007

Stereoisomeric (1R*,3R*)‐ and (1R*,3S*)‐6,7‐dimethoxy‐3‐methyl‐1,2,3,4‐tetrahydroisoquinoline‐1‐acetamides 5–8 react with formaldehyde or benzaldehyde to furnish stereoisomeric pyrimido[6,1‐a]isoquinolin‐2‐ones 9–18. The relative configurations and the predominant conformations of the products have been determined by NMR spectroscopy, and for (4S*,6R*,11bR*)‐9,10‐dimethoxy‐6‐methyl‐4‐phenyl‐1,3,4,6,7,11b‐hexahydropyrimido[6,1a]isoquinolin‐2‐one (11) by X‐ray diffraction.
Enantiopure Derivatives of 1,1,2‐Triphenylethane‐1,2‐diol by Unusual Ring Opening of Its Cyclic Sulfite
Authors: Fleischer Ralf , Galle Dietmar , Braun Manfred
Published: July 2007

The reaction of triphenylglycol (S)‐1with thionyl chloride leads to the cyclic sulfites2aand2bin a ratio of 90:10. When the mixture of diastereomers2a/bis treated with alcohols3or diols6, enantiomerically pure ethers5and7are obtained by an unexpected SN1‐type ring cleavage. Enantiopure triphenyloxirane (R)‐10arises under inversion of configuration upon treatment of2a/bwith sodium azide. The configuration of the major diastereomer2ais determined by NMR spectroscopy and by conversion into the sulfoxide (S)‐15.
Regulosides A–C: Glycosphingolipids from the Starfish Pentaceraster regulus
Authors: Venkannababu Uddagiri , Bhandari Shanker Pratap Singh , Garg Hari Shanker
Published: July 2007

The glycosphingolipid (GSL) composition of the starfish Pentaceraster regulus has been studied. The structure of the major component, a new cerebroside named Reguloside A (1) and two minor homologues, Regulosides B (1a) and C (1b), are described.
Evolution of the Concept of Synthesis Strategy in the COSYMA System: Introduction of the Synthesis Invariant
Authors: Ellermann Luc , Jauffret Philippe , Ostermann Claude , Kaufmann Gérard
Published: July 2007

COSYMA is a program for the computer‐assisted design of organic synthesis; its aim is to propose strategies for the synthesis of given compounds. These strategies are automatically learnt from global syntheses described in the literature, and adapted to the specifics of the target molecule. This paper describes an evolution of the formalization of synthesis strategy by taking into account untouched fragments, and the resulting improvement of the COSYMA program.
N,O Highly Regio‐ and Stereoselective Alkylation of Nucleophilic Glycine Equivalents with Carbonates of Allylic α‐Hydroxyphosphonates: A Convenient Route to Racemic 2‐Amino‐5‐phosphono‐4‐pentenoic Acids
Authors: Öhler Elisabeth , Kanzler Silvia
Published: July 2007

Palladium(0)‐catalyzed allylic alkylation of diethyl (acetyl‐amino)malonate (6), ethyl (diphenylmethyleneamino)acetate (7), and (diphenylmethyleneamino)acetonitrile (8), respectively, with the acrolein‐derived 1‐dialkoxyphosphinyl‐substituted carbonates 5 provides the γ‐substituted vinylphosphonates 9–11 in very good yields and with high regioselectivity. The stereochemical outcome is dependent on the mode of nucleophilic activation of the glycine equivalents 6–8: When the reactions are performed in the presence of N,O‐bis(trimethylsilyl)acetamide (BSA) the (Z) isomers (Z)‐9–(Z)‐11 are highly favoured, while in the absence of any additional activation of the nucleophiles the corresponding (E) isomers predominate. In the latter case, upon alkylation of the Schiff base derivatives 7 and 8, up to 30% of the α‐substitution products 12 and 13, respectively, are isolated as by‐products. The vinylphosphonates 9–11 are easily converted to the racemic 2‐amino‐5‐phosphono‐4‐pentenoic acids (Z)‐3 and (E)‐3, and to the saturated analogue 1.
Preparation and Structures of Cyclotetradeca‐4,11‐diynone, Cyclotetradeca‐4,11‐diyne‐1,8‐dione, Their Exomethylene Derivatives, and 1,8‐Dioxacyclotetradeca‐4,11‐diyne
Authors: Gleiter Rolf , Ramming Matthias , Weigl Hagen , Wolfart Volker , Irngartinger Hermann , Oeser Thomas
Published: July 2007

The following 14‐membered ring diynes have been synthesized: cyclotetradeca‐4,11‐diynone (4), cyclotetradeca‐4,11‐diyne‐1,8‐dione (6), the corresponding exomethylene derivatives 5 and 7, as well as 1,8‐dioxacyclotetradeca‐4,11‐diyne (8). The synthesis of the diketal of 4 was achieved by the reaction of the ethylene ketal of 1,5‐dibromopentan‐3‐one (9) with the dilithium salt of 1,8‐nonadiyne. Similarly, the diketal of 6 was prepared from the dilithium salt of the ethylene ketal of 1,8‐nonadiyn‐5‐one 11 with 9. The unprotected ketones 4 and 6 were obtained by treating the ketals 10 and 14, respectively, with HCl. The ketones 4 and 6 were transformed to the exomethylene derivatives by a Wittig reaction. The reaction of the dilithium salt of 5‐oxanona‐1,8‐diyne (16a) with 1,5‐dibromo‐3‐oxapentane (15) yielded 8. X‐ray investigations of single crystals of 6 and 8 revealed chair conformations with a zig–zag arrangement, employing two anti orientations of the two chains between the triple bonds. A zig–zag arrangement of the chain containing the carbonyl group was also found in 4. In 3b and 7 Ci symmetry was found, with only one anti conformation in each chain. Molecule 6 crystallizes with C2h symmetry and 8 with a center of symmetry.
Cycloaddition Reactions of 2H‐Benzo[b]thiete and Thiocarbonyl Compounds
Authors: Meier Herbert , Gröschl Dieter , Beckert Rainer , Weiß Dieter
Published: July 2007

2H‐Benzo[b]thiete (1) reacts in the o‐quinoid form 1′ with the cyclic trithiocarbonates 4 and 6a, b and with the thioketones 8, 10 and 12 in [8π + 2π] cycloaddition reactions to the spiro compounds 5, 7a, b, 9, 11a, b. Irrespective of the presence of CC double bonds, chemoselective and regioselective addition processes at the CS double bonds take place that lead to 4H‐1,3‐benzodithianes.
Total Synthesis of the Tolypothrix Pentaether from Enantiomerically Pure Homoallyl Alcohols by A Butyrolactone → 1,3‐Diol Strategy
Authors: Weigand Stefan , Brückner Reinhard
Published: July 2007

Following the retrosynthetic plan of Scheme 1 the permethyl ether 1 from Tolypothrix conglutinata was synthesized from aldehyde 2 and the hydroxylated butyrolactone 3b. Each of these building blocks was obtained from a homoallyl alcohol, i. e. aldehyde 2 from homoallyl alcohol 5 (Scheme 3; 98.1% ee) and lactone 3b from homoallyl alcohol 30 (Schemes 10, 11; 97.7% ee). These alcohols, in turn, stemmed from the Ti(OEt)4/S‐BINOL‐mediated enantioselective addition of the β‐substituted stannane 7 to hexanal (Scheme 3) and the Ti(OEt)4/R‐BINOL‐mediated enantioselective addition of the β‐substituted stannane 31 to aldehyde 32 (Scheme 10), respectively. After O‐methylation of hydroxy lactone 3b (Scheme 11), the resulting methoxy lactone 38 was condensed with aldehyde 2 by Larson's modification of the Peterson olefination to provide the γ‐alkylidene lactone 39 as a 65:35 mixture of Z/E isomers (Scheme 12). Hydrogenation of this mixture gave the cis‐configured γ‐alkyl lactone 40 (Scheme 12). It was accompanied by no more than 5 mol‐% of its trans isomer; this observation seems to imply the occurrence of butenolide 41 as an intermediate of this reaction. An oxidative degradation of lactone 40 via the Criegee rearrangement of a derived peroxonosylate provided the syn‐diol 42 from where another three steps led to the target ether 1 (Scheme 13).
Studies on the Conformation of Boc‐Protected (S)‐(+)‐Isovaline Homopeptide Methyl Esters in the Solid State and in Solution
Authors: Jaun Bernhard , Tanaka Masakazu , Seiler Paul , Kühnle Florian N. M. , Braun Christine , Seebach Dieter
Published: July 2007

X‐Ray diffraction analyses of the fully protected peptides Boc‐[(S)‐Iva]n‐OMe (n = 3, 4, 6) reveal two independent molecules in the asymmetric unit. The structures of these can be described as β‐turns or 310 helices (depending on the length of the oligopeptide) of alternating screw sense (M and P) in a head to tail alignment. This structure is stabilized by hydrogen bonds between the NH(1) of the (M)‐helix and the OC(ω‐1) of the (P)‐helix and the NH(2) (M) and the ester carbonyl group (P). Low temperature 1H‐NMR spectra of the hexamer in CD2Cl2 solution show two interchanging species in a ratio of 4:1; NOESY experiments prove that these are the two helical conformers found in the crystal (P:M, 4:1). The NOESY spectrum at −90°C indicates the pairing of (P) and (M) helices. Thermodynamic and kinetic parameters for the helix transformation P ⇌ M (unfolding/folding) are presented.
New cis‐Eudesm‐6‐ene Derivatives from Vetiver Oil
Authors: Weyerstahl Peter , Marschall Helga , Splittgerber Ute , Wolf Dietmar
Published: July 2007

The new cis‐eudesma‐6,11‐diene (1) has been isolated from vetiver oil as a main constituent of the sesquiterpene hydrocarbon fraction. Furthermore, six derivatives [13‐nor‐cis‐eudesm‐6‐en‐11‐one (2), cis‐eudesm‐6‐en‐11‐ol (4), cis‐eudesm‐6‐en‐12‐al (5, 2 epimers), 13‐nor‐cis‐eudesm‐6‐en‐8‐one (6), and cis‐eudesma‐6,11‐dien‐3‐ol (8)] have been identified in the oil. Three of these (2, 4, 5) have been prepared for comparison purposes, e.g. via ozonolysis or hydroboration starting from 1.
Synthesis and Metabolism of the myo‐Inositol Pentakisphosphates
Authors: Rudolf Marco T. , Kaiser Thorsten , Guse Andreas H. , Mayr Georg W. , Schultz Carsten
Published: July 2007

All six isomeric myo‐inositol pentakisphosphates (InsP5), consisting of the two meso compounds myo‐inositol 1,3,4,5,6‐pentakisphosphate [Ins(1,3,4,5,6)P5] (18) and myo‐inositol 1,2,3,4,6‐pentakisphosphate [Ins(1,2,3,4,6)P5] (22) and two pairs of enantiomers myo‐inositol 1,2,4,5,6‐pentakisphosphate [Ins(1,2,4,5,6)P5] (15) myo‐inositol 2,3,4,5,6‐pentakisphosphate [Ins(2,3,4,5,6)P5] (ent‐15) and myo‐inositol 1,2,3,5,6‐pentakisphosphate [Ins(1,2,3,5,6)P5] (20) myo‐inositol 1,2,3,4,5‐pentakisphosphate [Ins(1,2,3,4,5)P5] (ent‐20), respectively, were synthesized. These compounds have been found in tissue, and although not resolved as pure enantiomers, their primary metabolism in a cytosolic extract from fetal calf thymus was therefore investigated by analytical HPLC. Four isomers were dephosphorylated to singly defined inositol tetrakisphosphates, while Ins(1,2,4,5,6)P5 was phosphorylated to myo‐inositol hexakisphosphate (InsP6). Interestingly, Ins(2,3,4,5,6)P5 was the only isomer which was not metabolized. These data demonstrate that chemically synthesized, enantiomerically pure inositol pentakisphosphate isomers are valuable tools for the unravelling of the metabolic pathways of InsP5 turnover in living cells.