bluuebunny/crossref_metadata_2025 huggingface dataset:
Stereoselective synthesis of pyrrolo[2,3‐d]pyrimidine α‐ and β‐D‐ribonucleosides from anomerically pure D‐ribofuranosyl chlorides: Solid‐Liquid Phase‐Transfer Glycosylation and 15N‐NMR Spectra
Authors: Rosemeyer Helmut , Seela Frank
Published: December 2004

Solid‐liquid phase‐transfer glycosylation (KOH, tris[2‐(2‐methoxyethoxy)ethye]amine ( = TDA‐1), MeCN) of pyrrolo[2,3‐d]pyrimidines such as 3a and 3b with an equimolar amount of 5‐O‐[(1,1 ‐dimethylethyl)dimethylsilyl]‐2,3‐O‐(1‐methylethylidene)‐α‐D‐ribofuranosyl chloride (1) [6] gave the protected β‐D‐nucleosides 4a and 4b, respectively, stereoselectively (Scheme). The β‐D‐anomer 2 [6] yielded the corresponding α‐D‐nucleosides 5a and 5b with traces of the β‐D‐compounds. The 6‐substituted 7‐deazapurine nucleosides 6a, 7a, and 8 were converted into tubercidin (10) or its α‐D‐anomer (11). Spin‐lattice relaxation measurements of anomeric ribonucleosides revealed that T1 values of HC(8) in the α‐D‐series are significantly increased compared to HC(8) in the β‐D‐series while the opposite is true for T1 of HC(1′). 15N‐NMR data of 6‐substituted 7‐deazapurine D‐ribofuranosides were assigned and compared with those of 2′‐deoxy compounds. Furthermore, it was shown that 7‐deaza‐2′deoxyadenosine ( = 2′‐deoxytubercidin; 12) is protonated at N(1), whereas the protonation site of 7‐deaza‐2′‐deoxyguanosine (20) is N(3).
Facile Synthesis of Carbon Monoxide Isotopically Labelled at Oxygen from Enriched Water without Isotopic Dilution
Authors: Ioset Jacques , Roulet Raymond
Published: December 2004

O‐Labelled carbon monoxide was prepared on the gram scale from enriched water and acetals of norborn‐2‐en‐7‐one(= bicyclo[2.2.1]hept‐2‐en‐7‐one) in almost quantitative yields and without isotopic dilution.
8‐Aza‐7‐deazaadenine N8‐ and N8‐(β‐D‐2′‐Deoxyribofuranosides): Building blocks for automated DNA synthesis and properties of oligodeoxyribonucleotides
Authors: Seela Frank , Kaiser Klaus
Published: December 2004

Oligonucleotides with alternating 8‐aza‐7‐deaza‐2′‐deoxyadenosine (= c7z8Ad2) and dT residues (see 11, 14 and 16) or 4‐aminopyrazolo [3,4‐d] pyrimidine N2‐(β‐D‐2′‐deoxyribofuranoside) (= c7z8A′d1); (3) and dT residues (see 12) have been prepared by solid‐phase synthesis using P(III) chemistry, Additionally, palindromic oligomers derived from d(C‐T‐G‐G‐A‐T‐C‐C‐A‐G) but containing 2 or 3 instead of dA (see 18–22) have been synthesized. Benzoylation of 2 or 3, followed by 4,4′‐dimethoxytritylation and subsequent phosphitylation yielded the methyl or the cyanoethyl phosphoramidites 8a,b and 9. They were employed in automated. DNA synthesis. Alternating oligomers containing 2 or 3 showed increase dTm values compared to those with dA, in particular 12 with an unusual N2‐glycosylic bond. The palindromic oligomers 18‐22 containing 2 or 3 instead of dA outside of the enzymic recognition side reduced the hydrolysis rate, replacement within d(G‐A‐T‐C) abolished phosphodiester hydrolysis.
Photochemical Ring Slippage of Bis(pentafluorophenyl)titanocene: Reaction kinetics and matrix isolation of the primary photoproduct
Authors: Klingert Bernd , Roloff Achim , Urwyler Bernhard , Wirz Jakob
Published: December 2004

Laser flash photolysis and matrix‐isolation techniques were applied to elucidate the photochemistry of the orange complex bis(pentafluorophenyl)titanocene ( = bis(η5‐cyclopentadienyl)bis(pentafluorophenyl)titanium‐ (IV), Cp2TiIV{C6F5}2, Cp = η5‐C5H5, 1) which is used as a polymerization photo‐initiator. The primary photo‐reaction of 1 is the formation of a highly reactive blue isomer X with unit quantum yield. In carefully dried and degassed benzene solution, the photoisomer X rearranges to starting material 1 with a first‐order reaction, k = 5 · 103 s−1 at room temperature. X is highly reactive towards H2O, MeOH, acetone, MeCN, MeNO2, butane‐1,4‐diyl diacrylate, 2,2,6,6‐tetramethylpiperidine N‐oxide, CO, O2, and N2; absolute bimolecular rate constants range from 106 to 109 M−1 · s−1. The primary photoisomerization 1→X is tentatively ascribed to a cyclopentadienyl ring slippage from η5 to a lower hapticity, a process that opens up coordinative unsaturation.
Strained Ketenes from α‐Bromoacyl Phosphates. (Tricyclo[4.4.1.01,6]undeca‐3,8‐dien‐11‐ylidene)methanone and its Heptacyclic Dimer: a Dispirobridged Dipropellane (1,1″,4,4″,5,5″,8,8″‐Octahydrodispiro[[4a, 8a]methanonaphthalene‐9,1′‐cyClobutane‐3′,9″‐[4a, 8a]methanonaphthalene]‐2′, 4′‐dione)
Authors: Hoffmann H. Martin R. , Geschwinder Peter M. , Hollwege Hans‐Peter , Walenta Angela
Published: December 2004

Dehalogenation of the mixed anhydride 6 of 11‐bromotricyclo[4.4.1.01,6] undeca‐3,8‐diene‐11‐carboxylic acid (4) and of diethyl hydrogen phosphate with Zn‐Ag couple in THF gave the dispiro‐fused dipropellane 8(1,1″,4,4″,5,5″,8,8″‐octahydrodispiro[[4a, 8a]methanonaphthalene‐9,1′‐cyclobutane‐3′,9″‐[4a, 8a]methanonaphthalene]‐2′,4′‐dione) in 58% yield. Unlike other dispiro[2.1.2.1]octane‐4, 8‐diones (see 2a‐e), the new cyclodimer 8 is an O2‐sensitive compound. The 11‐bromobicyclo[4.4.1] undeca‐1,3,5,7,9‐pentaene‐11‐carboxylic acid (13) was prepared and converted into the acyl phosphate 14, which in turn was reduced with Zn‐Ag couple in THF/MeOD to give the deuterated ester 16. Other cyclopropylidenemethanones could be generated and dimerized advantageously by the Zn‐induced reduction of the mixed anhydride of the 1‐bromocyclopropanecarboxylic acid and diethyl hydrogen phosphonate.
Steric Crowding in Coordination Compounds: Electron‐transfer kinetics of the [Co(tmen)3]3+/2+ couple (tmen = 2,3‐dimethylbutane‐2,3‐diamine)
Authors: Hendry Philip , Ludi Andreas
Published: December 2004

The [Co(tmen)3]3+ complex ion (tmen = 2,3‐dimethylbutane‐2,3‐diamine) has been synthesized and its redox characteristics compared to those of its parent ion [Co(en)3]3+. The 12 peripheral Me groups significantly affect the properties of the [Co(tmen)3]3+ ion. The ligand‐field bands are shifted to lower energies by about 1700 cm−1 compared to [Co(en)3]3+. The reduction potential for [Co(tmen)3]3+ is +0.28 V (vs. NHE) compared to −0.18 V for [Co(en)3]3+. The rate of the self‐exchange reaction for the [Co(tmen)3]3+/2+ couple, k = 8.5 × 10−8 M−1·S−1 was determined by applying the Marcus cross‐relation with the reductants Cr2+, V2+, Eu2+, Ru2+, and [Co(sepulchrate)]2+.
Lithiated Azafulvenes by Halogen/Metal Interchange of Brominated 6‐(Diisopropylamino)‐1‐azafulvene Derivatives. Novel synthesis of 5‐mono‐ and 4,5‐disubstituted 1H‐pyrrole‐2‐carbaldehydes
Authors: Bray Brian L. , Hess Petr , Muchowski Joseph M. , Scheller Markus E.
Published: December 2004

The first known lithiated 1‐azafulvene derivatives were generated by low‐temperature halogen/metal interchange, with t‐BuLi, from the corresponding brominated 6‐diisopropylamino compounds 3b and 12. These Li species reacted with sundry eletrophilic reagents to give products which, on basic hydrolysis, were converted into 5‐mono‐ or 4,5‐disubstituted pyrrole‐2‐carbaldehydes 10 and 16, respectively.
Metal Complexes with Macrocyclic Ligands. Part XXVII. Cu2+‐promoted hydrolysis of carboxylic‐ and phosphonic‐acid esters in the side chain of tetraazamacrocycles
Authors: Tschudin Daniel , Riesen Andreas , Kaden Thomas A.
Published: December 2004

The X‐ray structures of the Cu2+ complexes of 1,4,8,11‐tetraazacyclotetradecane derivatives with an ethylpro‐pionate and diethylphosphonate group, 5 and 6, respectively, indicate that the metal ion is pentacoordinated by the four N‐atoms of the macrocycle and one O‐atom. In the case of 5, it is the carbonyl O‐atom of the carboxylate group, whereas for 6 it is the phosphonyl O‐atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu2+ complexes with the 1,4,8,11‐tetraazacyclotetradecanes 3–6 have been measured by pH‐stat and stopped‐flow techniques. The rate law for the hydrolysis of the carboxylates 3–5 is proportional to the complex concentration and to [OH−] up to pH 13, whereas that of the phosphonate 6 is proportional to [OH−] up to pH 11.5, becoming independent of [OH−] at pH > 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra‐ or an intermolecular OH− attack and the results of the X‐ray structure analyses.
New Spermine Alkaloids from Aphelandra tetragona (VAHL) NEES
Authors: Tawil Bassem F. , Zhu Ji‐Ping , Piantini Umberto , Hesse Manfred
Published: December 2004

18‐O‐Methylchaenorpine (1a) and iso‐18‐O‐methylchaenorpine (1b) two novel stereoisomeric spermine alkaloids were isolated from the roots of Aphelandra tetragona (VAHL) NEES. Their structures were established by chemical and spectroscopic studies.
Neue Zugänge zu einigen aromatischen Retinoiden
Authors: Soukup Milan , Broger Emil , Widmer Erich
Published: December 2004

New Approaches to Some Aromatic Retinoids

Starting from 2,3,5‐trimethylphenol (2), two pathways to ethyl (all‐E)‐9‐(4‐methoxy‐2,3,6‐trimethylphenyl)‐3,7‐dimethylnona‐2,4,6,8‐tetraenoate (1) and to some of its (Z)‐isomers have been developed. The first one is based on a Pd(O)‐catalyzed arylation of (Z)‐3‐methylpent‐2‐en‐4‐yn‐l‐ol (6) with 4‐bromo‐2,3,5‐trimethylanisol (5). The acetylenic C15−alcohol 9 was transformed into the corresponding acetylenic phosphonium salt 10, which was catalytically hydrogenated to the olefinic Wittig salt. Wittig olefination led, then, to the (6Z, 8Z)‐ and (4Z, 6Z, 8Z)‐isomers, 7 and 8, respectively. In a second approach, Friedel‐Crafts reaction of 3‐methylpent‐l‐en‐4‐yn‐3‐ol with the 2,3,5‐trimethylanisol gave a C15‐intermediate with a terminal CC bond in the side chain. After deprotonation and reaction with a C5 aldehyd, the corresponding C20‐intermediate could be isolated in high yield. Finally, further conversion led predominantly to the (all‐E)‐retinoid, accompanied by its (9Z)‐ and (13Z)‐isomers.
Elektrochemische Decarboxylierung von L.‐Threonin‐ und Oligopeptid‐Derivaten unter Bildung von N‐Acyl‐N, O‐acetalen: Herstellung von Oligopeptiden mit Carboxamid‐oder Phosphonat‐C‐Terminus
Authors: Seebach Dieter , Charczuk Roland , Gerber Christian , Renaud Philippe , Berner Heinz , Schneider Helmut
Published: December 2004

Electrochemical Decarboxylation of L‐Threonine and Oligopeptide Derivatives with Formation of N‐Acyl‐N, O‐acetals: Preparation of Oligopeptides with Amide or Phophonate C‐Terminus

Derivatives of α‐amino acids with two stereogenic centers (cf. L‐threonine) and of di‐, tri‐, and tetrapeptides are electrolyzed in MeOH or AcOH, with formation of N‐acyl‐N, O‐acetals (1b–15b, 20b), in an anodic oxidative substitution of the COOH by an OR group. The amine ends of the oligopeptides may be benzyloxycarbonyl(Z)‐ or (tert‐butoxy)carbonyl(Boc)‐protected. With unprotected dipeptides, an electrolytic decarboxylative cyclization to imidazolidinones (18c, 19c) may also occur (in H2O/NH4OAc). The electrolyses are carried out in simple flasks with cooling jackets (‘undivided cell’), using constant current conditions and anodes of Pt or glassy C. The electrolyte is generated in situ by adding 10–20 mol‐% of a tertiary amine. Mild acidic hydrolysis of electrolysis products thus obtained may lead to amino‐acid amides or peptide amides (10c, 11c, 12c, 17c) with one amino acid less than the starting material. The N, O‐acetals from L‐threonine and the oligopeptides also react with organometallic nucleophiles such as Grignard compounds (→21–26, 29), with formation of products in which the original COOH group has been replaced by alkyl or allyl (sometimes even with moderate stereoselectivity). By treatment of the peptide‐derived (open‐chain) N, O‐acetals with trialkyl or triaryl phosphites/TiCl4 the RO group is replaced by a phosphodiester group in a (non‐diastereoselective) Michaelis‐Arbuzov‐type reaction (1d, 1e, 2d–9d, 5e). Thus, the two‐step sequence of electrolysis and phosphonation converts an oligopeptide derivative to an analogue with a phosphonic‐acid end group. The diastereoisomeric N‐protected dimethyl and diethyl dipeptidephosphonates (also prepared from the corresponding diaryl esters by Ti(OR)4‐mediated transesterification) could be separated by preparative HPLC (SiO2, Lichrosorb Si 60, 10 μm); the dextrorotatory isomers of 1d–3d were assigned L, D‐, the laevoratory ones L, L‐configuration by hydrolysis to and identification of the known amino and aminophosphonic acids. The results described demonstrate a new simple route leading, from a given oligopeptide, to pure peptide analogues of known configuration.
New Hyperforin Derivatives from Hypericum revolutum VAHL with Growth‐Inhibitory Activity against a Human Colon Carcinoma Cell Line
Authors: Decosterd Laurent A. , Stoeckli‐Evans Helen , Chapuis Jean‐Charles , Msonthi Jerome D. , Sordat Bernard , Hostettmann Kurt
Published: December 2004

The crude petroleum‐ether extract of the root bark of Hypericum revolutum VAHL (Guttiferae) exhibited in vitro growth‐inhibitory activity against the Co‐115 human colon carcinoma cell line. Activity‐guided fractionation of this extract resulted in the isolation of two new hyperforin derivatives 1 and 2. The structure of 1 (hyperevolutin A) was established by X‐ray analysis as the 4‐hydroxy‐8‐exo‐methyl‐5,7‐exo‐bis(3‐methylbut‐2‐enyl)‐1‐(2‐methyl‐1‐oxopropyl)‐8‐endo‐(4‐methylpent‐3‐enyl)bicyclo[3.3.1]non‐3‐ene‐2,9‐dione. The structure of the homologue 2 was deduced by comparison of its UV and 1H‐ and 13C‐NMR spectra with those of 1.
Conformational Analysis of Didemnins. A multidisciplinary approach by means of X‐Ray, NMR, molecular‐dynamics, and molecular‐mechanics techniques
Authors: Kessler Horst , Will Martin , Antel Jochen , Beck Holger , Sheldrick George M.
Published: December 2004

We present the application of several homo‐ and heteronuclear 1D‐ and 2D‐NMR techniques to assign the 1H‐NMR chemical shifts of the dominant conformation of didemnin B (2; three different conformations in (D6)DMSO solution in the ratio 8:1:1) and its conformational analysis, as well as the solution conformation of didemnin A (1). The conformations were refined by restrained molecular‐dynamics calculations using the GROMOS program and by MOMO, a novel personal‐computer‐based interactive molecular‐graphics and molecular‐mechanics package, using experimental distances (via a H…H pseudo potential function) as restraints. The solution structures of 1 and 2 obtained by GROMOS and MOMO calculations were compared with each other and related to the recently solved crystal structure of 2. Focusing on the main conformer, the two kinds of the distance‐restrained conformational calculations for 2 yielded a ‘solution structure’ close to the crystal structure. Almost all of the 40 restrained H…H distances coincided (within the estimated standard deviations) with those observed in the crystal structure. One more hydrogen bond was detected in solution involving the lactoyl OH group (disordered in the crystal structure) and the dimethyltyrosine (Me2Tyr5) carbonyl O‐atom. The macrocyclic ring system in the modeled solution structure of 1 exhibited a topology close to those of the solution and crystal structures of 2. The main difference between 1 and 2 could be traced back to a significant change in the Ψ angle of the N‐methyl‐D‐leucine (MeLeu7) residue. In 1, the N‐methyl moiety of MeLeu7 points inward within the macrocyclic ring toward the 1st and Hip region. We also tested the suitability of structures obtained from NMR data as ‘search fragments’ in the ‘Patterson search approach’ of crystal‐structure analysis. It proved possible to resolve the crystal structure of 2 a posteriori with the Patterson search program PATSEE, in this way.
β‐Cleavage of Potassium Bicyclo[2.2.2]oct‐5‐en‐2‐olates. Stereoselective synthesis of (±)‐trichodiene
Authors: Snowden Roger L. , Brauchli Robert , Sonnay Philippe
Published: December 2004

The transformations of 12 bicyclo[2.2.2]oct‐5‐en‐2‐ols (V or VI) to 3‐(cyclohex‐3‐enyl)‐2‐alkanones (III or IV), via β‐cleavage of their potassium alkoxides in HMPA, has been investigated (cf. Table 1). As an illustration of this synthetic methodology, a stereoselective synthesis of (±)‐trichodiene ((±)‐1) is described which involves the β‐cleavage of the tricyclic potassium alkoxides 46a and 47a to cyclopentanone 4 (cf. Scheme 7).
Mono‐ and Dialkylation of Derivatives of (1R, 2S)‐2‐Hydroxycyclopentanecarboxylic Acid and ‐cyclohexanecarboxylic acidviabicyclic dioxanones: Selective generation of three contiguous stereogenic centers on a cyclohexane ring
Authors: Herradón Bernardo , Seebach Dieter
Published: December 2004

Ethyl (1R, 2S)‐2‐hydroxycyclopentanecarboxylate and ‐cyclohexanecarboxylate (1aand2a, respectively) obtained in 40 and 70% yield by reduction of 3‐oxocyclopentanecarboxylate and cyclohexanecarboxylate, respectively (Scheme 2), with non‐fermenting yeast, are converted to bicyclic dioxanone derivatives3and4with formaldehyde, isobutyraldehyde, and pivalaldehyde (Scheme 3). The Li‐enolates of these dioxanones are alkylated (→5a–5i,5j,6a–6g), hydroxyalkylated (→51, m, 6d, e), acylated (→5k, 6c) and phenylselenenylated (→7–9) with usually high yields and excellent diastereoselectivities (Scheme 3, Tables and 2). All the major isomers formed under kinetic control are shown to havecis‐fused bicyclic structures. Oxidation of the seleno compounds 7–9 leads to α, β‐unsaturated carbonyl derivatives10–13(Scheme 3) of which the products12a–cwith the CC bond in the carbocyclic ring (exocyclic on the dioxanone ring) are most readily isolated (70–80% from the saturated precursors).Michaeladdition of Cu(I)‐containing reagents to12a–cand subsequent alkylations afford dioxanones14a–iand16a–dwithtrans‐fused cyclohoxane ring (Scheme 4). All enolate alkylations are carried out in the presence of the cyclic urea DMPU as a cosolvent. The configuration of the products is established by NMR measurements and chemical correlation. Some of the products are converted to single isomers of monocyclic hydroxycyclopentane (17–19) and cyclohexane derivatives (20–23;Scheme 5). Possible uses of the described reactions for EPC synthesis are outlined. The observed steric course of the reactions is discussed and compared with that of analogous transformations of monocyclic and acyclic derivatives.
Synthesis of 11‐Oxaestrogens via Dye‐Sensitized Photo‐oxygenation of a 9,11‐Didehydroestrone Derivative
Authors: Planas Antoni , Sala Nuria , Bonet Juan‐Julio
Published: December 2004

The 3‐methoxy‐1 1‐oxaestrone (13) has been synthetized from estrone (3) following an approach that involves the ring‐C fragmentation of the estrogenic skeleton by dye‐sensitized photo‐oxygenation of the properly C(17)‐protected 9,11‐didehydroestrone derivative 6 as the key step. The C(13)‐side‐chain degradation of the 9‐oxo‐9,11‐seco‐aldehyde 7 followed by reduction to the 9β, 12‐diol 10 and further cyclization yields the 11‐oxaestrogenic skeleton. By this procedure, 13 is obtained in 9 steps from 3 with a non‐optimized overall yield of ca. 15%.
Notiz über mikrobiologische Umsetzungen mit Halobacterium halobium: Reduktion von 3‐Oxobutansäure‐ethylester und Hydrolyse von 3‐Hydroxybutansäure‐ethylester. Cooperative Effekte von Reduktase und Hydrolase
Authors: Ehrler Jürg , Seebach Dieter
Published: December 2004

Note on Biotransformations with Halobacterium halobium: Reduction of Ethyl 3‐Oxobutanoate and Hydrolysis of Ethyl 3‐Hydroxybutanoate. Cooperative Effects of Reductase and Hydrolase

The archaebacterium Halobacterium halobium, growing in saturated NaCl solution, is tested for its ability to achieve biotransformations. We found that this microorganism does accept only a small variety of compounds as substrates. Ethyl acetoacetate (1) is reduced to ethyl (S)‐3‐hydroxybutanoate (2) of optical purity of 40–76%, but in low chemical yields. The reduction is accompanied by hydrolysis of the hydroxy‐ester to 3‐hydroxybutanoic acid (3). Hydrolysis of rac‐ester 2 by Halobacterium halobium gives (R)‐2 of optical purity of up to 88%, depending upon reaction time, together with the almost racemic hydroxy‐acid 3, both in low chemical yields. Hopes that the ‘extremist’ Halobacterium halobium would be able to effect unique conversions were not fulfilled.
Radikalische Cyclisierungen von Alkenyl‐substituierten 4,5‐Dihydro‐1,3‐thiazol‐5‐thiolen
Authors: Jenny Christjohannes , Wipf Peter , Heimgartner Heinz
Published: December 2004

Radical Cyclizations of Alkenyl‐Substituted 4,5‐Dihydro‐1,3‐thiazole‐5‐thiols

Heating of 5‐alkenyl‐ or 5‐alkinyl‐4,5‐dihydro‐1,3‐thiazole‐5‐thiols of type 5 in the presence of a radical initiator gave dithiaspirobicycles in fair‐to‐excellent yield (Scheme 3). Under analogous conditions, the 4,5‐dihydro‐4‐vinyl‐1,3‐thiazole‐5‐thiol 5d underwent a cyclization to give the annellated dithiabicycle 7 (Scheme 4). In this reaction, a minor product 8 was formed by an unknown reaction mechanism. The structure of 8 was established by X‐ray crystallography. The starting 1,3‐thiazole‐5‐thiols 5 have been synthesized by carbophilic alkylation of me CS group of 1,3‐thiazole‐5(4H)‐thiones with Grignard‐reagents or alkylcuprates. The thiazolethiones were obtained by the reaction of 3‐amino‐2H‐azirines with thiobenzoic acid followed by sulfurization and cyclization. The 4‐benzyl derivative 1b was thermally rearranged via 1,3‐benzyl migration to yield the benzyl (1,3‐thiazol‐5‐yl) sulfide 11 (Scheme 5).
Einelektronen‐Redoxreaktionen von 4‐(1‐Pyridinio)phenolat‐Betain: ESR/ENDOR‐Charakterisierung seiner Radikalionen und ‘Batterie‐Effekt’
Authors: Bock Hans , Herrmann Hans‐Friedrich
Published: December 2004

One‐Electron Redox Reactions of 4‐(1‐Pyridinio)phenolate Betaine: ESR/ENDOR Characterization of its Radical Ions and ‘Battery Effect’

Blue zwitterionic 2,6‐Di(tert‐butyl)‐4‐(2,4,6‐triphenyl‐1‐pyridinio)phenolate 1a can be reduced to its blue‐green radical anion \documentclass{article}\pagestyle{empty}\begin{document}${\bf 1}^{- \atop \dot{}}$\end{document} using alkaline metals, and oxidized to its colorless radical cation 1 by Ag(OOCCF3) or electrochemically. ESR/ENDOR spectra of their aprotic THF solutions indicate predominant spin population either in the pyridinium (\documentclass{article}\pagestyle{empty}\begin{document}${\bf 1a}^{- \atop \dot{}}$\end{document}) or in the phenolate ring (\documentclass{article}\pagestyle{empty}\begin{document}${\bf 1a}^{+ \atop \dot{}}$\end{document}). Reduction with other alkaline metals Li, Na, or Cs yields no changes in the ESR/ENDOR signal patterns, i.e. provides no indication of radical ion pair formation. The cyclovoltammetrically determined first reduction and oxidation potentials at −1.11 V and +0.26 V, respectively, are both reversible and, in principle, allow to construct a molecular battery.
Cascade Reactions. A Simple One‐pot Synthesis of the Mitomycin Skeleton
Authors: Defoin Albert , Geffroy Guillaume , Le Nouen Didier , Spileers Didier , Streith Jacques
Published: December 2004

Nitroso‐arene dienophiles 1 react regiospecifically with the conjugated dienals 2 and 3a/3b, and lead thereby to the unstable Diels‐Alder cycloadducts 4 and 5. These undergo two types of cascade reactions which give pyridinium betaines 6 and pyrrolo‐indoles 8 as the major reaction products. The one‐pot syntheses of pyrroloindoles 8 represent a new and easy access to the basic skeleton of mitomycins 10. The scope and limitations of the cascade reactions were investigated.
A Novel Allenic Epoxycyclohexane and Related Compounds from Eutypa lata (Pers: F.) Tul
Authors: Renaud Jean‐Marc , Tsoupras Georges , Stoeckli‐Evans Helen , Tabacchi Raffaele
Published: December 2004

The novel allenic epoxycyclohexanes 1, and related compounds 2 and 3 have been isolated from the culture medium of Eutypa lata. Their structures were established by combination of spectroscopic and chemical techniques. Biogenetic origin and biological activity of these compounds are also discussed.
Ethylene Biosynthesis part 10. Synthesis and study of racemic, (1R, 2S)‐, and (1S, 2R)‐1‐Amino‐2‐(hydroxymethyl)cyclopropanecarboxylic Acid
Authors: Pirrung Michael C. , Dunlap Steven E. , Trinks Uwe P.
Published: December 2004

The preparation of optically active 1‐amino‐2‐(hydroxymethyl)cyclopropanecarboxylic acid has been achieved by a route involving cycloalkylation of dimethyl malonate with epichlorohydrin and subsequent Hofmann rearrangement. The reaction of epichlorohydrin with nucleophiles may occur al either electrophilic site, epoxide or halide. Based on the absolute configuration of the starting materials and the lactones obtained, it has been shown that the initial step of the cycloalkylation occurs at the epoxide moiety. The 1‐amino‐2‐(hydroxymethyl)‐cyclopropanecarboxylic acid, an analogue of the precursor to the plant growth hormone ethylene, is to be used in affinity purification techniques and in generation of antibodies.
Solid‐phase Synthesis of C‐Terminal Peptide Amino Alcohols
Authors: Neugebauer Witold , Escher Emanuel
Published: December 2004

The solid‐phase syntheses of enkephalin and somatostatin analogues with C‐terminal OH functions instead of the normal carboxylates are described. The OH function of the N‐terminal amino alcohol was acylated with succinic acid and esterified to the solid support. Normal Boc‐TFA solid‐phase strategy can be applied to build up and cleave these peptides. The succinic ‘handle’ can be removed by mild basic hydrolysis after cleavage.
Rearrangements of Radical Cations of [2.2]Paracyclophanes and of a bridged [14]annulene to those of pyrenes: An ESR and ENDOR study
Authors: Gerson Fabian , Huber Walter , Wellauer Thomas
Published: December 2004

ESR and ENDOR studies have been carried out on the radical cations obtained consecutively by reaction of trans‐10b, 10c‐dimethyl‐10b, 10c‐dihydropyrene (4) with AlCl3 in CH2C12. The primarily formed \documentclass{article}\pagestyle{empty}\begin{document}${\bf 4}^{+ \atop \dot{}}$\end{document} rearranges at 253 K to the radical cation(s) of 1,6‐ (5a) and/or 1,8‐dimethylpyrene (5b). At 323 K, the spectra of \documentclass{article}\pagestyle{empty}\begin{document}${\bf 5a}^{+ \atop \dot{}}$\end{document}/\documentclass{article}\pagestyle{empty}\begin{document}${\bf 5b}^{+ \atop \dot{}}$\end{document} are replaced by that of the highly persistent radical cation of 1,3,6,8‐tetramethylpyrene (6). Surprisingly, \documentclass{article}\pagestyle{empty}\begin{document}${\bf 6}^{+ \atop \dot{}}$\end{document} is also the only observable paramagnetic product resulting from a treatment of 4,5,7,8‐ (1), 4,7,13,16‐ (2), and 4,5,12,13‐tetramethyl[2.2]paracyclophane (3) with AlCl3 in CH2Cl2 at 353 K. The structures of the intermediates in the rearrangement [\documentclass{article}\pagestyle{empty}\begin{document}${\bf 1}^{+ \atop \dot{}}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}${\bf 2}^{+ \atop \dot{}}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}${\bf 3}^{+ \atop \dot{}}$\end{document}] → \documentclass{article}\pagestyle{empty}\begin{document}${\bf 6}^{+ \atop \dot{}}$\end{document} are discussed.
New chromonocoumarin (=6H, 7H‐[1]Benzopyrano[4,3‐b][1]benzopyran‐6,7‐dione) derivatives from Polygala fruticosa BERG
Authors: Di Paolo Ermindo R. , Hamburger Matthias O. , Stoeckli‐Evans Helen , Rogers Colin , Hostettmann Kurt
Published: December 2004

Three chromonocoumarins ( =6H, 7H‐[1]benzopyrano[4,3‐b][1]benzopyran‐6,7‐diones) 1–3 have been isolated from the leaves and the root bark of polygala fruticosa BERG. (syn. Polygala oppositifolia L.; Polygalaceae). The structure of frutinone A (1) was established by X‐ray diffraction analysis. The structures of the previously undescribed compounds frutinone B (2) and C (3) were deduced by spectroscopic methods (EI‐MS, UV, IR, 1H‐and 13C‐NMR, including NOE and COSY) in comparison with 1. Chromonocoumarins 1–3 are the first representatives of a new type of naturally occurring compounds. Frutinone A shows strong fungicidal activity against Cladosporium cucumerinum.
Dihydropentalene und 6‐Vinylfulvene aus cyclopentadienylcyclopropenen. Notiz zur Umsetzung von 1,2,3‐Tris[(tert‐butyl)thio]cyclopropenylium‐tetrafluoroborat mit cyclopentadienid
Authors: Gugisberg Dominik , Bigler Peter , Neuensehwander Markus , Engel Peter
Published: December 2004

Dihydropentalenes and 6‐Vinylfulvenes from Cyclopentadienyl‐cyctopropenes. Reaction of 1,2,3‐Tris[(tert‐butyl)thio]cyclopropenylium Tetrafluoroborate with Cyclopentadienide.

Reaction of 1,2,3‐tris[(tert‐butyl)thio]cyclopropenylium tetrafluoroborate (6a) with sodium Cyclopentadienide gives, besides of 7,8‐bis{(tert‐buty)thio calicene (7a), rearranged products 7,8,8‐tris[(tert‐butyl)thio]‐6‐vinylpentafulvene (9a) and 4,5.6‐tris[(tert‐butyl}thio]‐1,2‐dihydropentalene (10a)) in varying amounts depending on reaction conditions. Vinyl‐carbenes 12 and 13 are supposed to be possible intermediates.
Synthesis of Naphtho[2,3‐b]pyrandiones: (−)‐Cryptosporin
Authors: Brade Walter , Vasella Andrea
Published: December 2004

A new method for the synthesis of naphtho[2,3‐b]pyrandiones from sulfonyllactones and 1‐nitroglycals is presented. Thus, the sulfonyllactone 6 reacted with the 1‐nitroglycal 7 in the presence of LDA at room temperature to give the naphthopyrandione 9 in high yields (Scheme 1). Reaction at a lower temperature led to the (intermediate) Michael‐addition products 8. The sulfonyllactone 4 and the 1‐nitroglycal 5 were prepared for the synthesis of the naphthopyrandione 18 (Scheme 2). The base‐promoted condensation of 4 and 5 gave 17, which was deprotected to give 18, the enantiomer of the fungal metabolite (+)‐cryptosporin 1.
Interconversion of (η3‐Allyl)(η4‐conjugated‐diene)(η5‐cyclopentadienyl)zirconium and ‐hafnium Stereoisomers. Evidence for the simultaneous rearrangement of diene and allyl ligands
Authors: Sontag Christoph , Berke Heinz , Sarter Christian , Erker Gerhard
Published: December 2004

Reaction of (η3‐allyl)(cyclopentadienyl)zirconium(4+) chloride with (2,3‐dimethylbutadiene)magnesium or (2‐phenylbutadiene)magnesium gave the (η3‐allyl)(η4‐conjugated diene)(cyclopcntadienyl)zirconium complexes 3c and 3d, respectively. The analogous reaction between (η/3‐allyl)(cyclopentadienyl)hafnium(4+) chloride with (buta‐diene)magnesium afforded (η3‐allyl)(η4‐butadiene)(η5‐cyclopentadienyl)hafnium 3e. Photolysis of the complexes 3 produced their stereoisomers 4. The open‐chain π ligands in 3 open themselves towards the apical Cp ligand, in 4 they both are turned around by 180°. The Gibbs activation energy of the 4→3 rearrangement of the Hf complex does not deviate significantly from those of the Zr‐containing systems (4c→3e: ΔG≠ rearr. (−10°) = 81.3 ± 1.3 kJ/mol; 4d→3d: ΔG≠ (‐10°) = 85.7 ± 1.3 kJ/mol; 4e→3e: ΔG≠ (‐5°) = 84.4 ± 1.3 kJ/mol). A modified ex‐tended‐Hückel theory (MEHT) was used in order to simulate the thermally induced rearrangement of the diene ligand in 3/4. The calculations indicate that there should be a combinational interconversion of both the diene and allyl ligand. A diene inversion becomes energetically favoured, if a simultanous allyl rotation occurs. The transition state 9 lies ca. 90 kJ/mol above the optimized geometry of 4a and 115kJ/mol above 3a. Orbital considerations show that a spatially different ‘valence’ orbital of the [Zr(allyl)Cp] fragment 6 in comparison with [ZrCp2]7 causes the conformational preference of the diene ligand in 3a with a higher rearrangement barrier.
A Short, Simple Synthesis of (±)‐Monomorine
Authors: Jefford Charles W. , Tang Qian , Zaslona Alexander
Published: December 2004

Racemic monomorine (12) is prepared in six steps in 26% overall yield from 2‐butyl‐1H‐pyrrole and ethyl (E)‐but‐2‐enoate by exploiting the rhodium(II)‐acetate‐catalyzed decomposition of (4RS)‐4‐(2′‐butyl‐1′ H‐pyrrol‐1′‐yl)‐1‐diazopentan‐2‐one (7).
Tilcotil® Studies. Part 2. [4 + 2] Additions with Isothiazol‐3(2H)‐one 1,1‐Dioxide
Authors: Burri Kaspar F.
Published: December 2004

The isothiazole 1 is not only a dipolarophile but also a reactive and versatile dienophile: especially with oxy‐substituted ‘donor’ 1,3‐butadienes, it readily combines in Diels‐Alder fashion; the regiospecificity of the addition is governed by the carbonyl group of the dienophile, whereas the sulfo group can be ignored for the purpose of predicting regioselectivity. upon dehydrobromination of the [4 + 2] adducts with DBN, the cycloaromatization process is completed, generating saccharin‐like compounds. Besides the parent substance saccharin (14b), several hydroxylated derivatives have been synthesized by this new method; two of them, i.e. 16b and 18c, are of potential interest as non‐nutritive sweetening agents (Scheme 3). In an alternative version of this principle, the isothiazole 22 is reacted with the renowned oxazole 21, affording, after acid‐promoted rearrangement, pyrido‐annelated isothiazoles 25 (Scheme 4). Since both processes generate saccharin‐related structures, they may serve in syntheses of oxicams and analogs of ipsapirone. To demonstrate the viability of the approach, one representative of each series, i.e. 26a and 29, has been converted to an oxicam (7b and 31c, resp.; Scheme 5).
Synthesis and Properties of a 2‐Diazohistidine Derivative: A New Photoactivatable Aromatic Amino‐Acid Analog
Authors: Jaganathen Algen , Ehret‐Sabatier Laurence , Bouchet Marie‐Jeanne , Goeldner Maurice P. , Hirth Christian G.
Published: December 2004

Nα[(tert‐Butoxy)carbonyl]‐2‐diazo‐L‐histidine methyl ester 1 was synthesized starting from the corresponding L‐histidine derivative. The physico‐chemical properties of this new photoactivatable amino‐acid derivative were established. The synthetic precursor of 1, 2‐amino‐L‐histidine derivative 3, was best isolated and characterized as 2‐amino‐Nα‐[(tert‐butoxy)carbonyl]‐Nτ‐tosyl‐L‐histidine methyl ester (4). Selective deprotections of 4 (Nα‐Boc, Nα‐Tos, COOMe) were achieved, thus allowing the use of the corresponding products in peptide synthesis. The optically active dipeptides 8 and 9 were synthesized by coupling 2‐amino‐Nτ‐tosyl‐L‐histidine methyl ester (5) with N‐[(tert‐butoxy)carbonyl]‐L‐alanine and Nα‐[(tert‐butoxy)carbonyl]‐Nτ‐tosyl‐L‐histidine (6) with L‐alanine methyl ester, respectively. The question of selective diazotization of a 2‐aminohistidine residue in a synthetic peptide was studied using competitive diazotizations between 2‐amino‐1H‐imidazole and several amino‐acid derivatives susceptible to undergo nitrosylation. The results show that synthetic photoactivatable peptides incorporating a 2‐diazohistidine residue might become useful photoaffinity probes.
A Novel Nitrone Cycloaddition/Rearrangement
Authors: Toder Bruce H. , Mullen George B. , St. Georgiev Vassil
Published: December 2004

Adamantanone‐derived nitrone 4 and some other keto‐nitrones, when reacted with aromatic and aliphatic aldehydes in refluxing toluene or tetrahydrofuran, formed the corresponding aldonitrones (Z)‐10, the latter arising from the fragmentation of an initially formed 1,4,2‐dioxazolidine 6 to adamantan‐2‐one and an oxaziridine intermediate 11, which then rearranges to (Z)‐10.
A New Catalytic System for the Hydroformylation of Styrene Using Alkene Complexes of Platinum(0)
Authors: Botteghi Carlo , Paganelli Stefano , Matteoli Ugo , Scrivanti Alberto , Ciorciaro Rocco , Venanzi Luigi M.
Published: December 2004

The platinum(0) complexes [Pt(C2H4)(PP)] (PP = 1,2‐bis[(diphenylphosphino)methyl]benzene (2) and (+)‐DIOP = (+)‐1,4‐bis(diphenylphosphino)‐1,4‐dideoxy‐2,3‐O‐isopropyliden‐D‐threitol), when promoted by CH3SO3H, become active catalysts for styrene hydroformylation with total yields of aldehydes ranging from 44 to 67% und selectivities towards 3‐phenylpropanal ranging from 80 to 88%. Smaller amounts of the corresponding alcohols (3–18%) are also obtained with a selectivity towards 3‐phenylpropanol of 94–96%. When DIOP complexes were used, no stereoselectivity for asymmetric hydroformylation was observed.
A Facile Synthesis of Optically Pure (−)‐(S)‐Ipsenol Using a Chiral Titanium Complex
Authors: Oertle Konrad , Beyeler Harry , Duthaler Rudolf O. , Lottenbach Willi , Riediker Martin , Steiner Eginhard
Published: December 2004

A stereocontrolled synthetic route to optically pure (−)‐(S)‐ipsenol (1), the pheromone of Pityokteines curvidens and various other bark‐beetle species is described. Key step of the synthesis is an enantioselective aldol reaction using a chiral titanium–carbohydrate complex (Scheme 1). The carboxylate function of the optically pure β‐hydroxy acid 5 thus obtained in mol quantities is then elaborated to the diene moiety by standard methodology (Scheme 2).
Herstellung von ‘Semialdehyd’‐Derivaten von Asparaginsäure‐ und Glutaminsäure durch Rosenmund‐Reduktion
Authors: Bold Guido , Steiner Heinz , Moesch Luzia , Walliser Bernhard
Published: December 2004

Preparation of ‘Semialdehyde’ Derivatives of Aspartic and Glutamic Acid via the Rosenmund Reduction

Suitably protected aspartic‐acid ‘β‐semialdehyde’ and glutamic‐acid ‘γ‐aldehyde’ derivatives can be obtained, in good yield by Rosenmund reduction of the corresponding acid chlorides. Benzyloxycarbonyl (Z) and (tert‐butoxy)carbonyl (Boc) protecting groups are not affected under these reaction conditions. The sensitive aldehydes, which are obtained in higher purity than by hydride reductions, can directly be used for further transformations like aldol‐type reactions.
A Method for Preparing Oligodeoxynucleotides Containing an Apurinic Site
Authors: Groebke Katrin , Leumann Christian
Published: December 2004

In three steps, 2‐deoxy‐D‐ribose has been converted into a phosphoramidite building block bearing a (t‐Bu)Me2Si protecting group at the OH function of the anomeric centre of the furanose ring. This building block was subsequently incorporated into DNA oligomers of various base sequences using the standard phosphoramidite protocol for automated DNA synthesis. The resulting silyl‐oligomers have been purified by HPLC and selectively desilylated to the corresponding free apurinic DNA sequences. The hexamer d (A‐A‐A‐A‐X‐A) (X representing the apurinic site) which was prepared in this way was characterized by 1H‐ and 31P‐NMR spectroscopy. The other sequences as well as their fragments, which formed upon treatment with alkali base, were analyzed by polyacrylamide gel electrophoresis.
Stereoselectivity of Dienamine [4 + 2] Cycloadditions Synthesis of Functionalised Decalins and Drimanes
Authors: Snowden Roger L. , Brauehli Robert , Wüst Manfred
Published: December 2004

The [4 + 2] cycloaddition stereoselectivity of dienamines 1–4 with dimethyl fumarate and fumaronitrile has been investigated, and functionalised decalins 21–40 have been prepared by elimination of Me2NH from cycloadducts 7–11 and 15–20; in the context of the synthesis of drimane sesquiterpenes, the reduction of dienediesters 29 and 30 is also described.
Enantio‐ and Diastereoselective Aldol‐Reaction of 2,6‐Dimethylphenyl Propionate Using Titanium‐Carbohydrate Complexes
Authors: Duthaler Rudolf O. , Herold Peter , Wyler‐Helfer Susanne , Riediker Martin
Published: December 2004

Chloro(cyclopentadienyl)bis(1,2:5,6‐di‐O‐isopropylidene‐α‐D‐glucofuranos‐3‐O‐yl)titanium (1) is used for the transmetallation of Li‐enolates obtained from propionyl derivatives. While such Ti‐enolates of ketones and hydrazones appear to be unreactive, the (E)enolate13of 2,6‐dimethylphenyl propionate (11) adds to there‐side of aldehydes, affording varioussyn‐aldols14with high dia‐ and enantioselectivity (92–97% ds, 91–97% ee,cf.Scheme 2andTable 1). Racemicsyn‐aldols (±)‐14are obtained analogously from the achiral bis(2‐propyloxy)‐Ti‐enolate15(Scheme 2andTable 2). In contrast to the unstable Li‐enolate10, the Ti‐enolates13and15isomerize at −30°, presumably to the thermodynamically more stable (Z)‐enolates (Scheme 4), While the diastereoselectivity of the achiral enolate15is lost upon this equilibration, the chiral (Z)‐enolate27quite unexpectedly affordsanti‐aldols12of high optical purity (94–98% ec) and, in most cases, with acceptable‐to‐good diastereoselectivity (82–90% ds). Notable exceptions are branched unsaturated and aromatic aldehydes which form a greater proportion of synepimers of moderate optical purity (Scheme 5 and Table 3).Consistent with these findings, re‐facial‐and ami ‐selective aldol‐addition is also exhibited by the (Z)‐configurated Ti‐enolate22ofN‐propionyl‐oxazolidi‐none19(Scheme 3).
Cyclische Phenyl‐carbamate des Miotin‐Typs und ihre Wirkung auf die Acetylcholinesterase
Authors: Amstutz René , Enz Albert , Marzi Martin , Boelsterli Jakob , Walkinshaw Malcolm
Published: December 2004

Cyclic Phenyl Carbamates and Their Action on Acetylcholinesterase

Several six‐, seven‐, and eight‐membered cyclic phenyl carbamates of the miotin type have been synthesised and their in vitro potency as inhibitors of acetylcholinesterase determined. The eight‐membered rings were found to be the most potent and are comparable with physostigrnin or miotin. It was concluded that, for maximum potency, the orientation of the carbamate group relative to the aromatic plane has to be close to orthogonal.
The Syntheses of Purine and Pyrimidine Secoribo‐nucleosides: Acyclo‐uridine Derivative of Cyclophosphamide
Authors: Zakerinia Maryam , Davary Hady , Hakimelahi Gholam H.
Published: December 2004

The synthesis of secoribo‐nucleoside analogues is described. Compounds 4 and 5 possess interesting antiviral effects in vitro. A procedure is also developed for the conversion of acyclo‐uridine nucleoside 7 to a novel derivative of cyclophosphamide 8.
Synthesis of rel‐(3RS,3aSR,7aSR)‐3‐(4‐Chlorophenyl)‐3a,4,5,6,7,7a‐hexahydro‐1‐methylindolin‐6‐one, the Main Metabolite of the Analgesic Ro 15‐8081: A Potent Amine‐Uptake Inhibitor
Authors: Bös Michael , Burkard Willy P. , Moreau Jean‐Luc , Schönholzer Peter
Published: December 2004

The synthesis of the title compound 2 and its diastereoisomer 3 was accomplished using tricarbonyl[1‐5‐n‐(4‐methoxycyclohexa‐2,4‐dien‐1‐yl)]iron tetrafluoroborate (4) as a precursor to the cyclohexanone ring. The assignments of the relative configurations of 2 and 3 are based on the X‐ray analysis of compound 3. Both compounds 2 and 3 are potent inhibitors of neuronal noradrenaline uptake in rats with similar potencies in vitro as compared to amitriptyline and desipramine. Compounds 2 and 3 are less potent as serotonin‐uptake inhibitors, very weak inhibitors of dopamine uptake, and virtually devoid of antinociceptive activity.
Reaction of 3‐Amino‐2H‐azirines with 2‐Amino‐4,6‐dinitrophenol (Picramic Acid): Synthesis of Quinazoline‐ and 1,3‐Benzoxazole Derivatives
Authors: Villalgordo José M. , Vincent Beverly R. , Heimgartner Heinz
Published: December 2004

The reaction of 3‐(dimethylamino)‐2H‐azirines 1a–c and 2‐amino‐4,6‐dinitrophenol (picramic acid, 2) in MeCN at 0° to room temperature leads to a mixture of the corresponding 1,2,3,4‐tetrahydroquinazoline‐2‐one 5, 3‐(dimethylamino)‐1,2‐dihydroquinazoline 6, 2‐(1‐aminoalkyl)‐1,3‐benzoxazole 7, and N‐[2‐(dimethylamino)phenyl]‐α‐aminocarboxamide 8 (Scheme 3). Under the same conditions, 3‐(N‐methyl‐N‐phenyl‐amino)‐2H‐azirines 1d and 1e react with 2 to give exclusively the 1,3‐benzoxazole derivative 7. The structure of the products has been established by X‐ray crystallography. Two different reaction mechanisms for the formation of 7 are discussed in Scheme 6. Treatment of 7 with phenyl isocyanate, 4‐nitrobenzoyl chloride, tosyl chloride, and HCl leads to a derivatization of the NH2‐group of 7 (Scheme 4). With NaOH or NaOMe as well as with morpholine, 7 is transformed into quinazoline derivatives 5, 14, and 15, respectively, via ring expansion (Scheme 5). In case of the reaction with morpholine, a second product 16, corresponding to structure 8, is isolated. With these results, the reaction of 1 and 2 is interpreted as the primary formation of 7, which, under the reaction conditions, reacts with Me2NH to yield the secondary products 5, 6, and 8 (Scheme 7).
Synthesis and Circular Dichroism of Optically Pure (±)‐(1S,2S,5S)‐5‐Methoxy‐3,4,6,7‐tetramethylidenebicyclo[3.2.1]oct‐2‐yl Derivatives. Baker's Yeast Reduction of 4‐Methoxy‐5,6,7,8‐tetramethylidenebicyclo[2.2.2]octan‐2‐one
Authors: Burnier Gérald , Vogel Pierre
Published: December 2004

Baker's yeast reduction of 4‐methoxy‐5,6,7,8‐tetramethylidenebicyclo[2.2.2]octan‐2‐one (11) under fermenting conditions afforded (−)‐(1S,2S,4R)‐4‐methoxy‐5,6,7,8‐tetramethylidenebicyclo[2.2.2]octan‐2‐ol ((−)‐13) in 60% yield with an e.e. > 99.5%. Its methanesulfonate (−)‐14 was hydrolyzed and rearranged with high stereo‐selectivity into (+)‐(1S,2S,5S)‐5‐methoxy‐3,4,6,7‐tetramethylidenebicyclo[3.2.1]octan‐2‐ol ((+)‐15). The absolute configuration of (−)‐13 was deduced from the CD spectrum of its 4‐(dimethylamino)benzoate ((+)‐22) applying the chiral exciton‐coupling method. The CD spectrum of (+)‐15 and of its (tert‐butyl)dimethylsilyl ether ((+)‐23) showed exciton‐split type of Cotton effects attributed to through‐space interactions between the s‐gauche‐buta‐diene and s‐cis‐butadiene chromophores of these systems.
Pterin chemistry. Part 88. A simple synthesis of 5‐Deoxy‐L‐[5‐2H1]arabinose and L‐[3′‐2H1] biopterin
Authors: Adier Carmen , Curtius Hans‐Christoph , Datta Subir , Viscontini Max
Published: December 2004

A simple synthesis of 5‐deoxy‐L‐[5‐2H1]arabinose was performed to obtain L‐[3′‐2H1]biopterin. The reduced form of this model substance is needed to investigate the pathway of 7‐substituted pterins in patients with primapterinuria.
A New Combined Purification/Phosphorylation Procedure for Oligodeoxynucleotides
Authors: Banmvarth Willi , Wippier Jürgen
Published: December 2004

We describe a new principle for the purification of oligodeoxynucleotides using a purification handle which leads to a covalent linkage of the desired DNA sequence to a solid matrix. Truncated sequences are removed by washing steps. The release of the pure target sequence is performed in such a way that it is obtained directly in its 5′‐phosphorylated form which represents a further advantage. In addition, the system can be used for 5′‐thiol modifications of synthetic DNA.
Synthesis of 3‐Deaza‐2′‐deoxyadenosine and 3‐Deaza‐2′,3′‐dideoxyadenosine: Glycosylation of the 4‐Chloroimidazo[4,5‐c]pyridinyl Anion
Authors: Seela Frank , Rosemeyer Helmut , Fischer Sabine
Published: December 2004

The convergent syntheses of 3‐deazapurine 2′‐deoxy‐β‐D‐ribonucleosides and 2′,3′‐dideoxy‐D‐ribonucleosides, including 3‐deaza‐2′‐deoxyadenosine (1a) and 3‐deaza‐2′,3′‐dideoxyadenosine (1b) is described. The 4‐chloro‐lH‐imidazo[4,5‐c]pyridinyl anion derived from 5 was reacted with either 2′‐deoxyhalogenose 6 or 2′,3′‐dideoxyhalogenose 10 yielding two regioisomeric (N1 and N3) glycosylation products. They were deprotected and converted into 4‐substituted imidazo[4,5‐c]pyridine 2′‐deoxy‐β‐D‐ribonucleosides and 2′,3′‐dideoxy‐D‐ribonucleosides. Compounds 1a and 1b proved to be more stable against proton‐catalyzed N‐glycosylic bond hydrolysis than the parent purine nucleosides and were not deaminated by adenosine deaminase.
Stereochemistry of the Robinson Anellation: Studies on the Mode of Formation of the Intermediate Hydroxy Ketones
Authors: Nussbaumer Cornelius
Published: December 2004

The stereochemical outcome of the base‐catalyzed cyclization of diketones 5–8 has been investigated under protic conditions (Scheme 3). The more stable trans‐fused ketols are preferentially formed in kinetically controlled aldol reactions, when the incipient angular substituent R = H (6 → 10a) or CN (7 → 11a, 8a → 12a). For R = Me (as in 5), axial attack of the side‐chain enolate double bond on the ring CO group results in the rather selective formation of cis‐9b. It is assumed that these cyclizations are controlled by relative product stabilities (product‐like transition state) and steric effects. The competition between fused (e.g. 9) and bridged ketol (e.g. 13) formation in these cyclizations is discussed. The cis‐fused (‘steroid’) ketols were readily equilibrated with their trans‐counterparts (9b ⇄ 9a, 10b ⇄ 10a, 11b ⇄ 11a) under aprotic conditions (5 mol‐% of LDA, THF, 0°), thus, allowing assessments of relative stabilities.