bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radical Ions in the Pentalene Series. Part III. Three paramagnetic redox stages of a dicyclopenta[a,e]pentalene
Authors: Gerson Fabian , Gescheidt Georg , Hafner Klaus , Nimmerfroh Norbert , Stowasser Berndt 
Published: December 2004

AbstractFive redox stages have been observed for the recently synthesized 1,3,5,7‐tetra(tert‐butyl) derivative 1 of the dicyclopenta[a,e]pentalene, a novel non‐alternant hydrocarbon: the radical cation \documentclass{article}\pagestyle{empty}\begin{document}$1^{+ \atop \dot{}}$\end{document}, the neutral compound 1, the radical anion \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, the dianion 12−, and the radical trianion \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}. Information about the the electronic structure of the three paramagnetic stages, \documentclass{article}\pagestyle{empty}\begin{document}$1^{+ \atop \dot{}}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is provided by the use of ESR, ENDOR, and TRIPLE resonance spectroscopy. The unpaired electron in the trianion resides mainly on the ‘inner’ butadiene‐π‐system. Whereas in the cation and the anion, it is largely localized on the two ‘outer’ five‐membered rings.
Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations
Authors: Flury Peter , Grob Cyril A. , Wang Guang Yi , Lennartz Hans‐Werner , Roth Wolfgang R. 
Published: December 2004

AbstractFurther evidence is presented that the 2‐norbornyl cation is stabilized primarily by C(2)–C(6) bridging, and that C(2)–C(7) bridging leads to prohibitive strain. Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicyclo[3. 2. 0. 0.2,7]heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher that that of 17. Furthermore, 6‐exo‐2‐oxabicyclo[2. 2. 1]heptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12. In contrast, 2‐endo‐7‐oxabicyclo[2.2.1]heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15.
Leiopathic Acid, a Novel Optically Active Hydroxydocosapentaenoic Acid, and related compounds, from the black coral Leiopathes sp. of Saint Paul Island (S. Indian Ocean)
Authors: Guerriero Antonio , D'Ambrosio Michele , Peitra Francesco 
Published: December 2004

AbstractThe antipatharian Leiopathes sp., collected around Saint Paul Island, is shown here to contain, in relatively high amounts, the novel fatty acid leiopathic acid ( = (+)‐(10R,7Z,11E,13Z,16Z,19Z)‐10‐hydroxy‐7,11,13,16,19‐docosapentaenoic acid; (+)‐1), besides (+)‐(8R,5Z,9E,11Z,14Z,17Z)‐8‐hydroxy‐5,9,11,14,17‐icosapentaenoic acid ((+)‐11) and (+)‐(8R,5Z,9E,11Z,14Z,)‐8‐hydroxy‐05,9,11,14‐icosatetraenoic acid ((+)‐16) and their ethyl ester (+)‐2, (+)‐12, and (+)‐17.
Synthesis and 1H‐, 13C‐, and 57Fe‐NMR spectra of mono‐ and bis[tricarbonyl(η4‐diene)iron], and (η3‐allyl)tetracarbonyliron trifluoroborate complexes
Authors: Adams Christoph M. , Cerioni Giovanni , Hafner Andreas , Kalchhauser Hermann , von Philipsborn Wolfgang , Prewo Roland , Schwenk Andreas 
Published: December 2004

AbstractA variety of mono‐ and bis[Fe(CO)3(η4‐diene)] complex with alky, CH2OH, CHO, COCH3, COOR, and CN substituents on the 1,3‐diene system have been synthesized. Dienes with a (Z)‐configuration terminal Me group show steric inhibition of metal complexation resulting in lower yields and formation of tetracarbonyl(η2‐diene) and tricarbonyl(η4‐heterodiene) complexes as additional products. Regioselective attack by C‐nucleophiles at the carbonyl C‐atoms of the functional group with or without concomitant 1,3 mogration of the Fe(CO)3 group was used to synthesize polyenes and isoprenoid building blocks as mono‐ or dinucliar Fe(CO)3 complexes. Wittig‐Horner‐type reactions of Fe(co)3‐complexed synthons result in sterospecific formation of (E)‐configurated olefins. The 1H‐, 13C‐ and 57Fe‐NMR spectra of olefinic and allylic organoiron complexes are reported, H,H,C,H, and C,C coupling constants have been evaluated and are analyzed in terms of the geometry of the coordinated diene. The results are corroborated by the crystal structure of tricarbonyl[3–6‐η‐((E)‐6‐methyl‐3,5‐heptadiene‐2‐one)]iron(34) which shows an unusual distortion of the (CH3)2C = group, The 57Fe‐NMR chemical shifts extend over the ranges of 0–600 ppm for [Fe(CO)3(η4‐diene)] complexes, 780–1710 ppm for [Fe(CO)4(η3‐allyl)] [BF4] and [FeX(CO)3(η4‐allyl)] complexes, and 1270–1690 ppm for [Fe(CO)3(η4‐enone)] complexes, relative to Fe(CO)5.
[1,1‐bis (trimethylsilyl)]‐1H‐cyclopropa [b] napththalene[tricarbonyl‐chromium]: The first arene‐chromium complex of a cycloproparene
Authors: Müller Paul , Bernardinelli Gérald , Jacquier Yvan 
Published: December 2004

Abstract[1,1‐Bis (trimethylsilyl)]‐1H‐cyclopropa [b] naphthalene rricarbonylchromium (2) was synthesized by reaction of 1,1‐bis (trimethylsilyl) cyclopropa [b] naphthalene (1b) with tricarbonyltris(acetonitrile) chromium.
The solution structure and reactivity of decavanadate
Authors: Comba Peter , Helm Lothar 
Published: December 2004

AbstractThe oxygen‐exchange reaction of V10O with bulk water has been followed by time‐dependent 17O‐NMR spectroscopy (buffered solutions, pH ∼ 5.5, [V10]total ∼ 0.17m, T = 298 K). It is shown that all seven structurally different sites of O‐atoms are kinetically similar but, in contrast to earlier studies, not identical (6 h ⩽ ‘t1/2’ ⩽ 11 h). The kinetic similarity of the various structural sites implies the some (but not full) O scrambling is involved. Two possible mechanisms with a ‘half‐bonded’ and an ‘open’ intermediate are discussed in detail to interpret the experimental results. A computer simulation of the exchange reaction based on these models is presented. It is shown that the ‘half‐bonded‐intermediate’ mechanism is consistent with the experimental data and the following parameters are calculated: formation of the intermediate: k1 = 5.8 · 10−3 s−1, k−1 = 6.7 · 10−2 s−1, [intermediate]∞ ≈ 8%; all activated O‐atoms exchange within the lifetime of the intermediate (τ ∼ 15 s), and the calculated exchange rate of the intermediate (k2 ⩾ 0.60 s−1) is consistent with earlier assumptions (k2 ≈ 0.5 s−1). It is shown that a simulation based on the ‘open‐intermediate’ mechanism results in kinetic parameters which are not consistent with the kinetics of the formation of cyclic metavanadates ((VO)n, n = 4,5) from decavanadate, since the required formation rate is by a factor ∼ 102 too fast, and the equilibrium concentration of metavanadates is by a factor of ∼ 2 too large (under the conditions of the O‐exchange experiments of decavanadate (T = 298 K, [V10]total ≈ 0.17m, pH ∼ 5.55) the total amount of metavanadates present is ∼ 8%, with [(VO)4]/[(VO)5] ∼ 4:1; a qualitative analysis of the kinetics of the formation of metavanadates (vo kinetics; the exact mechanism of the back‐reaction (at least second‐order) is not known with certainty) leads to k1 ⩾ 4·10−5 s−1). O exchange of decavanadates via equilibrated metavanadates would lead to full scrambling of the O sites and is not consistent with the observed differences in the exchange rates. From the qualitative kinetic parameters of the metavanadate formation kinetics, it can be concluded that any contribution of an ‘open’ or an ‘metavanadate’ mechanism is of the order of 1–2% at most.
Lavandulifolioside: A New Phenylpropanoid Glycoside from Stachys lavandulifolia
Authors: Başaran Arif Ahmet , Çaliş İhsan , Anklin Clemens , Nishibe Sansei , Sticher Otto 
Published: December 2004

AbstractA new phenlypropanoid glycoside has been isolated from the methanolic extract of the aerial parts of Stachys lavandulifolia (Lamiaceae), lavandulifolioside (1). On the basis of chemical and spectral data the structure of the new compound 1 has been elucidated as β‐(3,4‐dihydroxyphenyl)ethyl O‐α‐L‐arabinopyranosyl‐(1→2)‐α‐L‐rhamnopyranosyl‐(1→3)‐4‐O‐caffeoyl‐β‐D‐glucopyranoside.
Rosafluin, ein neues Diapocarotindiol aus Rosenblüten. 8. Mitteilung über Rosenfarbstoffe
Authors: Märki‐Fischer Edith , Eugster Conrad Hans 
Published: December 2004

Rosafluine, a Novel Diapocarotenediol from Rose PetalsA strongly fluorescent trace compound from rose petals was identified as the as yet unknown 10,10′‐diapocarotene‐10,10′‐diol ( = 4,9‐dimethyldodeca‐2,4,6,8,10‐pentaene‐1,12‐diol; 2).
Polar Effects. Part 15. Twin γ‐substituent effects in the formation of adamantyl‐1‐cations
Authors: Grob Cyril A. , Gründel Martin , Sawlewicz Pawel 
Published: December 2004

AbstractSolvolysis rates of several adamant‐1‐yl ( = tricyclo[3.3.1.13,7]dec‐1‐yl) p‐toluenesulfonates and bromides 2 identically substituted at C(3) and C(5) (twin substitution) have been determined and compared with the rates of the corresponding 3‐monosubstituted compounds 1. As expected, the rate factors for twin substitution are much larger, but less than the square of the rate factors for single substitution. Also the rates factors per substitutent in 2 are considerably smaller than those for one substituent in 1. This attenuation is attributed to electron repulsion which limits the convergence of electron density to the cationic center. On the other hand, the inductivity for twin substitution (ρ1 = −2.55) is ca. twice as high as for mono‐substitution (ρ1 = −1.26).
The mild bromination of adamantane and (trimethylsilyl) adamantanes
Authors: Grob Cyril A. , Sawlewicz Pawel 
Published: December 2004

AbstractSmall amounts of H2O or MeOH catalyze the reaction of Br2 with adamantane and its 1‐(trimethylsilyl) and 1,3‐bis(trimethylsilyl) derivatives.
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

AbstractSolid‐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

AbstractO‐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

AbstractOligonucleotides 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

AbstractLaser 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

AbstractDehalogenation 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

AbstractThe [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

AbstractThe 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

AbstractThe 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

Abstract18‐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 RetinoidsStarting 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‐TerminusDerivatives 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

AbstractThe 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.