bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolierung und Strukturaufklärung von Mikrolin
Authors: Bollinger Pietro , Zardin‐Tartaglia Therese 
Published: December 2004

The Isolation and Structural Elucidation of Microline.The structure and absolute configuration of microline, a new metabolite isolated from culture filtrates of Gilmaniella humicola BARRON, has been shown to be 1, by spectral data and chemical transformations, and by X‐ray analysis [4].
The Irreversible Photochemistry of Bianthrone
Authors: Korenstein R. , Muszkat K. A. , Fischer E. 
Published: December 2004

AbstractA 4a,4b‐dihydrophenanthrene‐type cyclic photoisomer, the C isomer, is the major primary photoproduct of bianthrone in protic and aprotic polar solvents, and undergoes solvent‐dependent secondary reactions, including the formation of dihydrohelianthrone in protic solvents. The C isomer was shown to be formed through the singlet excited state while the B isomer is formed via the triplet manifold.
20, 21‐Azirdin‐Steroide: Reaktion von Derivaten der Oxime von 5‐Pregnen‐20‐on,9β,10α‐5‐Pregnen‐20‐on und 9β,10α‐5,7‐Pregnadien‐20‐on mit Lithiumaluminiumhydrid und von 3β‐Hydroxy‐5‐pregnen‐20‐on‐oxim mit Grignard‐Verbindungen
Authors: Tzikas Athanassios , Tamm Christoph , Boller Arthur , Fürst Andor 
Published: December 2004

20, 21‐Aziridine Steroids: Reaction of Derivatives of the Oximes of 5‐Pregnen‐20‐one, 9β, 10α‐5‐Pregnen‐20‐one and 9β, 10α‐5,7‐Pregnadiene‐20‐one with Lithium Aluminium Hydride, and of 3β‐Hydroxy‐5‐pregnen‐20‐one Oxime with Grignard Reagents.Reduction of 3β‐hydroxy‐5‐pregnen‐20‐one oxime (2) with LiAlH4 in tetrahydrofuran yielded 20α‐amino‐5‐pregnen‐3β‐ol (1), 20β‐amino‐5‐pregnen‐3β‐ol (3), 20β, 21‐imino‐5‐pregnen‐3β‐ol (6) and 20β, 21‐imino‐5‐pregnen‐3β‐ol (9). The aziridines 6 and 9 were separated via the acetyl derivatives 7 and 10. The reaction of 6 and 9 with CS2 gave 5‐(3β‐hydroxy‐5‐androsten‐17β‐yl)‐thiazolidine‐2‐thione (8). Treatment of the 20‐oximes 12 and 15 of the corresponding 9β,10α(retro)‐pregnane derivatives with LiAlH4 gave the aziridines 13 and 16, respectively. Their deamination led to the diene 14 and triene 17, respectively. Reduction of isobutyl methyl ketone‐oxime with LiAlH4 in tetrahydrofuran yielded 2‐amino‐4‐methyl‐pentane (19) as main product, 1, 2‐imino‐4‐methyl‐pentane (22) as second product and the epimeric 2,3‐imino‐4‐methyl‐pentanes 20 and 21 as minor products. – 3β‐Hydroxy‐5‐pregnen‐20‐one oxime (2) was transformed by methylmagnesium iodide in toluene to 20α, 21‐imino‐20‐methyl‐5‐pregnen‐3β‐ol (23) and 20β, 21‐imino‐20‐methyl‐5‐pregnen‐3β‐ol (26). Acetylation of these aziridines was accompanied by elimination reactions leading to 3β‐acetoxy‐20‐methylidene‐21‐N‐acetylamino‐5‐pregnene (30) and 3β‐acetoxy‐20‐methyl‐21‐N‐acetylamino‐5,17‐pregnadiene (32). The reaction of oxime 2 with ethylmagnesium bromide in toluene gave 20α, 21‐imino‐20‐ethyl‐5‐pregnen‐3β‐ol (24) and 20α,21‐imino‐20‐ethyl‐5‐pregnen‐3β‐ol (27). Acetylation of 24 and 27 led to 3β‐acetoxy‐20‐ethylidene‐21‐N‐acetylamino‐5‐pregnene (31), 3β‐acetoxy‐20‐ethyl‐21‐N‐acetylamino‐5,17‐pregnadiene 33 and 3β, 20‐diacetoxy‐20‐ethyl‐21‐N‐acetylamino‐5‐pregnene (37). With phenylmagnesium bromide in toluene the oxime 2 was transformed to 20β, 21‐imino‐20‐phenyl‐5‐pregnen‐3β‐ol (25) and 20β,21‐imino‐20‐phenyl‐5‐pregnen‐3β‐ol (28). Acetylation of 25 and 28 yielded 3β‐acetoxy‐20‐phenyl‐21‐N‐acetylamino‐5, 17‐pregnadiene (34) and 3β,20‐diacetoxy‐20‐phenyl‐21‐N‐acetylamino‐5‐pregnene (39). LiAlH4‐reduction of 39 gave 3β, 20‐dihydroxy‐20‐phenyl‐21‐N‐ethylamino‐5‐pregnene (41). – The 20, 21‐aziridines are stable to LiAlH4. Consequently they are no intermediates in the formation of the 20‐amino derivatives obtained from the oxime 2.
Etude des systèmes binaires formées par le chlorure de cyanogène et par les tétrachlorures de carbone, de silicium, de germanium et d'étain
Authors: Labaye Marie‐Hélène , Doucet André , Perrot Roger , Dubois Claude 
Published: December 2004

Study of binary systems formed by cyanogen chloride and the tetrachlorides of carbon, silicon, germanium and tin.The diagrams of binary mixtures of cyanogene chloride with the tetrachlorides of carbon, silicon, germanium and tin were studied. Only SnCl4 gives an addition compound: SnCl4 · 2ClCN. The existence of the complex was confirmed by X‐ray diffraction and vapour pressure measurements. This complex gives SnCl4 · 2NOCl on treatment with nitrosyl chloride.
A Specific Synthesis of Ethyl (2Z)‐2‐Bromomethyl‐2‐butenoate and its Conversion into Mikanecic Ester
Authors: Goldberg Ora , Dreiding André S. 
Published: December 2004

Eine spezifische Synthese von (2Z)‐2‐Brommethyl‐2‐butensäure‐äthylester und seine Umwandlung in Mikanezester.Das Lithiumsalz 12, hergestellt aus 2‐Bromorthopropensäure‐triäthylester (11) und n‐Butyl‐lithium, wurde mit Acetaldehyd umgesetzt, wobei 2‐Methyliden‐3‐hydroxy‐orthobutansäure‐triäthylester (13) und daraus, durch saure Hydrolyse, 2‐Methyliden‐3‐hydroxybutansäure‐äthylester (14) entstand. Behandlung von 14 mit N‐Bromsuccinimid und Dimethylsulfid lieferte den gewünschten (2Z)‐2‐Brommethyl‐2‐butensäure‐äthylester (6), der sich mit HBr zur entsprechenden Säure 4 hydrolysieren liess.Die (2Z)‐Konfiguration von 4 wurde aufgrund der vicinalen 1H/13C Kopplungen zwischen H–C(3) und COOH bzw. CH2Br im 13C‐NMR.‐Spektrum bestätigt. Die 1H‐NMR.‐Signale der beiden Methylidenprotonen in 9, 11, 13 und 14 liessen sich mit Hilfe von additiven Entschirmungsbeiträgen der Substituenten um die Doppelbindung zuordnen.1,4‐Eliminierung von HBr aus (2Z)‐2‐Brommethyl‐2‐butensäure‐äthylester (6) mit Kalium‐t‐butylat ergab Mikanezsäure‐diäthylester (21), der bei der Aufarbeitung teilweise zum Monoester 20 und zur MikanezsäureThe systematic name for mikanecic acid (19) is 4‐vinyl‐1‐cyclohexene‐1,4‐dicarboxylic acid.

(
19
) verseift wurde.
Synthese der enantiomeren 2‐Pyrrolidinessigsäuren
Authors: Cassal Jean‐Marie , Fürst Andor , Meier Werner 
Published: December 2004

Synthesis of the enantiomeric 2‐pyrrolidineacetic acids.Starting from the enantiomeric Z‐prolines (1) the title compounds 9 were prepared in optically pure form by using the Arndt‐Eistert process. It could be shown by chemical correlation that the stereochemical determining step of the reaction sequence, the Wolff rearrangement of the N‐acylated diazomethyl ketones 5, proceeds with strict retention of configuration. Some known chiroptical methods for determination of absolute configuration were applied to the target compounds.
Physico‐Chemical Properties of Deuteriated Compounds. 2nd Communication. The isotope partition coefficient in methylcyclohexane‐hydrogen
Authors: Dessauges Gérald , Gäumann Tino 
Published: December 2004

AbstractThe deuterium isotope partition coefficient α has been determined as a function of total pressure, temperature and degree of deuteriation for methylcyclohexane/hydrogen over Ni/Al2O3. Good agreement with theory has been obtained for the dependence on temperature but not for that on total pressure or on the degree of deuteriation.
The Photoelectron Spectrum of Dibenzo‐p‐quinodimethane
Authors: Allan Michael , Heilbronner Edgar , Kaupp Gerd 
Published: December 2004

AbstractThe lowest states of dibenzo‐p‐quinodimethane radical cation are 2B1u (7.95 eV); 2B2g (8.66 eV); [2B3g, 2Au, unresolved] (9.1 eV); [2B1u, 2B2g, unresolved] (10.7 eV). This confirms the assignment proposed by Koenig et al. [1] for the states of p‐quinodimethane radical cation.
Transformations of 9 α, 10 α‐Epoxy‐Hexahydrocannabinol Acetate
Authors: Petrzilka Theodor , Prasad Kapa K. , Schmid Gérard 
Published: December 2004

Abstract9α, 10α‐Epoxy‐hexahydrocannabinol acetate 1 in presence of boron trifluoride etherate rearranged to a fluoro compound 6 and to a ketone 5, and in perchloric acid to compound 11. The fluoro compound 6 had been considered erroneously in earlier literature as 4. Compounds 6 and 11 were produced by the initial opening of the epoxide followed by the acetyl transfer from the neighbouring phenolic group.Tetrahydrocannabinol acetates 2 and 3, on oxymercuration‐demercuration followed by reduction gave the known 9α‐hydroxy‐hexahydrocannabinol (13).
Homoisoflavanone. IV. Neue Inhaltsstoffe der Eucomin‐Reihe von Eucomis bicolor
Authors: Heller Werner , Andermatt Paul , Schaad Werner A. , Tamm Christoph 
Published: December 2004

Homoisoflavanones. IV. New constituents of the Eucomin Series of Eucomis bicolor.Four new homoisoflavanones, (E)‐7‐O‐methyl‐eucomin (2a), (—)‐7‐O‐methyleucomol (5), (+)‐3,9‐dihydro‐eucomin (7a) and 7‐O‐methyl‐3,9‐dihydro‐eucomin (8), were isolated from the bulbs of Eucomis bicolor Bak. (Liliaceae). Their structures were determined by spectral data and synthesis. These compounds occur exclusively in the waxy material between the bulb leaves. Furthermore it was shown that only (Z)‐eucomin (1b) is genuine, (E)‐eucomin (1a) being an artefact. It is likely that 2a is also not genuine. A new method for a selective 7‐O‐methylation is described.
Synthèse de sucres aminés ramifiés. IV Synthèse de quelques dérivés nouveaux par l'intermédiaire d'une hexose‐spiro‐aziridine
Authors: Bourgeois Jean‐Marc 
Published: December 2004

Treatment of 3‐C‐cyano‐1,2:5,6‐di‐O‐isopropylidene‐3‐O‐(toluene‐p‐sulfonyl)‐α‐D‐allofurannose with AlLiH4 yields a sugar‐spiro‐aziridine and a branched chain sulfonamide. Reaction mechanisms are briefly discussed and the configurations of the products obtained are proved by chemical reactions. With hydrogenation, the spiro compound is opened to a branched chain amino sugar with the same tertiary carbon as in vancosamine.Several derivatives of this new compound are described: the 6‐deoxy sugars in series L and D and the pentose resulting from its oxidation by periodic acid. The conformation around C(4)–C(5) bond is deduced for three compounds from NMR. data.
The Crystal Structure of Axillarine Hydrobromide Ethanol Solvate: A Pyrrolizidine Alkaloid
Authors: Stoeckli‐Evans Helen , Crout David H. G. 
Published: December 2004

AbstractThe crystal structure of axillarine hydrobromide ethanol solvate has been determined from analysis of photographic X‐ray data. The crystal system is orthorhombic, space group P212121, with unit cell dimensions a = 9.89, b = 11.23, c = 20.83 Å. The structure was determined by means of Patterson and Fourier syntheses, and refined by the method of least‐squares to an R index of 9.4%.The structural features of axillarine are noted and compared with those of several other pyrrolizidine alkaloids. The NMR. chemical shift difference between the signals due to the non‐equivalent C(9) protons in alkaloids derived from retronecine is also discussed.
Synthesis of L‐Propargylglycine and Derivatives
Authors: Leukart Othmar , Caviezel Mario , Eberle Alex , Escher Emanuel , Tun‐Kyi Aung , Schwyzer Robert 
Published: December 2004

AbstractThe chemical synthesis of L‐propargylglycine (L‐Pra) and of various derivatives is described. The new amino acid is a starting material for carboranylalanine (Car) and for tritiated norleucine.
Hormone‐Receptor Interactions. Synthesis and Conformational Study of cyclo‐L‐Cystathionine
Authors: Fauchère Jean‐Luc , Muthukumaraswamy Natesa , Tun‐Kyi Aung , Schwyzer Robert 
Published: December 2004

AbstractThe purpose of this work was to see whether the replacement of a sulfur atom in a cystine disulfide bridge by a methylene group is an only superficial ‘isosteric’ substitution, i.e. with regard to size, hydrophobia, bond angles, etc., or whether it would also encompass such parameters as preferred conformations in solution (M‐ or P‐helicity of the bridge). The methods involved the synthesis of a model compound, cyclo‐L‐cystathionine (cyclo‐L‐carbacystine), and its investigation by 1H‐ and 13C‐NMR. It is concluded that the conformations of the CH2(β)CH2(γ)SCH2(β') bridge, and of the diketopiperazine ring are closely similar to the analogous elements in cyclo‐L‐cystine (DMSO as solvent). This knowledge might help to explain the fact that carba analogs of heterodetic‐cyclic polypeptide hormones are often biologically very active.
Isolation and Identification of Three Urinary Metabolites of Retinoic Acid in the Rat
Authors: Hänni Ralph , Bigler Felix , Meister Walter , Englert Gerhard 
Published: December 2004

AbstractAfter the intraperitoneal administration of high doses of 14C‐ and 3H‐labelled retinoic acid (1) to rats three major urinary metabolites have been isolated in microgram amounts by use of column, thin‐layer and high‐pressure liquid chromatography. Their structures were elucidated by mass spectroscopy and Fourier transform 1H‐NMR. spectroscopy as 2 (5‐methyl‐5‐[2‐(2,6,6‐trimethyl‐3‐oxo‐1‐cyclohexen‐1‐yl)vinyl]‐2‐tetrahydrofuranone), 3 (5‐[2‐(6‐hydroxymethyl‐2,6‐dimethyl‐3‐oxo‐1‐cyclohexen‐1‐yl)vinyl]‐5‐methyl‐2‐tetrahydrofuranone) and 4 (6‐(6‐hydroxymethyl‐2,6‐dimethyl‐3‐oxo‐1‐cyclohexen‐1‐yl)‐4‐methyl‐4‐hexenoic acid). In these metabolites the tetraene side chain of 1 is shortened and the cyclohexene ring oxidized. The radioactivity of 2 and 3 accounted for about 10% (0.9% of the dose) each, metabolite 4 for about 6% (0.5% of the dose) of the total urinary radioactivity.
Preferred Spatial Arrangement of the Aromatic Side Chains in Linear Oligopeptides Containing Tyrosine
Authors: Wüthrich Kurt , De Marco Antonio 
Published: December 2004

Abstract1H‐NMR. studies of the protected linear tetrapeptides CF3CO‐Gly‐Gly‐L‐Tyr‐L‐Ala‐OCH3, CF3CO‐Gly‐L‐Ala‐L‐Tyr‐L‐Ala‐OCH3 and CF3CO‐Gly‐L‐Ala‐L‐Tyr‐Gly‐OCH3 showed that the side chain of the tyrosyl residue was in all three peptides preferentially oriented towards the amino terminus of the peptide chain. This preferred spatial arrangement of the aromatic side chain was manifested in the chemical shifts of the amino acid residue preceding tyrosine and in the vicinal spin‐spin coupling constants 3JHCαCβH of tyrosine.
Conversion of Penicillin to Cephalosporin Lactones. Preliminary Communication
Authors: Prasad Kapa K. , Schmid Gérard , Petrzilka Theodor 
Published: December 2004

AbstractPenicillin G (1, R  CH2Ph) was converted to cephaloram‐ and 6‐epicephaloram lactones 11 and 12 respectively by the initial replacement of thiazolidine part of penicillin by the mercaptan 9 followed by intramolecular cyclization and subsequent introduction of double bond at C(3).
Zum Mechanismus der Photochemie des Benzfurazans
Authors: Heinzelmann Willy , Gilgen Paul 
Published: December 2004

Mechanistic studies on the photochemical reactions of benzfurazan.From other works it is known that irradiation of benzfurazan (1) in methanol gives the carbaminacid‐ester 4, whereas in benzene the azepinederivative 3 is obtained (Scheme 1). The compounds 5–8 (Scheme 2) have been proposed as intermediates.In our investigations we detected and characterized by means of UV.‐ and IR.‐spectroscopy the two species 5 and 8. Irradiation of 1 with 350 nm light at room temperature in a strongly polar solvent (e.g. H2O) yields exclusively 5 (Fig. 1) with a quantum yield of 0.48. In non polar solvents (e.g. hexane) 5 isomerizes in a second photochemical step to 8 (quantum yield 0.43) (Fig. 3). Thermally, 5 can be converted back to 1. The rate constant for this reaction at room temperature is 2 · 10–5s–1.The transformation 5 → 8 was also investigated at low temperature. There was no direct evidence for any intermediates of the type oxazirene (6) or nitrene (7). However, the formation of azepine 3 upon irradiation of 5 in benzene suggests as intermediate the nitrene 7 which could be converted into 8 in a fast thermal reaction (Scheme 3).
The Cyclopropylcarbinyl‐Cyclobutyl‐Homoallylic Rearrangement. Part III. Evidence for a symmetrical intermediate and for two discrete rearrangement processes
Authors: Geisel Manfred , Grob Cyril A. , Traber René P. , Tschudi Werner 
Published: December 2004

AbstractIn buffered 70% aqueous dioxane the cyclopropylcarbinyl (1‐X), endo‐cyclobutyl (2‐X) and homoallylic (3‐X) derivatives (X = nucleofuge) react to give the same mixture of alcohols 1‐OH and 3‐OH by way of a common intermediate, the symmetrical homoallylic ion 22. This follows from a study of optically active reactants 1‐X and 3‐X and from the deuterium scrambling pattern in the products from deuteriated 1‐X, endo‐2‐X and 3‐X. The high solvolysis rates of 3‐X indicated π‐bond participation in the transition state, while the high rates of 1‐X and endo‐2‐X reflect strong σ‐bond participation which is absent in exo‐2‐X.Prolonged heating of 1‐X, endo‐2‐X and 3‐X in formic acid leads to a degenerate rearrangement of the initially formed 3‐formate. As evidenced by deuterium scrambling, carbon atoms 1, 3 and 7 eventually become positionally equivalent in the latter compound.
Synthese von Humaninsulin. III. Aufbau des geschützten zweikettigen Fragments A(14‐21) ‐ B(17‐30)
Authors: Kamber Bruno , Riniker Bernhard , Sieber Peter , Rittel Werner 
Published: December 2004

Synthesis of human insulin. III. Preparation of the A(14‐21) ‐ B(17‐30) fragment.In the recently published total synthesis of human insulin [1], one of the three principal intermediates is the protected fragment in which sequence 14‐21 of the A chain is linked to sequence 17‐30 of the B chain by the disulfide bridge between A 20 and B 19. The synthesis of this fragment, and its characterization are described in detail in the present report.This open‐chain asymmetrical cystine peptide was prepared by elongating the two chains in the already published intermediate first with fragment A(14–19), Bpoc‐Tyr(But)‐Gln‐Leu‐Glu(OBut)‐Asn‐Tyr(But)‐NH‐NH2 (azide coupling), and secondly with fragment B(21–30), H‐Glu(OBut)‐Arg‐Gly‐Phe‐Phe‐Tyr(But)‐Thr(But)‐Pro‐Lys(Boc)‐Thr(But)‐OBut (DCCI/HOBt).
Photocyclisierungen von 1, 1'‐Polymethylen‐di‐2‐pyridonen. 46. Mitteilung über Photoreaktionen
Authors: Nakamura Yushin , Zsindely Janos , Schmid Hans 
Published: December 2004

Photocyclization of 1, 1′‐Polymethylene‐di‐2‐pyridones.Benzophenone sensitized irradiation of the four dipyridones 1‐4 gave the internal photocyclization products 6 (64%, Scheme 4), 7 (60%, Scheme 5), 8 (Scheme 6), and 11 (26%, Scheme 7), respectively. The decamethylene compound 5 yielded only polymeric material.The primary [2+2] photoproduct 8 from dipyridone 3 (Scheme 6) is relatively unstable. Further irradiation or heating to 65° induced a Cope rearrangement to give compound 9 which, on heating to 137°, was converted into the isomeric compound 10. This product, as well as the other photoproducts mentioned, are rearranged back to their respective starting materials upon direct irradiation with 254 nm light or by heating to higher temperatures. The various possibilities for cycloadditions of pyridones are discussed as well as the possible factors which are responsible for the highly regioselective photoreactions of the dipyridones 1–4.
Concerning the Hydroxyazo‐Quinonehydrazone Equilibrium of a Trisazonaphthalene with an [18]annulene perimeter macrocyclic Aza compounds, III
Authors: Skrabal Peter , Steiger Jürg , Zollinger Heinrich 
Published: December 2004

AbstractThe hydroxyazo‐quinonehydrazone equilibrium of the cyclic triazonaphthalene 1 has been determined from the 1H‐NMR. spectrum of the 15N‐labelled compound. The size of the coupling constant J15N, H demonstrates that the equilibrium of 1 with respect to the non‐cyclic reference compound 6 is shifted towards the hydroxyazo form by factors of at least 5.1 and 3.9 in DMSO and H2O, respectively.
The Thermal Isomerizations of Bicyclo[2.1.0]pent‐5‐yl Methyl Ketones: endo‐exo stereomutation and cyclopropyl‐allylic rearrangement to cyclopent‐2‐enyl methyl ketones
Authors: Grosclaude Jean‐Pierre , Gonzenbach Hans‐Ulrich , Perlberger Jean‐Claude , Schaffner Kurt 
Published: December 2004

AbstractBicyclo[2.1.0]pent‐5‐yl methyl ketones undergo two thermal isomerization reactions. The endo‐exo stereomutation follows the ring‐flip path in better than 90%, with inversion of the configuration of the angular carbon atoms by cleavage and reclosure of the central bond. Stereomutation and cyclopropyl‐allylic rearrangement to cyclopent‐2‐enyl methyl ketone do not involve a common intermediate and proceed on separate potential energy surfaces. The activation parameters of the rearrangement suggest an allowed concerted cycloreversion process.
Heterotricyclodecane XXIII 2‐Thia‐7‐aza‐isotwistane
Authors: Szczepanski Henry , Ganter Camille 
Published: December 2004

2‐Thia‐7‐aza‐isotwistanes.The access to the 2‐thia‐7‐aza‐isotwistane system was achieved by water addition to the twistene 1 yielding the isotwistanol 2, characterized also as its acetate 4. Analogous D2O/D2SO4‐treatment of the twistene 1 (→ 3) allowed to deduce the reaction pathway for the formation of 2. The chloride 6, obtained from 2, on treatment with lithium aluminium hydride gave a mixture of unsubstituted isotwistane 8 and twistane 9, whereas silver acetate treatment of 6 led to the isotwistyl acetate 4 and possibly only to traces of the corresponding twistyl acetate 7.
Totalsynthese von Humaninsulin. IV. Beschreibung der Endstufen
Authors: Sieber Peter , Kamber Bruno , Hartmann Albert , Jöhl Albert , Riniker Bernhard , Rittel Werner 
Published: December 2004

Total synthesis of human insulin. IV. Description of the final steps.Recently a preliminary account was given of a new synthetic pathway leading to human insulin. In the present report the last steps of this synthesis – i.e. as from the unsymmetrical cystine derivative I – are described in detail. I contains the sequences A(14–21) and B(17–30), linked by the disulfide bridge A20‐B19. These last steps are: (1) selective removal by pH‐controlled acidolysis in trifluoroethanol of N(α)‐Trt from leucine B17, (2) completion of the B‐chain by coupling with the fragment B(1–16), (3) selective removal by trifluoroethanol of N(α)‐Bpoc at tyrosine A14, (4) completion of the A‐chain by coupling with the cyclic fragment A(1–13), (5) removal of the acid labile protecting groups, and (6) formation of the disulfide bond A7–B7 from the two S‐acetamido‐protected cysteine residues by treatment with iodine.As judged by the composition of the reaction mixture the closure of the 85‐membered ring proceeds with a cyclization yield of over 70%. From the last step in the synthesis two products were obtained after extensive purification by counter‐current distribution: pure human insulin in a yield of 50% and its [D‐tyrosine B16]Isomer in a yield of 25%. Although the partial racemization of tyrosine B16 occurred during coupling with sequence B(1–16), the [D‐tyrosine B 16]‐stereoisomer could only be separated at the endproduct stage.The available evidence indicates that the ease of formation of the disulfide bond A7–B7 does not depend on the precursor molecule already having an insulin‐like conformation.
Interaction between Non‐Conjugated Chromophores: 5,6‐Dimethylidene‐exo‐2‐norborneol, 5,6‐Dimethylidene‐exo, exo‐2,3‐norbornanediol and 5,6‐Dimethylidene‐2‐norbornanone
Authors: Chollet André , Mahaim Cyril , Foetisch Christophe , Hardy Michèle , Vogel Pierre 
Published: December 2004

AbstractPreparation of the title compounds 11, 12 and 13 is described. Preliminary kinetic results indicate that the hydroxyl substituents in 11 and 12 have a very small retardation effect on the Diels‐Alder reactivity of 2,3‐dimethylidene‐norbornane. The keto group in 13 exerts a larger retardation effect, although it is much smaller than the retardation effect introduced by an exo‐5,6‐epoxide ring in 2,3‐dimethylidene‐norbornane.