Reactivity of Ligands in Synthetic Cobalt(<scp>III</scp>)‐ and Nickel(<scp>II</scp>)‐corrin Complexes

Bormann, Dieter; Fischli, Albert; Keese, Reinhart; Eschenmoser, Albert

doi:10.1002/anie.196708681

Cited by 15 publications

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“…corrin cyclization within a non-robust Zn II complex. Most prominent among our studies of the properties of the metal-free corrin ligands are the complexations with various metal ions.W ealso describe experiments on the introduction of Me groups into the meso-positions of dicyano-Co 2,2,7,7,12,, i.e., experiments carried out as model study for corresponding methylations tepsi nt he finals tage of the Harvard/ETH vitamin B 12 project.Chapter A: A ! B Ring Closure by Sulfide Contraction via Oxidative Coupling:S ynthesiso frac-Chloro-zink(II)-15-cyano-1,2,2,7, 7, 12,12-heptamethylcorrinate [3][5] [6].…”

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“…Die NMR-Daten wären grundsätzlich auch mit dem Vorliegen eines Gemisches entsprechend diastereoisomerer Ionenpaare vereinbar gewesen, doch dagegens prach das Massenspektrum. 7 )D er intensive Molekularpik desS ulfanyl-corrin-Komplexes 6 besass die Masse 529 (C 27 H 34 N 5 35 Cl 66 Zn, bzw. 37 Cl 64 Zn, und entsprechende Isotopen-Piks).…”

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“…6 ! 7,the Zn II ion seems to play a triple role:f irst, it presumablyf acilitates the first two steps;s econd, it hamperst he third step,a nd supposedly has to leave the ligando f 5 in ordert oa llow the contraction proceed, and, third, it finally has to re-enter the ligand in order to stabilize it, such that 6 can be isolated and finally desulfurized under acidic conditions to give 7.Not only were all these observation important to optimize the preparative procedure for the synthesis of the Zn II complex 7 in the modelsynthesis of the metalfree corrin ligand 13 (Fig.5) B. Herstellungu nd Eigenschaften vonS alzen des rac- 2,2,7,7,12,[5] [6] [10]. -D er leicht in kristalliner Form erhältliche Chloro-Zn II -corrin-Komplex 7 erwies sich als ein zur Herstellungd es entsprechenden metallfreien Corrin-Liganden hervorragend geeignetes Zwischenprodukt.…”

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“…Um das Jahr 1968 hatten Edmond und Crawford-Hodgkin von dem hier beschriebenen rac- 2,2,7,7,12,). D ie Ergebnissed er Analyse sind in [23]d argelegt worden; Fig.6, b,g ibt hierüber einen qualitativen Überblick 20 ).…”

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“…B)-Ringschluss-Methoden [18]erwiesen 36 ).C. Über einige Ligandsystem-Eigenschaften synthetischerCorrin-Komplexe[7]. -In der Chemie des Cobalamins und seiner Derivate sind bislang keineR eaktionsbedingungen bekannt, unter welchen Versuche zur Dekomplexierung ohne Zerstçrung des Corrin-Chromophorsgelungen wären 37 ).…”

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Corrin Syntheses. Part V

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Winnacker

Fischli

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Helvetica Chimica Acta

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Preparation of Metal-Free Corrin Derivatives via A ! B Ring Closure. Complexationo fthe Corrin Chromophore withMetal Ions, and Some Properties of the Ligandsi nC orrin ComplexesIn 1965, J. I. Toohey [11],w orking in the laboratoryo fH. A. Baker at Berkeley,i solated Co-free natural corrinoids from photosynthesizingb acteria. This discovery,t ogether with the challenge to prepare and to study corrin complexes containing also metal ions other than those of transition metals, led to the quest for as ynthesis of metal-freec orrin ligands.H erein, we describe how this goal was achieved in 1968 in the heptamethyl series through adaptation of the sulfide contractionmethodology (cf.P art VI of this series)t ot he problemo fa chieving an A/B-secocorrin ! corrin cyclization within a non-robust Zn II complex. Most prominent among our studies of the properties of the metal-free corrin ligands are the complexations with various metal ions.W ealso describe experiments on the introduction of Me groups into the meso-positions of dicyano-Co 2,2,7,7,12,, i.e., experiments carried out as model study for corresponding methylations tepsi nt he finals tage of the Harvard/ETH vitamin B 12 project.Chapter A: A ! B Ring Closure by Sulfide Contraction via Oxidative Coupling:S ynthesiso frac-Chloro-zink(II)-15-cyano-1,2,2,7, 7, 12,12-heptamethylcorrinate [3][5] [6]. Thec hapter describes the adaptation of the sulfide contraction C,C-condensation method (cf.P art VI of this series)t ot he A/B-secocorrin ! corrin-cyclizationstep in the synthesiso faZ n II -corrin complex. Corrin complexes of non-transition metals such as Zn are non-robust in the sense that the metal ion can be removed without destruction of the corrin ligand. Thes earch for optimal reaction conditions of the C,C-bondforming sulfide-contraction step required extensivee xperimentation and led to observations that turned out to be essential for the application of the A ! B macroring-closure method in the synthesis of vitamin B 12 . Chapter B: Preparationand Properties of Salts of rac-15-Cyano-1,2,2,7,7,12,12-heptamethylcorrinium Cations [3][5][6]. Azidolytic decomplexation of aZ n II -heptamethyl-corrin complex led to the first Helv eticaChimica Acta -V ol. 98 (2015)1845 2015 Verlag Helvetica Chimica Acta AG,Z ürich 1 ) Teile I und IV vgl. [1] und [2]. Der Teil V umfasst Ergebnisse aus den Promotionsarbeiten von A. Fischli [3] (1964 -1967), vgl. Fussnote 1i n[ 2], E.-L. Winnacker [4] (1964 -1968) und H.-U.B laser [5] (1967 -1970), sowie aus Postdoktoratsarbeiten von D. Bormann (1966, J. Schossig ( ) und N. Hashimoto (1970). Ein Te il der hier beschriebenenE rgebnisse war Gegenstand vorläufiger Mitteilungen[ 6-8] und Vorträge[ 9] [10].synthesis of ac orrin as metal-free N-protonated corrinium salt. Metal ions were introducedi nto the corrinium ligand to form aw ide variety of robust and non-robust corrin complexes.I mportantly,t he neutral form of the synthetic corrin ligand prefers to exist in as ensitive tautomeric form, featuring a second NH group and an olefinic bond in an e...

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Corrin Syntheses. Part V

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Vitamin B12: Experimente zur Frage nach dem Ursprung seiner molekularen Struktur

Eschenmoser

1988

Angew. Chem.

186

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Die im Anschluß an die Arbeiten zur Synthese des Vitamins B12 begonnene Suche nach einer potentiell biomimetischen Dunkelvariante der photochemischen A/D‐Secocorrin → Corrin‐Cycloisomerisierung hat seinerzeit zur Auffindung einer ganzen Familie von (A→D)‐Cyclisierungsvarianten geführt; nach den heutigen Kenntnissen über den Verlauf der Vitamin‐B12‐Biosynthese kommt in der Tat einer dieser Varianten der Rang eines chemischen Modells der Reaktionsstufe zu, durch welche die Biosynthese den kritischen Schritt der Corrinbildung vollzieht. Durch diese chemischen Studien zum Problem der Vitamin‐B12‐Biosynthese ließ sich experimentell die Tatsache aufdecken, daß die für das Corrinsystem typische A/D‐Ringverknüpfung, welche zu Beginn der B12‐Arbeiten als die schwierigste Hürde einer chemischen Vitamin‐B12‐Synthese gegolten hatte, in Wahrheit ein Strukturelement ist, das sich unter strukturgerechten Voraussetzungen auf vielfältige Weise und mit großer Leichtigkeit bildet. Analoges gilt, wie nun neuere Folgeuntersuchungen zeigen, auch für andere spezifische Strukturelemente des Vitamin‐B12‐Moleküls; hierzu gehören die charakteristische Anordnung der Doppelbindungen im Corrinchromophor, die spezielle Größe des Makroringes des Corrinliganden, die spezifische Haftung des Nucleotidringes an der Propionsäure‐Seitenkette des Ringes D, sowie das (allerdings nicht nur für Vitamin B12, sondern für alle uroporphinoiden Cofaktoren charakteristische) Substitutionsmuster der Seitenketten an der Ligandperipherie. Alle diese zunächst komplex erscheinenden Strukturelemente erweisen sich unter strukturgerechten Voraussetzungen in überraschendem Ausmaß als selbstkonstituierend, das heißt sie benötigen zu ihrer Bildung ein im Hinblick auf ihre Komplexität und Spezifität erstaunlich geringes Maß an externer Instruktion. Wir betrachten diese Befunde als Stationen auf dem Wege zu einer chemischen Rationalisierung der Vitamin‐B12‐Struktur, deren Ziel wir darin sehen, das dem Strukturtyp des Vitamins B12 immanente Potential zur Selbstkonstituierung experimentell zu erfassen. Es ist dieses Potential einer Cofaktorstruktur, welches zusammen mit deren spezifischer Reaktivitätsveranlagung für das Faktum der biologischen Selektion dieser Struktur mitverantwortlich ist. Die chemische Rationalisierung von Biomolekülstrukturen ist eine Aufgabe der organischen Naturstoffchemie. Die Forschungsdisziplin der Naturstoffsynthese bietet problemgerechte konzeptuelle und methodische Mittel, um diese Aufgabe experimentell anzugehen.

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Vitamin B₁₂: Experiments Concerning the Origin of Its Molecular Structure

Eschenmoser¹

1988

Angew. Chem. Int. Ed. Engl.

345

165

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Following the chemical synthesis of vitamin Biz, a search was begun for a potentially biomimetic "dark" variant of the photochemical A/D-secocorrin -+ corrin cycloisomerization, the central ring-closure step in one of the two cobyric acid syntheses. Significantly, not just one but a whole family of such variants was discovered. According to what is currently known, one of these variants can indeed be regarded as a chemical model for the reaction path followed by Nature in the biosynthetic construction of the corrin ring. These chemical studies of vitamin B l 2 biosynthesis had revealed that the A/D-ring junction, regarded as the main obstacle to a chemical vitamin BI2 synthesis at the outset, is in fact a structural element that is formed readily and in a variety of ways from structurally appropriate precursors. More recent investigations have shown that the same holds for other specific structural elements of the vitamin Bl2 molecule, including the characteristic arrangement of double bonds in the corrin chromophore, the special dimension of the macrocyclic ring of the corrin ligand, the specific attachment of the nucleotide loop to the propionic acid side chain of ring D, and the characteristic constitutional arrangement of the side chains around the ligand periphery (which vitamin B I 2 shares with all uroporphinoid cofactors). All these outwardly complex structural elements are found to "self-assemble" with surprising ease under structurally appropriate preconditions; the amount of "external instruction" required for their formation turns out to be surprisingly small in view of the complexity and specificity of these structural elements. We view these findings as steps on the way toward a chemical rationalization of the vitamin BIZ structure. The goal is to arrive experimentally at a perception of the biomolecule's intrinsic potential for structural self-assembly. This potential, together with the specific type of reactivity related to the biological function, is considered to be responsible for the biomolecule having been chosen by natural selection. The chemical rationalization of the structure of biomolecules is an objective of organic natural product chemistry. The field of natural product synthesis provides appropriate conceptual and methodological tools to approach this objective experimentally. Introduction: Concerning the Origin of Cofactors and the Emergence of Biosynthetic PathwaysThe (organic) cofactors occupy an exquisite position with respect to structure and function among the low-molecular-weight natural products. Their diverse and sometimes quite unusual structures, often occurring in families, are distinguished by their disposition to special types of reactivity. In partnerships between cofactors and specific proteins these dispositions are expressed and functionally exploited to a high degree of perfection with respect to both efficiency and selectivity. This perfection may seem natural to biologists, but it never ceases to surprise and amaze chemists to whom it represents a source of perman...

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Reactivity of Ligands in Synthetic Cobalt(III)‐ and Nickel(II)‐corrin Complexes

Cited by 15 publications

References 10 publications

Corrin Syntheses. Part V

Corrin Syntheses. Part V

Vitamin B12: Experimente zur Frage nach dem Ursprung seiner molekularen Struktur

Vitamin B₁₂: Experiments Concerning the Origin of Its Molecular Structure

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Reactivity of Ligands in Synthetic Cobalt(III)‐ and Nickel(II)‐corrin Complexes

Cited by 15 publications

References 10 publications

Corrin Syntheses. Part V

Corrin Syntheses. Part V

Vitamin B12: Experimente zur Frage nach dem Ursprung seiner molekularen Struktur

Vitamin B12: Experiments Concerning the Origin of Its Molecular Structure

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Vitamin B₁₂: Experiments Concerning the Origin of Its Molecular Structure