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Macrocyclic Ligands: Functional Host Guest Systems.

Macrocyclic Ligands: Functional Host Guest Systems. Post Graduate Lecture Course January 2000 Lecture 1. 1. Introduction. Definitions What is a macrocycle?

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Macrocyclic Ligands: Functional Host Guest Systems.

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  1. Macrocyclic Ligands: Functional Host Guest Systems. Post Graduate Lecture Course January 2000 Lecture 1

  2. 1. Introduction • Definitions • What is a macrocycle? “A macrocycle is a large ring molecule, normally having 12 or more atoms in the ring and normally containing heteroatoms capable of binding substrates” Small Rings (3-6), Mesocycles (7-11), Macrocycles (12)

  3. Macrocyclic Ligands Usually stretch the definition to include: Ring sizes  9 At least 3 donor atoms

  4. Why Macrocycles? Biological Systems for: Photosynthesis Oxygen transport Redox reactions Ion transport

  5. 2. Natural Macrocycles 2.1 Cyclic Antibiotics 2 types: Neutral Macrocycles Acyclic Monobasic Acids

  6. Enniatin B 18-membered ring Depsipeptide alternating -amino acid and - hydroxy acid residues • Valinomycin 36-membered ring Also Depsipeptide

  7. Nonactin 32-membered ring Macrotetrolide - Alternating ester and ether groups All complex K+ selectively vs other alkali metal ions. Consider some of their X-ray structures….

  8. Biological Action • Transport of ions through biological membranes (e.g. cell walls) Construction: Lipids/proteins Thickness: ca 70Å Function: selective transport Substances capable of transporting ions across such membranes are IONOPHORES

  9. Porphyrins and Related Systems • By far the most common biological macrocycles • three main ring types: Porphyrin Chlorin Corrin

  10. Vitamin B12 Coenzyme

  11. Vitamin B12 Coenzyme • Naturally Occurring Organometallic! • Cobalt(III) with R-. • Reduction to Co(II) and Co(I) ? R =

  12. Chlorophyll • Initiates Photo-synthesis • Absorbs in red • Oxidation of H2O to O2 • Glucose formation from CO2 and H2O

  13. Haem Proteins Two functions: - O2 transport and storage - Electron Transfer Contain Fe porphyrin complexes Examples: - Haemoglobin - Myoglobin - Cytochrome P450

  14. 3. Synthetic Macrocycles 3.1 History Baeyer, 1886 - First Reported Macrocycle Chem. Ber. 1886, 19, 2184

  15. Metal Phthalocyanines, first reported 1928 The only well known synthetic macrocycle pre-1960

  16. Other Pre-1960 Macrocycles • Cyclam (Cyclic Amine) Alphen, Recl. Trav. Chim, 1937, 56, 343. • Dibenzoaza-crowns Krässig and Greber, Makromol. Chem., 1953, 11, 231.

  17. 3.2 Nomenclature • 1,4,7-trithiacyclononane: trithia-9-crown-3; 9aneS3 • 1,4,8,11-tetraazacyclotetradecane: tetraaza-14- crown-4; 14aneN4. • 4,13-diaza-1,7,10,16-oxacyclooctadecane: diaza-18-crown-6; 18aneN2O4.

  18. 3.4 Synthesis: General Methodology • Formation of One Bond: Linear compound with a reactive group on each end.

  19. Examples • This “head to tail” method is sometimes known as the snake reaction!

  20. Formation of two Bonds: 1 + 1 Cyclisation Most Commonly Used Method of Macrocycle Preparation

  21. Examples

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