Structural Elucidation and Total Synthesis

1. Azaspiracid-1 Structural Elucidation and Total Synthesis Thivisha Rajagopal January 29, 2009 University of Ottawa

2. A New Marine Toxin • Occurrence • Mussels (Mytilus edulis) cultivated at Killary Harbour, • Symptoms: • Nausea, vomiting, severe diarrhea, and stomach cramps • Similar to diarrhetic shellfish poisoning, DSP • A new marine toxin

3. Discovery of Azaspiracid • Produced by marine dinoflagellate, Protoperidinium crassipes • Absorbed by mussels, oysters, scallops, clams and cockles • Discovered in Europe • Harmful to the environment and human health • Damage to lung, liver, spleen, and lymphocyte, as well as lung tumor formation in mice

4. Azaspiracid-1 Structural Elucidation Structure Elucidation by NMR Stereochemistry via NOE

5. AZA Analogues AZA 1 is the predominant toxin in shellfish Analogues determined by tandem mass spectrometry (LC-MS)

6. Closer Look at Azaspiracid-1 Structure

7. Nicolaou - Retrosynthesis

8. Forward Synthesis

12. Structural Comparison Synthetic NMR DOES NOT match the Natural Azaspiracid-1 Synthetic NMR Natural NMR

13. Structural Comparison Synthetic NMR DOES NOT match the Natural Azaspiracid-1 Synthetic NMR Natural NMR

14. Structural Comparisons Synthetic NMR DOES NOT match the Natural Azaspiracid-1

15. Chemical Degradation

16. Structural Identity of Amino Lactone A

17. Natural vs Synthetic Amino Lactone MATCH

18. Natural vs Synthetic Amino Lactone MATCH

19. Absolute Stereochemistry • Synthetic interconversions and comparison of optical rotation • NMR based methods – Mosher Ester Analysis • For Carboxylic Acids Alcohols and Amines

20. Degradative Fragments

21. MATCH

22. MATCH

23. Confirmation of EFGHI Absolute Stereochemistry

24. Chemical Degradation

25. Comparison of Degradation vs Synthetic Fragment Synthetic Compound NMR Does Not Match the Degradation Fragment

26. Position of the Double Bond Degradation Fragment Weak HMBC correlation b/w C10 and 7-H Weak COSY correlation b/w6-H and 9-H

27. Double Bond Correction: Synthesis Synthetic Compound DID NOT MATCH Degradation Fragment Something more than the double bond location was wrong with the synthetic compound…

28. Two Key Observations: • Degradation ABCD fragment is Thermodynamically Stable • NOE between H-6 and C-14 Methyl

29. Anomeric Effect

31. Two Possible Structures

32. On the way to 3rd Possible Fragment

33. Construction of 4th Possible Fragment MATCH Absolute Stereochemistry was unknown

35. MATCH

36. MATCH

37. Initial Structure vs Correct Structure “Like several other total syntheses, this endeavor demonstrated once again the continued role of chemical synthesis in structural elucidation of natural products and its indispensable nature as a source of scarce, but highly valuable, substances for biological investigations.”

38. (-) and (+)-Azaspiracid-1

39. EVANS Total Synthesis • Development of C2-symmetric CuII-complexes • Integration of 3 key catalytic enantioselective processes • Hetero-Diels Alder • Glyoxylate-Ene • Mukaiyama Aldol

40. Retrosynthetic Analysis

41. ABCD-aldehyde

42. ABCD-aldehyde

43. Glyoxylate-ene Reaction

44. Glyoxylate-ene: Stereochemistry Ene (Re face) Ene (Si face) Bidentate coordination Distorted square planar Cu(II) ligand complex

45. CD Ring

47. ABCD-aldehyde

48. AB Ring

50. General Mechanism for CBS Reduction