Epothilone A: The Nature, Synthesis, Characterization, and Conformation of an Anti-Cancer Drug

1. Epothilone A: The Nature, Synthesis, Characterization, and Conformation of an Anti-Cancer Drug University of Notre Dame Benjamin L. Hechler Thursday, April 12, 2007

2. Discovery, Nature, Prospects 1995 – potency determined Myxobacterium Sorangium cellulosum (So ce 90)1 Stabilizes microtubules, initiating apoptosis Advantages over Taxol: 1) highly effective against Taxol- resistant strains 2) structure more manageable 3) fewer side effects2 1 Taylor, R.E.; Zajicek, J., J. Org. Chem. 1999 2 Nicolaou, K. C. et al., Angew. Chem. Int. Ed., 1998 Title slide image: Nicolaou, K. C. et al., Angew. Chem. Int. Ed., 1998

3. Biosynthesis of Epothilones Epothilones C and D are primary products Epoxidation by enzymes produces epothilones A and B Hydroxylation of terminal carbon produces epothilones E and F1 epoxidation hydroxylation 1 Hofle, G. et al., J. Nat. Prod. 2001

4. Laboratory Synthesis of Epothilones Danishefsky, Nicolaou, and Schinzer groups first to synthesize1 Nicolaou approach #1: Olefin Metathesis 1 Nicolaou, K. C. et al., Angew. Chem. Int. Ed. Engl. 1996

5. Aldol Condensation Wittig Reaction Difficulties: Stereochemistry Esterification Olefin Metathesis Figures: Nicolaou, K. C. et al. Angew. Chem Int. Ed. Engl.1997

6. Characterization of Epothilone A Was my synthesis successful? Formula: C26H39NO6S Molecular Weight: 493.66 Appearance: colorless crystals Melting Point: 95 Celsius1 Water Solubility: .7 g/L2 IR: characteristic peaks at 3464 (-OH), 1737, 1689 (carbonyl) cm- 1 1 Hofle, G. et al., J. Nat. Prod. 2001 2 Hofle, G. et al., Angew. Chem. 1996 H1 NMR: Taylor, R.E.; Zajicek, J., J. Org. Chem. 1999 C13 NMR: Meiler, J. et al., J. Chem. Inf. Comput. Sci., 2000

7. Of Interest: Two Conformers Richard E. Taylor – University of Notre Dame (1999) Energetic Consequences1 (1) polypropionate rigidity (2) other regions see flexibility 1 Taylor, R.E.; Zajicek, J., J. Org. Chem. 1999

8. Summary • Action determined in 1995, prospects are favorable • Biosynthetic Pathways of Epothilones A-F identified • Laboratory syntheses continually manipulated1 - Assumes two conformations in solution… - …Yet studies on tubulin binding remain 1 Taylor, R. E.; Haley, J. D., Tetrahedron Lett., 1997

9. Epothilone A: The Nature, Synthesis, Characterization, and Conformation of an Anti-Cancer Drug University of Notre Dame Benjamin Doe Thursday, April 12, 2007

10. Laborartory Synthesis of Epothilones Problems with Olefin Metathesis Approach (1) aldol condensation stereoselectivity(3:2) (2) olefin metathesis stereoselectivity(~1:1) Benefits of MacrolactonizationApproach (1) wittig reaction largely favors Z-isomer1 (2) olefin metathesis more difficult with tri-substituted DB2 1 Bergelson, L. D.; Shemyakin, M. M., Angew. Chem. Int. Ed. Engl. 1964 2 Nicolaou, K. C. et al., Angew. Chem. Int. Ed., 1998

11. Conformers Involved in Binding (?) Higher-Energy Conformations Appears that a the syn-pentane- esque conformation assumed1 Major differences: C3 –OH and thiazole side chain rotatation2 Experimentation involving FRET suggests “the emission maximum of the microtubule-bound species was similar to that of the fluorophore in DMSO”3 1 Heinz, D. W., et al., Agnew. Chem. Int. Ed.,2005 2 Griesinger, C. et al., Agnew. Chem. Int. Ed., 2003 3 Kingston, D. G. I. et al., Tetrahedron, 2003