Lessons Learned from Organic Synthesis

1. Joshua J. Nyman Howard Hughes Medical Institute Summer Scholar Research Project Lessons Learned from Organic Synthesis Mentor: Dr. Yan Zhang, Department of Medicinal Chemistry, VCU School of Pharmacy

2. Background • Anibamine is a natural product, but recently it has been successfully synthesized in the laboratory. • Anibamine can be used as an anti-HIV drug • It has a unique chemical structure. _ TFA Anibamine

3. The Research Project • The objective of the research project was to synthesize the ring system of anibamine; and then to alter the stereochemistry of its side-chains. _ TFA Anibamine

4. My Synthesis Route K2CO3 acetylacetone + 3-cyano-4,6-dimethyl-2-hydroxypyridine (2-hydroxy-4,6-dimethyl-nicotinonitrile) , TFA, H2SO4 cyanoacetamide CuCN, DMF under nitrogen gas 5-bromo-2-hydroxy-4,6-dimethyl-nicotinonitrile 1,2-dihydro-4,6-dimethyl-2-oxopyridine-3,5-dicarbonitrile Tetrabutylammonium bromide, P2O5 2-bromo-4,6-dimethylpyridine-3,5-dicarbonitrile

5. Forming the Pyridine Ring • An aqueous solution of potassium carbonate was prepared. • Acetylacetone and cyanoacetamide were added to the solution. • A stir bar was placed into the resulting mixture and the mixture was allowed to stir at room temperature for 24 hours. K2CO3 acetylacetone cyanoacetamide 3-cyano-4,6-dimethyl-2-hydroxypyridine

6. Forming the Pyridine Ring • After 24 hours of stirring, the mixture was vacuum filtrated, yielding a white powder. • Melting point was on the high end of the literature melting point, and the thin-layer chromatography provided a positive presumptive test for the pyridine ring product. • A proton-NMR was also done on the resultant compound, but was later to found to be of little value based on the solvent used to dissolve the sample. Images: Barnard College Organic Chemistry Lab

7. Brominating the Pyridine Ring • The product of the previous reaction was dissolved in concentrated sulfuric acid and trifluoracetic acid, while in an ice bath. N-bromosuccinimide was then added. ** • This reaction was run multiple times with varying degrees of purity. • Melting points taken of the product(s) were 10 to 15 degrees too high in a couple of cases. • Thin-layer chromatography suggested some compounds were impure. • Product appeared to be a light yellow in the more impure products and white in the purer products. , TFA, H2SO4

8. Brominating the Pyridine Ring • It seems the purity of this reaction could have been affected by certain techniques. • For example: • Removing the reaction mixture from the ice bath: Exothermic reaction • Rate of addition: Adding the NBS too quickly likely resulted in an undesired side reaction. • Acid-Base reaction. , TFA, H2SO4

9. Adding a Cyano- Group to the Pyridine Ring • This reaction had some special considerations: • One of the chemicals used in this reaction is a highly toxic compound called cuprous cyanide (a.k.a. copper (I) cyanide). • Handling the cyanide required great care CuCN, DMF under nitrogen gas

10. Adding a Cyano- Group to the Pyridine Ring • All reactants had to be very dry!!! Oil Pump

11. Adding a Cyano- Group to the Pyridine Ring • The cuprous cyanide was dissolved in dimethylformamide along with the product from the previous reaction. • The mixture was then refluxed for 48 hours under nitrogen gas. CuCN, DMF under nitrogen gas

12. Adding a Cyano- Group to the Pyridine Ring • My compound being refluxed under nitrogen protection

13. Adding a Cyano- Group to the Pyridine Ring • This reaction gave me multiple problems • Proton NMR, Thin-Layer Chromatograhy tests, and melting point tests = impure. • Because of this, I wasn’t able to proceed further before the end of this program. CuCN, DMF under nitrogen gas

14. Lessons Learned • Organic synthesis can be very tricky, especially when trying to form natural products. • I learned not only to think about the products I am trying to synthesize, but also about which products I do not want to synthesize (i.e. impurities) and how to prevent them. • It’s not just what chemicals you add, but how you add them. Temperature, rate of addition, and other factors can have a considerable impact on the overall synthesis.

15. References and Acknowledgements • A special thanks to Dr. Yan Zhang (my mentor) for sharing his expertise, his laboratory, and for making this an exceptional research learning experience. • Also a special thanks to Dr. Guo Li and Kendra Haney, for generously sharing their time and for their guidance. • And to all of the others brilliant individuals in Dr. Zhang’s lab whose efforts contributed to my learning experience.

16. References and Acknowledgements • Literature (the primary source for my research project and background information presented in this presentation): • Guo Li, Karen Watson, Robert W. Buckheit, and Yan Zhang: Total Synthesis of Anibamine, a Novel Natural Product as a Chemokine Receptor CCR5 Antagonist Organic Letters 2007. Vol 9. 10: 2043-2046.

17. References and Acknowledgements • Pictures and Graphics: • Title Slide: Erlenmeyer Flasks – • Department of Chemistry & BiochemistryNorthern Arizona University www.nau.edu/~chem/Images/flasks.jpg • Slide 10: Reflux Apparatus and White Compound in Erlenmeyer Flask – • Barnard College Organic Chemistry Lab http://www.barnard.edu/chem/orgolab/lab2.htm