Dr. Renpeng Liu is currently a postdoctoral researcher in the field of glycomics at Emory University. Before that he was at the Eshelman School of Pharmacy at the University of North Carolina working on the synthesis of heparans which resulted in several publications including two that have been highlighted in F-Blog. Dr. Liu was born in Wuhan, China and received his BS from Wuhan University then a MS at Ohio State University before moving on to UNC, where he first started using fluorous tags. Outside of the lab he enjoys playing soccer, watching movies, and reading. We asked Dr. Liu a few questions regarding his work and the impact that fluorous methods had.
F-Blog: What are your research interests and what is your current project?
Dr. Liu: My area of research interest is cell surface glycans and their biological function. At the University of North Carolina I was working on the enzymatic synthesis of heparan sulfate and heparin, an important anticoagulant drug. Now I am working at Emory Univeristy on influenza virus and researching the role of glycans in influenza virus pathogenesis.
F-Blog: How have fluorous methods helped advance your research and how would you describe the impact it had?
Dr. Liu: Fluorous methods really helped a lot in my research. Purification and structural analysis of heparan sulfate oligosaccharides are major challenges in complex heparan sulfate/heparin synthesis. By introducing a fluorous tag, the purification of heparan sulfate became much simpler and faster. Also, the recovery yield increased to 80% using fluorous tagged samples versus about 40% for untagged samples. This method can also be used to conduct parallel synthesis of heparan sulfate oligosaccharides and carbohydrate microarray development. Furthermore the tag is excellent for MS analysis. One advantage is that the fluorous tag is non-fragmentary in MS and therefore is convenient for determining the reducing end and non-reducing end when we try to sequence the heparan sulfate using MS/MS.
F-Blog: How did you first hear about fluorous techniques?
Dr. Liu: I first heard about fluorous techniques during a chemistry class in UNC in 2006, but I didn’t realize its power until I heard a faculty candidate talk by Dr. Qisheng Zhang, who graduated from Dr. Dennis Curran’s lab. Dr. Zhang is currently a faculty member at the Eshelman School of Pharmacy at UNC and he gave me a lot of good advice on fluorous tags.
F-Blog: Were there any paper or papers in particular that really convinced you that you should try fluorous methods?
Dr. Liu: Yes, two papers really convinced me of the benefit of fluorous tags. One is from Dr. Dennis Curran (Science, 2001, 291, 1766), which demonstrated the power of parallel synthesis using fluorous techniques. The other one was published by Dr. Nicola Pohl on fluorous-based carbohydrate microarrays (J. Am. Chem. Soc. 2005, 127, 13162). The synthesis of complex carbohydrates is painful, so the ability to quickly and efficiently access structurally defined oligosaccharides and oligosaccharide libraries coupled with the formation of carbohydrate microarray should accelerate our knowledge of glycan function. At that time I was thinkging that once I prepared fluorous tagged heparan sulfate, these tagged carbohydrates would be ready for printing in a fluorous based microarray. This microarray will greatly advance our understanding of heparan sulfate-protein interacdtions. It is known that heparan sulfate/heparin interacts with more than 100 proteins and therefore, a heparan sulfate microarray will be extremely important and will be of interest to both chemists and biologists.
F-Blog: Describe how you have used fluorous techniques and your experience with it in the beginning?
Dr. Liu: We indeed had a lot of difficulties in the beginning. First, what would be a good choice as a fluorous tag? After careful thinking and discussion, we decided to choose a benzyl amine which has two advantages. First, it can react with the reducing end of the disaccharide by reductive amination. Second, a benzyl group has UV absorbance at 260 nm that facilitates HPLC analysis during preparation. The next question was how to obtain pure tagged disaccharide.
F-Blog: The disaccharide was the starting substrate for the enzymatic reactions in preparing longer oligosaccharides, right?
Dr. Liu: Correct. We could easily use FSPE to remove the tagged carbohydrate from a reaction mixture, but how to remove the excess fluorous tag is another problem. We finally relied on paper chromatography and reverse phase HPLC to obtain pure fluorous tagged disaccharide. Finally, we found that the traditional long (C8F17) tag had poor solubility in water, which was a problem since our enzymatic reactions are conducted in aqueous solution. Luckily we called Fluorous Technologies and we were told that we could switch to a shorter tag (C3F7) and the company could also prepare this short tag for us. So we were able to overcome these intial hurdles and successfully developed fluorous tagged based enzymatic synthesis of heparan sulfate, thanks to a little help from Fluorous Technologies.
F-Blog: What are your long-term plans?
Dr. Liu: I hope to be a professor in the future and I am very interested in drug-discovery related research, especially in glycan-based drug development. I would like to utilize all the modern technologies i learned from my Ph.D. and postdoctoral training, including fluorous technique, to achieve my goal.
F-Blog: Thanks Dr. Liu and good luck in your future endeavors.