Proline: its puckering and a sila- version

For the past two days I have been in La Grande Motte, which is not far from Montpellier in the South of France. The conference was put together by Professors Pascal Dumy and Jean Martinez, to whom we are most grateful for not only arranging a great program, but also for giving us an excuse to visit this part of the world in the Fall:

http://www.polechimie-balard.fr/rub/458/balard-conference-2014-speakers.htm

There have been some memorable talks thus far and I have learned many new things, particularly about proline. This molecule continues to amaze a whole lot of people, including myself. Professor Helma Wennemers of ETH-Zurich presented her research aimed at understanding collagen. I was impressed with the molecular-level details of this material that has been obtained by Helma’s lab. Collagen is a polymer that consists of proline, hydroxyproline, and glycine. Helma described the significance of how the proline ring puckers and the prevalence of n-to-pi* interactions that exist in this material (http://onlinelibrary.wiley.com/doi/10.1002/anie.201008118/abstract).

In the past, I mentioned these important interactions on my blog and talked about the work of Ron Raines (who is also here, by the way). In her crystallographic analysis of oligoprolines, Helma has now obtained evidence for the n-to-pi* interactions between the adjacent proline residues. Given the importance of proline in my own lab’s macrocyclization reactions, I am surprised that we have not considered the relevance of puckering on macrocycle conformation. Another proline-related vignette came from the lab of one of this conference organizers, Professor Martinez. Dr. Florine Cavelier, who belongs to the Martinez lab at the IBMM Institute in Montpellier, presented her work where silaproline was featured prominently. Prior to this conference, I had not been aware of the significance of this unnatural amino acid and I am glad that I had a chance to see its unique influence on peptide materials. By the way, the synthesis is rather simple and scalable: