I was asked to write a perspective on macrocycles for Chemical Science, which is why I am in the mood for some interesting nuggets this field is loaded with. I hope that the examples I choose will convince the readers that they are in for a big surprise if they think that cyclic peptides are essentially peptides, only cyclic. This is very far away from the truth, but let me use a specific example. What if I gave you a molecule shown below and asked you to invert the stereocenter that is circled from S into R? I cannot see how there would be an intuitively clear answer to this question. However, there is a set of simple conditions that effect this transformation. This chemistry is detailed in a cool paper published in Synlett by Oberhauser and co-workers from Novartis. If you read this work, you will note that there is a clear explanation for why this particular stereocenter is special. By the way, if you feel compelled to share an interesting facet of macrocycle chemistry with me, I will appreciate your insights.

https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-1999-3103