Back about 20 years ago, a medicinal chemist named Lipinski came up his “Rule of Five” for whether a chemical compound had “drug like properties”. Never mind what they are, unless you’re planning to start a lab in your garage. There have been variations on the “rule of five”, like, do you really need a drug right out of the starting gate? Why not look for lead-like compounds? What are the properties of those? And how did you come up with these rules anyway?

The bottom line answer is, well, after you’ve seen a bajillion compounds coming out of high throughput screening and have worked on thousands more, you just know. You can look at a compound and say, ehhhh, that’s never going to be a drug. The tailpiece has too many carbons or the scaffold is too skimpy or that compound is promiscuous. (Um, that’s as sexy as drug…