Opportunities and guidelines for discovery of orally absorbed drugs in beyond rule of 5 space.

Recent years have seen a dramatic increase in the number of drugs approved in chemical space outside of Lipinski's rule of 5, that is in what has been termed beyond rule of 5 (bRo5) space. The development of three major classes of oral drugs that treat HIV and HCV infections and the growing evidence that novel, difficult targets can be accessed has prompted research into understanding design of drugs displaying cell permeability, solubility and ultimately oral bioavailability in bRo5 space. Studies have found a consistent outer property limit for a reasonable chance of de novo designing oral bioavailability. In addition, several property-based guidelines, along with incorporation of chameleonic features, have emerged as strategies to aid design in bRo5 space. A more detailed understanding of the complex and environment dependent conformational landscape will likely be the focus of the next generation of guidelines allowing property predictions of ever more complex compounds. By pushing the boundaries of current orally designable chemical space we hope that discoveries will be made for fundamental science and also for discovery of novel therapeutics.