David Simon Millan

Intramolecular hydrogen bonding to improve membrane permeability and absorption in beyond rule of five chemical space

Utilising ‘beyond rule of five’ chemical space is becoming increasingly important in drug design, but is usually at odds with good oral absorption. The formation of intramolecular hydrogen bonds in drug molecules is hypothesised to shield polarity facilitating improved membrane permeability and intestinal absorption. NMR based evidence for intramolecular hydrogen bonding in several ‘beyond rule of five’ oral drugs is described. Furthermore, the propensity for these drugs to form intramolecular hydrogen bonds could be predicted for through modelling the lowest energy conformation in the gas phase. The modulation of apparent lipophilicity through intramolecular hydrogen bonding in these molecules is supported by intrinsic cell permeability and intestinal absorption data in rat and human.

Fragment based discovery of a novel and selective PI3 kinase inhibitor

We report the use of fragment screening and fragment based drug design to develop a PI3γ kinase fragment hit into a lead. Initial fragment hits were discovered by high concentration biochemical screening, followed by a round of virtual screening to identify additional ligand efficient fragments. These were developed into potent and ligand efficient lead compounds using structure guided fragment growing and merging strategies. This led to a potent, selective, and cell permeable PI3γ kinase inhibitor with good metabolic stability that was useful as a preclinical tool compound.

Discovery of Clinical Candidate 4-[2-(5-Amino-1H-pyrazol-4-yl)-4-chlorophenoxy]-5-chloro-2-fluoro-N-1,3-thiazol-4-ylbenzenesulfonamide (PF-05089771): Design and Optimization of Diaryl Ether Aryl Sulfonamides as Selective Inhibitors of NaV1.7

A series of acidic diaryl ether heterocyclic sulfonamides that are potent and subtype selective NaV1.7 inhibitors is described. Optimization of early lead matter focused on removal of structural alerts, improving metabolic stability and reducing cytochrome P450 inhibition driven drug-drug interaction concerns to deliver the desired balance of preclinical in vitro properties. Concerns over nonmetabolic routes of clearance, variable clearance in preclinical species, and subsequent low confidence human pharmacokinetic predictions led to the decision to conduct a human microdose study to determine clinical pharmacokinetics. The design strategies and results from preclinical PK and clinical human microdose PK data are described leading to the discovery of the first subtype selective NaV1.7 inhibitor clinical candidate PF-05089771 (34) which binds to a site in the voltage sensing domain.

Chapter 5:Contribution of Structure-Based Drug Design to the Discovery of Marketed drugs

Structure-based drug design has played a role in the discovery of many drugs from many different disease areas, and it is now arguably an essential contributor to addressing the need to improve research and development productivity faced by the pharmaceutical industry. The purpose of this review is to highlight the impact of protein structures solved by X-ray and NMR techniques, as well as other techniques such as isothermal titration calorimetry, on structure-based discovery. The importance of these methods in drug discovery will be underscored by examples of drugs approved up until the end of 2009, which were discovered utilising structural information. These examples will highlight that structure-based drug design has moved on from just using structural knowledge to optimise potency to using it also with selectivity, pharmacokinetic and pharmaceutical properties in mind. Following on from this, a medicinal chemists perspective aims to highlight the benefits and advantages of structure-based drug design but also to provide an opinion on the pitfalls and hype surrounding this technology. In particular, this section will draw on examples to highlight its impact and limitations on assessing druggability, as well as factors to consider when using structure-based drug design in lead generation and the optimisation of leads for potency, selectivity and pharmacokinetic properties. Finally, some forward looking thoughts will be proposed with regard to the future of structure-based drug design and where emphasis could be placed to increase the impact of this approach on drug discovery productivity.

Chapter 11:Future Targets and Chemistry and ADME Needs

This chapetr examines drug targets within the human genome and looks at the likely future targets small molecule drug discovery will try top exploit. The chapter suggests that it is unlikely that small molecule drug targets will come from new gene families. The largest gap appears in the ability to translate some of the famileis into drugs with good or reasonable pharmacokinetics. There is a gap in understanding drug disposition, particularly as compounds move to higher lipophilicities and polar surface areas. Also discussed are the new chemical processes that are required to exploit these targets.