Fragment based drug design (FBDD) is an established means of drug discovery. A key difficulty in working with fragments is that initial fragment hits generally display weak binding affinity. As such, there is often a need to generate a large number of analogues to improve potency. In this regard, parallel synthesis is an efficient means of generating large numbers of compounds.
Improvements in potency within a compound series are often driven by slower dissociation from the target. As such, Off-rate Screening (ORS) via Surface Plasmon Resonance (SPR) provides a means to evaluate products of parallel synthesis [1]. Furthermore, we may take advantage of the sensitivity of this assay such that parallel synthesis may be conducted on microscale, and there is little need for purification as we are able to distinguish the slowest dissociating component from the reaction. This increases the efficiency of early stage optimisation as purification of compounds is often lengthy, and we need not waste this time pursuing undesirable analogues. The original description of ORS by SPR relied on structural information for a protein-ligand complex. During early stage development, it is often difficult to obtain structural information of the weak initial fragments bound to the target, which presents a limitation.
We present a means to overcome the lack of structural information using our “Rapid Expansion of Fragments into Leads” (REFiL) workflow. REFiL employs chemoinformatically designed diverse reagents sets to efficiently explore chemical space around a vector. The reagent sets support all of the most commonly used medicinal chemistry reactions. The workflow provides a means to establish synthetic conversion (LCMS), evaluate compound binding (ORS by SPR); and provide kinetic, affinity and selectivity information. We demonstrate the practical application of REFiL to overcome key difficulties in fragment development.