Daniel Chelsky

Identification of potent inhibitors of Plasmodium falciparum plasmepsin II from an encoded statine combinatorial library.

An encoded 13,020-member combinatorial library was synthesized containing a statine core. Evaluation of this library with plasmepsin II, an aspartyl protease required for hemoglobin metabolism in the malaria parasite, led to the identification of potent and selective inhibitors as well as novel structure-activity relationships.

Biological Characterization of Neurokinin Antagonists Discovered Through Screening of a Combinatorial Library

Recent advances in combinatorial chemistry have resulted in the rapid screening of libraries against biological targets. Another advance in biological screening is the ability to design and utilize novel, automated, nonradioactive assays for targets of pharmaceutical interest. Using encoding technology and europium time-resolved fluorescence, we have designed primary receptor binding assays to define active compounds against the neurokinin-1 and neurokinin-2 receptor subtypes. In addition, a secondary, cell-based, functional assay measuring intracellular calcium flux with calcium sensitive fluorophores was used to determine receptor agonist or antagonist activities. We adapted a cuvette based assay to a CCD camera and digital imaging system that allowed us to demonstrate functional receptor antagonist activity in all 96 wells of a microtiter plate simultaneously. The screening of a 20,000 member library using europium labeled neurokinin ligands resulted in the identification of 43 active compounds for neurokinin-1 and 27 for neurokinin-2. Through medicinal chemistry and structure-activity relationships, a compound was synthesized with balanced dual antagonist activity at both neurokinin receptors with greater than 100-fold less activity against the neurokinin-3 receptor subtype. The structure-activity relationships generated from this initial library can now be used to design a new focused library to improve on neurokinin-1/neurokinin-2 receptor potency and selectivity.

Binary encoded small-molecule libraries in drug discovery and optimization

A variety of small-molecule combinatorial libraries have been prepared on solid support using a binary encoding strategy employing non-sequenceable encoding molecules. Library members are attached to the support using photolabile linkers which permit their release for assay free in solution. The encoding molecules are attached using a carbene insertion reaction and are released via oxidation. A wide variety of synthetic reactions have been utilized for library synthesis including, for example, cyclocondensations, reductive aminations, and heteroaromatic halide displacements, as well as acylations and sulfonylations. Initial screening of two such libraries identified lead structures for the inhibition of carbonic anhydrase. Subsequently, based upon these leads a smaller focused combinatorial library was constructed and used to analyze the structure-activity relationships (SARs) governing enzyme inhibition and isozyme selectivity. The combination of random screening with a broad diversity of compounds, followed by focused libraries for detailed SARs and selectivity, demonstrates the power of binary encoded small-molecule combinatorial libraries for drug discovery.

Exploring structure-activity relationships of tricyclic farnesyltransferase inhibitors using ECLiPS libraries.

The development of structure-activity relationships (SARs) relating to the function of a biological protein is often a long and protracted undertaking when using an iterative medicinal chemistry approach. High throughput screening of ECLiPS (Encoded Combinatorial Libraries on Polymeric Support) libraries can be used to simplify this process. In this paper, we illustrate how a large ECLiPS library of 26,908 compounds, based on a tricyclic core structure, was used to define a multitude of SARs for the oncogenic target, farnesyltransferase (FTase). This library, FT-2, was prepared using a split-and-pool approach in which small molecules are constructed on resin that contains tag/linker constructs to track the synthetic process [1-5] Highly defined SARs were produced from this screen that enhanced our understanding of FTase binding site interactions. The pivotal compounds culled from this library were potent in both cell-free and cell-based FTase assays, selective over the closely related enzyme, geranylgeranyltransferase I (GGTase I), and inhibited the adherent-independent growth of a transformed cell line.