The Significance of Chirality in Drug Design and Synthesis of Bitopic Ligands as D3 Receptor (D3R) Selective Agonists.

Because of the large degree of homology among dopamine D2-like receptors, discovering ligands capable of discriminating between the D2, D3, and D4 receptor subtypes remains a significant challenge. Previous work has exemplified the use of bitopic ligands as a powerful strategy in achieving subtype selectivity for agonists and antagonists alike. Inspired by the potential for chemical modification of the D3 preferential agonists (+)-PD128,907 (1) and PF592,379 (2), we synthesized bitopic structures to further improve their D3R selectivity. We found that the (2S,5S) conformation of scaffold 2 resulted in a privileged architecture with increased affinity and selectivity for the D3R. In addition, a cyclopropyl moiety incorporated into the linker and full resolution of the chiral centers resulted in lead compound 53 and eutomer 53a that demonstrate significantly higher D3R binding selectivities than the reference compounds. Moreover, the favorable metabolic stability in rat liver microsomes supports future studies in in vivo models of dopamine system dysregulation.

Discovery of a novel small molecule agonist scaffold for the APJ receptor.

The apelinergic system includes a series of endogenous peptides apelin, ELABELA/TODDLER and their 7-transmembrane G-protein coupled apelin receptor (APJ, AGTRL-1, APLNR). The APJ receptor is an attractive therapeutic target because of its involvement in cardiovascular diseases and potentially other disorders including liver fibrosis, obesity, diabetes, and neuroprotection. To date, pharmacological characterization of the APJ receptor has been limited due to the lack of small molecule functional agonists or antagonists. Through focused screening we identified a drug-like small molecule agonist hit 1 with a functional EC50 value of 21.5±5µM and binding affinity (Ki) of 5.2±0.5µM. Initial structure-activity studies afforded compound 22 having a 27-fold enhancement in potency and the first sub-micromolar full agonist with an EC50 value of 800±0.1nM and Ki of 1.3±0.3µM. Preliminary SAR, synthetic methodology, and in vitro pharmacological characterization indicate this scaffold will serve as a favorable starting point for further refinement of APJ potency and selectivity.

Chiral Resolution and Serendipitous Fluorination Reaction for the Selective Dopamine D3 Receptor Antagonist BAK2-66.

The improved chiral synthesis of the selective dopamine D3 receptor (D3R) antagonist (R)-N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)-3-hydroxybutyl)1H-indole-2-carboxamide (( R )-PG648) is described. The same chiral secondary alcohol intermediate was used to prepare the enantiomers of a 3-F-benzofuranyl analogue, BAK 2-66. The absolute configurations of the 3-F enantiomers were assigned from their X-ray crystal structures that confirmed retention of configuration during fluorination with N,N-diethylaminosulfur trifluoride (DAST). ( R )-BAK2-66 showed higher D3R affinity and selectivity than its (S)-enantiomer; however, it had lower D3R affinity and enantioselectivity than ( R )-PG648. Further, importance of the 4-atom linker length between the aryl amide and 4-phenylpiperazine was demonstrated with the 4-fluorobutyl-product (8).

Surface-immobilized self-assembled protein-based quantum dot nanoassemblies.

Luminescent semiconductor quantum dot (QD)-based optical biosensors have the potential to overcome many of the limitations associated with using conventional organic dyes for biodetection. We have previously demonstrated a hybrid QD-protein-based fluorescence resonance energy transfer (FRET) sensor. Although the QD acted as an energy donor and a protein scaffold in the sensor, recognition and specificity were derived from the proteins. Transitioning this hybrid prototype sensor into flow cells and integrated devices will require a surface-immobilization strategy that allows the QD-based sensor to sample the environment and still maintain a distinct protein-covered QD architecture. We demonstrate a self-assembled strategy designed to accomplish this. Using glass slides coated with a monolayer of neutravidin (NA) as the template, QDs with maltose binding protein (MBP) and avidin coordinated to their surface were attached to the glass slides in discrete patterns using an intermediary bridge of biotinylated MBP or antibody linkers. Control of the surface location and concentration of the QD-protein-based structures is demonstrated. The utility of this self-assembly strategy is further demonstrated by assembling a QD-protein structure that allows the QDs to engage in FRET with a dye located on the surface-covering protein.