Part 1: Design and Synthesis of BRDT Selective Inhibitors as Male Contraceptive Agents Part 2: Focused Library Synthesis for TGR5 (Takeda G Protein-Coupled Receptor 5) Antagonist

Abstract

Unintended pregnancies can have significant adverse socioeconomic effects and health risks for women. One approach to reducing unintended pregnancies is the use of effective contraceptive methods. While women have multiple reversible contraceptive options, there is an unmet need for men to pursue safe and reversible infertility. Chapter 1 provides a brief overview of two pharmacological approaches to male contraception: disrupting the hormonal milieu (hormonal) and targeting key cellular components in sperm maturation and function (non-hormonal). Because of adverse effects resulting from hormonal disruption, we aim to develop safe novel non-hormonal male contraceptive agents. To this end, we have targeted the testis-specific bromodomain (BRDT), an epigenetic reader protein essential for spermatogenesis. Chapter 2 describes the validation of a tricyclic dihydropyridine hit from a virtual screening campaign. Based on the sequence alignment, we hypothesized that engaging the unique Arg54 in the first bromodomain of BRDT (BRDT-1), would achieve BRDT-1 selectivity over other bromodomain isoforms. Guided by this hypothesis, we explored three structural modifications on the scaffold: conversion its lactone functionality to a lactam, lactone ring-opening, and conformational restriction by macrocyclization. Cellularly active analogs with a greater than 10-fold increase in affinity were obtained. However, the desired BRDT-1 selectivity was not achieved for any of the three subsets. Additionally, novel mechanisms of action for targeting BRDT were pursued, including proteolysis-targeted chimeras (PROTACs) for selective protein degradation and bivalent molecules for simultaneous occupancies of two bromodomains. Chapter 3 focuses on an inherited genetic disorder, polycystic liver disease (PLD). The G protein-coupled receptor TGR5 activation was identified as strongly associated with PLD. To develop a TGR5 antagonist, we hypothesized that known TGR5 agonists could be converted to antagonists via systematic structural modifications. After selecting the nicotinamide core as our starting point, we used combinatorial chemistry to generate a focused library with over 100 analogs. The screenings for agonist and antagonist activity, however, only yielded TGR5 agonists rather than antagonists. Nevertheless, the results provide novel structure-activity relationship insight for TGR5 agonists based on the nicotinamide core. This experiment highlights the need to obtain additional information including the co-crystal structures for future TGR5 antagonist discovery efforts.