The
leucine-rich repeat kinase 2 (LRRK2) protein has been genetically
and functionally linked to Parkinson’s disease (PD), a disabling
and progressive neurodegenerative disorder whose current therapies
are limited in scope and efficacy. In this report, we describe a rigorous
hit-to-lead optimization campaign supported by structural enablement,
which culminated in the discovery of brain-penetrant, candidate-quality
molecules as represented by compounds 22 and 24. These compounds exhibit remarkable selectivity against the kinome
and offer good oral bioavailability and low projected human doses.
Furthermore, they showcase the implementation of stereochemical design
elements that serve to enable a potency- and selectivity-enhancing
increase in polarity and hydrogen bond donor (HBD) count while maintaining
a central nervous system-friendly profile typified by low levels of
transporter-mediated efflux and encouraging brain penetration in preclinical
models.
The action of arginase,
a metalloenzyme responsible for the hydrolysis
of arginine to urea and ornithine, is hypothesized to suppress immune-cell
activity within the tumor microenvironment, and thus its inhibition
may constitute a means by which to potentiate the efficacy of immunotherapeutics
such as anti-PD-1 checkpoint inhibitors. Taking inspiration from reported
enzyme–inhibitor cocrystal structures, we designed and synthesized
novel inhibitors of human arginase possessing a fused 5,5-bicyclic
ring system. The prototypical member of this class, 3, when dosed orally, successfully demonstrated serum arginase inhibition
and concomitant arginine elevation in a syngeneic mouse carcinoma
model, despite modest oral bioavailability. Structure-based design
strategies to improve the bioavailability of this class, including
scaffold modification, fluorination, and installation of active-transport
recognition motifs were explored.
Research in the field of asymmetric catalysis over the past half century has resulted in landmark advances, enabling the efficient synthesis of chiral building blocks, pharmaceuticals, and natural products. A small number of asymmetric catalytic reactions have been identified that display high selectivity across a broad scope of substrates; not coincidentally, these are the reactions that have the greatest impact on how enantioenriched compounds are synthesized. We postulate that substrate generality in asymmetric catalysis is rare not simply because it is intrinsically difficult to achieve, but also because of the way chiral catalysts are identified and optimized. Typical discovery campaigns rely on a single model substrate, and thus select for high performance in a narrow region of chemical space. Here, we put forth a practical approach for using multiple model substrates to select simultaneously for both enantioselectivity and generality in asymmetric catalysis from the outset. Multisubstrate screening is achieved by conducting high-throughput chiral analyses via supercritical fluid chromatography-mass spectrometry (SFC-MS) with pooled samples. When applied to Pictet–Spengler reactions, the multi-substrate screening approach revealed a promising and unexpected lead for the general enantioselective catalysis of this important transformation.
Inhibition
of leucine-rich repeat kinase 2 (LRRK2) kinase activity
represents a genetically supported, chemically tractable, and potentially
disease-modifying mechanism to treat Parkinson’s disease. Herein,
we describe the optimization of a novel series of potent, selective,
central nervous system (CNS)-penetrant 1-heteroaryl-1H-indazole type I (ATP competitive) LRRK2 inhibitors. Type I ATP-competitive
kinase physicochemical properties were integrated with CNS drug-like
properties through a combination of structure-based drug design and
parallel medicinal chemistry enabled by sp3–sp2 cross-coupling technologies. This resulted in the discovery
of a unique sp3-rich spirocarbonitrile motif that imparted
extraordinary potency, pharmacokinetics, and favorable CNS drug-like
properties. The lead compound, 25, demonstrated exceptional
on-target potency in human peripheral blood mononuclear cells, excellent
off-target kinase selectivity, and good brain exposure in rat, culminating
in a low projected human dose and a pre-clinical safety profile that
warranted advancement toward pre-clinical candidate enabling studies.
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