No abstract

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.

An alanine scan performed in the 1970s suggested that Phe(6) and Phe(11) are required for the binding of somatostatin (SRIF-14). Molecular modeling studies and replacement of Phe(6) and Phe(11) with a cystine bridge affording ligands with the retention of high biological activity, however, led to the alternate conclusion that Phe(6) and Phe(11) stabilize the bioactive conformation of SRIF-14. Subsequent studies revealed that Phe(11) shields Phe(6) in a "herringbone" arrangement. More recently, a report from this laboratory demonstrated that Spartan 3-21G MO calculations can be invaluable in explaining SARs in medicinal chemistry. For example, the ability of benzene and indole rings to bind the Trp(8) binding pocket for SRIF-14 and the inability of pyrazine to do so was explained through differences in electrostatic potentials. To investigate the role of Phe(6) and Phe(11) more fully, we report here the synthesis of two analogues of D-Trp(8)-SRIF in which Phe(6) and Phe(11) were replaced by the pryazinylalanine congeners, respectively. The NMR spectra in D(2)O and the K(i)s fully support the proposition that Phe(11) stabilizes the bioactive conformation through pi-bonding or aromatic edge-to-face interaction and that pyrazinylalanine(6) can be shielded by Phe(11). The data also show unexpectedly that Phe(6), via the pi-bond, interacts with the receptor, consistent with the original interpretation of the alanine scan. Heretofore it had only been known that Lys(9) interacts with an aspartate anion of the receptor. These conclusions are supported by recent studies of Lewis et al. on the effects on K(i)s of Ala(6)-SRIF-14-amide at the five receptor subtargets. We also found that pyrazinylalanine(7)-D-Trp(8)-SRIF-14 does not bind, suggesting a repulsive interaction with the receptor. Taken together, our results not only validate predictions based on Spartan 3-21G MO analysis but also provide valuable information about the nature of the receptor interaction at the molecular level. Finally, the chirality of Trp(8) was unexpectedly found to have a striking effect on NMR spectra in methanol, especially at lower temperatures.

ABSTRACT:We have been focused on identifying a structurally different next generation inhibitor to MK-5172 (our Ns3/4a protease inhibitor currently under regulatory review), which would achieve superior pangenotypic activity with acceptable safety and pharmacokinetic profile. These efforts have led to the discovery of a novel class of HCV NS3/4a protease inhibitors containing a unique spirocyclic-proline structural motif. The design strategy involved a molecular-modeling based approach, and the optimization efforts on the series to obtain pan-genotypic coverage with good exposures on oral dosing. One of the key elements in this effort was the spirocyclization of the P2 quinoline group, which rigidified and constrained the binding conformation to provide a novel core. A second focus of the team was also to improve the activity against genotype 3a and the key mutant variants of genotype 1b. The rational application of structural chemistry with molecular modeling guided the design and optimization of the structure−activity relationships have resulted in the identification of the clinical candidate MK-8831 with excellent pan-genotypic activity and safety profile.

In conjunction with sodium borohydride as stoichiometric reagent a catalytic quantity of bis(4-perfluorohexylphenyl) diselenide converts vicinal dimesylates to the corresponding alkenes in good yield on warming in ethanol. The diselenide is recovered in high yield by continuous fluorous extraction.