Addressing Atropisomerism in the Development of Sotorasib, a Covalent Inhibitor of KRAS G12C: Structural, Analytical, and Synthetic Considerations

Abstract

Conspectus Nearly a century after its first description, configurationally stable axial chirality remains a rare feature in marketed drugs. In the development of the KRASG12C inhibitor sotorasib (LUMAKRAS/LUMYKRAS), an axially chiral biaryl moiety proved a critical structural element in engaging a “cryptic” protein binding pocket and enhancing inhibitor potency. Restricted rotation about this axis of chirality gave rise to configurationally stable atropisomers that demonstrated a 10-fold difference in potency. The decision to develop sotorasib as a single-atropisomer drug gave rise to a range of analytical and synthetic challenges, whose resolution we review here. Assessing the configurational stability of differentially substituted biaryl units in early inhibitor candidates represented the first challenge to be overcome, as differing atropisomer stability profiles called for differing development strategies (e.g., as rapidly equilibrating rotamers vs as single atropisomers). We relied on a range of NMR, HPLC, and computational methods to assess atropisomer stability. Here, we describe the various variable-temperature NMR, time-course NMR, and chiral HPLC approaches used to assess the configurational stability of axially chiral bonds displaying a range of rotational barriers. As optimal engagement of the “cryptic” pocket of KRASG12C was ultimately achieved with a configurationally stable atropisomeric linkage, the second challenge to be overcome entailed preparing the preferred (M)-atropisomer of sotorasib on industrial scale. This synthetic challenge centered on the large-scale synthesis of an atropisomerically pure building block comprising the central azaquinazolinone and pyridine rings of sotorasib. We examined a range of strategies to prepare this compound as a single atropisomer: asymmetric catalysis, chiral chromatographic purification, and classical resolution. Although chiral liquid and simulated moving bed chromatography provided expedient access to initial multikilo supplies of this key intermediate, a classical resolution process was ultimately developed that proved significantly more efficient on metric-ton scale. To avoid discarding half of the material from this resolution, this process was subsequently refined to enable thermal recycling of the undesired atropisomer, providing an even more efficient commercial process that proved both robust and green. While the preparation of sotorasib as a single atropisomer significantly increased both the analytical and synthetic complexity of its development, the axially chiral biaryl linkage that gave rise to the atropisomerism of sotorasib proved a key design element in optimizing sotorasib’s binding to KRASG12C. It is hoped that this review will help in outlining the range of analytical techniques and synthetic strategies that can be brought to bear in addressing the challenges posed by such axially chiral compounds and that this account may provide helpful guidelines for future efforts aimed at the development of such single atropisomer, axially chiral p...

Perspectives on Nuclear Magnetic Resonance Spectroscopy in Drug Discovery Research

“…The structure of 12 centers around a quinazolinone chemical scaffold that presented improved metabolic stability over prior scaffolds. 89 Linked to this core moiety is an isopropylmethylpyridine group capable of accessing the cryptic pocket (Figure 18). The molecule presents as two atropisomers with a 10-fold difference in potency between atropisomer M (more potent) and atropisomer P. This difference prompted the advancement of only one of the atropisomers, which in turn, required analytical solutions to better understand its structural complexities and guide its development.…”

“…This classical resolution could be performed on metric-ton scale and was critical to the sotorasib manufacturing process. 89,90 Drug molecule 12 is one of only four FDA-approved class-3 atropisomers and the only one manufactured as an atropisomerically pure compound. The advancement of new drug modalities also necessitates studies to better understand the structural attributes and behavior of the molecules being pursued as shown by the following metabolic stability studies of ADC payloads using 19 F NMR.…”

Expanding Chemical Probe Space: Quality Criteria for Covalent and Degrader Probes

“…Covalently acting molecules can have very high rates of inactivation while showing only moderate intrinsic warhead reactivity. For example, the KRasG12C inhibitor sotorasib is reported to have an extremely high k inact of 0.85 s –1 , while the compound shows low intrinsic chemical reactivity, with a half-life in the presence of 5 mM GSH of 200 min …”

Stereodynamic Strategies to Induce and Enrich Chirality of Atropisomers at a Late Stage

“…The utility and potential of stereodynamic processes were recently highlighted in the process development of sotorasib (see Figure 1, 1.1). 36 Despite efforts to construct the atropisomeric core using asymmetric catalysis, the most efficient synthesis produced a racemic mixture (rac-1.2). Although chromatographic separation of the enantiomers was feasible on smaller scales, this was not feasible on the scale required for industrial synthesis and a classical resolution was developed to achieve isolation of the desired enantiomer ((M)-1.2).…”

“…The utility and potential of stereodynamic processes were recently highlighted in the process development of sotorasib (see Figure , 1.1 ) . Despite efforts to construct the atropisomeric core using asymmetric catalysis, the most efficient synthesis produced a racemic mixture ( rac- 1.2 ).…”