Pure and Applied Chemistry of Trisubstituted Hydroxylamines: From Reaction Discovery to Drug Design

The presence of a heteroatom-heteroatom bond is a “structural alert” in medicinal chemistry, of which the hydroxylamine N-O bond, with its bond dissociation energy of 55-65 kcal·mol^-1 and reputation for inherent mutagenicity and genotoxicity, is a pertinent example.^1-3  Due to this broad moratorium, hydroxylamines are overwhelmingly excluded in medicinal chemistry optimization schemes and have thus received little attention from the synthetic chemistry or drug discovery communities. To access novel chemical space available by trisubstituted hydroxylamines, we have developed practical, convergent approaches towards the trisubstituted hydroxylamine moiety by direct N-O bond formation.^4-6 Enabled by these methods, we recently conducted a matched molecular pair (MMP) analysis across four series of compounds ranging from the pre-clinical investigational to FDA approved status that revealed similarities in lipophilicity between trisubstituted hydroxylamines and weakly basic morpholine heterocycles.⁷  To fully explore the potential of this novel bioisosteric design strategy, we embarked on a small-molecule drug discovery program that culminated in the discovery of an orally bioavailable, highly selective, brain-penetrant epidermal growth factor receptor (EGFR) inhibitor, DC-PHRM-206, which bears a trisubstituted hydroxylamine unit as a key structural motif.  In addition to providing a novel bioisostere for drug discovery purposes, discovery of DC-PHRM-206, which exhibits excellent stability in vitro and in vivo, efficacy in an intracranial patient-derived xenograft (PDX) murine model and potent activity in osimertinib resistant non-small-cell lung cancer (NSCLC) cell lines, could represent an important lead in treating NSCLC. This is because there is currently an urgent unmet medical need for an orally active, brain penetrant EGFR inhibitor to treat the up to 40% of patients who develop brain metastases in EGFR+ NSCLC and especially the 12.5% of NSCLC patients who develop resistance to osimertinib, with DC-PHRM-206 satisfying both criteria.^8-11 Collectively, this seminar will describe the discovery efforts towards our convergent approaches for trisubstituted hydroxylamine assembly by direct N-O bond formation and will challenge the long-held belief that trisubstituted hydroxylamines are structural alerts in medicinal chemistry by describing our discovery of DC-PHRM-206.

References

1) Yum B.; Reynisson, J. Bond stability of the “undesirable” heteroatom-heteroatom molecular moieties for high-throughput screening libraries. Eur. J. Med. Chem. 2011, 46 (11), 5833-5837.

2) Bruns, B. F.; Watson, I. A. Rules for identifying potentially reactive or promiscuous compounds. J. Med. Chem. 2012, 55 (22), 9764-9772.

3) Bach, D. R.; Schlegel, H. B. The bond dissociation energy of the N-O bond. J. Phys. Chem. A 2021, 125 (23), 5014-5021.

4) Hill, J.; Hettikankanamalage, A. A.; Crich, D. Diversity-oriented synthesis of N,N,O-trisubstituted hydroxylamines from alcohols and amines by direct N-O bond formation. J. Am. Chem. Soc. 2020, 142 (35), 14820-14825.

5) Hill, J.; Crich, D. Synthesis of O-tert-butyl-N,N-disubstituted hydroxylamines by direct N-O bond formation. Org. Lett. 2021, 23 (16), 6396-6400.

6) Hill, J.; Beckler, T. D.; Crich, D. Recent advances in the synthesis of di- and trisubstituted hydroxylamines. Molecules. 2023, 28 (6), 2816.

7) Hill, J.; Crich, D. The N,N,O-trisubstituted hydroxylamine isostere and its influence on lipophilicity and related parameters. ACS Med. Chem. Lett. 2022, 13 (5), 799-806.

8) Rangachari, D.; Yamaguchi, N.; VanderLaan, P. A.; Folch, E.; Mahadevan, A.; Floyd, S. R.; Uhlmann, E. J.; Wong, E. T.; Dahlberg, S. E.; Huberman, M. S.; Costa, D. B. Brain metastases in patients with EGFR-mutated or ALK-rearranged non-small-cell lung cancers. Lung Cancer. 2015, 88 (1), 108-111.

9) Nayak, L.; Lee, E. Q.; Wen, P. Y. Epidemiology of brain metastases. Curr. Oncol. Rep. 2012, 14 (1), 48-54.

10) Coclough, N.; Chen, K.; Johnström, P.; Strittmatter, N.; Yan, Y.; Wrigley, G. L.; Schou, M.; Goodwin, R.; Varnäs, K.; Adua, S. J.; Zhao, M.; Nguyen, D. X.; Maglennon, G.; Barton, P.; Atkinson, J.; Zhang, L.; Jandefeldt, A.; Wilson, J.; Smith, A.; Takano, A.; Arakawa, R.; Kondrashov, M.; Malmquist, J.; Revunov, E.; Vazquez-Romero, A.; Moein, M. M.; Windhorst, A. D.; Karp, N. A.; Finlay, M. R. V.; Ward, R. A.; Yates, J. W. T.; Smith, P. D.; Farde, L.; Cheng, Z.; Cross, D. A. E. Preclinical comparison of the blood-brain barrier permeability of osimertinib with other EGFR TKIs. Clin. Cancer Res. 2021, 27 (1), 189-201.

11) Leonetti, A.; Sharma, S.; Minari, R.; Perego, P.; Giovannetti, E.; Tiseo, M. Resistance mechanisms to osimertinib in EGFR-mutated non-small cell lung cancer. Br. J. Cancer 2019, 121 (9), 725-737.