For more than two decades investigators around the world, in both academic and industrial institutions, have been developing inhibitors of human neutrophil elastase. A number of very elegant and insightful strategies have been reported. In the case of reversible peptidic inhibitors, this has resulted in the identification of some extremely potent compounds with dissociation constants in the 10(-11) M range. This is quite an accomplishment considering that these low molecular-weight inhibitors are only tri- and tetrapeptides. In the case of the heterocyclic-based inhibitors, the challenge of balancing the heterocycle's inherent reactivity and aqueous stability with the stability of the enzyme-inhibitor adduct has been meet by either using a latent, reactive functionality which is only activated within the enzyme, or by incorporating features which selectively obstruct deacylation but have little effect on the enzyme acylation step. The underlying goal of this research has been the identification of agents to treat diseases associated with HNE. Several animal models have been developed for evaluating the in vivo activity of elastase inhibitors, and compounds have been shown to be effective in all of these models by the intravenous, intratrachael or oral routes of administration. However, only a very small percentage of compounds have possessed all the necessary properties, including lack of toxicity, for progression into the clinic. The peptidyl TFMK ICI 200,880 (25-12) has many of the desired characteristics of a drug to treat the diseases associated with HNE: chemical stability, in vitro and in vivo activity, a long duration of action, and adequate metabolic stability. Currently ICI 200,880 is the only low molecular-weight HNE inhibitor known to be undergoing clinical trials, and may be the compound which finally demonstrates the clinical utility of a synthetic HNE inhibitor.

Mutations in the mitochondrial fusion protein mitofusin (MFN) 2 cause the chronic neurodegenerative condition Charcot-Marie-Tooth disease type 2A (CMT2A), for which there is currently no treatment. Small-molecule activators of MFN1 and MFN2 enhance mitochondrial fusion and offer promise as therapy for this condition, but prototype compounds have poor pharmacokinetic properties. Herein, we describe a rational design of a series of 6-phenylhexanamide derivatives whose pharmacokinetic optimization yielded a 4-hydroxycyclohexyl analogue, 13, with the potency, selectivity, and oral bioavailability of a preclinical candidate. Studies of 13 cis- and trans-4-hydroxycyclohexyl isostereomers unexpectedly revealed functionality and protein engagement exclusively for the trans form, 13B. Preclinical absorption, distribution, metabolism, and excretion (ADME) and in vivo target engagement studies of 13B support further development of 6-phenylhexanamide derivatives as therapeutic agents for human CMT2A.

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The effects of changes in substitution in a series of 5-amino-2-pyrimidin-6-ones on both in vitro activity and oral activity in an acute hemorrhagic assay have been explored. These compounds contained either a trifluoromethyl ketone or a boronic acid moiety to bind covalently to the Ser-195 hydroxyl of human leukocyte elastase (HLE). Boronic acid-containing inhibitors were found to be more potent than the corresponding trifluoromethyl ketones in vitro but were less active upon oral administration. Compound 13b was found to offer the best combination of oral potency, duration of action, and enzyme selectivity and, as such, was selected for further biological testing. X-ray crystallography of a cocrystallized complex of compound 19m and porcine pancreatic elastase demonstrated that the inhibitor is bound to the enzyme in a manner similar to that found previously for a closely related series of pyridone-containing inhibitors of HLE.