Discovery of further pyrrolidine trans-lactams as inhibitors of human neutrophil elastase (HNE) with potential as development candidates and the crystal structure of HNE complexed with an inhibitor (GW475151).

Described herein is a modern approach to the rapid preparation and evaluation of compounds as potential back-up drug candidates. GW311616A, 1, a derivative of pyrrolidine trans-lactams, has previously been described as a potent, orally active inhibitor of human neutrophil elastase (HNE) for the treatment of respiratory disease. These properties made it a suitable candidate for development. Described here is the discovery of three further derivatives of pyrrolidine trans-lactams, which fulfill the criteria required for back-up candidates 28, 29, and 32. These include increased activity in inhibiting HNE in human whole blood (HWB) and comparable pharmacokinetic properties, in particular clearance, in two species. To provide a rapid assessment of clearance, cassette dosing in dog was used. Modern array techniques, including the synthesis of mixtures, were used to synthesize compounds rapidly. Having selected three potential compounds as back-up candidates, they were prepared as single enantiomers and profiled in in vitro and in vivo assays and evaluated pharmacokinetically in rat and dog. These compounds are highly potent and selective HNE inhibitors, with a prolonged pharmacodynamic action. Pharmacokinetically, these compounds are comparable with 1 while they are more potent in HWB. Compound 28, however, has a higher clearance. One of these compounds, 32, was cocrystallized with HNE, and features of this structure are described and compared with the cocrystal structure of 1 in porcine pancreatic elastase.

A Flexible, Practical, and Stereoselective Synthesis of Enantiomerically Pure trans-5-Oxohexahydropyrrolo[3,2-b]pyrroles (Pyrrolidine-trans-lactams), a New Class of Serine Protease Inhibitors, Using Acyliminium Methodology.

A flexible, practical, and stereoselective synthesis of enantiomerically pure trans-5-oxohexahydropyrrolo[3,2-b]pyrroles (pyrrolidine-trans-lactams) is described. The key reaction involves addition of Z-ketene acetal 24 to the acyliminium ion derived from 48. This reaction is mediated by BF3·OEt2 and introduces the 6S and 6aS stereocenters stereoselectively. The acyliminium precursor was prepared in four different ways: from racemic 2,4-diaminobutyric acid 8, from (R)-asparagine, from (R)-methionine, and via a crystallization-induced dynamic resolution of a salt of the racemic amine 56. (R)-Methionine is the preferred starting material for the preparation of enantiomerically pure material. The best conditions for addition of the ketene acetal to the acyliminium ion derived from 48 were determined by systematically screening a range of ketene acetals and Lewis acids. The best ketene acetal was Z-(1-ethoxy-3-methylbut-1-enyloxyl)triisopropylsilane 24. In this series, the bulk of the silyl group of the Z-ketene acetal can be correlated with increased 6S isopropyl product. Use of the E-ketene acetal does not lead to a significant change in stereoselectivity for the 6R isopropyl product. In contrast, variation of the Lewis acid has a considerable effect on the product stereochemistry. While BF3·OEt2 gives predominantly 6S,6aS product, AlCl3 and TiCl4 give predominantly mixtures of the 6R,6aS and 6S,6aS products and TMSOTf gives 6aR material with predominantly one unknown isopropyl isomer (trans-lactam numberings used). The synthesis can conveniently be carried out on a large scale to produce multigram quantities of the trans-lactam 28, which is a key precursor of pharmacologically active molecules such as 1, a selective and orally active human neutrophil elastase inhibitor. The overall chemical yield of 1 is 1.3%, corresponding to an average of >70% yield for each of the 14 steps, and the synthesis contains only one chromatographic purification.