Discovery of a novel tetrahydroimidazo[1,2-a]pyridine-5-carboxylic acid derivative as a potent and selective heparanase-1 inhibitor utilizing an improved synthetic approach.

Heparanase-1 (HPSE1) is an endo-ß-d-glucuronidase that catalyzes degradation of heparan sulfate proteoglycans. Inhibition of HPSE1 appears to be a useful therapeutic target against cancer and proteinuric kidney diseases. We previously reported tetrahydroimidazo[1,2-a]pyridine 2 as a potent HPSE1 inhibitor after optimization of the synthetic reaction. However, synthesis of 2 involves a total of 19 steps, including a cyclization process that accompanies a strong odor due to the use of Lawesson's reagent and an epimerization reaction; furthermore, 2 exhibited insufficient selectivity for HPSE1 over exo-ß-d-glucuronidase (GUSß) and glucocerebrosidase (GBA), which also needed to be addressed. First, the cyclization reaction was optimized to synthesize tetrahydroimidazo[1,2-a]pyridine without using Lawesson's reagent or epimerization, with reference to previous reports. Next, 16 and 17 containing a bulkier substituent at position 6 than the 6-methoxyl group in 2 were designed and synthesized using the improved cyclization conditions, so that the synthetic route of 16 and 17 was shortened by five steps as compared with that of 2. The inhibitory activities of 16 and 17 against GUSß and GBA were reduced as compared with those of 2, that is, the compounds showed improved selectivity for HPSE1 over GUSß and GBA. In addition, 16 showed enhanced inhibitory activity against HPSE1 as compared with that of 2. Compound 16 appears promising as an HPSE1 inhibitor with therapeutic potential due to its highly potent inhibitory activity against HPSE1 with high selectivity for HPSE1.

Discovery of novel indole derivatives as potent and selective inhibitors of proMMP-9 activation.

Matrix metalloproteinase-9 (MMP-9) is a secreted zinc-dependent endopeptidase that degrades the extracellular matrix and basement membrane of neurons, and then contributes to synaptic plasticity by remodeling the extracellular matrix. Inhibition of MMP-9 activity has therapeutic potential for neurodegenerative diseases such as fragile X syndrome. This paper reports the molecular design, synthesis, and in vitro studies of novel indole derivatives as inhibitors of proMMP-9 activation. High-throughput screening (HTS) of our internal compound library and subsequent merging of hit compounds 1 and 2 provided compound 4 as a bona-fide lead. X-ray structure-based design and subsequent lead optimization led to the discovery of compound 33, a highly potent and selective inhibitor of proMMP-9 activation.

Lead identification of novel tetrahydroimidazo[1,2-a]pyridine-5-carboxylic acid derivative as a potent heparanase-1 inhibitor.

Heparanase-1 (HPSE1) is an endo-ß-d-glucuronidase that cleaves heparan sulfate proteoglycans into short-chain heparan sulfates (HS). The inhibition of HPSE1 has therapeutic potential for proteinuric diseases such as nephrotic syndrome because increased HPSE1 expression is associated with the loss of HS in the glomerular basement membrane, leading to the development of proteinuria. The present study examined the generation of a lead compound focusing on chemical structures with a sugar moiety, such as glycosides and sugar analogs, taking their physical properties into consideration. Compound 10, an exo-ß-d-glucuronidase (GUSß) inhibitor, was found to have a weak inhibitory activity against endo-ß-d-glucuronidase HPSE1. A structure-activity relationship study using the X-ray co-crystal structure of 10 and HPSE1 resulted in 12a, which showed a more than 14-fold increase in HPSE1 inhibitory activity compared with that of 10. Compound 12a could be a novel lead compound for the development of a potent HPSE1 inhibitor.

Structure-based lead optimization to improve potency and selectivity of a novel tetrahydroimidazo[1,2-a]pyridine-5-carboxylic acid series of heparanase-1 inhibitor.

Heparanase-1 (HPSE1) is an endo-ß-d-glucuronidase that is the only mammalian enzyme known to cleave heparan sulfate (HS) of heparan sulfate proteoglycans (HSPG), a key component of the glycocalyx layer of the vascular endothelium matrix. Inhibition of HPSE1 has therapeutic potential for cancer and proteinuric kidney diseases. We previously reported that 2 showed a moderate potency as an HPSE1 inhibitor and an issue of selectivity against exo-ß-d-glucuronidase (GUSß) and glucocerebrosidase (GBA) remained. A structure-based lead optimization of 2 using X-ray co-crystal structure analysis and fragment molecular orbital calculation resulted in 4e, which showed a more than 7-fold increase in HPSE1 inhibitory activity. The subsequent introduction of a methyl group into the 6-hydroxy group of 4e resulted in 18 with reduced inhibitory activities against GUSß and GBA while maintaining the inhibitory activity against HPSE1. The inhibitory activities of 18 against serum HPSE1 in mice were significant and lasted for 4 h at doses of 3, 30, and 100 mg/kg. Compound 18 could be a novel lead compound for HPSE1 inhibitors with improved inhibitory activity against HPSE1 and increased HPSE1 selectivity over GUSß and GBA.