Stereospecific total syntheses of proteasome inhibitors omuralide and lactacystin

Synthesis of proteasome inhibitor 6-deoxy-omuralide and its enantiomer using stereoselective alkylation of substituted proline ester

A potent 20S proteasome inhibitor, 6-deoxy-omuralide was stereoselectively synthesized in 20 steps with 5.1% overall yield staring from a chiral boron agent and d-glyceraldehyde acetonide. The stereoselective alkylation of the substituted proline ester with 3-iodo-2-methylprop-1-ene served as the key step. The enantiomer of 6-deoxy-omuralide was achieved in 20 steps with 4.6% overall yield by just changing the chiral boron reagents in the first step. Our current work provides a flexible approach to 6-deoxy-omuralide and its enantiomer with the adornment at the C4 position.

Effect of lysosomal and ubiquitin-proteasome system dysfunction on the abnormal aggregation of α-synuclein in PC12 cells

The aim of this study was to investigate the effect of lysosomal and ubiquitin-proteasome system dysfunction on the abnormal aggregation of α-synuclein, and to analyze its role in the pathogenesis of Parkinson's disease (PD). PC12 cells subjected to nerve growth factor-induced differentiation were used as the cell model to study the dopaminergic neurons, and the lysosomal and proteasomal inhibitors trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane (E64) and, respectively, were used exclusively and in combination to treat the PC12 cells. The viability and metabolic state of the cells was assessed using the MTT assay; flow cytometry was used to measure the rate of cell apoptosis; and the double immunofluorescence method was applied to observe the formation of thioflavin S- and α-synuclein protein-positive aggregates and inclusion bodies in the PC12 cells. In addition, the Hoechst 33258 staining method was used to observe the apoptosis of the α-synuclein protein and thioflavin-S double-labeled cells. Following the administration of the lysosomal and proteasomal pathway inhibitors, the cell viability decreased in a concentration-dependent manner and the cell apoptosis rate increased. The proportion of PC12 cells with α-synuclein protein-positive aggregates and inclusion bodies in the E64 group was 7.94%, compared with 20.33 and 36.77% in the lactacystin and combination treatment groups, respectively. Statistical analysis indicated that the number of inclusion body-positive cells in the treatment groups was significantly higher than that in the control group (3.78%) (P<0.05). Apoptosis was evident in the double-positive cells with α-synuclein protein-positive inclusion bodies (17.29±1.54%). In conclusion, lysosomal and proteasomal dysfunction may play an important role in the pathogenesis of PD through the induction of abnormal α-synuclein protein aggregation in dopaminergic neurons.

Inhibition of CatA: an emerging strategy for the treatment of heart failure

The lysosomal serine carboxypeptidase CatA has a very important and well-known structural function as well as a, so far, less explored catalytic function. A complete loss of the CatA protein results in the lysosomal storage disease galactosialidosis caused by intralysosomal degradation of β-galactosidase and neuraminidase 1. However, mice with a catalytically inactive CatA enzyme show no signs of this disease. This observation establishes a clear distinction between structural and catalytic functions of the CatA enzyme. Recently, several classes of orally bioavailable synthetic inhibitors of CatA have been identified. Pharmacological studies in rodents indicate a remarkable influence of CatA inhibition on cardiovascular disease progression and identify CatA as a promising novel target for the treatment of heart failure.