synthesized a structurally simplified syringolin A analogue 4, which could have a switched hydrogen bonding interaction with the beta5 subunit of 20S proteasome. This analogue exhibits potent beta5 proteasome inhibitory activity with an IC50 value of 107 nM. It also shows cytotoxicity against a range of human cancer cells at submicromolar level (109-254 nM). This analogue is expected to be a lead compound