Abstract:
Phospholipases are an important family of enzymes that bind to the plasma membrane and can act as an essential mediator of intracellular and intercellular signalling pathways when they are activated by external signals. Phosphatidylcholine-specific phospholipase C (PC-PLC) is a major enzyme in the phosphatidylcholine (PC) cycle and is involved in many long-term cellular responses such as activation, proliferation, and differentiation events. These secrete pathogenicity factors that act as lytic agents against eukaryotic cells and affect the immune system of the host. Nowadays the mechanisms, structures and functions of mammalian PIPLCs are well understood and developed, but mammalian PC-PLC does not have well characterised structural information available since no cloning or sequencing has been completed yet on it. Only prokaryotic PC-PLCs have been purified and characterised, from the Bacillus cereus (PC-PLCBc). PC-PLCBc has been used for studying mechanisms, structure and functions of mammalian PC-PLC because both have similar features and responses. However, few PC-PLC inhibitors are known and all are not considered to be drug-like. Recently Chatchakorn identified the novel PC-PLCBc inhibitors, the 2,3,4,9-tetrahydro-1H-pyrido[3,4- b]indole derivatives, through a virtual high screening (vHTS) approach, with the most potent inhibitor having ~75 % inhibition activity against PC-PLC. This thesis described the synthesis of analogues of pyrido[3,4-b]indole derivatives, aiming to further increase their PC-PLC inhibition activity. We successfully synthesized different analogues of 2,3,4,9-tetrahydro-1Hpyrido[ 3,4-b]indoles and 9H-pyrido[3,4-b]indoles. With the assistance of the molecular modelling using four different algorithms Piecewise Linear Potential (ChemPLP), GoldScore, ChemScore and Astex Statistical Potential (ASP), the binding interactions between different compounds of the pyrido[3,4-b]indoles and the active site of the PC-PLCBc enzyme was studied. A total of 22 compounds were sent to the Auckland Cancer Society Research Centre (ACSRC) for biological testing. Comparing the results of molecular modelling with the results of biological testing, correlations were identified for the inhibitors, and a structure-activity relationship (SAR) of the analogues established. This will allow further improvements to ligand design.