Exploring IPC Synthase:
A POTENTIAL ANTI -LEISHMANIAL DRUG TARGET

Abstract

Leishmaniasis is a widespread disease affecting 12 million people with about 2 million new cases recorded annually and 350 million people considered to be at risk worldwide. Consequently, it has been ranked category „1‟ by WHO–TDR in 2004. Currently available drugs are expensive and difficult to administer with toxic and/or teratogenic side effects. In addition, there are increasing levels of drug resistance. Therefore, there is a need for new effective drug treatments.

Earlier work in the group identified Leishmania major Inositol Phosphorylceramide Synthase (LmjIPCS) as a functional orthologue of the fungal IPC synthase. This membrane bound enzyme has no mammalian equivalent therefore represents an attractive anti-Leishmanial drug target.
The aim of this chemical biology project was to functionally characterise this enzyme and synthesise lead compounds for inhibitor design. The first aspect of the project focused on the establishment of a robust assay system that was used in the determination of the kinetic
parameters of the enzyme. The established protocol was amenable to scaling-up processes and HTS. Validation of the assay was achieved using Aureobasidin A, a known fungal IPCS specific inhibitor, and two substrate mimics.

Phase two of the project involved the use of synthetic chemistry towards the enantioselective and diastereoselective synthesis of an array of substrate mimics to help identify the structural requirements for the substrate binding to the enzyme. The key reactions were asymmetric PT amino acid alkylation of benzophenone glycine imine and a stereospecific reduction of protected
N-Boc-enones formed from the corresponding amino acid. The prepared alkenes were utilised in olefin cross metathesis reactions to yield a library of ceramide mimics variable in the sphingosine backbone. Deprotection-acylation sequence of the protected amino group resulted in variable N-acyl ceramide mimics. Screening of the substrate mimics library together with other putative inhibitors generated preliminary SAR data. Future work will involve using the SAR data generated in this study to design and synthesise new generations of inhibitors as well as substrate probes to help map the active site of the enzyme.