Abstract

(1)

Copyright

IIT Kharagpur

ix

O Ph NHPh

NH H H

(AA)n

Type A: n = 1 Type B: n = 2 Type C: n = 3

syn / anti diastereomer AA= Amino acid

residues

NH

COOR O

CP CE

(CH₂)n

R= H, Et

Design and Synthesis of Cyclic Peptides and Enediynyl Amides: Inhibition Studies against Mycobacterium tuberculosis Protein Tyrosine Phosphatase A

Tuberculosis, an extremely communicable and chronic infectious disease, is the leading cause of mortality of one third of the world population over the past few decades by slow growing intracellular facultative parasite, called Mycobacterium tuberculosis (Mtb). In order to coordinate the growth and metabolism, Mtb secretes protein tyrosine phosphatase A (MPtpA) which has turned out to be one of the most important regulatory cellular signaling enzyme implicated in the pathogenesis of Mtb as well as an essential virulence factor required for the survival of Mycobacteria in the cytoplasm of host macrophages through dephosphorylation of host protein. The thesis has focused on the design of two classes of structure based small molecule inhibitors namely cyclic peptides (CP) and cyclic enediyne (CE) against the signaling pathway of MPtpA. Following the structure-based virtual screening protocol, three types of CPs having -alanine as a common residue (Type A-C) have been successfully synthesized utilizing

‘lactam synthon strategy’. All the CPs were found to be potent inhibitors of MPtpA exhibiting reversible mixed type of inhibition with inhibition constant (Ki) in micro molar range. CPs bearing the polar residues exhibited better inhibition as compared to those containing hydrophobic moiety. This was evident from extensive Circular Dichroism (CD) and steady state fluorescence quenching studies. Finally, the significance of PTP-loop directed major hydrogen bonding interaction with MPtpA has been confirmed by calculated thermodynamic parameters as well as by theoretical docking studies.

Following a fragment-based approach, the enediyne framework in cyclic enediyne malonamic acid has been, for the first time, identified as an important template in the inhibition of MPtpA through predominant hydrophobic reorganization. It displayed PTP-loop directed reversible and tight binding non-competitive inhibition at micomolar concentrations as evident from CD and extensive steady state fluorescence quenching studies. All the kinetic and biophysical results were well supported by theoretical docking studies. In summary, by targeting the signaling pathway of Mtb, we were able to develop a new class of CPs and a cyclic enediyne (CE) as inhibitors. In future, their potential as antituberculosis agent may be explored.

Basic templates of Cyclic peptides and Cyclic Enediyne

Key words: Mycobacterium tuberculosis, cyclic peptides, enediyne, macrophage, inhibitor.