Synthesis of small molecule anthrax inhibitors and cysteine free native chemical ligation
Abstract
Computational design of the heterotrimeric inhibitors to disrupt the PA/CMG2 interaction and the partial synthesis of the inhibitors were discussed. Anthrax inhibitors were synthesized from the readily available starting materials: p-hydroxybenzaldehyde, furfuryl alcohol, imidazole and 4-hydroxyphenylacetic acid. MTT cytotoxicity assays and cell rescue assays in the presence of protective antigen (PA) and lethal factor (LF) of the inhibitors were performed. Even though, all inhibitors were not cytotoxic up to 250–500 &mgr;M, they only showed a maximum of 8–12% inhibition at 25–75 &mgr;M. Therefore, complete assembly and further modification are required to improve their bioactivities. Native chemical ligation is a powerful method that enables synthetic access to many proteins. However, the generality of this method is limited by the requirement for cysteine-containing ligation sites. Even though several approaches have been developed to overcome this limitation, several challenges remain to broaden the scope of NCL. These include expanding the ligation site to include amino acids other than cysteine, increasing the ligation ability with bulky residues and improving the removal of the auxiliary with no sideproduct formation or reverse reaction. Novel photolabile auxiliaries have been developed to promote the native chemical ligation (NCL) of peptide thioesters with peptides lacking an N-terminal Cys residue. These new auxiliaries extend the scope of ligation sites to include those with Ala, Leu and Val residues. The auxiliaries promote amide bond formation between the peptide fragments using chemoselective transthioesterification to initiate a cascade of S-to- O-to-N acyl transfer reactions. Installation of the auxiliaries via reductive amination, ligation and photochemical removal of the auxiliary all proceed in high yield. The expanded scope of these new auxiliaries should broaden the applicability of NCL to the chemical synthesis of large peptides and proteins.
Degree
Ph.D.
Advisors
Lipton, Purdue University.
Subject Area
Organic chemistry
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