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Synthesis of (alpha,alpha-difluoromethylene)phosphate analogues of phosphosugars and phospho-amino acids
Abstract
($\alpha,\alpha$-Difluoromethylene) phosphonates are potential hydrolytically stable mimics of naturally occuring phosphate esters. Due to the importance of biological phosphates as metabolic intermediates and as vehicles for signal transduction, there is currently great interest in this class of compounds. However, few members of this class have been studied because of the limited number of synthetic strategies available. The first efficient direct displacement approach to ($\alpha,\alpha$-difluoroalkyl)phosphonates is described. Simple primary alkyl triflates and those derived from several monosaccharides are cleanly displaced by diethyl (lithiodifluoromethylene) phosphonate at $-$78$\sp\circ$C in 15 minutes. This methodology has allowed, for the first time, the synthesis of several fluorinated analogues of metabolically important sugar phosphates, such as glucose 6-phosphate and mannose 6-phosphate. The first synthesis of the ($\alpha,\alpha$-difluoroalkyl)phosphonate analogue of phosphoserineis also reported. Diethyl (lithiodifluoromethylene) phosphonate also readily undergoes acyl substitution with unactivated methyl esters. Expeditious treatment of the resulting ($\alpha,\alpha$-difluoroalkyl)phosphonate with hydride or Grignard reagents followed by deoxygenation efficiently provides analogues of primary or secondary phosphates. This method has been applied to the synthesis of ($\alpha,\alpha$-difluoroalkyl)phosphonate analogues of L-phosphoserine ($\geq$96% ee), and L-phosphoallothreonine (93% ee) from D-serine and of L-phosphoserine (91% ee) from L-glycerate. Solid phase peptide synthesis has been utilized to incorporate the ($\alpha,\alpha$-difluoroalkyl)phosphonate analogues of L-phosphoserine, L-phosphoallothreonine and L-phosphoserine into the peptide sequence R-R-A-X-V-A (where X is a phospho-amino acid analogue). The deprotected peptides have been purified by HPLC and analyzed by FAB-MS. A time point assay was performed with ($\sp{32}$P) -labeled phosphorylase a as the substrate. The K$\rm\sb{m}$ and V$\rm\sb{max}$ of PP2A$\rm\sb{c}$ was determined to demonstrate that the assay worked properly. Assays were performed utilizing okadaic acid as an inhibitor of protein serine/threonine phosphatase 2A$\rm\sb{c}$. Initial studies of the peptide RRA(S$\sp*$)VA, where S$\sp*$ is the unnatural phosphoserine analogue, as a potential inhibitor were undertaken.
Subject Area
Organic chemistry
Recommended Citation
Eggen, MariJean, "Synthesis of (alpha,alpha-difluoromethylene)phosphate analogues of phosphosugars and phospho-amino acids" (1996). ETD collection for University of Nebraska-Lincoln. AAI9715961.
https://digitalcommons.unl.edu/dissertations/AAI9715961