Sulfur incorporation generally improves Ricin inhibition in pterin-appended glycine-phenylalanine dipeptide mimics.
Wiget, P.A., Manzano, L.A., Pruet, J.M., Gao, G., Saito, R., Monzingo, A.F., Jasheway, K.R., Robertus, J.D., Anslyn, E.V.(2013) Bioorg Med Chem Lett 23: 6799-6804
- PubMed: 24432385 
- DOI: https://doi.org/10.1016/j.bmcl.2013.10.017
- Primary Citation of Related Structures:  
4MX1, 4MX5 - PubMed Abstract: 
Several 7-aminoamido-pterins were synthesized to evaluate the electronic and biochemical subtleties observed in the 'linker space' when N-{N-(pterin-7-yl)carbonylglycyl}-l-phenylalanine 1 was bound to the active site of RTA. The gylcine-phenylalanine dipeptide analogs included both amides and thioamides. Decarboxy gly-phe analog 2 showed a 6.4-fold decrease in potency (IC50 = 128 μM), yet the analogous thioamide 7 recovered the lost activity and performed similarly to the parent inhibitor (IC50 = 29 μM). Thiourea 12 exhibited an IC50 nearly six times lower than the oxo analog 13. All inhibitors showed the pterin head-group firmly bound in their X-ray structures yet the pendants were not fully resolved suggesting that all pendants are not firmly bound in the RTA linker space. Calculated log P values do not correlate to the increase in bioactivity suggesting other factors dominate.