RESUMO
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.
Assuntos
Dipeptídeos/química , Inibidores Enzimáticos/química , Inibidores Enzimáticos/farmacologia , Pterinas/química , Ricina/antagonistas & inibidores , Enxofre/química , Cristalografia por Raios X , Dipeptídeos/síntese química , Dipeptídeos/metabolismo , Ativação Enzimática/efeitos dos fármacos , Inibidores Enzimáticos/síntese química , Inibidores Enzimáticos/metabolismo , Ligação Proteica , Ricina/metabolismo , Relação Estrutura-Atividade , Tioamidas/síntese química , Tioamidas/química , Tioamidas/metabolismo , Tioureia/síntese química , Tioureia/química , Tioureia/metabolismoRESUMO
Several 7-peptide-substituted pterins were synthesized and tested as competitive active-site inhibitors of ricin toxin A (RTA). Focus began on dipeptide conjugates, and these results further guided the construction of several tripeptide conjugates. The binding of these compounds to RTA was studied via a luminescence-based kinetic assay, as well as through X-ray crystallography. Despite the relatively polar, solvent exposed active site, several hydrophobic interactions, most commonly π-interactions not predicted by modeling programs, were identified in all of the best-performing inhibitors. Nearly all of these compounds provide IC50 values in the low micromolar range.
Assuntos
Substâncias para a Guerra Química , Modelos Moleculares , Oligopeptídeos/síntese química , Pterinas/síntese química , Ricina/antagonistas & inibidores , Ligação Competitiva , Domínio Catalítico , Substâncias para a Guerra Química/química , Cristalografia por Raios X , Interações Hidrofóbicas e Hidrofílicas , Cinética , Medições Luminescentes , Estrutura Molecular , Oligopeptídeos/química , Oligopeptídeos/farmacologia , Ligação Proteica , Pterinas/química , Pterinas/farmacologia , Ricina/química , Relação Estrutura-AtividadeRESUMO
The optimization of a series of pterin amides for use as Ricin Toxin A (RTA) inhibitors is reported. Based upon crystallographic data of a previous furan-linked pterin, various expanded furans were synthesized, linked to the pterin and tested for inhibition. Concurrently, hetero-analogs of furan were explored, leading to the discovery of more potent triazol-linked pterins. Additionally, we discuss a dramatic improvement in the synthesis of these pterin amides via a dual role by diazabicycloundecene (DBU). This synthetic enhancement facilitates rapid diversification of the previously challenging pterin heterocycle, potentially aiding future medicinal research involving this structure.
RESUMO
Ricin is a potent toxin found in castor seeds. The A chain, RTA, enzymaticlly depurinates a specific adenosine in ribosomal RNA, inhibiting protein synthesis. Ricin is a known chemical weapons threat having no effective antidote. This makes the discovery of new inhibitors of great importance. We have previously used 6-substituted pterins, such as pteroic acid, as an inhibitor platform with moderate success. We now report the success of 7-carboxy pterin (7CP) as an RTA inhibitor; its binding has been monitored using both kinetic and temperature shift assays and by X-ray crystallography. We also discuss the synthesis of various derivatives of 7CP, and their binding affinity and inhibitory effects, as part of a program to make effective RTA inhibitors.