RESUMO
The development of new therapeutic agents against malaria has become urgent during the past few decades, due to an increased prevalence of drug-resistant strains of malaria-causing Plasmodium parasites. Possible targets are the hemoglobin-degrading aspartic proteases, the plasmepsins. While acyclic alpha,alpha-difluoroketone hydrates have been introduced into peptidomimetics to bind to the catalytic Asp dyad of aspartic proteases, alicyclic derivatives were unknown. This paper describes a versatile synthesis of hydrated alicyclic alpha,alpha-difluoro-cyclopentanones and -cyclohexanones, decorated with appropriate substituents to fill the S1/S3 and the "flap-open" pocket at the enzyme active sites. Their biological activity was tested against plasmepsin II and IV, revealing an IC(50) value (concentration of an inhibitor at which 50% maximum initial velocity is observed) of 7 microM for the best ligand. Reference inhibitors with a protonated secondary ammonium centre to address the catalytic dyad showed similar binding affinities. The X-ray crystal structure of a cyclic alpha,alpha-difluoroketone hydrate revealed the ability of these novel building blocks to participate in H-bonding networks. The hydration of difluoroketones was also investigated in solution. An exemplary study showed that the equilibrium constants for the hydration of alpha,alpha-difluorinated cyclohexanones are much higher than those for the corresponding cyclopentanones.
Assuntos
Ácido Aspártico Endopeptidases/antagonistas & inibidores , Flúor/química , Cetonas/química , Cetonas/farmacologia , Malária/enzimologia , Inibidores de Proteases/química , Inibidores de Proteases/farmacologia , Antimaláricos/síntese química , Antimaláricos/química , Antimaláricos/metabolismo , Antimaláricos/farmacologia , Ácido Aspártico Endopeptidases/química , Ácido Aspártico Endopeptidases/metabolismo , Cristalografia por Raios X , Humanos , Cetonas/síntese química , Cetonas/metabolismo , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação Molecular , Inibidores de Proteases/síntese química , Inibidores de Proteases/metabolismo , Água/químicaAssuntos
Ácido Aspártico Endopeptidases/antagonistas & inibidores , Malária/tratamento farmacológico , Plasmodium/enzimologia , Animais , Antimaláricos/síntese química , Antimaláricos/química , Sítios de Ligação , Catepsinas/antagonistas & inibidores , Humanos , Modelos Químicos , Modelos Moleculares , Inibidores de Proteases/síntese química , Inibidores de Proteases/química , Ligação Proteica , Proteínas de Protozoários , Relação Estrutura-AtividadeRESUMO
A network of orthogonal C=O...C=O interactions was identified in the X-ray crystal structure of an alpha,alpha-difluorocyclopentanone derivative. This finding inspired investigations of self-association driven by these weak dipolar interactions in apolar solvents, which was proven by (1)H NMR spectroscopy.
Assuntos
Cetonas/química , Cristalografia por Raios X , Ciclopentanos/química , Espectroscopia de Ressonância Magnética , Conformação Molecular , TermodinâmicaRESUMO
A series of 16 tricyclic thrombin inhibitors was prepared by using the 1,3-dipolar cycloaddition of azomethine ylides derived from 3- or 4-hydroxyproline and 4-bromobenzaldehyde, with N-(4-fluorobenzyl)maleimide as the key step. The terminal pyrrolidine ring of the inhibitors was systematically substituted to explore the potential bioisosteric behavior of C-F, C-OH, and C-OMe residues pointing into the environment of the catalytic center of a serine protease. X-ray crystal structure analyses revealed a distinct puckering preference of this ring. Substitution by F, HO, and MeO has a strong effect on the basicity of the adjacent pyrrolidine nitrogen center which originates from two sigma-inductive pathways between this center and the electronegative O and F atoms. gem-Difluorination decreases the pKa value of this tertiary amine center to <2, making the conjugated ammonium ion a moderately strong acid. Unexpectedly, F substitution next to the nitrogen center reduced the lipophilicity of the ligands, as revealed by measurements of the logarithmic partition coefficient log D. The biological assays showed that all compounds are thrombin inhibitors with activities between Ki=0.08 and 2.17 microM. Bioisosteric behavior of F, HO, and MeO substituents was observed. Their electronegative F and O atoms undergo energetically similar polar interactions with positively polarized centers, such as the N atom of His 57 which is hydrogen bonded to the catalytic Ser 195. However, for energetically similar polar interactions of C-F, C-OH, and C-OMe to occur, sufficient space is necessary for the accommodation of the Me group of the C-OMe residue, and a H-bond acceptor must be present to prevent unfavorable desolvation of the C-OH residue.