Molecular interactions between thiostrepton and the TipAS protein from Streptomyces lividans.

In Streptomyces lividans, the expression of several proteins is stimulated by the thiopeptide antibiotic thiostrepton. Two of these, TipAL and TipAS, autoregulate their expression after covalently binding to thiostrepton; this irreversibly sequesters the antibiotic and desensitizes the organism to its effects. In this work, additional molecular recognition interactions involved in this critical event were explored by utilizing various thiostrepton analogues and several site-directed mutants of the TipAS antibiotic binding protein. Dissociation constants for several thiostrepton analogues ranged from 0.19 to 12.95 µM, depending on the analogue. The contributions of specific structural elements of the thiostrepton molecule to this interaction have been discerned, and an unusual covalent modification between the antibiotic and a new residue in a TipAS mutant has been detected.

Development and evaluation of multifunctional agents for potential treatment of Alzheimer's disease: application to a pyrimidine-2,4-diamine template.

We investigated a group of 2-benzylpiperidin-N-benzylpyrimidin-4-amines with various electron-withdrawing or electron-donating groups (EWGs or EDGs, respectively) as multi-targeted Alzheimer's disease (AD) therapeutics. The synthesized derivatives were screened for anti-cholinesterase (AChE and BuChE), anti-Aß-aggregation (AChE- and self-induced) and anti-ß-secretase (BACE-1) activities in an effort to identify lead, multifunctional candidates as part of our multi-targeted approach to treat AD. Biological assessment revealed that the nature of the substituent on the C-4 benzylamine group (e.g., halogen vs methoxy-based) greatly affected the biological profile. In vitro screening identified N(2)-(1-benzylpiperidin-4-yl)-N(4)-(3,4-dimethoxybenzyl)pyrimidine-2,4-diamine (7h) as the lead candidate with a dual ChE (AChE IC(50)=9.9 µM; BuChE IC(50)=11.4 µM), Aß-aggregation (AChE-induced=59.3%; self-induced=17.4% at 100 µM) and BACE-1 (34% inhibition at 10 µM) inhibitory profile along with good cell viability (% neuroblastoma cell viability at 40 µM=81.0%). Molecular modeling studies indicate that a central pyrimidine-2,4-diamine ring serves as a suitable template to develop novel small molecule candidates to target multiple pathological routes in AD.

Development of 2-substituted-N-(naphth-1-ylmethyl) and N-benzhydrylpyrimidin-4-amines as dual cholinesterase and Aß-aggregation inhibitors: Synthesis and biological evaluation.

A group of 2-substituted N-(naphth-1-ylmethyl)pyrimidin-4-amines (6a-k) and N-benzhydrylpyrimidin-4-amines (7a-k) in conjunction with varying steric and electronic properties at the C-2 position were designed, synthesized and evaluated as dual cholinesterase and amyloid-ß (Aß)-aggregation inhibitors. The naphth-1-ylmethyl compound 6f (2-(4-cyclohexylpiperazin-1-yl)-N-(naphth-1-ylmethyl)pyrimidin-4-amine) exhibited optimum dual ChE (AChE IC(50)=8.0 µM, BuChE IC(50)=3.9 µM) and hAChE-promoted Aß-aggregation inhibition (30.8% at 100 µM), whereas in the N-benzhydryl series, compound 7f (N-benzhydryl-2-(4-cyclohexylpiperazin-1-yl)pyrimidin-4-amine) exhibited optimum combination of dual ChE (AChE IC(50)=10.0 µM, BuChE IC(50)=7.6µM) and hAChE-promoted Aß-aggregation inhibition (32% at 100 µM). These results demonstrate that a 2,4-disubstituted pyrimidine ring serves as a suitable template to target multiple pathological routes in AD, with a C-2 cyclohexylpiperazine substituent providing dual ChE inhibition and potency whereas a C-4 diphenylmethane substituent provides Aß-aggregation inhibition.