Design and synthesis of new C-nucleosides as potential adenosine deaminase inhibitors

Identification of Adenosine Deaminase Inhibitors by Metal-binding Pharmacophore Screening

Adenosine deaminase (ADA) is a human mononuclear Zn²⁺ metalloenzyme that converts adenosine to inosine. ADA is a validated drug target for cancer, but there has been little recent work on the development of new therapeutics against this enzyme. The lack of new advancements can be partially attributed to an absence of suitable assays for high-throughput screening (HTS) against ADA. To facilitate more rapid drug discovery efforts for this target, an in vitro assay was developed that utilizes the enzymatic conversion of a visibly emitting adenosine analogue to the corresponding fluorescent inosine analogue by ADA, which can be monitored via fluorescence intensity changes. Utilizing this assay, a library of ∼350 small molecules containing metal-binding pharmacophores (MBPs) was screened in an HTS format to identify new inhibitor scaffolds against ADA. This approach yielded a new metal-binding scaffold with a K_i value of 26±1 μM.

Ascertaining the activity and inhibition of adenosine deaminase via fluorescence-based assays

A fluorescence-based assay for adenosine deaminase (ADA) activity and inhibition, which may also be formatted as an inhibitor discovery assay, is described. It relies on differences in fluorescence between an isothiazolo-based adenosine analogs (^tzA) and its deaminated product, the corresponding inosine derivative (^tzI), which facilitates a real-time monitoring of enzymatic activity. Inhibitors are added to the enzyme-substrate reaction mixture at various concentrations and the fluorescence signal is recorded over 10min. The percent inhibition is calculated from the signal change at 10min relative to the uninhibited reaction. The percent inhibition is plotted against inhibitor concentration and fitted to a Hill curve. IC₅₀ values are then calculated.

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

Novel nucleoside analogues targeting HCV replication through an NS5A-dependent inhibition mechanism

A series of new tricyclic nucleosides were synthesized and evaluated as hepatitis C virus (HCV) replication inhibitors. Initial screening in a HCV replicon system, derived from a genotype 1b isolate, identified 9-benzylamino-3-(β-D-ribofuranosyl)-3H-imidazo[4',5':5,6]pyrido[2,3-b]pyrazine (15d) as the most potent analogue. Comparative assessment of 15d activity against HCV full-length viruses or subgenomic replicons derived from genotypes 1 to 4 revealed a specificity of the compound for genotypes 1 and 3. Surprisingly, resistance mutations selected against 15d were mapped to domains II and III of the non-structural protein 5A (NS5A), but not to the RNA-dependent RNA polymerase residing in NS5B. These results argue that compound 15d might represent a lead for the development of a novel class of NS5A inhibitors.

Progress of the synthesis of condensed pyrazole derivatives (from 2010 to mid-2013)

Condensed pyrazole derivatives are important heterocyclic compounds due to their excellent biological activities and have been widely applied in pharmaceutical and agromedical fields. In recent years, numerous condensed pyrazole derivatives have been synthesized and advanced to clinic studies with various biological activities. In this review, we summarized the reported synthesis methods of condensed pyrazole derivatives from 2010 until now. All compounds are divided into three parts according to the rings connected to pyrazole-ring, i.e. [5, 5], [5,F 6], and [5, 7]-condensed pyrazole derivatives. The biological activities and applications in pharmaceutical fields are briefly introduced to offer an orientation for the design and synthesis of condensed pyrazole derivatives with good biological activities.