Guanosine (DL-Guanosine) is a purine nucleoside formed from a beta-N9-glycosidic bond between guanine and a ribose ring and is essential for metabolism.

Guanosine是一种由鸟嘌呤核苷通过β-N9糖苷键与一种核糖（环状核糖）环相连而形成的嘌呤核苷。Guanosine能够被磷酸化生成Guanosine monophosphate（GMP）和环状Guanosine monophosphate （cGMP）。

Tyrosine kinase assays: The tyrosine kinase activities are determined in 96-well ELISA plates precoated with 20 μg/mL Poly (Glu,Tyr)4:1. First, 80 μL of 5 μM ATP solution diluted in kinase reaction buffer (50 mM HEPES pH 7.4, 20 mM MgCl2, 0.1 mM MnCl2, 0.2 mM Na3VO4, 1 mM DTT) is added to each well. Various concentrations of AST-1306 diluted in 10 μL of 1% DMSO (v/v) are then added to each reaction well, with 1% DMSO (v/v) used as the negative control. Subsequently, the kinase reaction is initiated by the addition of purified tyrosine kinase proteins diluted in 10 μL of kinase reaction buffer solution. Experiments at each concentration are performed in duplicate. After incubation for 60 min at 37 °C, the plate is washed three times with phosphate buffered saline (PBS) containing 0.1% Tween 20 (T-PBS). Next, 100 μL anti-phosphotyrosine antibody (PY99, 1:500 dilution) diluted in T-PBS containing 5 mg/mL BSA is added. After 30 min incubation at 37 °C, the plate is washed three times as before. Horseradish peroxidase-conjugated goat anti-mouse IgG (100 μL) diluted 1:2000 in T-PBS containing 5 mg/mL BSA is added. The plate is reincubated at 37 °C for 30 min, and then washed with PBS. Finally, 100 μL of a solution containing 0.03 % Water2 and 2 mg/mL o-phenylenediamine in 0.1 M citrate buffer, pH 5.5, is added and samples are incubated at room temperature until color emerged. The reaction is terminated by the addition of 50 μL of 2 M H2SO4, and the plate is read using a multi-well spectrophotometer at 490 nm. The inhibition rate (%) is calculated using the following equation: [1-(A490 treated /A490 control)] ×100%. IC50 values are determined from the results of at least three independent tests and calculated by Logit method.