The purity of St-Gly-OEt 3 was determined by RP-HPLC using the following conditions; detection at 220 nm and using Agilent 1200 PDA detector. An Eclipse plus C18 column (3.5 lm 4.6 100 mm) was used for the separation of the compounds using a linear gradient of 84–55% CH3CN in H2O/ (pH 5, H3PO4), over 15 min at a flow rate of 1.0 ml/min. The retention time tR of St-Gly-OEt was 5.43 min (100%).