Thin-layer chromatography (TLC) was performed using aluminum-backed silica plates (Merck Keiselgel 60 F254) and visualized by UV light (λ = 254-213 nm), and/or by staining with ninhydrin which were subsequently heated by hot gun. The ninhydrin stain was made with 0.3 g of ninhydrin and 2 mL of acetic acid in 100 mL EtOH.