This study was aimed to extract rosmarinic acid from Orthosiphon stamineus Benth. (Lamiaceae) in high yield. The mixture of chloroform–ethyl acetate (70:30) was chosen as the solvent system because rosmarinic acid gave the lowest solvation free energy in that solvent system based on the computational solubility prediction. The crude extract of the plant was fractionated by C18 reversed phase absorbent to recover rosmarinic acid. The content of rosmarinic acid was increased from 4.0% w/w to 6.7% w/w after fractionation. The radical scavenging activity of rosmarinic acid rich fraction (IC50 = 38.3 �g/mL) was higher than the crude extract (IC50 = 58.85 �g/mL) based on the DPPH assay. Several phytochemicals were also identified based on the detection of fragment ions of target compounds. Fractions 1 to 3 could be combined to be a rosmarinic acid rich fraction. Simultaneously, the combination of fractions 4 to 6 could obtain a plant fraction rich in rosmarinic acid, sinensetin and eupatorin, whereas fractions 7 to 9 could be combined as a sinensetin rich fraction. The preparation of known phytochemical profile of O. stamineus fraction is highly required for value added product formulation and pharmacological studies, particularly for anti-diabetes and kidney related diseases which had previously been reported attributed to this herbal plant. This is the first study using solvation free energy to predict the suitable solvent system for rosmarinic acid extraction from highly complex herbal sample using the technology of solid phase extraction. The use of solvation free energy simulation is convenient and reliable before wet experiments for time and cost saving
