Phenolic compound isolated from Struthanthus venetus (HBK) Blume whith hypotensive effect in normotensive anesthetized rats

It was found from a previous study that methanolic extract (ME) from Struthanthus venetus (Loranthaceae) leaves, Vaucher 33393 Herbario Nacional de Mexico, Instituto de Biología UNAM, produced immediate and long lasting hypotension in anesthetized rats [1]. In order to identify the responsible compounds, a fractionation was carried out through liquid-liquid extraction, bioguided by the activity observed in the anesthetized normotensive rat cardiovascular system. 6g of ME from S. venetus dry leaves, were dissolved in water (50 mL), poured into a separatory funnel and extracted with 50 mL of ethyl acetate. This procedure was carried out 11 times. The residues were grouped. Once ethyl acetate was evaporated, the liquid phase was treated and extracted with dichloromethane. Comparing the three obtained extracts (the aqueous, the ethyl acetate and the one from dichloromethane); the aqueous extract conserved the hypotensive effect. This extract was submitted to chromatographic fractionation on silica gel column and it gave a positive green colour with FeCl₃ and pink colour when it was examined by TLC with vanillin–H₂SO₄ reagent. TLC was eluted using methanol– dichloromethane –acetonitrile 6:3:1 (v/v/v). The substance that diminished significantly (p<0.05, Students t-test) the blood pressure and the heart rate was a hydroquinone glycoside-type, according to its ¹H and ¹³C NMR, MS, and IR data. The action mechanism of this compound is not yet well know.

Reference: 1. Lorenzana-Jiménez M. et al. (2006). Pharmacologyonline 3: 359–364.