Selective fractionation and isolation of allelopathic compounds from Helianthus annuus L. leaves by means of high-pressure techniques

•SFE and ESE technique were used to extract bioactive compounds from H. annuus leaves.•Fractionation of extracts using three separators was evaluated for both techniques.•High overall yields were obtained with ESE and adding water to the solvent system.•Fraction S3 using CO2+50% H2O was rich in potential allelopathic compounds.•2 sesquiterpenes, 1 flavonoid and 1 lignan presented high inhibitory activity profiles.