High performance liquid chromatographic profiling of antioxidant and antidiabetic flavonoids purified from Azadirachta indica (neem) leaf ethanolic extract

Azadirachta indica (neem) is a tropical and semi-tropical tree native to the whole Indian subcontinent. Neem leaves are rich in flavonoids, which exhibit important pharmacological activities targeting almost all human organs. In order to produce a purified extract of neem leaves enriched of antioxidant and antidiabetic flavonoids, the ethanolic extract of neem leaves has been further undergone to liquid-liquid extractions by using three different organic solvents, i.e. dichloromethane, n-butanol and ethyl acetate. Qualitative and quantitative analyses were performed on the extracts obtained by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Astragalin, quercitrin, isoquercitrin, nicotiflorin and rutin were the only flavonoids found among those screened. By comparing all HPLC chromatograms of purified extracts as obtained with different solvents, it was found that the qualitative-quantitative composition of flavonoids depends upon the extraction solvent used; in particular, dichloromethane allows extraction of 89.5 % quercitrin, 5.3 % isoquercitrin, 5.2 % rutin; n-butanol allows extraction of 6.0 % isoquercitrin, 6.2 % nicotiflorin, 87.8 % rutin; ethyl acetate allows extraction of 4.2 % astragalin, 12.0 % quercitrin, 50.3 % isoquercitrin, 6.7 % nicotiflorin, 26.9 % rutin. Thus, depending on the specific purposes and needs, each of these three extraction solvents has the potential to prepare formulations enriched with the most suitable flavonoids composition.