Isolation and HPLC Quantitative Determination of 5α-Reductase Inhibitors from Tectona grandis L.f. Leaf Extract

Abstract

Steroid 5α-reductase plays a crucial role in catalyzing the conversion of testosterone to dihydrotestosterone, which is involved in many androgen-dependent disorders. Leaf-hexane extract from Tectona grandis L.f. has shown promise as a 5α-reductase inhibitor. The objectives of this current study were to isolate and identify 5α-reductase inhibitors from T. grandis leaves and to use them as the bioactive markers for standardization of the extract. Three terpenoid compounds, (+)-eperua-8,13-dien-15-oic acid (1), (+)-eperua-7,13-dien-15-oic acid (2), and lupeol (3), were isolated and evaluated for 5α-reductase inhibitory activity. Compounds 1 and 2 exhibited potent 5α-reductase inhibitory activity, while 3 showed weak inhibitory activity. An HPLC method for the quantitative determination of the two potent inhibitors (1 and 2), applicable for quality control of T. grandis leaf extracts, was also developed. The ethanolic extract showed a significantly higher content of 1 and 2 than found in the hexane extract, suggesting that ethanol is a preferable extraction solvent. This study is the first reported isolation of 5α-reductase inhibitors (1 and 2) from T. grandis leaves. The extraction and quality control methods that are safe and useful for further development of T. grandis leaf extract as an active ingredient for hair loss treatment products are also reported.

Keywords: 5α-reductase inhibitor; Tectona grandis; diterpenes; quality control.

Figure 1

Chemical structures of three compounds isolated from T. grandis leaf extract.

Figure 2

HPLC-DAD chromatograms of (a) 100 µg/mL T. grandis leaf-hexane extract, (b) 100 µg/mL T. grandis leaf-ethanolic extract, and (c) a mixture of 50 µg/mL isolated compounds 1 and 2.