title: [Isolation and quantitative analysis of the alpha-amylase inhibitor in Lagerstroemia speciosa (L.) Pers. (Banaba)].
abstract: Banaba [Lagerstroemia speciosa (L.) Pers.] has been used as a folk medicine for diabetes in the Philippines. Using bioassay-guided separation, valoneaic acid dilactone (1) was isolated from the leaves as a potent alpha-amylase inhibitor. A simple and efficient method for the quantitative determination of valoneaic acid and its derivatives in Banaba extract was established. Valoneaic acid exists as the structural part of the polyphenols, which like flosin A, reginin A, and lagerstroemin, are characteristic constituents of Banaba. These derivatives were hydrolyzed to valoneaic acid by HCl and extracted with 2-butanone. This extract was subjected to HPLC analysis, and the contents of valoneaic acid determined as the whole valoneaic acid contents. Using this method, the whole valoneaic acid contents were measured in eight Banaba leaf decoctions. The alpha-amylase-inhibiting activities of the decoctions were dependent on the whole valoneaic acid contents. In addition, a strong linear correlation was observed between the whole valoneaic acid contents and total polyphenol contents. This analytical procedure is applicable to the chemical evaluation of Banaba.
authors.affiliation: Central Research Institute, ITO EN, Ltd., 21 Mekami, Sagara-cho, Haibara-gun, Shizuoka 421-0516, Japan. h-hosoyama@itoen.co.jp
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Hosoyama
authors.forename: Akio
authors.initials: A
authors.lastname: Sugimoto
authors.forename: Yuko
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Iwao
authors.initials: I
authors.lastname: Sakane
authors.forename: Takami
authors.initials: T
authors.lastname: Kakuda
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000032:analysis* / Q000302:isolation & purification*; D006576:Heterocyclic Compounds, 4 or More Rings / Q000032:analysis* / Q000302:isolation & purification*; D006868:Hydrolysis; D007783:Lactones / Q000032:analysis* / Q000302:isolation & purification*; D031563:Lagerstroemia / Q000737:chemistry*; D010940:Plant Proteins / Q000032:analysis* / Q000302:isolation & purification*; D014361:Trypsin Inhibitors; D000516:alpha-Amylases / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D006576:Heterocyclic Compounds, 4 or More Rings; D007783:Lactones; D010940:Plant Proteins; D014361:Trypsin Inhibitors; C477814:valoneaic acid dilactone; D000516:alpha-Amylases