Isolation and Quantitative Analysis of the α-Amylase Inhibitor in <i>Lagerstroemia speciosa</i> (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.

Inhibitory effect of Gymnema Montanum leaves on α-glucosidase activity and α-amylase activity and their relationship with polyphenolic content

“…Scarlett O'Hara) flowers were reported to effectively inhibit rat yeast a-glucosidase and human a-amylase (Matsui et al, 2002). There are also reports that tannins and ellagic acid derivatives from banaba (Lagerstroemia speciosa L.) leaves are potent inhibitors of a-amylase (Hosoyama et al, 2003). A positive and significant correlation was found between polyphenolic content and a-glucosidase inhibition (r 2 = 0.92) as well as a-amylase inhibition (r 2 = 0.97).…”

Constituents of Stem Bark of Callistemon rigidus Showing Inhibitory Effects on Mouse .ALPHA.-Amylase Activity

“…Some constituents of plants that exhibit inhibitory effects on a-amylase activities have recently been reported. [15][16][17] Here, piceatannol (1) and scirpusin B (2) have been newly applied. It is known that 1 inhibits various enzyme activities.…”

Xanthine oxidase inhibitors from the leaves of Lagerstroemia speciosa (L.) Pers.

“…jor compounds were isolated and identified as valoneic acid dilactone (VAD) and ellagic acid (EA) by direct comparisons with the authentic materials available commercially or in our laboratory (Hosoyama et al, 2003) (Fig. 4).…”