(6R,9S)-6"-(4"-hydroxybenzoyl)-roseoside, a new megastigmane derivative from Ouratea polyantha and its effect on hepatic glucose-6-phosphatase.

A new megastigmane derivative, (6R,9S)-6'-(4"-hydroxybenzoyl)-roseoside (1) and two known compounds, the biflavoneagathisflavone (2) and 4-hydroxybenzoic acid (3) were isolated and purified from leaves and stems of Ouratea polyantha Engl. Agathisflavone was isolated in a single high-speed countercurrent chromatography run, while the megastigmane was purified in two steps, by using a combination of high-speed countercurrent chromatography and analytical column chromatography. All structures were elucidated on the basis of spectral evidence and comparison with literature data.

Inhibition of glucose intestinal absorption by kaempferol 3-O-α-rhamnoside purified from Bauhinia megalandra leaves.

Glucose intestinal absorption (GIA) is one of the factors that increase glycemia. Its reduction could be an important factor in decreasing hyperglycemia in diabetic patients. It has been shown that the aqueous extract of Bauhinia megalandra leaves inhibits GIA.

Evaluation of flavonoids from Bauhinia megalandra leaves as inhibitors of glucose-6-phosphatase system.

From the methanol extract of Bauhinia megalandra fresh leaves, eight flavonoids were isolated and evaluated by rat liver microsomal glucose-6-phosphatase (G-6-Pase) bioassay, which might be a useful methodology for screening antihyperglycaemic substances. All the flavonoids assayed showed an inhibitory effect on the intact microsomal G-6-Pase: quercetin and kaempferol exhibited the lowest effect; astilbin, quercetin 3-O-alpha-rhamnoside, kaempferol 3-O-alpha-rhamnoside and quercetin 3-O-alpha-arabinoside an intermediate effect. The highest inhibitory activity was shown by quercetin 3-O-alpha-(2''-galloyl)rhamnoside and kaempferol 3-O-alpha-(2''galloyl)rhamnoside.

Inhibition of hepatic neoglucogenesis and glucose-6-phosphatase by quercetin 3-O-alpha(2''-galloyl)rhamnoside isolated from Bauhinia megalandra leaves.

In intact microsomes, quercetin 3-O-alpha-(2''-galloyl)rhamnoside (QGR) inhibits glucose-6-phosphatase (G-6-Pase) in a concentration-dependent manner. QGR increased the G-6-Pase K(m) for glucose-6-phosphate without change in the V(max). The flavonol did not change the kinetic parameters of disrupted microsomal G-6-Pase or intact or disrupted microsomal G-6-Pase pyrophosphatase (PPase) activity.