New prenylated flavanones from stem bark of Erythrina abyssinica

In the course of investigation on Protein Tyrosine Phosphatase 1B (PTP1B) inhibitors from nature, we found that an EtOAc extract of the stem bark of Erythrina abyssinica greatly inhibited PTP1B activity in an in vitro assay [1]. Further bioactivity-guided fractionation of this fraction led to the isolation of twelve new flavanones (1–12) bearing a 2,2-dimethylpyran ring, named abyssinoflavone VIII–XIX. Their structures were determined on the basis of spectroscopic (UV, CD, 1D and 2D NMR, HR-MS) and physicochemical analyses. Compounds 1, 3, 5, 6, 8, and 9 exhibited inhibitory effect on PTP1B activity with IC₅₀ values ranging from 13.9±2.1 to 19.0±1.8µM. This result suggests that prenyl and methoxy groups on B ring are responsible for the inhibitory activity of flavanones against PTP1B.

Table 1. Inhibitory effect of active compounds on PTP1B

Compound	Inhibitory effect (IC50 a, µM)
1	13.9±2.1
3	17.9±1.7
5	14.9±1.6
6	18.2±2.1
8	19.0±1.8
9	18.2±1.2
Ursolic acidb	3.6±0.2

References: 1. Cui, L. et al. (2007)J. Nat. Prod. 70:1039–1042.