Immunosuppressant flavonoids from Scutellaria baicalensis

A library of 435 extracts from plants used in Traditional Chinese Medicine was screened for their inhibitory potential on the proliferation of human T-lymphocytes in vitro. A dichloromethane extract from roots of Scutellaria baicalensis Georgi (Lamiaceae) inhibited T-lymphocyte proliferation with an IC₅₀ of 12.9 μg/mL. To localize compounds responsible for the activity, 600 μg of the extract was submitted to HPLC-based activity profiling. Of the 33 one-minute micro-fractions collected, suppression of T-cell lymphocyte proliferation was detected in micro-fractions at r_T 10, 14 and 17 minutes, respectively.

Preparative isolation led to seventeen flavonoids. Twelve compounds (2, and 5-15) were localized in the active time windows, and structurally related flavones 4, 16, and 17, and flavanones 1 and 3 were isolated from fractions adjacent to the active time windows. All flavonoids possess an unusual substitution pattern on the B-ring, with absence of substituents at C-3 and C-4.

Fig. 1