Four new flavan-4-ol glycosides from Pneumatopteris pennigera

From the fronds of Pneumatopteris pennigera, four new flavan-4-ol glycosides, named pneumatopterins A, B, C and D, were isolated. Their structures were determined as (2S,4R)-5,7-di-beta-D-glucopyranosyloxy-6-hydroxymethyl-8-methylflavan-4-ol, (2S,4R)-5,7-di-beta-D-glucopyranosyloxy-6,8-dimethylflavan-4-ol, (2S,4R)-5-beta-D-glucopyranosyloxy-7-hydroxy-6-hydroxymethyl-8-methyl-4,2 ''-oxo-flavan and (2S,4R)-5-beta-D-glucopyranosyloxy-7-hydroxy-6,8-dimethyl-4,2 ''-oxo-flavan, respectively, on the basis of spectroscopic data and chemical correlations.