The isolation from Castanospermum australe and identification by X-ray crystal structure analysis of (1R,2R,3S,7S,8R)-3-hydroxymethyl-1,2,7-trihydroxypyrrolizidine [(2S,3R,4R,5S,6R)-2-hydroxymethyl-1-azabicyclo[3.3.0]octan-3,4,6-triol]—the second example of a pyrrolizidine alkaloid with a carbon substituent at C-1, is described. A study of the inhibition of glycosidases by 3,8-diepialexine is reported.