The molecule is a trisaccharide that is lactose in which the hydroxy group at the 2' positions has been glycosylated by an alpha-L-fucopyranosyl group. It is the most abundant human milk oligosaccharide. It derives from a lactose and an alpha-L-fucose.
(2S,3S,4R,5S,6S)-2-[(2S,3R,4S,5R,6R)-4,5-dihydroxy-6-(hydroxymethyl)-2-[(2R,3S,4R,5R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxan-3-yl]oxy-6-methyloxane-3,4,5-triol