The milk carbohydrate of monotremes (egg-laying mammals: platypus and echidna) differs from that of marsupials and of placental mammals, notably in its high content of fucose'. The principal neutral carbohydrates of echidna and platypus milk are, respectively, fucosyl-lactose and difucosyl-lactose'*'. These compounds are also minor components of human milk2-6. Human milk contains two isomers of fucosyl-lactose 7 in one of which (2'-fucosyl-lactose)3 a+fucose is , linked to position 2 of D-gakICtOSf5; in the other (3-fucosy1-1actose)4, it is attached to position 3 of D-glucose. We now show by '3C-n.m.r. spectroscopy that the trisaccharide from echidna milk is 2'-fucosyl-lactose (1) and that the tetrasaccharide from platypus milk is 3,2'-difucosyl-lactose
(2). The 13C-n.m.r. spectrum (accumulated at 50.3 MHz for 64 h) of a 0.4% solution of the trisaccharide 1 (6 mg) in 'Hz0 contained twelve, readily observable resonances of approximately equal intensity, corresponding to the twelve carbons of the non-reducing sugar residues, and eleven resonances of small intensity (the apeaks are also smaller than the p-peaks), corresponding to the reducing-end residue. One (8 72.1) of the larger of the latter resonances apparently contained two coincident a-resonances. The chemical shifts and assignments are given in Table I.
The assignment procedure for 1 (in which D-glucose, D-galactose, and L-fucose are present in equimolar amounts') commences with the reducing residue'. The chemical shift data for the eleven signals of the reducing residue are compared with those for the monosaccharides D-glucose, D-galactose, and L-fucose. Because of their downfield positions, the resonances involved in the linkage of the reducing sugar residue are those at 6 76.7 and 76.6 (a and p, respectively, based on their relative intensities); the signal of the carbon involved in a linkage is shifted downfield compared with that of the unsubstituted monosaccharide, and the magnitude is the same for both the (Y and j3 forms'. Furthermore, of the chemical shifts of the C-2,3,4 signals for the monosaccharides, only those of C-h and C-4p are similar;