Aniline condenses with D-ribose under different conditions to give two distinct crystalline aniline-N-D-ribosides, one of which, it has been suggested, is a pyranoside, whereas the other is a furanoside2. However, as has already been pointed out1, further evidence is necessary before the structures assigned to these compounds can be accepted. We have now shown that when aniline reacts with ribose in alcoholic solution the isomer which is obtained depends on the presence or absence of water. By heating aniline with ribose in anhydrous ethanol, we have invariably obtained isomer A, of melting point about 130, MV + 186 (c, 0-8 in pyridine). If the reaction is carried out with moist ethanol there results isomer B, of melting point about 115, [a]1/,5 -f 62 (c, 1-0 in pyridine). A is the furanoside of earlier workers2"4, and B their pyranoside. Attempts to recrystallize A from moist ethanol give B ; similarly, B is converted to A in dry ethanol. Although there are some discrepancies in the specific rotations of the two compounds as determined by different workers (see accompanying table), it is clear that in methanol, at least, the specific rotations of the two compounds change to approximately the same final value, which does not lie between the individual values. If the methanolic solution of constant specific rotation is allowed to evaporate to dryness in the laboratory atmosphere, the crystals deposited are B in every case.The simplest explanation of this behaviour is that each of the two compounds A and B is converted in solution into an equilibrium mixture of A, B and the acyclic, Schiffs base type of compound. We have no evidence in support of the existence of this third form. The contrast in behaviour between the stable O-glycosides and the labile N-glycosides is very striking. This facile interchange of forms in solution, apparently general for arylamine-N-glycosides, renders inapplicable most of the chemical methods normally used for elucidating structure. The use of infra-red absorption spectra measurements appears promising, but has not yet been widely investigated4. It is noteworthy, however, that all the characterized derivatives prepared from arylamine-N-glycosides have the pyranose ring system. For example, aniline-N-glucoside has been shown to yield, on acetylation, a mixture of a- and p-aniline-N-glucopyranoside tetra-acetates1. After many experiments, we have now been able to methylate aniline-N-glucoside under mild conditions with dimethyl sulphate to obtain 2:3:4: 6-tetramethyl p -aniline-N-gluco-pyranoside in rather low yield. In addition, the two aniline-N-ribosides have been shown to give aniline-N-ribopyranoside tri-acetate2-3, and p-aniline-N-gal-actoside is acetylated to the pyranoside tetra-acetates4. Although in many cases two crystalline isomers of the arylamine-N-glycoside have been obtained, this is not invariably true. Aniline-N-glucoside is known only as an amorphous solid, whereas p-toluidine-N-glucoside and aniline-N-galactoside have each been isolated in one crystalline form only, probably the (3-pyranoside1'5. By using anhydrous conditions for the preparation of N-glycosides, we have been successful, in certain cases, in obtaining a new isomer. The case of p-toluidine-N-glucoside illustrates this. The only isomer previously known has melting point 117-118, [alp 101 -> 46 (c, 0-5 in methanol), whereas the compound obtained using anhydrous ethanol has melting point 135-136, MD + 209 -45 (c, 0-6 in methanol), and is probably oc-p-toluidine-N-glucopyranoside. In the same way we have obtained evidence for the existence of an aniline-1ST-galactoside distinct from the previously known one. It appears to be general, where two isomers have been obtained from the same sugar and amine, that their specific rotations in methanol change to the same final equilibrium value. [alD of A[QL]D of BRef. In methanolIn pyridine In methanolIn pyridine 2Not given + 176-5-+ 156-6 Not given+ 63-4-> + 48-6 3Not given + 180Not given + 60(dry solvent) + 180 -+ 161 (dry solvent) + 60-+ 48-4 44- 135 -> + 12 (moist solvent) + 182 - -f- 52-3+ 23 - + 13 (moist solvent)-f 62 -> + 50 Present authors+ 1710- + 14 + 135 -> + 14 + 186+ 24-> + 10 + 62We acknowledge our indebtedness to Roche Products, Ltd., for a generous gift of ribose, to the Chemical Society for a grant from the Research Fund, and to Merioneth County Education Committee for a scholarship awarded to one of us (G. P. E.).