As part of a programme involving X-ray crystallographic studies" of cis-and tpuns-fused hexopyranosides, we now report on the crystal structures of methyl 2-~-methyl-~-D-glucop~anoside* (11, which was obtained by debe~lidenation of methyl 4,~-O-benzyIidene-2-O-methyI-3-O-~-tolylsulfonyl-~-~-glucopyranoside3 followed by detosylation, and methyl 4,6-O-benzylidene-2-0-methyl-cr_D-galactopyranoside (21, which was prepared4 by selective tosylation of methyl 4,6-O-benzylidene-cY-D-galactopyranoside followed by Purdie methylation and detosylation.
Perspective views of 1 and 2 are depicted in Figs. 1 and2, respectively. The final atomic co-ordinates for 1, with their standard deviations in parentheses, are listed in Tables I andII, and the corresponding parameters for 2 are given in Tables III andIV.
For 1, the C-C bond lengths in the sugar ring have a mean value of 1.52 A, in agreement with values observed for other carbohydrates, and there is a 4C, conformation with C-2, C-3, C-5, and O-5 coplanar (C-4 and C-l, respectively, lie 0.67 A above and 0.69 A below this plane). There are intermolecular hydrogen bonds involving O-2 and O-4,0-3 and O-6, and O-3 and O-4. The hydrogen atoms attached to O-3, O-4, and O-6 were not located. All other hydrogen atoms were attached in calculated positions with fixed thermal parameters.
In the crystal structure of 2, there is the expected5 double-chair conformation with the phenyl group equatorial. For 2, C-5 lies 0.637 A below and C-7 lies 0.66 A above plane 1 (C-6, O-6, C-4, and O-41, and C-4 lies 0.65 A above, and C-l lies 0.69 A below plane 2 (C-2, C-3, C-5, and O-5 of the pyranose ring'. Plane 2 of the pyranose ring lies at an angle of 76.82" to plane 1. The phenyl ring is oriented at an angle of 75.97" to plane 1. There is an intermolecular hydrogen bond involving O-3 and O-6 (2.83 A>.