Addition of 2,6-anhydro-7-deoxy-7-nitro-L-glycero-L-gu~uc~~-heptitol
(2,6-anhydro-l-deoxy-l-nitro-D-gfycero-L-manno-heptitol, /%D-galactopyranosylnitromethane)' to glycolaldehyde in methanol in the presence of 4 equiv. of sodium methoxide yielded a mixture of four diastereomers2, from which, after partial fractionation by chromatography, one isomer (1) could be crystallised from moist ethanol. Because of ambiguities in the configurational assignments by 'H-and '3C-n.m.r. spectroscopy, 1 was subjected to X-ray analysis.
The relevant crystallographic data of 1 are given in Table I. The structure was solved by direct methods in the usual way with the help of the programs SHELXS-903 and SHELX-76".
All atoms, hydrogens included, were refined. The final fractional co-ordinates of C, N, and 0 with equivalent isotropic thermal parameters are listed in Table II**. Selected torsion angles are given in Table III, and a perspective view (Schakal plot') of 1 is presented in Fig. 1, which clearly shows that the structure is 4,8-anhydro-3-deoxy-3nitro-D-lyxo-D-gluco-nonitol.
The six-membered ring adopts a chair conformation [puckering parameters'? Q = 59.5(5) pm, 0 = 6.5(5)", 0 = 26.5( 4)"] with C-3 and C-9 equatorial, and C-2 truns to C-5 and gauche to O-4. This is the geometry generally observed7 in "C-glycosides".
The nitro group is gauche to O-4, C-5, and O-2 in * To whom correspondence should be addressed. l * Lists of observed and calculated structure amplitudes, anisotropic thermal parameters, fractional co-ordinates of hydrogen atoms with isotropic thermal parameters, tables of bond distances and angles, and further information have been deposited with, and can be obtained from, Elsevier Science Publishers B.V.,