(2S,3R,4R,5S)-3,4-O-Iso­propyl­idene-2-methyl-1-oxa-6,9-diaza­spiro[4.5]decane-7,10-dione

The title spiro­carbopeptoid, C11H13N2O5, was prepared from l-fucose in a sequence that gave this and another anomer. The crystal structure determination removes ambiguities in the synthetic sequence.

The title spirocarbopeptoid, C 11 H 13 N 2 O 5 , was prepared from l-fucose in a sequence that gave this and another anomer.The crystal structure determination removes ambiguities in the synthetic sequence.

Comment
Sugar amino acids (SAAs) provide an extensive family of peptidomimetics (Baron et al., 2004;Chakraborty et al., 2004), an important sub-class of which incorporate an -amino acid at the anomeric position of a carbohydrate.Such SAAs may form spiro derivatives, some of which have been demonstrated to possess signi®cant biological activity.Thus hydantocidin, (5), which is a potent and environmentally friendly herbicide, is a spirohydantoin of ribose (Nakajima et al., 1991;Harumaya et al., 1991); similar derivatives of glucose have been shown to be potent inhibitors of glycogen phosphorylase (Watson et al., 1994;Bichard et al., 1995).
In an investigation of spiro carbopeptide analogues retaining the footprint of the furanose form of l-fucose, (2), the sugar (2) was transformed into a separable anomeric mixture of the acetonides (1) and (3); one of these anomers, (3), was highly crystalline and its structure has been shown by X-ray crystallographic analysis to have the relative stereochemistry shown in Fig. 1.The acetonide (3) was transformed into the deprotected analogue, (4), for biological evaluation.Fig. 2 is a packing diagram viewed down the c axis.The molecules containing the disordered atoms are, as is not uncommon for Z H = 2 structures, con®ned to a distinct layer through the crystal structure.The overall geometry is essen-tially the same in the ordered and the disordered molecules and is unexceptional.

Experimental
The title material (Ble Á riot et al., 2004) was crystallized by vapour diffusion of hexane into a solution in ethyl acetate to give small chunky crystals.The data were collected on a single-axis image plate diffractometer, leading to missing re¯ections in the cusp volume.In the absence of signi®cant anomalous scattering effects, Friedel pairs were merged.The absolute con®guration was assigned on the basis of the known con®guration of the starting material.Part of one molecule was modelled with disordered atoms (Fig. 3).The occupancies of the organic papers Figure 3 The disordered molecule, with displacement ellipsoids drawn at the 50% probability level.H atoms are of arbitrary radii.two disorder components were re®ned to 0.566 (13) and 0.434 (13).Anisotropic displacement parameters were constrained to be equal for corresponding atoms, and restraints were applied to the geometry of the disordered portions to keep them similar to the ordered molecules.Fig. 4 is a part of the F o electron density map in the region of the disordered atoms.Attempts to model the `split' atoms with electron density distributed along a line (Schro È der et al., 2004) led to slightly higher R values, possibly because the disorder trajectory is actually curved.It appears that both the split-atom and a very large displacement model would ®t equally well.All H atoms were found in difference density syntheses.They were initially re®ned with soft geometry restraints to regularize their geometry (bond lengths to accepted values, angles either set by symmetry or to accepted values), after which they were re®ned with riding constraints only.CÐH distances are all close to 0.98 A Ê , NÐH distances are 0.83±1.09A Ê , and U iso (H) = 1.2U eq (carrier atom).

Figure 4 F
Figure 4F o electron density map in the region of the disordered atoms, contoured at 2 (green), 4 (blue) and 6 e A Ê À3 (red).Note the continuous electron density at each disordered atom.A model with ordered atoms and very large displacement parameters is an alternative interpretation.

Figure 2
Figure 2 Packing diagram, viewed along the c axis.The molecules with the disordered atoms are con®ned to a single layer in the crystal structure.Dashed lines indicate hydrogen bonds.