(S)-3-Dimethylamino-2-{(4S,5R)-5-[(R)-2,2-dimethyl-1,3-dioxolan-4-yl]-2,2-dimethyl-1,3-dioxolan-4-yl}-2-hydroxypropanoic acid

The Kiliani reaction on 1-deoxy-(N,N-dimethylamino)-d-fructose, itself readily available from reaction of dimethylamine and d-glucose, proceeded to give access to the title β-sugar amino acid, C15H27NO7. X-ray crystallography determined the stereochemistry at the newly formed chiral center. There are two molecules in the asymmetric unit; they are related by a pseudo-twofold rotation axis and have very similar geometries, differing only in the conformation of one of the acetonide rings. All the acetonide rings adopt envelope conformations; the flap atom is oxygen in three of the rings, but carbon in one of them. There are two strong hydrogen bonds between the two independent molecules, and further weak hydrogen bonds link the molecules to form infinite chains running parallel to the a axis.

The Kiliani reaction on 1-deoxy-(N,N-dimethylamino)-dfructose, itself readily available from reaction of dimethylamine and d-glucose, proceeded to give access to the titlesugar amino acid, C 15 H 27 NO 7 . X-ray crystallography determined the stereochemistry at the newly formed chiral center. There are two molecules in the asymmetric unit; they are related by a pseudo-twofold rotation axis and have very similar geometries, differing only in the conformation of one of the acetonide rings. All the acetonide rings adopt envelope conformations; the flap atom is oxygen in three of the rings, but carbon in one of them. There are two strong hydrogen bonds between the two independent molecules, and further weak hydrogen bonds link the molecules to form infinite chains running parallel to the a axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CF2175).

Comment
Sugar amino acids are a versatile class of conformationally biased building blocks, and have use as both glyco-and peptidomimetics (Risseeuw et al., 2007). The Kiliani reaction on ketoses has been successfully utilized in the synthesis of branched carbohydrate building blocks (Hotchkiss et al., 2004;Soengas et al., 2005;Parker et al., 2006;Simone et al., 2007) to produce, for example, methyl or hydroxymethyl branched lactones. With Amadori products, 1-amino-1-deoxy-ketoses, as substrates, the Kiliani ascension should provide access to β-sugar amino acids. The reaction of 1-deoxy-1-(N,N-dimethylamino)-D-fructose, 2, an Amadori product readily available from D-glucose, 1, with sodium cyanide in water was found to give, after acetonide protection, the title compound, 3, as the major product. The stereochemistry at C-2 was unequivocally assigned by X-ray crystallography (Fig. 2) and the absolute stereochemistry was determined by the use of D-glucose as the starting material.
The asymmetric unit contains of two crystallographically distinct molecules which are related by a pseudo-2-fold rotation axis. These are similar in geometry with the exception of one of the isopropylidene rings: in the first molecule the atoms C20, O13, O14 and C28 are approximately coplanar while C21 is displaced from this plane, whereas in the second molecule C120, C121, O113 and C128 are approximately coplanar while O114 is displaced. The r.m.s. bond length deviation for the two molecules, excluding hydrogen atoms, is 0.007 Å.
Hydrogen bonding links molecules to form infinite chains running parallel to the crystallographic a axis (Fig. 3). There are two weak hydrogen bonds between the layers and two strong hydrogen bonds linking the two molecules in the asymmetric unit ( Fig. 4).

Experimental
The title compound was prepared as described by Hotchkiss et al. (2008) and shown in the reaction scheme of Fig

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the starting material. The refinement, on F values, used only data for which F 2 > 3σ(F 2 ).
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.