β-d-Gulose

The title compound, C6H12O6, a C-3 position epimer of d-galactose, crystallized from an aqueous solution, was confirmed as β-d-pyranose with a 4 C 1 (C1) conformation. In the crystal, O—H⋯O hydrogen bonds between the hydroxy groups at the C-1 and C-6 positions connect molecules into a tape structure with an R 3 3(11) ring motif running along the a-axis direction. The tapes are connected by further O—H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, C 6 H 12 O 6 , a C-3 position epimer of dgalactose, crystallized from an aqueous solution, was confirmed as -d-pyranose with a 4 C 1 (C1) conformation. In the crystal, O-HÁ Á ÁO hydrogen bonds between the hydroxy groups at the C-1 and C-6 positions connect molecules into a tape structure with an R 3 3 (11) ring motif running along the aaxis direction. The tapes are connected by further O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.
Supporting information for this paper is available from the IUCr electronic archives (Reference: IS5352).

Comment
The crystal system (orthorhombic), space group (P2 1 2 1 2 1 ), and number of molecules in the unit cell (Z = 4) of the title compound are the same as for the typical hexose (C 6 H 12 O 6 ) monosaccharides (Fukada et al., 2010). There is a difference in the hydrogen bonding patterns, having a circular chain network returning to the same molecule, and the intermolecular interactions between two adjacent β-D-gulose molecules in the crystal.
In an equatorial OH group at C-2 position, the hydrogen bond can be confirmed as a donor, which connects to the OH group at C-3 position of the neighboring molecule. However, for the axial OH groups at C-3 and C-4 positions, each has hydrogen bonds both as a donor and an acceptor to the OH groups at either the C-2 and C-4, or the C-3 and C-6 positions, respectively. In the OH group at the C-6 position, there is an intermolecular hydrogen bond between the OH group at C-4 position of the neighboring molecule, and there are two additional hydrogen bonds with the OH groups at different C-1 positions in these two different D-gulose molecules. There is an infinite hydrogen bonding chain along to the a-axis (···O1-H1A···O6-H6A···O1-H1A···), which is connecting to a finite chain (O2-H2A···O3-H3A···O4-H4A···O6-H6A). Therefore, the hydrogen bonding network can be categorized as Jeffrey's class (iv) (Jeffrey & Saenger, 1994;Jeffrey & Mitra, 1983). There is a step for returning to the same gulose molecule in an infinite chain (···gulose O1 -H1A···O6-H6A···O1-H1A···gulose O6-H6A···). Such a significant circular hydrogen bonding ring should be treated differently from the typical infinite chain.

Experimental
D-Gulose was prepared from disaccharide lactitol by a combination of microbial and chemical reactions. 3-Ketolactitol, oxidized from lactitol by Agrobacterium tumefaciens, was reduced by chemical hydrogenation. The resulting product, Dgulosyl-(β-1, 4)-D-sorbitol containing D-gulose, was hydrolyzed by acid hydrolysis, and its subsequent hydrolysates were separated by chromatography. Lastly, a crude crystal from the concentrated D-gulose syrup was recovered by ethanol precipitation, and then its aqueous solution was recrystallized, resulting in pure D-gulose. The D-gulose was concentrated to a brix value in a range of approximately 85-90%. Ethanol (twice the volume of the resulting syrup) was added and the resulting solution was mixed vigorously. The resulting crystals were dissolved in ultrapure water and then concentrated and crystallized at room temperature. The specific optical rotation of D-gulose was analyzed using a polarimeter (JASCO P-1030 Tokyo). An optical rotation was also performed, providing [α] 20 D = -24.10 (authentic sample = -24.74). The 13 C-NMR spectra of the isolated D-gulose was measured at 600 MHz in D 2 O using an ALPHA 600 system (Jeol Datum, Tokyo). All spectra were collected at 30 °C using trimethylsilyl propanoic acid as internal reference. All of the chemical shifts [δ = 94.6 (C1), 74.5 (C5), 71.9 (C3), 70.2 (C4), 69.8 (C2), 61.7 (C6)] corresponded well with an authentic D-gulose sample. These results indicate that the isolated material was D-gulose and that the current study was successful in preparing D-gulose. The gulose is a specialized member of the rare sugar family, therefore, the details regarding the synthesis, purification, and crystallization of gulose should be reported in a specialized journal (Morimoto et al., 2013).   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.14 e Å −3 Δρ min = −0.14 e Å −3 Extinction correction: SHELXL2013 (Sheldrick, 2008) Extinction coefficient: 0.0063 (12) Special details Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).