Crystal structure of potassium (1R)-d-ribit-1-ylsulfonate

The anion of potassium (1R)-d-ribit-1-ylsulfonate has an open-chain structure with the potassium cation seven-coordinated in an approximately pentagonal–bipyramidal coordination environment by six different anions through K—O coordinate bonds.


Chemical context
Addition compounds formed between carbonyl compounds and the bisulfite anion have found use in purification of liquid aldehydes when, as is often the case, the adduct is crystalline, in facilitating cyanohydrin formation, and also in conferring required water solubility to certain hydrophobic compounds (Clayden et al., 2012). Less well known is the fact that aldoses, despite existing preferentially in the hemiacetal form, can react with the bisulfite anion to give open-chain adducts which, as chiral hydroxysulfonic acids, have potentially useful but largely unexplored applications in synthesis. The knowledge of such compounds was initially centred on the their possible role in the stabilization of food stuffs (Gehman & Osman, 1954) (note: nearly all wines are labelled 'contains sulfites') and evidence for their acyclic nature was first provided by Ingles (1959), who prepared such adducts from dglucose, d-galactose, d-mannose, l-arabinose and l-rhamnose. However, conclusive proof for their acyclic structure awaited X-ray studies, initially by Cole et al. (2001) who reported the crystal structures of d-glucose-and d-mannose-derived potassium sulfonates, and later we studied the sodium sulfonate derived from d-glucose (Haines & Hughes, 2012) and the potassium sulfonate from d-galactose (Haines & Hughes, 2010) by X-ray crystallography. The crystal structure of the potassium bisulfite adduct of dehydro-l-ascorbic acid, first prepared by Ingles (1959), has also been reported (Haines & Hughes, 2013).
C-Sulfonic acid derivatives of carbohydrates have been prepared at non-glycosidic atoms by the radical-mediated addition of the bisulfite ion to methyl 6-deoxyhexopyranosid-5-enes (e.g. in the synthesis of 6-sulfoquinovose; Lehmann & Benson, 1964), by trifluoromethanesulfonate-mediated nucleophilic displacement reactions with the bisulfite ion (Liptá k et al., 2004) or by oxidation of a thioacetyl substituent on a protected glycose (Liptá k et al., 2004). Although oxidation of C1-thioesters of protected aldoses affords a route to ISSN 1600-5368 C1-sulfonic acids, the facile preparation of the bisulfite adducts of certain aldoses provides an attractive route to chiral hydroxysulfonic acids, which merit further exploration as possible synthetic intermediates.
Preparation of aldose adducts requires reaction at high concentrations, with the bisulfite anion produced in situ by hydrolysis of the corresponding metabisulfite. Obtaining suitable material for X-ray crystallography is not always straightforward, either in the initiation of crystallization or in isolating crystals of suitable quality. We report here the preparation in crystalline form of the hitherto unknown potassium bisulfite adduct from d-ribose, (1), and its solidstate structure.

Figure 2
View approximately along the a axis, showing the hydrogen-bonding contacts and all the K-O coordination bonds. Symmetry codes as in Fig. 1. Table 1 Hydrogen-bond geometry (Å , ).
High-resolution mass spectrometry in negative-ion mode identified the anion at m/z 231.0187 but the base peak was at m/z 213.0082, representing loss of water from the parent ion. A large peak was also observed at 299.0987 for C 10 H 19 O 10 , which corresponds to the ion of the product formed by reaction between (1) and d-ribose with displacement of potassium bisulfite; in the aqueous solution used for MS analysis, some decomposition of (1) to afford d-ribose undoubtedly occurs and this is supported by NMR data on the aqueous solution reported below.
The 1 H NMR spectrum of (1) in D 2 O indicates considerable stability of the adduct in aqueous solution, with the speciesfuranose, -furanose, -pyranose, -pyranose, and bisulfite adduct, identified by their H-1 resonances, present in the % ratios of 3.6:6.2:10.9:5.1:74.2, which changed only marginally after 18 days. A complete assignment of the spectrum for (1) and consideration of derived coupling constants indicated overall similarity of the conformation in the crystalline state and in solution. Notably, J 1,2 was close to zero and assuming Newman projection angles of 120 and using measured torsional angles, a Karplus relationship suggests a value of about 0.3 Hz. The value J 2,3 = 8.6 Hz is in accord with an antiperiplanar arrangement of H2 and H3, whereas J 3,4 = 4.6 Hz is consistent with the synclinal disposition of H3 and H4, resulting from a gauche arrangement for C2-C3-C4-C5.
The 13 C NMR spectrum confirmed the presence of the four ring forms of d-ribose as indicated by their C1 signals and the major peak for C1 in the adduct at C 82.25 was accompanied by a much smaller peak at C 84.19 which suggests the presence in solution of the diastereoisomer of (1) having the S-configuration at C1.

Supramolecular features
A three-dimensional network exists in the crystal structure through the coordination of each potassium cation (overall seven coordinate) to six different ribose bisulfite residues and through extensive hydrogen bonding between hydroxy hydrogens and oxygen atoms of hydroxyl groups or those on sulfur. Although the addition of the sulfite anion to C1 of the ribose moiety can theoretically afford two isomers, only the Rdiastereomer was present in the crystal studied.

Synthesis, crystallization and spectroscopic analysis
Water (0.5 ml) was added to potassium metabisulfite (0.37 g), which did not dissolve completely even on warming but which appeared to change its crystalline form as it underwent hydrolysis to yield potassium hydrogen sulfite. To this suspension was added a solution of d-ribose (0.5 g) in water (0.35 ml), leading to immediate and complete solution of the reaction mixture. Seed crystals were obtained by complete evaporation of a small proportion of the solution, and these were added to the bulk of the solution which was then stored at 277 K, leading to the formation of large, well-separated crystals. The syrupy nature of the mother liquor required its removal with a Pasteur pipette, after which the crystals were dried by pressing between filter papers, to give potassium    Integration of the various signals for H-1 in the 1 H NMR spectrum, 5 minutes after sample dissolution, indicated the species -furanose, -furanose, -pyranose, -pyranose, bisulfite adduct were present in the % ratios of 3.6:6.2:10.9:5.1:74.2. Re-measurement after 18 days, gave these % ratios as 1.5:2.6:16.2:8.7:70.9.
HRESMS (negative-ion mode, measured in H 2 O/MeOH, solution) gave an expected peak at m/z 231.0187 ([C 5 H 11 O 8 S] À ), the base peak at 213.0082 ([C 5 H 11 O 8 SÀ H 2 O] À ) and a significant peak at 299.0987 ([C 10 H 19 O 10 ] À ). The last peak corresponds to the ion of the product formed by reaction between the bisulfite adduct and d-ribose with displacement of potassium bisulfite.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms bound to the carbon atoms were included in idealized positions (with C-H distances of 0.98 and 0.97 Å for methyne and methylene groups respectively) and their U iso values were set to ride on the U eq values of the parent atoms; hydroxyl hydrogen atoms were located in difference maps and were refined freely.  (Johnson, 1976) and ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 2012).

Special details
Experimental. Absorption correction: CrysAlisPro RED, Oxford Diffraction Ltd., Version 1.171.33.55 Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq K 0.00261 (5)