(−)-Benzyl 2,3-dide­oxy-β-d-erythro-hex-2-eno­pyran­oside

Shigeru Ohba; Hayato Okazaki; Yuji Ueda; Kengo Hanaya; Mitsuru Shoji; Takeshi Sugai

doi:10.1107/S1600536813031140

. 2013 Nov 23;69(Pt 12):o1811. doi: 10.1107/S1600536813031140

(−)-Benzyl 2,3-dideoxy-β-d-erythro-hex-2-enopyranoside

Shigeru Ohba ^a,^*, Hayato Okazaki ^b, Yuji Ueda ^b, Kengo Hanaya ^b, Mitsuru Shoji ^b, Takeshi Sugai ^b

PMCID: PMC4004438 PMID: 24860294

Abstract

In the title compound, C₁₃H₁₆O₄, the six-membered ring of the sugar moiety shows a half-chair conformation. In the crystal, molecules are connected via O—H⋯O hydrogen bonds, forming columns around twofold screw axes along the b-axis direction. There is a disorder of the benzyloxy group, which has two possible orientations with the phenyl group lying on a common plane [site-occupancy factors = 0.589 (9) and 0.411 (9)].

Related literature

For the phenolic Ferrier reaction, see: Ferrier & Prasad (1969 ▶); Noshita et al. (1995 ▶). For the structure of the related compound α-glycoside, see: Wingert et al. (1984 ▶). For the synthesis of β-glycoside, see: Di Bussolo et al. (2002 ▶, 2004 ▶). For the enzymatic regioselective acylation of d-glucal, see: Calveras et al. (2010 ▶). graphic file with name e-69-o1811-scheme1.jpg

Experimental

Crystal data

C₁₃H₁₆O₄
M _r = 236.26
Monoclinic,
a = 19.500 (9) Å
b = 5.291 (2) Å
c = 6.0809 (15) Å
β = 94.27 (3)°
V = 625.7 (4) Å³
Z = 2
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 292 K
0.60 × 0.40 × 0.20 mm

Data collection

Rigaku AFC-7R diffractometer
1713 measured reflections
1585 independent reflections
786 reflections with F ² > 2σ(F ²)
R _int = 0.034
3 standard reflections every 150 reflections intensity decay: 0.8%

Refinement

R[F ² > 2σ(F ²)] = 0.056
wR(F ²) = 0.255
S = 1.04
1579 reflections
193 parameters
33 restraints
H-atom parameters constrained
Δρ_max = 0.16 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Data collection: WinAFC Diffractometer Control Software (Rigaku, 1999 ▶); cell refinement: WinAFC Diffractometer Control Software (Rigaku, 1999 ▶); data reduction: CrystalStructure (Rigaku, 2010 ▶); program(s) used to solve structure: SIR92 (Altomare et al., 1993 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEPII (Johnson, 1976 ▶); software used to prepare material for publication: CrystalStructure (Rigaku, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) General, I. DOI: 10.1107/S1600536813031140/is5321sup1.cif

e-69-o1811-sup1.cif^{(28.4KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536813031140/is5321Isup2.hkl

e-69-o1811-Isup2.hkl^{(77.8KB, hkl)}

Click here for additional data file.^{(2.2KB, cdx)}

Supplementary material file. DOI: 10.1107/S1600536813031140/is5321Isup3.cdx

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2⋯O3ⁱ	0.82	1.95	2.692 (8)	151
O3—H3⋯O2ⁱⁱ	0.82	1.89	2.614 (8)	147

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

This work was supported by the Keio Gijuku Academic Development Funds.

supplementary crystallographic information

1. Experimental

1.1. Synthesis and crystallization

To a solution of 1c (669 mg, 2.17 mmol) in CH₃CN (22 ml) were added Cs₂CO₃ (1.41 g, 4.33 mmol) and BnOH (4.53 ml, 43.5 mmol) and the mixture was stirred for 8 h at room temperature. The mixture was diluted H₂O and organic materials were extracted with CHCl₃. The combined extract was washed with brine, dried over Na₂SO₄, and concentrated in vacuo. The residue was purified by silica gel column chromatography (20 g). Elution with hexane-EtOAc (2:1) afforded the title compound (I) as a colorless solid (414 mg, 81%). The plate-like crystals of (I) were grown by slow cooling of a t-butylmethylether/hexane solution from ca 340 K to the room temperature. The specific rotation [α]_D of (I) at 295 K is -107° (c 1.33, EtOH).

1.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The absolute structure was assigned based on the known absolute configuration around the C6 atom, which originated from (+)-D-glucose. In the absence of significant anomalous scattering effects, Friedel pairs were averaged before the final refinement. There is an orientational disorder of the benzyloxy group, where the split phenyl group moieties lie on a common plane. The site occupation factor of the major part (O4A, C11A—C17A) was refined to 58.9 (9)%. All the H atoms were positioned geometrically, and refined as riding, with C—H = 0.93–0.98 Å and O—H = 0.82 Å, and with U_iso(H) = 1.2U_eq(C,O). The hydroxy groups were allowed to rotate but not to tip.

2. Comment

Glycosidic bond formation on glycals such as (1a in Fig. 3) accompanied with the migration of double bond from C₁—C₂ to C₂—C₃ had been recognized as Ferrier reaction to give 2-enopyranosides (2) (Ferrier & Prasad, 1969; Noshita et al., 1995). Generally, α-glycosides predominate by the well known oxygen anomeric stabilizing effect, and the anomeric stereochemistry was elucidated by X-ray structure analysis of 2a (Wingert et al., 1984). In contrast, Di Bussolo et al.(2002, 2004) have demonstrated unique β-selective approach, starting from glycals such as 3 with leaving group at C₄—OH. By neighboring group participation with free C₃—OH, via an epoxide intermediate (4), Ferrier-like rearrangement occurred to give 5. Their proposed mechanism is shown in Fig. 3. In this case, a hydrogen bonding between epoxy ring in 4 and nucleophile dominates the stereochemistry to β rather than α. We submitted 3,6-di-O-acetyl-D-glucal (1b), which is very easily available by an enzymatic regioselective acylation of D-glucal (Calveras et al., 2010), to Crotti's protocol. Introduction of methylsulfonyl group on free C₄—OH (1c) and subsequent nuleophilic attack with benzyl alcohol provided the title compound, (I)(81%).

In the present study, the regio- and stereochemistry of (I) has been determined, although there is a complicated disorder. The benzyloxy group has two possible orientations, O4A/C11A—C17A and O4B/C11B—C17B, and their site occupation factors are 58.9 (9) and 41.1 (9)%, respectively. The C10—O4A and C10—O4B bond directions make an angle of 25.4 (7)°.