2,3,4,6-Tetra-O-acetyl-β-d-galactopyranosyl butyrate

The title compound, C18H26O11, was synthesized by a condensation reaction of 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide and butyric acid. The acetoxymethyl and butyrate groups are located on the same side of the pyran ring, showing the β configuration for the d-glycosyl ester; the butyl group adopts an extend conformation, the C—C—C—C torsion angle being 179.1 (7)°. In the crystal, the molecules are linked by weak C—H⋯O hydrogen bonds.

The title compound, C 18 H 26 O 11 , was synthesized by a condensation reaction of 2,3,4,6-tetra-O-acetyl--d-galactopyranosyl bromide and butyric acid. The acetoxymethyl and butyrate groups are located on the same side of the pyran ring, showing the configuration for the d-glycosyl ester; the butyl group adopts an extend conformation, the C-C-C-C torsion angle being 179.1 (7) . In the crystal, the molecules are linked by weak C-HÁ Á ÁO hydrogen bonds.

Comment
Carbohydrates provide excellent platforms upon which to explore unique features for the drug-discovery process. Numerous natural glycosyl esters such as phyllanthostatin family (Li et al., 1992) and dimeric ellagitannin coriariin A have been total synthetized (Smith et al., 1986). Some of them were proved to possess anti-tumor activities (Feldman et al., 2000). Also the glycosyl esters have long drawn attention as potential glycosyl donors. Several crystal structures of carbohydrate derivatives were reported (Sambaiah et al., 2001;Parkanyi et al., 1987;Roslund et al., 2004;Liu et al., 2009;Kumar et al., 2005).
Recently we have synthetized the title compound and report its crystal structure herein.
The molecular structure of the title compound is shown in Fig. 1. In the molecule, the acetoxymethyl and butyrate groups are located on the same side of the pyran ring, showing the β-configuration for the D-glycosyl ester; the butyl group adopts an extend conformation, the C6-C7-C8-C9 torsion angle being 179.1 (7)°. The molecules are linked by weak C-H···O hydrogen bonding in the crystal.

Refinement
Methyl H atoms were placed in calculated position with C-H = 0.96 Å and torsion angle was refined from electron density with U iso (H) = 1.5U eq (C). Other H atoms were placed in calculated positions with C-H = 0.97-0.98 Å, and included in the final cycles of refinement in riding model with U iso (H) = 1.2U eq (C). As no significant anomalous scatterings, Friedel pairs were merged. The enantiomer has been assigned by reference to the unchanging chiral C5 atom in the synthetic procedure.