Crystal structure of β-d,l-psicose

Bioproduction of D-allulose: Properties, applications, purification, and future perspectives

D-allulose is the C-3 epimer of D-fructose, which rarely exists in nature, and can be biosynthesized from D-fructose by the catalysis of D-psicose 3-epimerase. D-allulose is safe for human consumption and was recently approved by the United States Food and Drug Administration for food applications. It is not only able be used in food and dietary supplements as a low-calorie sweetener, but also modulates a variety of physiological functions. D-allulose has gained increasing attention owing to its excellent properties. This article presents a review of recent progress on the properties, applications, and bioproduction progress of D-allulose.

α-D,L-Sorbose

The racemic title compound, C6H12O6, consisting of C-4 epimers of psicose, was crystallized from an aqueous solution of an equimolar mixture of D- and L-sorboses. It was confirmed that D-sorbose (or L-sorbose) formed α-pyranose with a 4 C 1 (or 1 C 4) conformation where the anomer position was designated as carbon-1. The asymmetric unit comprises two crystallographically independent molecules. In the crystal, molecules are linked by O—H...O hydrogen bonds, forming a three-dimensional framework. The unit-cell volume of the title racemic α-D,L-sorbose is 1450.86 (6) Å3 (Z = 8), which is about 41 Å3 smaller than that of twice the amount of chiral α-L-sorbose [V = 745.942 Å3 (Z = 4)].

Crystal structure of 6-de-oxy-α-l-psico-furan-ose

The title compound, C6H12O5, was crystallized from an aqueous solution of 6-de-oxy-l-psicose (6-de-oxy-l-allulose, (3S,4S,5S)-1,3,4,5-tetra-hydroxy-hexan-2-one), and the mol-ecule was confirmed as α-furan-ose with a (3) T 4 (or E 4) conformation, which is a predominant tautomer in solution. This five-membered furan-ose ring structure is the second example in the field of the 6-de-oxy-ketohexose family. The cell volume of the title compound [742.67 (7) Å(3), Z = 4 at room temperature] is only 1.4% smaller than that of β-d-psico-pyran-ose, C6H12O6 (753.056 Å(3), Z = 4 at room temperature).

Crystal structure of β-d,l-fructose

The title compound, C6H12O6, was crystallized from an aqueous solution of equimolar mixture of d- and l-fructose (1,3,4,5,6-penta-hydroxy-hexan-2-one, arabino-hexulose or levu-lose), and it was confirmed that d-fructose (or l-fructose) formed β-pyran-ose with a (2) C 5 (or (5) C 2) conformation. In the crystal, two O-H⋯O hydrogen bonds between the hy-droxy groups at the C-1 and C-3 positions, and at the C-4 and C-5 positions connect homochiral mol-ecules into a column along the a axis. The columns are linked by other O-H⋯O hydrogen bonds between d- and l-fructose mol-ecules, forming a three-dimensional network.