Carbon Dioxide → (3S,4S,5R)-1,3,4,5,6-pentahydroxyhexan-2-one

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A 100 ml flask containing 10.0 g lactose and 50 ml water was warmed to 50° C. and treated with 80 mg lactase 30,000 enzyme as in Example 3. After 6 hours the solution was analyzed by HPLC and found to contain 10% lactose, 45% D-glucose, and 45% D-galactose, based on the lactose added. The mixture was heated to 75° C. briefly to denature the protein, and was then filtered. A 2.5 cm interior diameter by 60 cm length glass column was packed with about 300 ml of BIO-RAD AG 50W-X8 resin in the calcium form, minus 400 mesh. BIO-RAD AG 50W-X8 is the trademark for a cationic ion exchange resin sold by Bio-Rad, Richmond, Calif. The column was heated to 70° C. The mobile phase was deionized water which had been filtered and degassed and which was pumped at a flow rate of 4.0 ml per minute. Typical pressure was 30 psig. The sample injection loop was 10 ml. The run time was approx. 55 minutes. The filtered reaction mixture described above was concentrated to 30% by weight solids, then injected in portions into the column. By using a refractive index detector to monitor the eluant, the mixture was separated into two groups of fractions. The combined first group of fractions contained 0.8 g of lactose and 4. 2 g D-glucose. The combined second group of fractions contained 0.3 g of D-glucose and 4.4 g of D-galactose. The second group of fractions was concentrated to 10% by weight solids for the isomerization step. The D-galactose solution, stirred at room temperature in a small flask, was treated with 2.0 g calcium hydroxide and 0.15 g calcium chloride, and the precipitate formed within 1.5 hours. The precipitate of calcium hydroxide-tagatose complex was neutralized with CO2 to give 2.2 g D-tagatose.

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