Synthesis of natural/ 13 C-enriched d-tagatose from natural/ 13 C-enriched d-fructose.

A concise, easily scalable synthesis of a rare ketohexose, d-tagatose, was developed, that is compatible with the preparation of d-[UL- ¹³ C ₆ ]tagatose. Epimerization of the widely available and inexpensive ketohexose d-fructose at the C-4 position via an oxidation/reduction (Dess-Martin periodinane/NaBH ₄ ) was a key step in the synthesis. Overall, fully protected natural d-tagatose (3.21 g) was prepared from d-fructose (9 g) on a 50 mmol scale in 23% overall yield, after five steps and two chromatographic purifications. d-[UL- ¹³ C ₆ ]Tagatose (92 mg) was prepared from d-[UL- ¹³ C ₆ ]fructose (465 mg, 2.5 mmol) in 16% overall yield after six steps and four chromatographic purifications.
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