Formation of 4-deoxy-glycero-hexo-2,3-diulo-furanose from microthecin

4-Deoxy-glycero-hexo-2,3-diulose was formed from microthecin [2-hydroxy-2-(hydroxymethyl)-2H-pyran-3(6H)-one] in neutral water solutions by a Michael addition. The compound was determined by NMR spectroscopy, MS and polarimetry to be a racemic mixture of d-and l-forms and existing mainly as two furanosidic C-2 epimers in equilibrium with microthecin. GC–MS analysis showed that 4-deoxy-glycero-hexo-2,3-diulose and microthecin were present in extracts of the red alga Gracilariopsis lemaneiformis.