| Summary: | <span style="font-variant: small-caps;">l</span>-Hexoses are important components of biologically relevant compounds and precursors of some therapeuticals. However, they typically cannot be obtained from natural sources and due to the complexity of their synthesis, their commercially available derivatives are also very expensive. Starting from one of the cheapest <span style="font-variant: small-caps;">d</span>-hexoses, <span style="font-variant: small-caps;">d</span>-mannose, using inexpensive and readily available chemicals, we developed a reaction pathway to obtain two orthogonally protected <span style="font-variant: small-caps;">l</span>-hexose thioglycoside derivatives, <span style="font-variant: small-caps;">l</span>-gulose and <span style="font-variant: small-caps;">l</span>-galactose, through the corresponding 5,6-unsaturated thioglycosides by C-5 epimerization. From these derivatives, the orthogonally protected thioglycosides of further two <span style="font-variant: small-caps;">l</span>-hexoses (<span style="font-variant: small-caps;">l</span>-allose and <span style="font-variant: small-caps;">l</span>-glucose) were synthesized by C-4 epimerization. The preparation of the key intermediates, the 5,6-unsaturated derivatives, was systematically studied using various protecting groups. By the method developed, we are able to produce highly functionalized <span style="font-variant: small-caps;">l</span>-gulose derivatives in 9 steps (total yields: 21–23%) and <span style="font-variant: small-caps;">l</span>-galactose derivatives in 12 steps (total yields: 6–8%) starting from <span style="font-variant: small-caps;">d</span>-mannose.
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