Large-Scale Synthesis of Crystalline 1,2,3,4,6,7-Hexa--acetyl-l-α-d--heptopyranose.

The higher-carbon sugar l--d--heptose is a major constituent of the inner core region of the lipopolysaccharide (LPS) of many Gram-negative bacteria. All preparative routes used to date require multiple steps, and scalability has been rarely addressed. Here a highly practical synthesis of crystalline 1,2,3,4,6,7-hexa--acetyl-l--α-d--heptopyranose by a simple four-step sequence starting from l-lyxose is disclosed. Only two recrystallisations are required and the process was demonstrated on a >100 mmol scale, yielding 41 g of the target compound.