The biosynthesis of nojirimycins
Streptomyces subrutilus ATCC 27467, when grown on a glucosecontaining soyabean medium, produces both 1-deoxymannonojirimycin (DMJ) and 1-deoxynojirimycin (DNJ) in its culture medium. When 1- or 2-[2H]-D-glucose is used, the deuterium label appears at C6 in both alkaloids and the labelling pattern suggests that the first step in the biosynthesis of both DNJ and DMJ is a glucose to fructose isomerisation. Studies with 5-[2H]-D-glucose and 6,6-[2H2]-D-glucose indicate that oxidation of the 6-position of the glucose/ fructose occurs during the biosynthesis and that mannonojirimycin is the first amino sugar to be formed. Mannonojirimycin can then undergo dehydration and reduction to DMJ. Alternatively, epimerisation of mannonojlrlmycin can occur at C2 to give nojirimycin which is then dehydrated and reduced to DNJ. Studies with another microorganism, B. subtilis var niger ATCC 9372, indicate that a similar biosynthetic pathway is in operation. DMJ, however, is not produced by this microorganism and only low levels of NJ are postulated from enzyme inhibition and deuterium labelling studies. A minor biosynthetic route is also evident from labelling studies with 1-[13C]-D-glucose and 1-[13C]-D, L-glyceraldehyde. It is suggested that the fructose at the beginning of the biosynthesis can split into two C3 trioses which are in equilibrium with each other. These can then recombine to continue in the usual biosynthetic pathway. New chemical routes to 542H]-D-glucose and 2-[2H]-D-glucose are described in Chapter 3 along with a method for introducing deuterium or tritium into DNJ or NJ. Other isotopically enriched glucoses or intermediates have also been prepared using literature methodology. Studies have been undertaken to assess whether S. subrutilus can utilise glucose analogues in the biosynthetic pathway. To this end, new or modified routes to these glucose derivatives have been investigated and some work has focused on the chemical synthesis of DNJ analogues themselves.