NEOMYCIN BIOSYNTHESIS - THE INCORPORATION OF D-6-DEOXY-GLUCOSE DERIVATIVES AND VARIOUSLY LABELED GLUCOSE INTO THE 2-DEOXYSTREPTAMINE RING - POSTULATED INVOLVEMENT OF 2-DEOXYINOSOSE SYNTHASE IN THE BIOSYNTHESIS

D-[6-H-3(3)]6-Deoxy-5-ketoglucose (10) and D-[5,6-H-3(2)]6-deoxyglucose (11) were incorporated into neomycins B and C using a growing culture of Streptomyces fradiae. D-[6-H-3]6-Deoxy-5-ketoglucose was incorporated into neomycin, as efficiently as the well established precursor D-glucose, and was found to label exclusively the 2-deoxystreptamine ring of the antibiotic. The results strengthened the previous proposals that in the formation of 2-deoxystreptamine the C-6 hydroxyl group of D-glucose is removed prior to the cyclisation reaction. Studies using the incorporation of D-[3-H-3]glucose,D-[3,4-H-3(2)]glucose and D-[5-H-3]glucose into neomycin followed by the degradation of the latter established that in the biosynthesis of the 2-deoxystreptamine ring the C-4 and C-5 hydrogen atoms of glucose are removed. The loss of the C-4 hydrogen atom of the glucose is attributed to the formation of a 4-keto derivative which facilitates the removal of the C-5 hydrogen atom thus setting the stage for the expulsion of the C-6 hydroxyl group. The 5,6-olefinic intermediate formed in the process then undergoes cyclisation eventually releasing 2-deoxyinosose. The enzyme systems which participate in the conversion of D-glucose equivalent into 2-deoxyinosose may be described as 2-deoxyinosose synthase that in broad mechanistic terms resembles dehydroquinate synthase.