Stereochemical Aspects of the Biosynthesis of Spectinomycin

The biosynthesis of spectinomycin (1) has been studied with specifically and stereospecifically labeled glucose as precursors. The results further define the mode of conversion of glucose into the actinamine (2) moiety of 1 and show that the formation of the cyclitol portion by myo-inositol-1-phosphate synthase involves stereospecific loss of the pro-R hydrogen from C-6 of glucose 6-phosphate. The TDP-glucose oxidoreductase reaction is implicated in the formation of the 4,6-dideoxyhexose moiety of 1 by the demonstration of an intramolecular hydrogen transfer from C-4 to C-6 of the hexose, which occurs with the same stereochemistry, i.e., replacement of OH at C-6 by H-4 in an inversion mode, that has been demonstrated for the enzyme from E. coli and from another streptomycete.