Streptose dihydro

In experiments in which sodium borohydride was added to the enzyme incubation mixture of the apiose/xylose synthase, no reduction products could be found that would arise from epimerization at C-3 of the 4-ketose intermediate.44 In the synthesis of apiose, ring contraction therefore seems to take place with the L-threo-pentos-4-ulose 27 (see Scheme 11), and not with the L-erythro intermediate, which would be analogous to the ring contraction in the biosynthesis of L-dihydro-streptose. 

Streptidine phosphate was incubated with dTDP-L-[U-14C]dihydro-streptose, obtained in situ from dTDP-D-[U-14C]glucose with a cell-free extract from S. griseus. Two new, positively charged, radioactive products were obtained which, upon hydrolysis, gave dihydrostreptose as the only radioactive product. Comparison with a synthetic sample of 0-a-L-dihydrostreptose-(l- 4)-streptidine (43, see Scheme 14) proved that one of the products was identical with this pseudodisaccharide, and the second product was identified as the corresponding 6-phosphate (44). It was concluded that the phospho-rylated product had been partially hydrolyzed during the incubation by streptomycin 6-phosphate phosphatase present in the cell-free extract. No transfer-products were formed in controls in which (a) denatured extract was used,(fe) streptidine phosphate was absent, or(c) streptidine was substituted for streptidine phosphate. 

---