The biosynthesis of thiamine. Syntheses of [1,1,1,5-2H4]-1-deoxy-D-threo-2-pentulose and incorporation of this sugar in biosynthesis of thiazole by Escherichia coli cells
Non-growing, washed cells of Escherichia coli, depressed for the synthesis of thiamine, were incubated in the presence of [1,1,1,5-2H4]-1-deoxy-D-threo-2-pentulose (9) in a medium containing the pyrimidine moiety of thiamine, L-tyrosine, and glucose. The thiamine thus biosynthesized was extracted and cleaved to give 5-(2-hydroxyethyl)-4-methylthiazole (HET) which was examined as the trifluoroacetate derivative by electron-impact mass spectrometry. The distribution of the label in the fragments indicated that the pentulose (9) was a precursor of the C5-chain of HET without C–C bond cleavage. Several routes to 1-deoxypentuloses are described. Condensation of 2,4-O-benzylidene-D-[4-2H1]threose (23) with trideuteriomethylmagnesium iodide gave the protected 1-deoxypentitols (24) and (25). Brominolysis of the mixed dibutylstannylidenes then afforded [1,1,1,5-2H4]-3,5-O-benzylidene-1-deoxy-D-threo-2-pentulose (26), which was converted into the free sugar (9) by acidic hydrolysis. 1-Deoxy-D-erythro-2-pentulose was prepared in similar manner. Condensation of 2-([2H3]-methyl)-1,3-dithian with 2,3-O-isopropylidene-D-glyceraldehyde, followed by a C-3 epimerization step also led, after deprotection, to a mixture of [1,1,1-2H3]-1-deoxy-D-erythro- and [1,1,1-2H3]-1-deoxy-D-threo-2-pentulose, (5) and (6).