| Abstract
| - Streptothricin F (STF, 1) is a peptidyl nucleoside antibiotic produced by Streptomyceslavendulae.Studies were conducted to address the formation and timing of incorporation of the arginine-derivedbase streptolidine (4) during the biosynthesis of 1. [guanidino-13C]Streptolidine (10) was preparedby modification of an established method and used in whole-cell incorporation experiments. Analysisof the purified STF by 13C NMR revealed a 1.9% enrichment of the guanidino carbon, confirming4 as an advanced precursor to 1 and supporting proposals that 1 is assembled via a convergentbiosynthetic pathway. To identify advanced intermediates in the conversion of l-arginine to 4,(2S,3R)-[guanidino-13C]capreomycidine (32) was prepared from oxazolidine aldehyde (18) via 1,1-dimethylethyl (4R,1‘S)-4-(1‘,3‘-diaminopropyl)-2,2-dimethyl-3-oxazolidinecarboxylate (30). Treatmentof 30 with Br13CN yielded the corresponding diprotected amino alcohol, which was readily convertedto 32. The STF isolated from whole-cell incorporation experiments with 32 showed no significant13C enrichment at the guanidino carbon. These results suggest that 32 may be an enzyme-boundintermediate, unable to enter the cell, or is not a precursor to STF.
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