Studies on the formation and incorporation of streptolidine in the biosynthesis of the peptidyl nucleoside antibiotic streptothricin F

Streptothricin F (STF, 1) is a peptidyl nucleoside antibiotic produced by Streptomyces lavendulae. Studies were conducted to address the formation and timing of incorporation of the arginine-derived base streptolidine (4) during the biosynthesis of 1. [guanidino-C-13]Streptolidine (10) was prepared by modification of an established method and used in whole-cell incorporation experiments. Analysis of the purified STF by C-13 NMR revealed a 1.9% enrichment of the guanidino carbon, confirming 4 as an advanced precursor to 1 and supporting proposals that 1 is assembled via a convergent biosynthetic pathway. To identify advanced intermediates in the conversion of L-arginine to 4, (2S,3R)-[guanidino-C-13]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). Treatment of 30 with (BrCN)-C-13 yielded the corresponding diprotected amino alcohol, which was readily converted to 32. The STF isolated from whole-cell incorporation experiments with 32 showed no significant C-13 enrichment at the guanidino carbon. These results suggest that 32 may be an enzyme-bound intermediate, unable to enter the cell, or is not a precursor to STF.