Genetically engineered production of 1,1′-bis-valienamine and validienamycin in Streptomyces hygroscopicus and their conversion to valienamine

The antifungal agent validamycin A is an important crop protectant and the source of valienamine, the precursor of the antidiabetic drug voglibose. Inactivation of the valN gene in the validamycin A producer, Streptomyces hygroscopicus subsp. jinggangensis 5008, resulted in a mutant strain that produces new secondary metabolites 1,1′-bis-valienamine and validienamycin. The chemical structures of 1,1′-bis-valienamine and validienamycin were elucidated by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy in conjunction with mass spectrometry and bioconversion employing a glycosyltransferase enzyme, ValG. 1,1′-Bis-valienamine and validienamycin exhibit a moderate antifungal activity against Pellicularia sasakii. Chemical degradation of 1,1′-bis-valienamine using N-bromosuccinimide followed by purification of the products with ion-exchange column chromatography only resulted in valienamine, whereas parallel treatments of validoxylamine A, the aglycon of validamycin A, resulted in an approximately 1:1 mixture of valienamine and validamine, underscoring the advantage of 1,1′-bis-valienamine over validoxylamine A as a commercial source of valienamine.