Stereoselective total synthesis of 10-epi-tirandamycin E

Engineering P450 TamI as an Iterative Biocatalyst for Selective Late-Stage C-H Functionalization and Epoxidation of Tirandamycin Antibiotics

Iterative P450 enzymes are powerful biocatalysts for selective late-stage C-H oxidation of complex natural product scaffolds. These enzymes represent useful tools for selectivity and cascade reactions, facilitating direct access to core structure diversification. Recently, we reported the structure of the multifunctional bacterial P450 TamI and elucidated the molecular basis of its substrate binding and strict reaction sequence at distinct carbon atoms of the substrate. Here, we report the design and characterization of a toolbox of TamI biocatalysts, generated by mutations at Leu101, Leu244, and/or Leu295, that alter the native selectivity, step sequence, and number of reactions catalyzed, including the engineering of a variant capable of catalyzing a four-step oxidative cascade without the assistance of the flavoprotein and oxidative partner TamL. The tuned enzymes override inherent substrate reactivity, enabling catalyst-controlled C-H functionalization and alkene epoxidation of the tetramic acid-containing natural product tirandamycin. Five bioactive tirandamycin derivatives (6-10) were generated through TamI-mediated enzymatic synthesis. Quantum mechanics calculations and MD simulations provide important insights into the basis of altered selectivity and underlying biocatalytic mechanisms for enhanced continuous oxidation of the iterative P450 TamI.

Isolation of manumycin-type derivatives and genome characterization of a marine Streptomyces sp. C1-2

A marine actinomycete strain C1-2 was taxonomically characterized as the genus Streptomyces, based on whole-genome sequence analysis. The highest average nucleotide identity (ANI) value (98.96%) and digital DNA-DNA hybridization (DDH) value (90.4%) were observed between Streptomyces sp. C1-2 and Streptomyces griseoaurantiacus. Thus, Streptomyces sp. C1-2 could be identified as S. griseoaurantiacus. Genome analysis revealed that Streptomyces sp. C1-2 contained 22 biosynthetic gene clusters (BGCs) for secondary metabolites, where among them, 54% have low similarities with known BGCs. The chemical investigation led to the isolation of three new manumycin-type derivatives and two known analog antibiotics named SW-B and cornifronin B. All compounds showed antioxidant activity with the half-maximal inhibitory concentration (IC₅₀) values in a range of 50.82 ± 0.8-112.04 ± 1.0 μg/mL with no cytotoxicity against Vero cells. This is the first report of the antioxidant property of manumycin-type derivatives. Moreover, two known compounds exhibited antifungal activity against Phytophthora capsici, Fusarium oxysporum f. sp. cucumerinum, and Magnaporthe grisea, with the minimum inhibitory concentration (MIC) values in a range of 125-500 μg/mL.