Iterative P450 enzymes are powerful biocatalysts for selective late-stage C-H oxidation of complex natural product scaffolds. These enzymes represent new 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 new, bioactive tirandamycin derivatives (6-10) were generated through TamI-mediated enzymatic synthesis. Quantum mechanics calculations and MD simulations provide important insights on the basis of altered selectivity and underlying biocatalytic mechanisms for enhanced continuous oxidation of the iterative P450 TamI.