| The existence of post-transition state bifurcations(PTSB)has been acknowledged for several decades.PTSB has received increasing attention from the scientific community due to their complexity and importance.This paper introduces PTSB phenomenon in the cycloaddition reaction,and finds that the micro-environment can affect the proportion of the PTSB products.In addition to the PTSB in enzymes,we also studied the PTSB reactions under non-enzymatic conditions.At the same time,we also studied the mechanism of enzyme-catalyzed reaction in detail and explored the active sites of enzymes.Our main studies are summarized as follows:1.The mechanism of enzyme-catalyzed [6 + 4]/[4 + 2] reaction was studied,and it was found that the enzyme-catalyzed [6 + 4]/[4 + 2] cycloaddition reaction was a bifurcation reaction in a post-transition state,and the distribution of [6 + 4]/[4 + 2]product ratio in the gas phase was studied by quasi-classical molecular dynamics simulation.We performed molecular docking and molecular dynamics simulation combining with electrostatic potential analysis and distance analysis.The key active sites of the enzyme was found by computation and verified by mutation experiment.2.We study the influence of microenvironment on the bifurcation of post-transition state in enzyme-catalyzed [6 + 4]/[4 + 2] cycloaddition reaction.Thequasi-classical molecular dynamics trajectory simulation was carried out in the gas phase,water environment and enzyme,respectively.We explain the influence of microenvironment on the proportion of post-transition bifurcation products from the environmental polarity,molecular dipole moment,molecular collision and molecular volume,and so on.3.We report the dynamical trajectory study of the transannular [6 + 4] and ambimodal cycloaddition proposed in the biosynthesis of heronamides natural products.The originally proposed bifurcation of potential energy surface is found to strongly favor the formation of the [6 + 4] product,both in the gas phase and in explicit water environment,as evidenced by our trajectory simulations.The detailed information of how the bonds are formed was analyzed at the femtosecond time scale.4.The following reactions are calculated using quantum chemistry :a pair of flavin-dependent oxidoreductases,Stm O1 and Stm O2,catalyze the direct hydroxylation at [6 + 4] adduct.Subsequently,a spontaneous [3,3]-Cope rearrangement and an enol-ketone tautomerization will result in the formation of10/6/6-tricyclic intermediate,which can be further converted to a stable10/6/6-tricyclic alcohol through a ketoreduction by Stm K.It can eventually produce streptoseomycin by a series of downstream enzymes. |
