Based on the test of CP dimerization, we established the BGAN-EPS method as a new strategy to evaluate entropic profiles from a few hundred trajectories. Furthermore, we employed the method to investigate the role of entropy in mediating bifurcation selectivity for NgnD enzyme-catalyzed Diels-Alder reaction in the gas phase (Figure ). NgnD-catalyzed Diels-Alder reaction involves an ambimodal TS that leads to the formation of the [6+4]-and [4+2]-adduct without further barriers (ca. 3:1 ratio of [6+4]:[4+2], upper right, Figure ). Although trajectories simulations have been conducted to quantitatively determine the bifurcation selectivity, This is consistent with the observation that [6+4] adduct is more energetically favorable. In contrast, the entropic profiles (i.e., represented by -TS) trend downhill and then rebound at about -0.6 Å. The uptrend likely continues with further formation of bonds and exceeds the starting ambimodal transition state due to a more compact configuration of the adducts. However, these trends cannot be fully reflected in the current profiles due to the under-sampling of pseudomolecular configurations in the product-forming region.