H-Bond network during MD simulation. The H-bond occupancy of each compound in N1 is summarized in Table 3 Figure 7 . The distance between Xylopine_2 and Glu228 was maintained between 2-3 Å ( Figure 7A ). The distance of Rosmaricine_14 and Glu119 and Glu 228 also remained between 2-3 Å ( Figure 7B ). From Table 3 , Rosmarcine_15 and TamifluH did not form high occupancy H-bonds with Tyr402. Intriguingly, bond distance profiles indicate that Tyr402 was one of the key amino acids for H-bond formation ( Figure 7C , 7D). Tyr402 bond distance generally exceeded 2.5 Å in Rosmaricine_15, thus explaining the low occupancy rate in Table 3 . For TamifluH, the distance in the first ns was between 3-4 Å and then decreased to 2-3 Å from 1-20 ns, thus accounting for the low occupancy rate as well. Despite the low occupancy rates, the bond distance profiles suggest that Tyr402 is an important N1 binding site for Rosmaricine_15 and TamifluH.