Complex sentence: Despite Edward's pleas not to, Hohenheim tells him to give Alphonse his regards as he tries to destroy Envy, his jaws shut, killing Hohenheim but, his blood activating the transmutation circle above that destroys Envy.
Split into simpler sentences: Despite Edward's pleas not to, Hohenheim tells him to give Alphonse his regards as he tries to destroy Envy. However, Envy's jaws shut, killing Hohenheim, but his his blood activating the transmutation circle in turn destroys Envy.