▁research ers ▁focused ▁on ▁comp ounds ▁that ▁could ▁act ▁as ▁h D AA O ▁in hib itors . ▁Over ▁ 5 0 0 ▁different ▁comp ounds ▁have ▁been ▁observed ▁in ▁vit ro / in ▁v ivo ▁to ▁act ▁as ▁in hib itors ▁on ▁the ▁ox id ase ▁and ▁most ▁of ▁them ▁do ▁by ▁compet itive ▁in hib ition . ▁All ▁of ▁these ▁comp ounds ▁have ▁two ▁similar , ▁main ▁port ions . ▁The ▁first ▁portion ▁is ▁the ▁plan ar ▁portion ▁which ▁interact s ▁with ▁the ▁active ▁site ▁of ▁h D AA O . ▁The ▁plan ar ▁site ’ s ▁chemical ▁structure ▁is ▁formed ▁by ▁one ▁or ▁two ▁f used ▁rings ▁and ▁must ▁have ▁a ▁neg atively ▁charged ▁car box y lic ▁group . ▁The ▁second ▁portion ▁is ▁the ▁substr ate ▁chain , ▁which ▁can ▁particip ate ▁in ▁the ▁active ▁zone ▁or ▁entrance ▁of ▁the ▁en zym e . ▁ ▁Furthermore , ▁the ▁different ▁comp ounds ▁are ▁divided ▁into ▁multiple ▁categories ▁( class ical , ▁novel , ▁second ▁generation , ▁third ▁generation ) ▁depending ▁on ▁the ▁chemical ▁structures . ▁An ▁example ▁of ▁a ▁comp ound ▁is ▁ben zo ate , ▁which ▁is ▁a ▁classical ▁in hib itor . ▁The ▁car box y lic ▁group ▁of ▁ben zo ate ▁interact s ▁with ▁Arg 2 3 8 , ▁and ▁the ▁a rom atic ▁interact s ▁with ▁T yr 2 2 4 ▁on ▁the ▁active ▁zone ▁of ▁the ▁ox id ase . ▁ ▁App lications ▁ ▁Bi ote chn ology ▁ ▁Ce phal os por in ▁synth