A compound according to the following Formula I, its individual enantiomers, its individual diastereoisomers, its hydrates, its solvates, its crystal forms, its individual tautomers or a pharmaceutically acceptable salt thereof, wherein the compound is a bacterial Type II glutaminyl cyclase inhibitor; wherein L is selected from the group consisting of single bond, -CR 5 (R 6 )-, -CR 5 (R 6 )-CR 7 ( R 8 )- and -C(R 5 )=C(R 6 )-; wherein R 3 , R 4 , R 5 , R 6 , R 7 and R 8 are the same or different from each other and are independently selected from the group consisting of H, F, Cl, Br, I, OH, optionally substituted alkyl and optionally substituted heteroalkyl; wherein within each pair of groups R 3 /R 4 , R 5 /R 6 and R 7 /R 8 , the two groups can be optionally joined together to form a carbocyclic or a heterocyclic ring, or can optionally represent =O, wherein: (i) each of R 1 and R 2 is H; each of R 3 and R 4 is H, or R 3 and R 4 are independently selected from the group consisting of optionally substituted C 1-6 alkyl and optionally substituted C 1-6 heteroalkyl; and Ar is selected from the group consisting of aryl, optionally substituted alkoxyaryl, optionally substituted carboxyaryl, optionally substituted cyanoaryl, haloaryl, optionally substituted hydroxyaryl, optionally substituted alkoxyheteroaryl, optionally substituted cyanoheteroaryl, optionally substituted haloheteroaryl, optionally substituted heteroarylaryl, optionally substituted hydroxyheteroaryl and optionally substituted carboxyheteroaryl; or (ii) R 1 and R 2 together represent =O; and Ar is optionally substituted aryl selected from the group consisting of carboxyaryl, cyanoaryl, hydroxyaryl, heteroarylaryl, 2,3-dichlorophenyl, 2,3-dihydro-1,4-benzodioxin-6-yl, 3-chloro-5-methoxyphenyl, 3,4,5-trifluorophenyl, 3,5-dichlorophenyl, 4-(benzyloxy)phenyl, 4-[2-(morpholin-4-yl)ethoxy]phen-1-yl, 4-butoxyphenyl, 4-fluoro-3-methoxyphenyl and naphthalen-2-yl, or is optionally substituted heteroaryl selected from the group consisting of alkoxyheteroaryl, cyanoheteroaryl, haloheteroaryl, hydroxyheteroaryl and carboxyheteroaryl. (i) each of R 1 and R 2 is H; each of R 3 and R 4 is H, or R 3 and R 4 are independently selected from the group consisting of optionally substituted C 1-6 alkyl and optionally substituted C 1-6 heteroalkyl; and Ar is selected from the group consisting of aryl, optionally substituted alkoxyaryl, optionally substituted carboxyaryl, optionally substituted cyanoaryl, haloaryl, optionally substituted hydroxyaryl, optionally substituted alkoxyheteroaryl, optionally substituted cyanoheteroaryl, optionally substituted haloheteroaryl, optionally substituted heteroarylaryl, optionally substituted hydroxyheteroaryl and optionally substituted carboxyheteroaryl; or (ii) R 1 and R 2 together represent =O; and Ar is optionally substituted aryl selected from the group consisting of carboxyaryl, cyanoaryl, hydroxyaryl, heteroarylaryl, 2,3-dichlorophenyl, 2,3-dihydro-1,4-benzodioxin-6-yl, 3-chloro-5-methoxyphenyl, 3,4,5-trifluorophenyl, 3,5-dichlorophenyl, 4-(benzyloxy)phenyl, 4-[2-(morpholin-4-yl)ethoxy]phen-1-yl, 4-butoxyphenyl, 4-fluoro-3-methoxyphenyl and naphthalen-2-yl, or is optionally substituted heteroaryl selected from the group consisting of alkoxyheteroaryl, cyanoheteroaryl, haloheteroaryl, hydroxyheteroaryl and carboxyheteroaryl. <EOS>