A compound of Formula I or a pharmaceutically acceptable salt: X is S; Y 1 is N or CR 1; Y 2 is N or CR 2; R 1 combines with R 3, or R 2 combines with R 3, to form a 5-10 member heteroaryl, 5-10 member carbocyclic ring or 5-10 member heterocyclic ring, wherein each of the ring systems is independently optionally substituted with halogen, -CN, -OH, -NR 8 R 9, -N 3, -NO 2, carbonyl, =O, oxo, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, or C R 8; when R 1 combines with R 3 to form a 5-10 member heteroaryl, 5-10 member carbocyclic ring or 5-10 member heterocyclic ring, R 2 is -H, halogen, -CN, -OH, -NH 2, -N 3, -NO 2, substituted or unsubstituted C 1-6 alkoxy, or substituted or unsubstituted C 1-6 alkyl; when R 2 combines with R 3 to form a 5-10 member heteroaryl, 5-10 member carbocyclic ring or 5-10 member heterocyclic ring, R 1 is -H, halogen, -CN, -OH, -NH 2, -N 3, -NO 2, substituted or unsubstituted C 1-6 alkoxy, or substituted or unsubstituted C 1 - 6 alkyl; R 4 is halogen, -CN, -OH, -NR 8 R 9, -N 3, -NO 2, substituted or unsubstituted C 1-6 alkoxy, substituted or unsubstituted C 1-6 alkyl, C 5-18 heterocyclic ring or C 5-18 carbocyclic ring; wherein each of the ring systems is independently optionally substituted with halogen, -CN, -OH, -NO 2, carbonyl, =O, oxo, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, -NR 8 R 9 or -CH 2 NR 8 R 9; R 5 is -H, halogen, -CN, -OH, -NR 8 R 9, -N 3, -NO 2, C 1-6 alkyl, C 1-6 alkoxy, C 6-10 aryl, C 6-10 arylalkyl, C 6-10 heteroaryl, C 5-18 heterocyclic ring or C 5-18 carbocyclic ring; and each of which is independently optionally substituted with halogen, -CN, -OH, -N 3, -NO 2, -NH 2, carbonyl, =O, oxo, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, (CH 2) k NR 8 R 9, (CH 2) k NHC OR 6 or C R 8; and k is 0, 1 or 2; each R 8 and R 9 is independently -H, halogen, -CN, -OH, -N 3, -NO 2, C 1-6 alkyl, C 1-6 alkoxy, C 2-6 alkenyl, NH(C 1-6 alkyl), N(C 1-6 alkyl) 2, C 5-10 heterocyclic ring or C 5-10 carbocyclic ring; and each of which may be independently optionally substituted with halogen, -CN, -OH, -NH 2, -N 3, -NO 2, -C 1-6 alkylene-NH 2, -C 1-6 alkylene-NH-C 1-6 alkyl, -C 1-6 alkylene-N(C 1-6 alkyl) 2, -NHBoc, -CH 2 NHBoc, -NH-C 1-6 alkyl, -N(C 1-6 alkyl) 2, -NH-C 1-6 alkoxy, -N(C 1-6 alkoxy) 2, substituted or unsubstituted C 1-6 alkyl, or substituted or unsubstituted C 1-6 alkoxy; and each heterocyclic ring contains 1, 2, 3 or 4 heteroatoms selected from N, O or S; wherein alkyl is saturated monovalent hydrocarbon radicals having straight, branched or cyclic moieties, alkoxy is straight, branched chain or cyclic alkyl group, and heterocyclic is unsubstituted and substituted mono- or polycyclic non-aromatic ring system containing one or more heteroatoms. X is S; Y 1 is N or CR 1; Y 2 is N or CR 2; R 1 combines with R 3, or R 2 combines with R 3, to form a 5-10 member heteroaryl, 5-10 member carbocyclic ring or 5-10 member heterocyclic ring, wherein each of the ring systems is independently optionally substituted with halogen, -CN, -OH, -NR 8 R 9, -N 3, -NO 2, carbonyl, =O, oxo, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, or C R 8; when R 1 combines with R 3 to form a 5-10 member heteroaryl, 5-10 member carbocyclic ring or 5-10 member heterocyclic ring, R 2 is -H, halogen, -CN, -OH, -NH 2, -N 3, -NO 2, substituted or unsubstituted C 1-6 alkoxy, or substituted or unsubstituted C 1-6 alkyl; when R 2 combines with R 3 to form a 5-10 member heteroaryl, 5-10 member carbocyclic ring or 5-10 member heterocyclic ring, R 1 is -H, halogen, -CN, -OH, -NH 2, -N 3, -NO 2, substituted or unsubstituted C 1-6 alkoxy, or substituted or unsubstituted C 1 - 6 alkyl; R 4 is halogen, -CN, -OH, -NR 8 R 9, -N 3, -NO 2, substituted or unsubstituted C 1-6 alkoxy, substituted or unsubstituted C 1-6 alkyl, C 5-18 heterocyclic ring or C 5-18 carbocyclic ring; wherein each of the ring systems is independently optionally substituted with halogen, -CN, -OH, -NO 2, carbonyl, =O, oxo, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, -NR 8 R 9 or -CH 2 NR 8 R 9; R 5 is -H, halogen, -CN, -OH, -NR 8 R 9, -N 3, -NO 2, C 1-6 alkyl, C 1-6 alkoxy, C 6-10 aryl, C 6-10 arylalkyl, C 6-10 heteroaryl, C 5-18 heterocyclic ring or C 5-18 carbocyclic ring; and each of which is independently optionally substituted with halogen, -CN, -OH, -N 3, -NO 2, -NH 2, carbonyl, =O, oxo, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, (CH 2) k NR 8 R 9, (CH 2) k NHC OR 6 or C R 8; and k is 0, 1 or 2; each R 8 and R 9 is independently -H, halogen, -CN, -OH, -N 3, -NO 2, C 1-6 alkyl, C 1-6 alkoxy, C 2-6 alkenyl, NH(C 1-6 alkyl), N(C 1-6 alkyl) 2, C 5-10 heterocyclic ring or C 5-10 carbocyclic ring; and each of which may be independently optionally substituted with halogen, -CN, -OH, -NH 2, -N 3, -NO 2, -C 1-6 alkylene-NH 2, -C 1-6 alkylene-NH-C 1-6 alkyl, -C 1-6 alkylene-N(C 1-6 alkyl) 2, -NHBoc, -CH 2 NHBoc, -NH-C 1-6 alkyl, -N(C 1-6 alkyl) 2, -NH-C 1-6 alkoxy, -N(C 1-6 alkoxy) 2, substituted or unsubstituted C 1-6 alkyl, or substituted or unsubstituted C 1-6 alkoxy; and each heterocyclic ring contains 1, 2, 3 or 4 heteroatoms selected from N, O or S; wherein alkyl is saturated monovalent hydrocarbon radicals having straight, branched or cyclic moieties, alkoxy is straight, branched chain or cyclic alkyl group, and heterocyclic is unsubstituted and substituted mono- or polycyclic non-aromatic ring system containing one or more heteroatoms.