A compound selected from Formula IIa: or a stereoisomer, tautomer, or pharmaceutically acceptable salt thereof, wherein: L 1 is S; R 1 is selected from phenyl, heteroaryl, bicyclic aryl, bicyclic heterocyclyl, and bicyclic heteroaryl, wherein the phenyl, heteroaryl, bicyclic aryl, bicyclic heterocyclyl and bicyclic heteroaryl are optionally substituted with one or more groups selected from the group consisting of halogen, OH, oxo, cyano, alkyl optionally substituted with halogen, cyano or OH, -O(alkyl) optionally substituted with halogen, cyano or OH, NHR a, and a heterocycle optionally substituted with halogen, cyano, OH or alkyl optionally substituted with OH or oxo; R 2 is: X 11 is selected from CR 13 R 14, SiR 13 R 14, NH and O; X 12 is selected from CHR 15 and NH, wherein one or both of X 11 and X 12 must be carbon; R 10 is selected from hydrogen and alkyl; R 11 is selected from hydrogen, OH and CH 2 NH 2; R 12, R 16 and R 17 are hydrogen; R 13 is selected from hydrogen, OH, and (C 0 -C 3 alkyl)NR b R c; R 14 is selected from hydrogen, OH, alkyl optionally substituted with halogen, OH, methyl, OCH 3 and a heteroaryl; R 15 is selected from hydrogen or NH 2; or one of the following groups may join together: R 10 and R 11 may join together as CH 2 NHCH 2 to form a fused bicyclic, R 10 and R 15 may join together as alkyl to form a bridged bicyclic, R 11 and R 12 may join together as alkyl substituted with NH 2 to form a spirocycle, R 13 and R 14 may join together as a group selected from cycloalkyl, heterocycle, bicyclic carbocycle, and bicyclic heterocycle, wherein the cycloalkyl, heterocycle, carbocycle and heterocycle are optionally substituted with F, Cl, OH, OCH 3, CN, methyl or NH 2 to form a spirocycle, R 10 and R 16 may join together as alkyl, O or NH to form a bridged bicyclic, R 11 and R 15 may join together as alkyl to form a bridged bicyclic, R 11 and R 16 may join together as alkyl or O to form a bridged bicyclic, R 11 and R 17 may join together as alkyl to form a bridged bicyclic, or R 13 and R 15 may join together as NHCH 2, or cycloalkyl wherein the cycloalkyl is substituted with NH 2 to form a fused bicyclic; R 48 is selected from hydrogen and methyl; R a is hydrogen, alkyl optionally substituted with OH, methoxy, halogen or cyano, or cyclopropyl; R b and R c are independently selected from hydrogen, alkyl and a Boc group; and a, b, c and d are selected from 0 and 1. L 1 is S; R 1 is selected from phenyl, heteroaryl, bicyclic aryl, bicyclic heterocyclyl, and bicyclic heteroaryl, wherein the phenyl, heteroaryl, bicyclic aryl, bicyclic heterocyclyl and bicyclic heteroaryl are optionally substituted with one or more groups selected from the group consisting of halogen, OH, oxo, cyano, alkyl optionally substituted with halogen, cyano or OH, -O(alkyl) optionally substituted with halogen, cyano or OH, NHR a, and a heterocycle optionally substituted with halogen, cyano, OH or alkyl optionally substituted with OH or oxo; R 2 is: X 11 is selected from CR 13 R 14, SiR 13 R 14, NH and O; X 12 is selected from CHR 15 and NH, wherein one or both of X 11 and X 12 must be carbon; R 10 is selected from hydrogen and alkyl; R 11 is selected from hydrogen, OH and CH 2 NH 2; R 12, R 16 and R 17 are hydrogen; R 13 is selected from hydrogen, OH, and (C 0 -C 3 alkyl)NR b R c; R 14 is selected from hydrogen, OH, alkyl optionally substituted with halogen, OH, methyl, OCH 3 and a heteroaryl; R 15 is selected from hydrogen or NH 2; or one of the following groups may join together: R 10 and R 11 may join together as CH 2 NHCH 2 to form a fused bicyclic, R 10 and R 15 may join together as alkyl to form a bridged bicyclic, R 11 and R 12 may join together as alkyl substituted with NH 2 to form a spirocycle, R 13 and R 14 may join together as a group selected from cycloalkyl, heterocycle, bicyclic carbocycle, and bicyclic heterocycle, wherein the cycloalkyl, heterocycle, carbocycle and heterocycle are optionally substituted with F, Cl, OH, OCH 3, CN, methyl or NH 2 to form a spirocycle, R 10 and R 16 may join together as alkyl, O or NH to form a bridged bicyclic, R 11 and R 15 may join together as alkyl to form a bridged bicyclic, R 11 and R 16 may join together as alkyl or O to form a bridged bicyclic, R 11 and R 17 may join together as alkyl to form a bridged bicyclic, or R 13 and R 15 may join together as NHCH 2, or cycloalkyl wherein the cycloalkyl is substituted with NH 2 to form a fused bicyclic; R 10 and R 11 may join together as CH 2 NHCH 2 to form a fused bicyclic, R 10 and R 15 may join together as alkyl to form a bridged bicyclic, R 11 and R 12 may join together as alkyl substituted with NH 2 to form a spirocycle, R 13 and R 14 may join together as a group selected from cycloalkyl, heterocycle, bicyclic carbocycle, and bicyclic heterocycle, wherein the cycloalkyl, heterocycle, carbocycle and heterocycle are optionally substituted with F, Cl, OH, OCH 3, CN, methyl or NH 2 to form a spirocycle, R 10 and R 16 may join together as alkyl, O or NH to form a bridged bicyclic, R 11 and R 15 may join together as alkyl to form a bridged bicyclic, R 11 and R 16 may join together as alkyl or O to form a bridged bicyclic, R 11 and R 17 may join together as alkyl to form a bridged bicyclic, or R 13 and R 15 may join together as NHCH 2, or cycloalkyl wherein the cycloalkyl is substituted with NH 2 to form a fused bicyclic; R 48 is selected from hydrogen and methyl; R a is hydrogen, alkyl optionally substituted with OH, methoxy, halogen or cyano, or cyclopropyl; R b and R c are independently selected from hydrogen, alkyl and a Boc group; and a, b, c and d are selected from 0 and 1.