The present invention provides a compound of Formula (I) wherein R1 is H or C1-6 alkyl, R2, is H or C1-6 alkyl or CH2OH, R3 is H or C1-6 alkyl, and R4 is H or C1-6 alkyl, provided that when R1, R2, and R3 are H, R4 is C1-6 alkyl, and when R1, R2, and R4 are H, then R3 is C1-6 alkyl, and when R1, R3, and R4 are H, R2 is C1-6 alkyl or —CH2OH, and when R2, R3, and R4 are H, then R1 is C1-6 alkyl; A is 1) a 9-10 membered bicyclic heterocycle having 1-3 heteroatoms independently selected from N, S and O, which 9-10 membered bicyclic heterocycle is unsubstituted or substituted with R5 and unsubstituted or substituted with R6 and unsubstituted or substituted with NH2, or 2) a 6-9 membered monocyclic or bicyclic carbocyclic ring system unsubstituted or substituted with R5, unsubstituted or substituted with R6, and unsubstituted or substituted with —CH2NH2; and B is 1) a 5- or 6-membered monocyclic heterocycle having 1 or 2 heteroatoms independently selected from N, S or O, which is unsubstituted or substituted on a carbon or nitrogen atom with R7, unsubstituted or substituted on a carbon or nitrogen atom with R8, and unsubstituted or substituted on a carbon or nitrogen atom with R9, or 2) an 8- or 9-membered fused bicyclic heterocycle having 1, 2 or 3 nitrogen atoms which is unsubstituted or substituted on a carbon or nitrogen atom with R7, and unsubstituted or substituted on a carbon or nitrogen atom with R8; and pharmaceutical compositions comprising one or more said compounds, and methods for using said compounds for treating or preventing thromboses.