Inhibitors of histone deacetylase useful for the treatment or prevention of hiv infection

A compound of the formula:

• wherein
• is a five-membered heteroaryl ring which is optionally substituted with halo, cyano or C1-3 alkyl;
• is a five-membered heteroaryl ring which is optionally substituted with C1-3 alkyl;
• R1 is phenyl or heteroaryl, which may be monocyclic or bicyclic, wherein said phenyl and heteroaryl groups are optionally substituted with one to three groups independently selected from the group consisting of halo, oxo, cyano, R4, R6, OR4, OR6 and SO2R4;
• R2 is selected from the group consisting of hydrogen, NH(C═O)R6, NH(C═O)CH2R6, NH(C═O)R4, NH(C═O)R5, NH(C═O)OR5 NH2, NHR4, NHR6, NHCH2R6 and R6;
• R3 is selected from hydrogen or C1-6 alkyl;
• or R2 and R3 can be taken together with the atoms to which they are attached to form a 5, 6 or 7 membered heterocyclyl group which is optionally substituted with oxo;
• each R4 is independently hydrogen or C1-6 alkyl, which is optionally substituted with one to three halo;
• each R5 is independently hydrogen or C1-6 alkyl, which is optionally substituted with N(R4)2 or OR4;
• R6 is
• (a) heterocyclyl, which may be monocyclic or bicyclic,
• (b) C3-6 cycloalkyl,
• (c) phenyl, or
• (d) heteroaryl, which may be monocyclic or bicyclic,
• wherein said heterocyclyl, cycloalkyl, phenyl and heteroaryl groups are optionally substituted with one to two groups independently selected from the group of oxo, R5, OR4 and heteroaryl;
• Ra is hydrogen or halo;
• Rb is hydrogen or halo;
• or a pharmaceutically acceptable salt thereof.