Substituted aminobutyric derivatives as neprilysin inhibitors

A compound of the formula (IIB):

• or a pharmaceutically acceptable salt thereof, wherein:
• R1 is C1-7alkyl;
• for each occurrence, R2 is independently C1-7alkyl, NO2, CN, halo, C3-7cycloalkyl, hydroxy, C1-7alkoxy, halo-C1-7alkyl, NRbRc, C6-10aryl, heteroaryl or heterocyclyl;
• wherein Rb and Rc for each occurrence, are independently H or C1-7alkyl;
• R2a is halo;
• X and X1 are independently OH, —O—C1-7alkyl, —NRbRc, —NHS(O)2—C1-7alkyl, —NHS(O)2-benzyl or —O—C6-10aryl;
• wherein alkyl is optionally substituted with one or more substituents independently selected from the group consisting of aryl, heteroaryl, heterocyclyl, —C(O)NH2, —C(O)NH— C1-6alkyl, and —C(O)N(C1-6alkyl)2;
• A1 is a bond or a linear C1-4alkylene substituted with one or more substituents independently selected from the group consisting of halo, O-acetate, C1-7 alkyl and C3-7cycloalkyl;
• in which two geminal alkyl can optionally combine to form a C3-7cycloalkyl;
• or
• p is 0, 1, 2, 3 or 4;
• and
• wherein each heteroaryl is a monocyclic or bicyclic aromatic ring comprising 5-10 ring atoms selected from carbon atoms and 1 to 5 heteroatoms, and
• each heterocyclyl is a monocyclic saturated or partially saturated but non-aromatic moiety comprising 4-7 ring atoms selected from carbon atoms and 1-5 heteroatoms, wherein each heteroatom of a heteroaryl or a heterocyclyl is independently selected from O, N and S.